m60b40 missing, low idle, back firing

[Jonsku]

Nope. The engine is dead quiet so I figured there's no reason to.

Yes, main thought was that if it is old & tired, it could affect on the timing (especially when letting of throttle => oil pressure drops).

In any case, it all sounds very weird. Just to be on the safe side, I'd replace the tensioner and verify that timing is ok.

[dirty30]

Just thinking out loud here...

The E32 I bought to slaughter for my swap was a pretty nice car. Ran and shifted really well and was really quiet throughout the rev range. Despite the seemingly perfect mechanical condition of the engine based on the way it ran it was far from sound. All the guides were heavily grooved and extremely brittle. The upper chain tensioner "slide rails" also had heavy grooving. I was suprised by the significant wear despite how quiet the engine was. Just food for thought.

[JGood]

STILL battling this. The main symptoms are as follows:

After coasting/engine braking, if I hit the gas lightly, it lets out a loud crack/backfire through the exhaust, stumbles for a second, then goes. The lighter I get on the gas, the harder it stumbles. If I just slam the gas to the floor, I still get the crack/backfire in the exhaust, but no noticeable hesitation or stumble.

Also, when engine braking to a stop, if I leave off the gas above 1500 RPM's, the engine will return to idle without issue. If I leave off the gas below 1500 RPM's, it will usually stall. It will restart and idle perfectly at 600 RPM's all day though. It's only when leaving off the gas below 1500 RPM's that it tries to stall, it's almost as if the ICV doesn't respond and catch the engine in time.

I have replaced the following, some of these parts 3-4 times, most with new OEM parts. All have been fully tested regardless:

DME
Engine harness
MAF
TPS
Coolant temp sensor
Air temp sensor
ICV
Crank sensor
Cam sensor
Coil packs and boots
Spark plugs
Fuel injectors
FPR
Fuel lines
Fuel filter
Fuel pumps
Throttle body
All intake gaskets
Oxygen sensors

I added about 20 lbs of extra engine grounds at one point too, as a test. I ran 16 gauge wire to each coil pack bolt, to some valve cover bolts, an extra block ground, an extra harness ground, and replaced the battery ground. It made no change.

The engine has been smoke tested for vacuum leaks. It's been fuel pressure tested. It's been on a Snap-on Modis scanner graphing data from all sensors, all is well.

I compression tested it again last night, got the following:
215
200
210
210
220
215
180
225

The 180, although strangely low, isn't going to cause the issues I'm having. I put a squirt of oil in that cylinder and retested, it jumped up to 220.

My buddy is bringing home his Autologic scanner tonight, hopefully that will pull some useful info. They are supposed to be almost as good as the GT1.

If that doesn't give me any info, I'm going to buy the timing tools and make sure the timing is correct.

After that, I don't know... There's nothing else to replace/check.

[dirty30]

Mine backfires in the same manner, just minus the stalling. I don't think the backfire will end up being related once you fix this, I think even jonsku said he has heard of the backfire issue also.

[JGood]

Mine backfires in the same manner, just minus the stalling. I don't think the backfire will end up being related once you fix this, I think even jonsku said he has heard of the backfire issue also.

Yours backfires when you get on the gas? It's not the normal rumble/crackle most BMW's do when you leave off the gas, it's when I get on the throttle. I don't think I've ever heard of a single other car do that.... none of the 540i's, 740i's that my friends have owned have done it.

Honestly, I've learned to drive around the stalling. I can prevent it, and it really doesn't bother me any more. It's the stumbling EVERY time I touch the gas pedal that's pissing me off. The smoother I try to drive it, the more it hesitates and bucks around. It makes for a jerky ride, the car feels like a piece of shit. So I usually just hammer the thing.

PS, your P/S pump will be arriving tomorrow.

[dirty30]

Yours backfires when you get on the gas?
PS, your P/S pump will be arriving tomorrow.

Yeah its always just one loud crack but it does backfire when you are coasting in gear and get back on the gas.

PS- Awesome!

[JGood]

Yeah its always just one loud crack but it does backfire when you are coasting in gear and get back on the gas.

PS- Awesome!

That seems really strange to me. My 4.4 X5 never did it, my buddies 4.4 740i doesn't do it, and I've been around plenty of e34 and e39 540i's that never did it.

I forget if I already asked you, are you coming to Bimmerfest?

[dirty30]

That seems really strange to me. My 4.4 X5 never did it, my buddies 4.4 740i doesn't do it, and I've been around plenty of e34 and e39 540i's that never did it.

I forget if I already asked you, are you coming to Bimmerfest?

I remember Jonsku saying that the M60 swap cars backfire like that at one point in time, my E32 never did though. Maybe he could chime in here.

I'm skipping it this year, the venue is lame (large parking lot) and the Pittsburgh Gran Prix is the same weekend. I really want to get started on my M coupe trailing arm swap, finned diff cover swap, power steering project etc. I also want to play around with shorter subframe spacers or none all together. I've been kicking around the idea of doing an HPDE in the car sometime in the fall so I may pull the seats in favor of something more grippy and add some loops for harnesses. Might as well have some fun in the car, its literally been sitting in the garage all summer save for a few short trips and The Vintage.

[JGood]

I'm skipping it this year, the venue is lame (large parking lot) and the Pittsburgh Gran Prix is the same weekend. I really want to get started on my M coupe trailing arm swap, finned diff cover swap, power steering project etc. I also want to play around with shorter subframe spacers or none all together. I've been kicking around the idea of doing an HPDE in the car sometime in the fall so I may pull the seats in favor of something more grippy and add some loops for harnesses. Might as well have some fun in the car, its literally been sitting in the garage all summer save for a few short trips and The Vintage.

Nobody likes a garage queen! I've thought about running no spacers as well, I just don't feel like rebuilding my headers for the third time, or cutting up the oil pan, and one of those would need to be done. You should definitely track that car though!



My buddy came over with the Autologic scanner. All seemed well except for one thing.

Question: Where do you have your road speed signal hooked up to? Pin 14 on the x20 is road speed signal. It should go to the cluster. I have it hooked up to one of the three pins below (they are all the same, they all have continuity)




However, with the Autologic scanner hooked up, my road speed signal was wrong. It read based off of engine RPM instead of my actual road speed. It read 40 km/h at idle, with the car not moving, and shot up to like 300 km/h at redline. When driving, the actual road speed had no effect on DME's road speed. It seems as though Motronic uses RPM as a 'backup' to do the calculation, although I'm not sure how it assumes what gear you'd be in, unless it's an auto. My DME is from an auto...

My speedometer works, so the road speed signal to my cluster is good. And I swapped clusters, with another known good one, and the Autologic still read incorrectly. I checked continuity from the road speed wire, from the end connecting to the cluster to the end connected to the DME, no resistance. And I've tried multiple DME's.

So either I am wrong in pulling road speed signal from there, or the Autologic is not reading it properly. Weird thing is, I'm not getting a code for a missing speed signal, even if I unplug that wire to the cluster. I did get it once in the past though when messing with stuff, but I don't remember what triggered it.

[dirty30]

Should be in pin 1 of the green C6 plug. At least that's what the ETM says. I'm pretty sure all three positions do VSS output though.

Does your idle stay around 800-900ish when the vehicle is coasting in neutral then slowly fall to 600 when it is stopped? Mine does, it's seems like the only thing the VSS input to the DME does. Did your engine harness have the plug for the gear switch thing too? I guess it tells the DME that the car is in gear? (1-5/6) does not actually know what gear it is in, just closes a switch when not in neutral.

Nobody likes a garage queen! I've thought about running no spacers as well, I just don't feel like rebuilding my headers for the third time, or cutting up the oil pan, and one of those would need to be done. You should definitely track that car though!



My buddy came over with the Autologic scanner. All seemed well except for one thing.

Question: Where do you have your road speed signal hooked up to? Pin 14 on the x20 is road speed signal. It should go to the cluster. I have it hooked up to one of the three pins below (they are all the same, they all have continuity)




However, with the Autologic scanner hooked up, my road speed signal was wrong. It read based off of engine RPM instead of my actual road speed. It read 40 km/h at idle, with the car not moving, and shot up to like 300 km/h at redline. When driving, the actual road speed had no effect on DME's road speed. It seems as though Motronic uses RPM as a 'backup' to do the calculation, although I'm not sure how it assumes what gear you'd be in, unless it's an auto. My DME is from an auto...

My speedometer works, so the road speed signal to my cluster is good. And I swapped clusters, with another known good one, and the Autologic still read incorrectly. I checked continuity from the road speed wire, from the end connecting to the cluster to the end connected to the DME, no resistance. And I've tried multiple DME's.

So either I am wrong in pulling road speed signal from there, or the Autologic is not reading it properly. Weird thing is, I'm not getting a code for a missing speed signal, even if I unplug that wire to the cluster. I did get it once in the past though when messing with stuff, but I don't remember what triggered it.

[JGood]

Should be in pin 1 of the green C6 plug. At least that's what the ETM says. I'm pretty sure all three positions do VSS output though.

Does your idle stay around 800-900ish when the vehicle is coasting in neutral then slowly fall to 600 when it is stopped? Mine does, it's seems like the only thing the VSS input to the DME does. Did your engine harness have the plug for the gear switch thing too? I guess it tells the DME that the car is in gear? (1-5/6) does not actually know what gear it is in, just closes a switch when not in neutral.

The idle bounces around a bit when coasting in neutral. Not severely, but noticeable, maybe 600-800 rpm? It sits at 500-600 at idle.

I'm not aware of that connector. The only thing hooked to my trans is the reverse light connector. There is a few extra connectors on the harness, which I left alone.

[JGood]

I put the stock DME back in, and all the problems are gone. It doesn't try to stall at all, and the hesitation is 99% gone. It still feels a little jerky when on/off the gas around 2k RPM's, but it's very very minor compared to before.

I have no idea how/why it's working now. I've tried the stock DME in the past, but I have done a few things since the last time I tried it.

It does still let out a loud crack from the exhaust every single time I get on the gas, which is very annoying/embarrassing. I'm wondering if it's my lack of cats? I know you said yours does it Ryan, but there's no reason m60's should backfire only when installed in the e30 chassis, not when they are in e34's and e32's.

I'm going to put the Autologic back on the car with the stock DME and see if it's getting a road speed signal. If so, I'll try swapping chips between the two DME's to see if the problems follow the chip or the DME. And if it's following the chip, I'm going to buy a real reputable chip, maybe Mark D.

[Jonsku]

Great that you have finally found (at least to some extent) the solution for the problem!

Some backfiring seems to be quite normal (because of the missing cats?) with M60's, at least both of the M6x E30's I've done backfire a bit when getting back on gas after letting the gas earlier. Nothing serious, they have been tuned at dyno and work exactly as they should. At least I like the sound on my cabrio, gives it bit more grunt :)

Now as you mention it, that backfiring doesn't exist in E32 / E34 / E38 / E39's - so it's really quite a mysterious thing altogether..

Question: Where do you have your road speed signal hooked up to? Pin 14 on the x20 is road speed signal. It should go to the cluster. I have it hooked up to one of the three pins below (they are all the same, they all have continuity)

However, with the Autologic scanner hooked up, my road speed signal was wrong. It read based off of engine RPM instead of my actual road speed. It read 40 km/h at idle, with the car not moving, and shot up to like 300 km/h at redline. When driving, the actual road speed had no effect on DME's road speed. It seems as though Motronic uses RPM as a 'backup' to do the calculation, although I'm not sure how it assumes what gear you'd be in, unless it's an auto. My DME is from an auto...

My speedometer works, so the road speed signal to my cluster is good. And I swapped clusters, with another known good one, and the Autologic still read incorrectly. I checked continuity from the road speed wire, from the end connecting to the cluster to the end connected to the DME, no resistance. And I've tried multiple DME's.

So either I am wrong in pulling road speed signal from there, or the Autologic is not reading it properly. Weird thing is, I'm not getting a code for a missing speed signal, even if I unplug that wire to the cluster. I did get it once in the past though when messing with stuff, but I don't remember what triggered it.

You take the speed-signal from wrong place. The INPUT signal to instrument cluster comes from sensor in differential, but you need the OUTPUT signal (e.g. from OBC connector, can be seen in the schematics) from the instrument cluster. To my understanding these two signals are different, which would explain why your DME is not getting it and thus doesn't work correctly..

[JGood]

You take the speed-signal from wrong place. The INPUT signal to instrument cluster comes from sensor in differential, but you need the OUTPUT signal (e.g. from OBC connector, can be seen in the schematics) from the instrument cluster. To my understanding these two signals are different, which would explain why your DME is not getting it and thus doesn't work correctly..

According to the schematics, that green plug on the cluster is the an output from the cluster. That's where the cruise control gets it's signal, and it's also directly connected to pin 26 on the yellow connector (OBC).




C3 is the yellow connector. C6 is the green connector, and the 3 pins that provide VSS are labeled 'A' on the connector.

[JGood]

In any case, I bought a Mark D chip for the car, and it's running better then ever. Still have the exhaust backfire, so I'll throw some cats on it this winter. I may build a 4.4 hybrid as well, should be very minimal work at this point.

Thanks to everyone who helped through this whole ordeal. Can't believe it took a year to get everything sorted. I guess it was a combo of the bad chip from the start, the exhaust leaks causing the o2 sensors to throw codes, and the exhaust backfire which I didn't realize was normal.