Dead M3

[Split_S]

After a nice drive to my country place back in August the m3 refused to start after sitting for a few hours. She turned over just fine but no firing nor smell of gas. The same happened in my 91 318iS a few days prior and it was a dead fuel pump which I swapped out in 15 minutes.

Thinking it was the same after verifying the fuel pump was not spinning during cranking I ordered a new one and swapped her a few days later. No difference.. Now I have a spare LP fuel pump...

Since then Ive done the following:

1) New low pressure fuel pump. I originally thought that was the problem. OEM. Main fuel pump is new from last summer. Bosch.
2) New TDC sensor. This one was actually dead so I thought that would solve the problem.. It didnt.
3) New CIS sensor. Engine speed sensor was fine: tested good at 850 ohms.
Confirmed the reference pin on the flywheel was actually there. It is.
4) New main relay.
5) New Fuel pump relay.
6) Tested the coil - 12V with key on 2, 12V cranking.
6.5) Checked the plugs from the rotor but not the individual spark plugs
7) Tried to jumper the OBC ignition wires - no effect.
New OBC relay - not the problem.
9) Disconnected/reconnected the DME a few times - no effect.
10) Ran a wire direct from the #11 fuse to the LP fuel pump while cranking to see if there was a broken wire - the pump did not function (I tested the pump on 12V directly just before and it worked.)
11) I managed to swap the ECU into another m3 back in September - that car ran fine - so ECU is not the problem...

It must be a wiring or ground issue... maybe the M3 gods are angry at me..

Its important to note the car had been flawless until this. Never an issue starting idling or running... I posted this on s14.net and got a lot of help but no solution yet..

Any ideas anyone????

The horror...

[Yeti]

have you even checked for a spark as it not on the list lol nice though dude

[Split_S]

Coil was checked and it had voltage - also checked the plugs from the rotor but not the individual spark plugs..... didn't check the plugs as the fuel pumps weren't priming during cranking. On the M3 the fuel pumps only run during the crank (when the TDC sensor senses the flywheel spinning).

Edited the list now..thanks..

[Brianmoooore]

have you even checked for a spark as it not on the list lol nice though dude

[Yeti]

ok you should always check the spark plugs for a spark as with a car not starting always go with the basics to help i identify the issue so fuel,air and spark. as the other work was potentially unnecessary work as a no spark would of pointed you in the right direction if that was the case and saving you money.

so i would pull fuse 11 for the fuel pump to stop it priming.pull the plugs out and lean them on the engine with the ht lead on obviously so it earths out and turn it over to see if there is a spark and have you continuity tested the ht leads as i think they should be about 5k ohms.

[Split_S]

Thanks yeti.
But the critical issue is that the pumps are not priming. At all. That's why I haven't bothered checking the individual spark plugs although I've checked to make sure there was power to the coil and leads. Ive been thru the electrical schematics front and back in order to understand the system better and that's why Ive checked all that I have checked..

Im just stubborn and dont want to give up and haul her to a specialist... maybe I should...

[Yeti]

ah yea ok sorry dude missed that lol i saw the coil check but not the spark plugs so i jumped at that lol what FP do they have? internal fuel pump or external ? either way i would run 12 volts and earth to the pump the right way so pumps and not sucks and start the car because if it runs that will confirm a wiring fault . also when you tested the pump did fuel come out as ive had fuel pumps pop there clogs so they run but dont actually pump fuel as that could be another issue too.

[bss325i]

Check terminal 30 at the main relay for a permanent 12V.

If there in no voltage at that terminal then there is an inline fuse near the battery in the boot part way along the smaller wire coming off the + terminal on the battery. Its this wire that feeds terminal 30 of the main relay and without that relay switching neither with the fuel pump relay.

I have had this problem on another M3 and it gives the symptoms you describe.

[Split_S]

yeti - no worries.. and thanks I haven't checked the pumps that way yet..

bss...I havent done that, although I did test for voltage on that line in the boot.. Still I will check for voltage at the relay..... thanks!

[Split_S]

bss - I owe you a tonne of beer my friend!

I had checked that line with a friend and it supposedly had 12V - somehow we screwed up. I should have stripped away the rubber from the fuse to check it but I trusted my friends measurement (NOT blaming him - it was my fault for not double checking).. I just stripped it now and see for yourself:



Im happy and I want to shoot myself.... the car has been off the road since August for THAT!! Now there is a foot of snow outside..the car wont move till April!

Thanks!

[Speedtouch]

But, what caused the fuse to blow in the first place?

[Brianmoooore]

Things aren't adding up here! With that fuse blown, there will be no electrical activity of the engine whatsoever, except for cranking. There will be 12 volts + on both terminals of the ignition coil, but without triggering by the ECU, there should, be no sparks, and, as Speedtouch has alluded to, a blown fuse is NOT a fault - it's the result of a fault.

[Split_S]

Good point. Weirder still is that the reference sensor was DEAD. Reading 0 ohms. I initially thought that was the problem as without it reading flywheel spin the ECU doesnt think the engine is turning.. So that failed for sure right away and the fuse also failed - but when? The fuse looks fatigue cracked - not melted at all. Simply cracked.

As I said earlier - I never checked for spark at the plugs as the pumps were not priming - that to me - was the problem. I did get 12V at the coil BUT I was supposed to as power to the coil is routed thru the OBC relay. I understood that. What I didnt fully understand (no info on this in the electrical diagrams) is how power from that line in the pic above is routed to the main relay. I will go back and once again study the electrical diagrams as Im pretty stupid and may have missed it completely!!

All I know is that the car now works fine - 4 starts and I even took her out for a drive this morning as the roads are dry.

I still want to know exactly what happened though...

[Speedtouch]

I had one of those 'fusible links' from the battery power lead in the boot blow on an E34 535i after I accidentally shorted a spanner to earth while doing something under the bonnet. It took me quite a while to figure out what had actually blown!

IIRC, mine looked like it had just cracked too.

[bss325i]

http://www.armchair.mb.ca/~dave/BMW/e30/e30m3_89.pdf

If you look at page 1364-4 you will see that the terminal 30 of the main relay comes from what the diagram shows as battery junction block but does not show it as a fuse.

[bss325i]

As for having 12v when your friend checked it, when i had this problem it seemed be intermittent and that i put down to the broken fusible link intermittently making contact so you may have had the same.

Glad i could help.

[Brianmoooore]

http://www.armchair.mb.ca/~dave/BMW/e30/e30m3_89.pdf

If you look at page 1364-4 you will see that the terminal 30 of the main relay comes from what the diagram shows as battery junction block but does not show it as a fuse.

That needs to be read in conjunction with 0670-2, which, although it still doesn't show the inline fuse, does show the separate wires from the battery to the battery junction block, and the wire that feeds pin 30 of the fuel pump and main relays.

Fuses that feed items with large inrush currents, such as motors, do sometimes fail from fatigue, as they experience thermal stress from the brief high current at switch on, but I wouldn't classify engine management electronics in that group.

[Split_S]

All in all it is a tricky situation to diagnose correctly - especially when you are ignorant of said fuse!

Should the M3 or my iS fail to start in the future - that damn fuse will be the first thing I check!!

Thanks gents!

[Brianmoooore]

Should the M3 or my iS fail to start in the future - that damn fuse will be the first thing I check!!

You'll have trouble finding it on an iS! Only fitted on E30s with rear mounted batteries.
The idea of twin wires from the rear mounted battery to the front of the car is to isolate the engine electrics from the voltage drop and general voltage fluctuations caused by varying currents in the long thick cable. The engine takes a relatively small and constant current, so only requires a relatively small wire from the battery to the engine, which, because of that small size, requires protection against short circuits to the body. With a front mounted battery, a stable voltage is available right at the battery terminal, and the wire to the engine is only short, so no fuse is required.

[Split_S]

Thanks Brian - I have it in the iS - NA cars all have rear mounted batteries. Thanks for clarifying it's purpose, very much appreciated!