Hello everyone!
I am here in hopes someone has the knowledge to help me bring my newly acquired E30 back to life.
This is a US spec 1991 318i with M42 engine and 5 speed manual transmission. It only has 78,000 miles on it.
When I acquired the car, this was the issue: Car starts and runs great. After 20-30 minutes of driving (or idling), car will cut out and will not restart until it cools down.
To make long story short, I narrowed it down to the DME (ECU? Engine computer?) overheating. Here is how I came to this conclusion: bought a spare DME and once the car dies, I can swap in my spare DME and the car immediately starts back up and runs until that DME get hot and then the car dies again.
What I have done along the way:
New BMW Crankshaft Position Sensor and Camshaft Position Sensors (twice. Previous owners replaced with Ebay parts, I didn't trust that and I replaced again with BMW parts)
New BMW Spark Plugs and Ignition Cables
New BMW DME Relay. Used Fuel Pump Relay, Oxygen Sensor relay (tried 2-3 different ones with same result).
New BMW Fuel Pump (and previous owners tried a used fuel pump to no avail)
**checked to make sure all grounds are good - at engine block, at ignition coils, and at DME**
**checked for voltage drop between chassis ground and engine and grounds at DME - hardly any drop noted (0.03v)**
**Installed a small computer cooling fan on top of one of the DMEs. THIS MOD HELPED: the car will now run for 1 hr+ before cutting out.**
DME gets hot enough that it's uncomfortable to hold it in my hand, but can be held. I don't know if that's normal, but I don't think so.
None of the things I tried made any difference except for putting a fan on the DME.
I should also mention that the charging system is working fine putting out anywhere between 13.9 and 14.5 volts at all times.
Please help me, I don't have tons of money to keep throwing parts at this issue. I need to narrow it down.
I have access to this car's wiring diagrams and a comprehensive set of tools, including a Snap On scanner with BMW adapter.
Thank you in advance!
E30 M42 Stalls after 30 minutes and will not restart until cools down
Moderator: martauto
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carswithcharacter614
- E30 Zone Newbie
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- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
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twright
- E30 Zone Newbie
- Posts: 70
- Joined: Tue Sep 01, 2020 11:21 am
- Location: Indianapolis, Indiana USA
An overheating engine computer just seems like being really unlikely. Before you buy any more parts, I would answer a few questions:
1,) If you drive it for 30 minutes and get the stall condition, plug and replug in the engine computer. If you do this, does the engine start right up? If it does, its unlikely that over heating of the engine computer is the cause, because the computer would still be hot.
2,) When the engine stalls, is it no spark or no fuel that is causing the problem?
To find out if it is no spark, when the stall occurs, pull a spark plug and lead and check for spark.
To find out if there is no fuel, connect a fuel pressure gauge onto the fuel rail and see what your fuel pressure is . If its less that 10 psi, this can be the cause of your stalling.
Its possible that a new wiring loom will fix your problem. But if you go through the steps above, it might give you a better idea which wires are causing the problem and you can just replace the bad wires,
1,) If you drive it for 30 minutes and get the stall condition, plug and replug in the engine computer. If you do this, does the engine start right up? If it does, its unlikely that over heating of the engine computer is the cause, because the computer would still be hot.
2,) When the engine stalls, is it no spark or no fuel that is causing the problem?
To find out if it is no spark, when the stall occurs, pull a spark plug and lead and check for spark.
To find out if there is no fuel, connect a fuel pressure gauge onto the fuel rail and see what your fuel pressure is . If its less that 10 psi, this can be the cause of your stalling.
Its possible that a new wiring loom will fix your problem. But if you go through the steps above, it might give you a better idea which wires are causing the problem and you can just replace the bad wires,
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Thank you for the replies everyone.
Dan, although your suggestion is valid, I have my doubts that it's the loom. Here is why: I opened up part of the loom that runs along the firewall and leads up to the 3 relays. It is so clean and nice inside, none of the insulation is dry rotted or cracked and there is no water or any other kind of damage. It looks brand new. In fact, most everything on this car looks brand new. When the car is idling, I tried to pull, twist, move and otherwise mess with the loom to duplicate the problem - and nothing. It continues to run until the DME gets hot.
Twright, I have gone through these tests: When the car refuses to start, it loses spark and fuel pump relay no longer gets energized - I believe the same would happen if crankshaft position sensor was unplugged, as DME does not energize the fuel pump relay if there is no pulse from crank sensor (correct me if i'm wrong). Once the car shuts down. only installing my spare, COLD DME gets it to run again - and it starts immediately and runs PERFECT. Unplugging and plugging back the HOT DME does nothing.
In my opinion, something that DME supplies power to (Ignition coils? Fuel Pump Relay? Oxygen Sensor Relay? what else, not sure) is drawing too much power making the transistor or microprocessor or whatever electronic components inside DME overheat so much that it is no longer able to perform its function.
I have to admit, I did not do anything to the ignition coils, didn't even ohm them. Maybe I should. Anyone have the spec handy? I just have a hard time believing it could be a coil - while it runs, it runs perfect, no misses or anything.
How hot does your DME get after 30-40 minutes of running on a warm day?
I have an infrared thermometer, I will measure the temperature of the DME case when the car shuts down. Maybe one of the members on here can do the same, and we can compare readings.
Thanks everyone for your insight, hopefully we can get this car figured out.
Dan, although your suggestion is valid, I have my doubts that it's the loom. Here is why: I opened up part of the loom that runs along the firewall and leads up to the 3 relays. It is so clean and nice inside, none of the insulation is dry rotted or cracked and there is no water or any other kind of damage. It looks brand new. In fact, most everything on this car looks brand new. When the car is idling, I tried to pull, twist, move and otherwise mess with the loom to duplicate the problem - and nothing. It continues to run until the DME gets hot.
Twright, I have gone through these tests: When the car refuses to start, it loses spark and fuel pump relay no longer gets energized - I believe the same would happen if crankshaft position sensor was unplugged, as DME does not energize the fuel pump relay if there is no pulse from crank sensor (correct me if i'm wrong). Once the car shuts down. only installing my spare, COLD DME gets it to run again - and it starts immediately and runs PERFECT. Unplugging and plugging back the HOT DME does nothing.
In my opinion, something that DME supplies power to (Ignition coils? Fuel Pump Relay? Oxygen Sensor Relay? what else, not sure) is drawing too much power making the transistor or microprocessor or whatever electronic components inside DME overheat so much that it is no longer able to perform its function.
I have to admit, I did not do anything to the ignition coils, didn't even ohm them. Maybe I should. Anyone have the spec handy? I just have a hard time believing it could be a coil - while it runs, it runs perfect, no misses or anything.
How hot does your DME get after 30-40 minutes of running on a warm day?
I have an infrared thermometer, I will measure the temperature of the DME case when the car shuts down. Maybe one of the members on here can do the same, and we can compare readings.
Thanks everyone for your insight, hopefully we can get this car figured out.
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fixedwheelnut
- E30 Zone Regular
- Posts: 906
- Joined: Sun Nov 20, 2005 11:00 pm
- Location: South East London
May sound too simple have you changed/swapped the DME relay and Fuel pump relay? They suffer from dry solder joints inside when old this causes erratic voltage supply and cutting out. You can try tapping the relay with a screwdriver handle to see if it cuts out. They should be under a small black cover on the left inner wing, or under the plastic trim left side of the bulkhead.
As you lose both spark and fuel I would start with the DME relay it will be white if original or pale green if it has had a later replacement.
Edit-- I see you already have in that case check the voltages too and from each relay with a voltmeter to check they are OK and see if the earths are all good.
As you lose both spark and fuel I would start with the DME relay it will be white if original or pale green if it has had a later replacement.
Edit-- I see you already have in that case check the voltages too and from each relay with a voltmeter to check they are OK and see if the earths are all good.
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RossDavies
- E30 Zone Newbie
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- Joined: Wed Oct 14, 2020 6:32 pm
I agree that something maybe drawing too much current. Is the loom getting hot aswell? Maybe you could find the cause by finding a hot wire? Or perhaps you could try running an earth to the earth pins? Incase of a bad earth, causing it to over heat? Maybe worth a try.
Could you "borrow" another loom from a member , this guy is very good and it would eliminate one area as well.
Mart.
Only the E46 cab left now.
Just got too old.
Just got too old.
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twright
- E30 Zone Newbie
- Posts: 70
- Joined: Tue Sep 01, 2020 11:21 am
- Location: Indianapolis, Indiana USA
It appears as though you have too much current somewhere. Here are few more things to try:
1.) Look at all of your fuses and see if someone replace one with a MUCH higher value. This might be a clue as to where to look for the extra current.
2.) After the car has run for a while, start checking for a wire that is warm, or hot, to the touch. This will narrow down where the problem might be
1.) Look at all of your fuses and see if someone replace one with a MUCH higher value. This might be a clue as to where to look for the extra current.
2.) After the car has run for a while, start checking for a wire that is warm, or hot, to the touch. This will narrow down where the problem might be
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Thank you all !
I found an engine loom on Ebay and bought it, it was reasonably priced so I figured it's worth a try.
I couldn't borrow a loom from a member here, I am in US and not only is the shipping probably not worth it, but RHD is probably different from LHD.
While I wait on the loom to arrive, as suggested, I will start looking for a wire that gets hotter than others. I will also recheck all of my ground points, especially at the DME...
I really appreciate everyone's input, and I will keep this updated as I make some progress (hopefully !)
I found an engine loom on Ebay and bought it, it was reasonably priced so I figured it's worth a try.
I couldn't borrow a loom from a member here, I am in US and not only is the shipping probably not worth it, but RHD is probably different from LHD.
While I wait on the loom to arrive, as suggested, I will start looking for a wire that gets hotter than others. I will also recheck all of my ground points, especially at the DME...
I really appreciate everyone's input, and I will keep this updated as I make some progress (hopefully !)
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Check out this interesting thread:
https://www.r3vlimited.com/board/forum/ ... -hot-start
I know for a fact that this little plug is connected on my car (according to this thread, it should NOT be connected). My symptoms are more severe than what the thread describes, however this might be a step in the right direction. My car is in storage, can't get to it right now, but can't wait until tomorrow morning so I can try it !
I will keep you posted.
Thank you!
https://www.r3vlimited.com/board/forum/ ... -hot-start
I know for a fact that this little plug is connected on my car (according to this thread, it should NOT be connected). My symptoms are more severe than what the thread describes, however this might be a step in the right direction. My car is in storage, can't get to it right now, but can't wait until tomorrow morning so I can try it !
I will keep you posted.
Thank you!
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paultv
- E30 Zone Squatter
- Posts: 1541
- Joined: Mon Apr 21, 2014 11:00 pm
- Location: Auf dem Schnee: Germany
Not sure anyone suggested this, check the coil primary and secondary resistances...if it's breaking down especially the secondary winding it will have lower resistance to start with therefore pulls more current and as it gets hotter the resistance drops more, causing more current draw...making it hotter...ends up with thermal runaway....this stresses the ECU...
Primary 4 cylinder 0.82 ohms pins - and +
6 cylinder 0.5 ohms same pins on coil
Secondary 4 cylinder 8250 ohms pins- and 4 ( centre )
6 cylinder 5000 ohms same pins
Test hot and cold !
The resistances are for M20....but you get idea.
Just a thought
Paul
Primary 4 cylinder 0.82 ohms pins - and +
6 cylinder 0.5 ohms same pins on coil
Secondary 4 cylinder 8250 ohms pins- and 4 ( centre )
6 cylinder 5000 ohms same pins
Test hot and cold !
The resistances are for M20....but you get idea.
Just a thought
Paul
4th May 1990 325i Convertible.
BMW E30 Cabriolet Best Mod Ever:
https://bmwe30cabriolet-wdm.blogspot.com/
BMW E30 Cabriolet Best Mod Ever:
https://bmwe30cabriolet-wdm.blogspot.com/
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Thanks again to everyone for great suggestions.
This issue may be taking a different turn, as I work on the car more and I drive it more. And try to pretend that I am the Sherlock Holmes of auto mechanics
DME only overheats in traffic and at idle. It DOES NOT get hot at all during highway driving. I can drive on the highway for hours (today I did 3 hours of non stop highway driving at 3500rpm) without a glitch. It is when I hit stop-and-go traffic or stop the car and let it idle, that the DME starts to get hot and the car starts to act up.
On the highway, DME temperature is around 20-22*C. In stop and go traffic, DME temp goes to 40-45*C. Car will not shut off until DME temp gets to about 52-55*C. However, if I shut the car off myself when DME is at 45*C, it will not restart until it cools down for a few minutes.
Per suggestion from Paul, I checked the resistance of ignition coils. Low voltage side 0.8-1.0 ohms when cold, 0.7-0.8 ohms when hot. High voltage side is around 8.1-8.2Kohms both hot and cold. All coils read pretty much the same, which eliminates the coils, right?
This brings me to a question: could it be the Idle Control Valve? Logic suggests that DME should not need to energize the ICV at all during highway driving. It should only supply (pulsed?) ground to it during city driving and idling. If its internal resistance is low, it will overload the circuit inside the DME that supplies ground to it, causing the DME to get hotter than it should.
Please fire away with suggestions. If anyone has the resistance spec for the ICV, that would be a huge help.
As always, THANKS TO EVERYONE WHO IS TAKING THE TIME TO READ AND POST SUGGESTIONS.
This issue may be taking a different turn, as I work on the car more and I drive it more. And try to pretend that I am the Sherlock Holmes of auto mechanics
DME only overheats in traffic and at idle. It DOES NOT get hot at all during highway driving. I can drive on the highway for hours (today I did 3 hours of non stop highway driving at 3500rpm) without a glitch. It is when I hit stop-and-go traffic or stop the car and let it idle, that the DME starts to get hot and the car starts to act up.
On the highway, DME temperature is around 20-22*C. In stop and go traffic, DME temp goes to 40-45*C. Car will not shut off until DME temp gets to about 52-55*C. However, if I shut the car off myself when DME is at 45*C, it will not restart until it cools down for a few minutes.
Per suggestion from Paul, I checked the resistance of ignition coils. Low voltage side 0.8-1.0 ohms when cold, 0.7-0.8 ohms when hot. High voltage side is around 8.1-8.2Kohms both hot and cold. All coils read pretty much the same, which eliminates the coils, right?
This brings me to a question: could it be the Idle Control Valve? Logic suggests that DME should not need to energize the ICV at all during highway driving. It should only supply (pulsed?) ground to it during city driving and idling. If its internal resistance is low, it will overload the circuit inside the DME that supplies ground to it, causing the DME to get hotter than it should.
Please fire away with suggestions. If anyone has the resistance spec for the ICV, that would be a huge help.
As always, THANKS TO EVERYONE WHO IS TAKING THE TIME TO READ AND POST SUGGESTIONS.
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paultv
- E30 Zone Squatter
- Posts: 1541
- Joined: Mon Apr 21, 2014 11:00 pm
- Location: Auf dem Schnee: Germany
Disconnect the ICV and set the idle using a pad in the butterfly end stop screw if you need to and leave it running for half an hour...stays cool?
Paul
Paul
4th May 1990 325i Convertible.
BMW E30 Cabriolet Best Mod Ever:
https://bmwe30cabriolet-wdm.blogspot.com/
BMW E30 Cabriolet Best Mod Ever:
https://bmwe30cabriolet-wdm.blogspot.com/
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
I am back with an update!
Thanks to all your suggestions, I think this issue is on its way to being resolved. Paul, you hit the nail on the head. I'm excited!!!
First I checked the resistance of the ICV. It was 4 ohms (not sure what it should be, I can't find a spec) Then I disconnected the ICV and let the car idle - for 2 hours. The DME temperature didn't go up at all. Hovered around 18-22*C. Before, it would take 30 minutes to 1 hour for DME to get to 50-60*C and the car would shut off...
I purchased a used ICV on Ebay and waiting on it to arrive. I will keep this thread updated as this new-to-me ICV gets installed, hopefully resulting in a successful repair.
Meanwhile, an engine wiring loom I ordered earlier has arrived. I will be installing that as well, mainly to clean up the mess I made when I opened up the old loom to look for damage/corrosion/etc. It also came with the plastic cover that goes on the firewall that hides the loom and the relays (mine was missing).
Stay tuned for updates and pictures (once I get her detailed)
Thanks for the help everyone!
Thanks to all your suggestions, I think this issue is on its way to being resolved. Paul, you hit the nail on the head. I'm excited!!!
First I checked the resistance of the ICV. It was 4 ohms (not sure what it should be, I can't find a spec) Then I disconnected the ICV and let the car idle - for 2 hours. The DME temperature didn't go up at all. Hovered around 18-22*C. Before, it would take 30 minutes to 1 hour for DME to get to 50-60*C and the car would shut off...
I purchased a used ICV on Ebay and waiting on it to arrive. I will keep this thread updated as this new-to-me ICV gets installed, hopefully resulting in a successful repair.
Meanwhile, an engine wiring loom I ordered earlier has arrived. I will be installing that as well, mainly to clean up the mess I made when I opened up the old loom to look for damage/corrosion/etc. It also came with the plastic cover that goes on the firewall that hides the loom and the relays (mine was missing).
Stay tuned for updates and pictures (once I get her detailed)
Thanks for the help everyone!
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Aaaand back to square one 
DME getting hot again, car will not restart again once turned off - until the DME cools down. New engine wire loom, new Idle Air Control valve (but still gets hot with IAC disconnected altogether)
I got a set of ignition coils on the way, but I doubt this will fix anything... they ohmed out within specs.
I am out of ideas at this point.
Time for a LS3 swap?
DME getting hot again, car will not restart again once turned off - until the DME cools down. New engine wire loom, new Idle Air Control valve (but still gets hot with IAC disconnected altogether)
I got a set of ignition coils on the way, but I doubt this will fix anything... they ohmed out within specs.
I am out of ideas at this point.
Time for a LS3 swap?
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
A few shorted turns in the secondary of an ignition coil will not only damp its output, but will also increase the primary current somewhat, and won't be easily detectable by resistance readings.
Don't give up until you've tried a fresh coil set.
Don't give up until you've tried a fresh coil set.
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Thank you Brianmoooore and Mark for the suggestions. I am so grateful for this forum and the people here.
New set of coils went in - no improvement.
New development: Today was the first hot day here, the car sat out in the sun and the temperature inside the car was probably 45*c if not more. The car has not been ran in 3-4 days. I started the car, and it stalled out after 30 seconds, and wouldn't restart. DME was burning hot (I assume from the heat inside the car, because everything else in the car was also burning hot due to sitting in the sun all day). Replaced DME with spare (which was under the seat, it was also hot to the touch but not nearly as hot). and made it about 5-7 minutes before it shut off again. Plugged the original DME back in - no start! Carried one of the DME's inside the house, put it on top of the AC vent so it would cool down, brought it back out - car started right up and didn't stall until I turned it off - but by that time, the sun was gone and the temperature outside had gone down considerably.
My thoughts:
-DME should not quit working just because of the heat of the car being parked outside. If the DME quits simply because it's hot inside the car, there is something wrong with the DME.
-Although unlikely, it is possible that both DME's have an identical mode of failure.
-It could NOT be anything but the DME. Cold DME works, hot DME does not. Engine temperature makes no difference.
-I should buy another DME and try it
What do you think about this mess of a car? What's next if the 3rd DME does the same thing?
I love the car. I need to fix it.
Thanks in advance.
New set of coils went in - no improvement.
New development: Today was the first hot day here, the car sat out in the sun and the temperature inside the car was probably 45*c if not more. The car has not been ran in 3-4 days. I started the car, and it stalled out after 30 seconds, and wouldn't restart. DME was burning hot (I assume from the heat inside the car, because everything else in the car was also burning hot due to sitting in the sun all day). Replaced DME with spare (which was under the seat, it was also hot to the touch but not nearly as hot). and made it about 5-7 minutes before it shut off again. Plugged the original DME back in - no start! Carried one of the DME's inside the house, put it on top of the AC vent so it would cool down, brought it back out - car started right up and didn't stall until I turned it off - but by that time, the sun was gone and the temperature outside had gone down considerably.
My thoughts:
-DME should not quit working just because of the heat of the car being parked outside. If the DME quits simply because it's hot inside the car, there is something wrong with the DME.
-Although unlikely, it is possible that both DME's have an identical mode of failure.
-It could NOT be anything but the DME. Cold DME works, hot DME does not. Engine temperature makes no difference.
-I should buy another DME and try it
What do you think about this mess of a car? What's next if the 3rd DME does the same thing?
I love the car. I need to fix it.
Thanks in advance.
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
3rd DME arrived and installed today - same problem. Gets hot and car cuts out. All 3 DME's same symptoms.
Do you think I need to shift focus away from DME and onto something else?
Do you think I need to shift focus away from DME and onto something else?
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
The BMW M42 engine is a good, strong and reliable example of the ICE, with no known weak points. AFAIK, your problem is unique, so yes, I think you need to go back to basics. There is something wrong, that when you find it, will probably stand out and think "how can I have missed that ! "
It's possible that your DMEs are being damaged as soon as you install them, so ideally you need to try them on another M42. This approach could also be used for other parts, with the ideal result being to transfer the fault to the other car.
It's possible that your DMEs are being damaged as soon as you install them, so ideally you need to try them on another M42. This approach could also be used for other parts, with the ideal result being to transfer the fault to the other car.
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
Brianmoooore, I completely agree with your logic.
I bought a portable heat gun and a bottle of freeze spray. I plan on driving with my DME open and once it's hot enough to start causing problems, I plan to spray components to cool them to see which one makes a difference. On the same token, when it's cold I am going to use the heat gun to apply heat to various components to see if I can narrow down the one that causes the car to cut off.
I wish someone here had an e30 with M42 motor. That would just be a godsend to have one to swap parts with... I have a few friends with e30's but all have 6 cylinders, so no dice.
I bought a portable heat gun and a bottle of freeze spray. I plan on driving with my DME open and once it's hot enough to start causing problems, I plan to spray components to cool them to see which one makes a difference. On the same token, when it's cold I am going to use the heat gun to apply heat to various components to see if I can narrow down the one that causes the car to cut off.
I wish someone here had an e30 with M42 motor. That would just be a godsend to have one to swap parts with... I have a few friends with e30's but all have 6 cylinders, so no dice.
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
New facts:
DME gets hot simply with ignition ON, engine not running. I don't know how I never thought to try this before, but today I did. And, If I let it sit with the key ON engine OFF for 30-45 minutes, it will crank and not start. Exactly the same as if the engine was running. Same with all 3 DME's.
I also went as far as unplugging everything that can be unplugged - IAC, O2, coils, injectors, purge valve, cam/crank sensors, TPS, MAF, Fuel Pump Relay, o2 relay. Only left DME relay plugged in so it continues to power the DME. Still getting hot.
I believe this excludes coils, injectors, oxygen sensor, fuel pump and oxygen sensor relays, etc etc from possible culprits. I already changed the wiring loom with a known good part, so that can't be it either.
Where do I go from here? Ideas?
Thank you !
DME gets hot simply with ignition ON, engine not running. I don't know how I never thought to try this before, but today I did. And, If I let it sit with the key ON engine OFF for 30-45 minutes, it will crank and not start. Exactly the same as if the engine was running. Same with all 3 DME's.
I also went as far as unplugging everything that can be unplugged - IAC, O2, coils, injectors, purge valve, cam/crank sensors, TPS, MAF, Fuel Pump Relay, o2 relay. Only left DME relay plugged in so it continues to power the DME. Still getting hot.
I believe this excludes coils, injectors, oxygen sensor, fuel pump and oxygen sensor relays, etc etc from possible culprits. I already changed the wiring loom with a known good part, so that can't be it either.
Where do I go from here? Ideas?
Thank you !
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paultv
- E30 Zone Squatter
- Posts: 1541
- Joined: Mon Apr 21, 2014 11:00 pm
- Location: Auf dem Schnee: Germany
So make a list of everything that is still connected...I guess you have the ECU pin connections... whats left?
Input from the speed sensor on the diff...have you pulled the dash connectors as well for all the warning lights...do you have abs? Pull the abs computer or whatever you have...do each thing in turn.... is you battery voltage correct? Stupid question but its all long shots from here on in...charging voltage when running? ...oh yeah you say its fine.
Paul
Input from the speed sensor on the diff...have you pulled the dash connectors as well for all the warning lights...do you have abs? Pull the abs computer or whatever you have...do each thing in turn.... is you battery voltage correct? Stupid question but its all long shots from here on in...charging voltage when running? ...oh yeah you say its fine.
Paul
4th May 1990 325i Convertible.
BMW E30 Cabriolet Best Mod Ever:
https://bmwe30cabriolet-wdm.blogspot.com/
BMW E30 Cabriolet Best Mod Ever:
https://bmwe30cabriolet-wdm.blogspot.com/
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Brianmoooore
- E30 Zone Team Member
- Posts: 49358
- Joined: Mon Jan 10, 2005 11:00 pm
Pull the DME relay and turn the ignition on. This will just power up a part of the ECU.
Just a few thoughts on how to isolate the problem.
Is it the relay or the base assy where it plugs into causing the heat?
Using male/female connectors and short lengths of cable between, connect DME relay to base with jumpers. Power up and see if it's the relay that's generating the heat or the base unit. Will be one or other. If it is the base unit then could be fault in base assy or overloaded circuit. Get an ammeter that can read the expected currents and via jumper cables etc see where the load is that is causing it all to overheat. If this identifies an excessive load then move ammeter checks to those items downstream. If they are all pulling expected currents then fault is between base unit and pump etc
Is it the relay or the base assy where it plugs into causing the heat?
Using male/female connectors and short lengths of cable between, connect DME relay to base with jumpers. Power up and see if it's the relay that's generating the heat or the base unit. Will be one or other. If it is the base unit then could be fault in base assy or overloaded circuit. Get an ammeter that can read the expected currents and via jumper cables etc see where the load is that is causing it all to overheat. If this identifies an excessive load then move ammeter checks to those items downstream. If they are all pulling expected currents then fault is between base unit and pump etc
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carswithcharacter614
- E30 Zone Newbie
- Posts: 15
- Joined: Mon Apr 12, 2021 2:02 am
- Location: Columbus, OH, USA
I'd like to thank everyone for your suggestions and ideas. This issue is now SOLVED.
The problem was in the crankshaft position sensor, but to be more exact, the bracket that holds the sensor. It was bent, positioning the sensor away from the tone wheel on the harmonic balancer - creating a bigger (3.5mm) air gap between the sensor and the tone wheel.
This caused the signal to be borderline too weak to read, and while the DME was able to read the weak signal when it was cold, once it warmed up it could no longer read the signal, especially at the lower RPM's. That's why I could cruise on the highway all day, but as soon as took an exit, the car stalled - RPMs dropped, causing the crank signal amplitude to go below what DME was able to read.
A couple of taps with a brass hammer (to bend the bracket back where it belongs) fixed this elusive issue, and I couldn't be happier! Car does not stall and runs smoother, has more power, starts easier, WOW.
Maybe this thread will help someone some day!
Everyone here, thank you so much for the help. I couldn't have figured it out without guidance and direction from this forum and its awesome members .
The problem was in the crankshaft position sensor, but to be more exact, the bracket that holds the sensor. It was bent, positioning the sensor away from the tone wheel on the harmonic balancer - creating a bigger (3.5mm) air gap between the sensor and the tone wheel.
This caused the signal to be borderline too weak to read, and while the DME was able to read the weak signal when it was cold, once it warmed up it could no longer read the signal, especially at the lower RPM's. That's why I could cruise on the highway all day, but as soon as took an exit, the car stalled - RPMs dropped, causing the crank signal amplitude to go below what DME was able to read.
A couple of taps with a brass hammer (to bend the bracket back where it belongs) fixed this elusive issue, and I couldn't be happier! Car does not stall and runs smoother, has more power, starts easier, WOW.
Maybe this thread will help someone some day!
Everyone here, thank you so much for the help. I couldn't have figured it out without guidance and direction from this forum and its awesome members .
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MickstrickE30
- E30 Zone Newbie
- Posts: 5
- Joined: Sat Apr 14, 2012 11:00 pm
Brilliant! That really is one of those things that no anount of forum time will diagnose for you 
Its a great feeling, I found this through troubleshooting my own car which turned out to be the electrical contacts in the AFM. Similar you you having an easy fix in the end, I just wish it was easy to find the problem originally
Its a great feeling, I found this through troubleshooting my own car which turned out to be the electrical contacts in the AFM. Similar you you having an easy fix in the end, I just wish it was easy to find the problem originally
