Iv finished building a turbo m20b25 and managed to get up to DmcL in Derry to live map it on his motronic tuning setup. Everything runs well until i reach full 8psi boost and then it wont rev any higher than 3300rpm, just hesitates, detonates and wont rev. It can rev further to around 5000 but only at a part throttle run. The boost gauge shows a clean rise to 8psi and then just stop there until i take my foot off. Lambda readings show that everything is perfect all the way up to the wall. The engine will rev to redline without issues at N/A.
We tried a very aggressive timing map and it seems to rev stronger and higher to around 4000 but still hit a wall there. Im not sure if its a mapping issues though.
specs;
m20b25 8;8;1 low comp.
medium intercooler 2.5" pipes.
ebay turbo .63 cold + hot with internal wastegate @8psi.
bosch saab turbo 1" BOV.
m20 AFM before turbo.
30lb injectors.
Could it be a mapping issue?
Could it be a internal wastegate issue?
Could it be a BOV/ boost leak issue?
325i turbo wont rev past 3300rpm @full 8psi.
Moderator: martauto
Is it a missfire ?
Check the plug gaps.
Check the plug gaps.
our suspicions on the ignition system might be the issue after all then 
what sort of plug gap would u suggest for mild boost? also would it be worth fitting a more powerful coil?
i dont think it was detonating when hitting the wall just not revving higher and AFR would start to lean out a bit if the throttle was held after hitting the wall. after thinking about it i dont think we shifted where the wall was but with more agressive ignition timing before and starting to come onto boost the revs were rising alot quicker so i think the wall seemed to shift up a little due to the revs climbing quicker and with more momentum when hitting the problem area.
also one thing im curious about.. occasionally (maybe 40-50% of the time) after revving the engien out a little and coming onto boost and then clutching in and letting the revs fall the engine would stall instead of returning to idle, any ideas there gunni? i tried a couple things briefly but didnt seem to have an impact. im thinking maybe i can increase closed loop idle speed somewhere around 1500-2000rpm so the ECU might hopefully catch it when the revs are dropping out of gear and bring the revs back down to idle speed nice and gently so as to avoid stalling without setting a rediculously high idle to combat the issue. maybe even try beefing up fuelling in the lowest load row of the low part throttle map as it seemed to be indicating lean when it would stall with the revs dropping and i know on engine decel it will peg the low load side of the low part throttle map as revs fall. also could a recirculating dump valve help with that?
boost seemed to hold steady at 8psi when we hit the wall and until the throttle was lifted even tho the revs would stop climbing around 3500rpm or so, seems like the turbo side of things was working as it should and the problem lies elsewhere. also no change with the problem running the AFM before or after the turbo and we also tried a known good AFM of my own and messed with the spring tension in that on the off chance but still no effect. no amount of raising/lowering ignition timing or richening/leaning the AFR had any real affect on the issue either which is why im leaning towards the ignition system the more i think about it.
what sort of plug gap would u suggest for mild boost? also would it be worth fitting a more powerful coil?
i dont think it was detonating when hitting the wall just not revving higher and AFR would start to lean out a bit if the throttle was held after hitting the wall. after thinking about it i dont think we shifted where the wall was but with more agressive ignition timing before and starting to come onto boost the revs were rising alot quicker so i think the wall seemed to shift up a little due to the revs climbing quicker and with more momentum when hitting the problem area.
also one thing im curious about.. occasionally (maybe 40-50% of the time) after revving the engien out a little and coming onto boost and then clutching in and letting the revs fall the engine would stall instead of returning to idle, any ideas there gunni? i tried a couple things briefly but didnt seem to have an impact. im thinking maybe i can increase closed loop idle speed somewhere around 1500-2000rpm so the ECU might hopefully catch it when the revs are dropping out of gear and bring the revs back down to idle speed nice and gently so as to avoid stalling without setting a rediculously high idle to combat the issue. maybe even try beefing up fuelling in the lowest load row of the low part throttle map as it seemed to be indicating lean when it would stall with the revs dropping and i know on engine decel it will peg the low load side of the low part throttle map as revs fall. also could a recirculating dump valve help with that?
boost seemed to hold steady at 8psi when we hit the wall and until the throttle was lifted even tho the revs would stop climbing around 3500rpm or so, seems like the turbo side of things was working as it should and the problem lies elsewhere. also no change with the problem running the AFM before or after the turbo and we also tried a known good AFM of my own and messed with the spring tension in that on the off chance but still no effect. no amount of raising/lowering ignition timing or richening/leaning the AFR had any real affect on the issue either which is why im leaning towards the ignition system the more i think about it.
WMMotorsports
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MJJ_ZX6RR
- E30 Zone Regular
- Posts: 660
- Joined: Mon Nov 10, 2008 11:00 pm
- Location: Wiltshire, UK
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Something as simple as the fuel pump not keeping up with demand?DmcL wrote:.... and AFR would start to lean out a bit if the throttle was held after hitting the wall.
Martin.
----------------------------------------------------
Lots of bikes, the odd modern BMW, and now an 88 e30 335i Cab project with E32 running gear
Lots of bikes, the odd modern BMW, and now an 88 e30 335i Cab project with E32 running gear
I have a walbro pump in the car. Iv tested it to flow twice as much fuel as the stock pump and pressure is good to so Im very happy that the fuel system is 100%.
I have had other e30s pop off air intake pipes that results in stalling when the engine winds down. Thats another reason why I think a dodgy BOV or boost leak might be the problem.
I have had other e30s pop off air intake pipes that results in stalling when the engine winds down. Thats another reason why I think a dodgy BOV or boost leak might be the problem.
The stock coil is good for about 1.1-1.2bar boost when using a 57mm compressor, so about 350-360hp is when it craps out. But then again maybe you don´t have dwell control and can´t up the dwell to make the coil charge itself a bit more, 3.2ms is about as far as a stock coil can do in terms of charging itself without over heating.
A missfire is also very evident as it´s almost like letting go of the throttle a bit, depends on how many plugs aren´t firing.
Check that the gap on the plugs is about 0.5mm or so
A MSD coil doesn´t really do any better then the stock one.
A missfire is also very evident as it´s almost like letting go of the throttle a bit, depends on how many plugs aren´t firing.
Check that the gap on the plugs is about 0.5mm or so
A MSD coil doesn´t really do any better then the stock one.
i have full control over dwell.. i actually tried increasing dwell a little bit but no change. i dont know what the dwell would have been in milliseconds tho as im not sure on the conversion from raw data (0-255 decimal or 0-FF in hex) to ms. i increased dwell up to a maximum of +10 which would be about 3.9% of an increase.
we never checked the gap on the plugs but they were pulled to clean them and just by eyeballing the gap id say they were in the 1.2-1.6mm region. would that be far too big of a gap for boost? if so that may be the problem. pity neither of us thought to re-gap the plugs when they were out
we never checked the gap on the plugs but they were pulled to clean them and just by eyeballing the gap id say they were in the 1.2-1.6mm region. would that be far too big of a gap for boost? if so that may be the problem. pity neither of us thought to re-gap the plugs when they were out
WMMotorsports
1.2-1.6 is abit on the high side.
sounds like regapping should solve the problem.
sounds like regapping should solve the problem.
good stuff.. hopefully we found our problem then. was joking saying its probably something small/stupid and it may well be if it turns out its just the plug gaps being too wide.
WMMotorsports
1.2 to 1.6mm plug-gap @ 8psi on the stock ignition is excessively high!
The problem you have experienced is brought about for two reasons:
1) the voltage at which the plug arcs-over (sparks) increases with both boost pressure and electrode gap - meaning that higher boost pressure requires more voltage to arc over a given dimension plug gap. I'm assuming you don't want to have to lower your boost pressure, so the obvious solution is to reduce your plug gap (or fit an ignition/coil that can generate sufficient voltage to arc the gap at that pressure).
2) Available dwell time on an electronic (ECU or distributor controlled) ignition system decreases with rising rpm.
This second point warrants some thinking about: At 3600rpm your crank is rotating 60 times per second. On a 6-cylinder engine the ignition produces 3 sparks per rotation of the crank, so that’s 180 sparks per second, or one spark every 0.00555 seconds (5.55 ms).
Now, as your engine rpm climb, the time interval between sparks will decrease. At 4800 rpm, for example, it has reduced to 0.00416 seconds (4.16ms). At 5400 rpm its down to 0.0037 seconds (3.7ms). See where I am going with this? The time between sparks is the absolute maximum that is available to your ECU as dwell time, and technically, even all of that cannot be consumed. As your engine rpm climb higher, the time available for dwell effectively reduces!
So why am I telling you this and who cares anyway? Simple, dwell time is the time duration over which current is delivered to the primary winding of the ignition coil in order to store energy in the coil. As a rule, the shorter the dwell time, the less the energy stored in the coil, and hence the less the voltage that is delivered to the spark plugs at progressively increasing rpm.
Now, lets say you set your dwell time (via your ECU) to 6ms because you determine experimentally that this gives you sufficient current through the primary of the coil to give you enough voltage across the secondary winding to spark your plugs under boost. All well and good. Problem is, above 3300rpm there isn’t enough time between sparks to execute 6ms of dwell. Hence, above 3300rpm, your ECU will start to reel in (progressively reduce) your dwell time, bringing about the progressive decline in the performance of your ignition ”“ right when you need it most! Hence the sensation that above certain rpm your ignition seems to run out of puff. It’s almost like having a built in rev limiter. Know the feeling?
Closing up your plug gap to ~0.6mm should see you come right at 8psi of boost. If not, look at fitting an improved ignition coil.
FYI, the most advocated and widely acknowledged solution to this problem is to fit a capacitive discharge ignition (CDI) unit. The operation of a CDI unit is independent of dwell time (take note of this), and thus the high voltage output of the ignition coil remains constant (does not decrease) with increased engine rpm (within the limitations of the CDI’s internal power supply that is). Probably the most popular CDI on the market is the 6 series manufactured by MSD in the US, see here. Don’t get me wrong, I am not suggesting that you need one, or that you go out and buy one. I mention this only for your interest.
The problem you have experienced is brought about for two reasons:
1) the voltage at which the plug arcs-over (sparks) increases with both boost pressure and electrode gap - meaning that higher boost pressure requires more voltage to arc over a given dimension plug gap. I'm assuming you don't want to have to lower your boost pressure, so the obvious solution is to reduce your plug gap (or fit an ignition/coil that can generate sufficient voltage to arc the gap at that pressure).
2) Available dwell time on an electronic (ECU or distributor controlled) ignition system decreases with rising rpm.
This second point warrants some thinking about: At 3600rpm your crank is rotating 60 times per second. On a 6-cylinder engine the ignition produces 3 sparks per rotation of the crank, so that’s 180 sparks per second, or one spark every 0.00555 seconds (5.55 ms).
Now, as your engine rpm climb, the time interval between sparks will decrease. At 4800 rpm, for example, it has reduced to 0.00416 seconds (4.16ms). At 5400 rpm its down to 0.0037 seconds (3.7ms). See where I am going with this? The time between sparks is the absolute maximum that is available to your ECU as dwell time, and technically, even all of that cannot be consumed. As your engine rpm climb higher, the time available for dwell effectively reduces!
So why am I telling you this and who cares anyway? Simple, dwell time is the time duration over which current is delivered to the primary winding of the ignition coil in order to store energy in the coil. As a rule, the shorter the dwell time, the less the energy stored in the coil, and hence the less the voltage that is delivered to the spark plugs at progressively increasing rpm.
Now, lets say you set your dwell time (via your ECU) to 6ms because you determine experimentally that this gives you sufficient current through the primary of the coil to give you enough voltage across the secondary winding to spark your plugs under boost. All well and good. Problem is, above 3300rpm there isn’t enough time between sparks to execute 6ms of dwell. Hence, above 3300rpm, your ECU will start to reel in (progressively reduce) your dwell time, bringing about the progressive decline in the performance of your ignition ”“ right when you need it most! Hence the sensation that above certain rpm your ignition seems to run out of puff. It’s almost like having a built in rev limiter. Know the feeling?
Closing up your plug gap to ~0.6mm should see you come right at 8psi of boost. If not, look at fitting an improved ignition coil.
FYI, the most advocated and widely acknowledged solution to this problem is to fit a capacitive discharge ignition (CDI) unit. The operation of a CDI unit is independent of dwell time (take note of this), and thus the high voltage output of the ignition coil remains constant (does not decrease) with increased engine rpm (within the limitations of the CDI’s internal power supply that is). Probably the most popular CDI on the market is the 6 series manufactured by MSD in the US, see here. Don’t get me wrong, I am not suggesting that you need one, or that you go out and buy one. I mention this only for your interest.
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti
great reply, plenty of info there.
i know dwell reduces with RPM, it has to to allow the spark plug firing to keep up with the increasing RPM. it also changed with voltage in motronic. here is the standard ignition dwell map displayed in raw data (0-255), percent and i believe also MS (not 100% sure on the conversion).
what im not sure of is just how much additional dwell i can add before risking damaging/overheating the coil (assuming its a standard M20 coil).
i have heard of CDI setups before but theres loads of M20 turbo's running on standard ECU's with/without tuning and with standard ignition dwell maps... allbeit with a proper plug gap.
i also noticed the coil on the car doesnt look like the standard M20 coil, its got a plastic bit on the top around where the + and - connections are but it is a bosch coil of some sort. i was thinking that may also be part of the problem if its a coil thats meant for a 4 cylinder engine rather than a 6 cylinder.
i know dwell reduces with RPM, it has to to allow the spark plug firing to keep up with the increasing RPM. it also changed with voltage in motronic. here is the standard ignition dwell map displayed in raw data (0-255), percent and i believe also MS (not 100% sure on the conversion).
what im not sure of is just how much additional dwell i can add before risking damaging/overheating the coil (assuming its a standard M20 coil).
i have heard of CDI setups before but theres loads of M20 turbo's running on standard ECU's with/without tuning and with standard ignition dwell maps... allbeit with a proper plug gap.
i also noticed the coil on the car doesnt look like the standard M20 coil, its got a plastic bit on the top around where the + and - connections are but it is a bosch coil of some sort. i was thinking that may also be part of the problem if its a coil thats meant for a 4 cylinder engine rather than a 6 cylinder.
WMMotorsports
It is for this purpose that I keep handy a portable oscilloscope and current clamp. So long as the current through the coil primary winding appears to rise linearly (looks like a ramp) the coil is safe. At such point as the current becomes non-linear and rapidly starts to tail upwards then the magnetic core of the coil is saturating, and it is at this point that the primary winding will begin to heat excessively and the ECU output transistors are placed at risk. If I see this happening then it is imperative that the dwell be reduced. Unfortunately, without a current clamp and oscilloscope this is impossible to see happening. If its happening without you knowing about it then both your coil and ECU are at risk.DmcL wrote:what im not sure of is just how much additional dwell i can add before risking damaging/overheating the coil (assuming its a standard M20 coil).
I only mentioned this for your interest. I have a CDI on my own car where I push up to 1.5bar of boost. From experience (before and after) I can attest that a CDI makes a world of difference. At 8psi, however, you won’t need oneDmcL wrote:i have heard of CDI setups before but theres loads of M20 turbo's running on standard ECU's with/without tuning and with standard ignition dwell maps... allbeit with a proper plug gap.
Sounds dodgy to me. It’s a misconception amongst some that a coil is a coil is a coil is a coil. I’d whip it out and put a stock coil back in.DmcL wrote:i also noticed the coil on the car doesnt look like the standard M20 coil, its got a plastic bit on the top around where the + and - connections are but it is a bosch coil of some sort. i was thinking that may also be part of the problem if its a coil thats meant for a 4 cylinder engine rather than a 6 cylinder.
"It is amazing how many drivers, even at the Formula-1 level, think that brakes are for slowing the car down." - Mario Andretti
yea i know all coils are not created equal.. he wasnt sure what it was, might have even been in there when he got the car.
would i be able to pick up a portable oscilloscope/current clamp fairly cheaply? maybe even if i found someone near me that had one i could borrow... id love to find out just how much additional dwell the standard M20 coil can handle. might even find i can reshape the dwell map and make some improvements over standard rather than just bumping the whole map by the same amount.
at what boost pressure will the normal coil/dizzy/plug setup become an issue with boost? i plan to turbocharge my 325i at some point and id like to see something in the 1-1.5 bar region ultimately. if i have control of dwell and can measure/adjust it and run a plug gap of 0.5-0.6mm with a healthy (possibly slightly better) coil should i run into spark issues or not?
the whole standard ignition setup/dwell/plug gap issue might not be a problem by the time i boost my M20 as i would like to retrofit M50 ECU to gain the perks of the M50's management system such as factory MAF, coil on plug, sequential injection and ofcourse better resolution out of the box in many maps in the ECU. at the rate im going id probably have an M50 ECU in there with all necessary bits long before i have a turbo on it.
would i be able to pick up a portable oscilloscope/current clamp fairly cheaply? maybe even if i found someone near me that had one i could borrow... id love to find out just how much additional dwell the standard M20 coil can handle. might even find i can reshape the dwell map and make some improvements over standard rather than just bumping the whole map by the same amount.
at what boost pressure will the normal coil/dizzy/plug setup become an issue with boost? i plan to turbocharge my 325i at some point and id like to see something in the 1-1.5 bar region ultimately. if i have control of dwell and can measure/adjust it and run a plug gap of 0.5-0.6mm with a healthy (possibly slightly better) coil should i run into spark issues or not?
the whole standard ignition setup/dwell/plug gap issue might not be a problem by the time i boost my M20 as i would like to retrofit M50 ECU to gain the perks of the M50's management system such as factory MAF, coil on plug, sequential injection and ofcourse better resolution out of the box in many maps in the ECU. at the rate im going id probably have an M50 ECU in there with all necessary bits long before i have a turbo on it.
WMMotorsports
Normally the stock ignition system starts becoming an issue around 1.3bar boost depending on the turbocharger used. Figure something close to 350hp after you start loosing dwell.
ok cool.. might give me another little challenge if i end up boosting it on the standard E30 management and start getting the 1 bar + ballpark.
WMMotorsports