Bad misfiring after exhaust work - undriveable

[RoDo]

UPDATE:
Since the "new" 173 ECU didn't cure the issue I re-installed the old 153.

Tested spark
- I used an old plug I had around - all 6 wires produced a consistent orange spark. So not nice & blue but spark was consistent and seemed to light up with the frequency expected.

- I did pull one of my new plugs and test with that. Spark was brighter but still in the orange spectrum. Definitely not blue.

- I broke rule #1 and got a no-name coil at the local parts store. It is out of spec per Bentley right out of the box. Tried it anyway. No change.

Tested plug wire resistance
- All are in spec EXCEPT #1. Plug wire #1 tests out at 21200 ohms which is 4x what an in spec wire should be (4x what all the other 5 were at as well).
- Coil wire failed as well with 2070 ohms.
- The Bentley is a little confusing on the test procedure. I'm testing resistance from the plug connector through the wire to the distributor cap connector. Is this the correct procedure?

[RoDo]

UPDATE:
- Installed new main relay & fuel pump relays - NO CHANGE.

[goldenbb]

This is a total shot in the dark because I haven't done a header/exhaust on my car (yet) but I had a motorcycle once that had an aftermarket exhaust on it and it ran like total shit because the engine didn't have enough back pressure and the owner never re-jetted the carbs because it required a special kit and some modding and no fool has time fo' dat.

I also had a Mustang 5.0 with an aftermarket exhaust on it and it had all kind of funny issues that I could never diagnose.

Take it fwiw, but if the long tube headers are causing less back pressure, you may need a custom chip and tune to solve your problem.

[RoDo]

This is a total shot in the dark because I haven't done a header/exhaust on my car (yet) but I had a motorcycle once that had an aftermarket exhaust on it and it ran like total shit because the engine didn't have enough back pressure and the owner never re-jetted the carbs because it required a special kit and some modding and no fool has time fo' dat.

I also had a Mustang 5.0 with an aftermarket exhaust on it and it had all kind of funny issues that I could never diagnose.

Take it fwiw, but if the long tube headers are causing less back pressure, you may need a custom chip and tune to solve your problem.

Thanks for the suggestion. It crossed my mind but the car ran fine with the header, cat & leaky exhaust before the exhaust work. The cat was removed so that would mean even less backpressure but the exhaust was sealed up with no more leaks so I think that would pretty much be a wash. I'll keep it on the list of potentials though, thanks again.

[RoDo]

UPDATE:
Per another r3v member who had very similar issues I installed (and adjusted) a new TPS today. NO CHANGE. I'm about ready to throw in the towel on this thing.

Recap: Car runs extremely rough and will barely respond to throttle as it stumbles badly. It is not driveable. It backfires fairly constantly. At each misfire the MPG gauge spikes. According to jlevie in multiple threads here the MPG gauge behavior means the ECU is not sending pulses to fire the injectors. Which points to loss of timing data, bad power or bad ground to the ECU. I have tested the wiring harness at the ECU connector and all tests pass. I replaced the ECU with a tested good 173. I've replaced CPS, CTS, TPS, O2, Main relay & Fuel pump relay. Nothing seems to make a difference.

I'm still a little suspicious of the wiring harness as it's one of the remaining parts I haven't swapped out. How difficult is this to replace?

Help!

[TurboJake]

Test the VAF.
CHECK THE TIMING. I don't see that anywhere in here. Maybe it's off a tooth or two.

Also, is it legitimately backfiring? A backfire is combustion that comes back through the intake. If it's puffing out the exhaust or if it's puffing out the intake that's a strong indicator of the cam timing being off. Firing too soon or too late, with the ECU not having a clue as to what's going on, knowing something is wrong, and going all hairbrained.

[Northern]

Verify the plug wires are attached in the right order. After a friend's second 24v swap, he had a weird backfire issue similar to this, and two of the coilpacks were switched. Once that was fixed, the backfire disappeared. I know the M20's ignition system is completely different, but it's easy enough to check for.

[RoDo]

Test the VAF.
CHECK THE TIMING. I don't see that anywhere in here. Maybe it's off a tooth or two.

Also, is it legitimately backfiring? A backfire is combustion that comes back through the intake. If it's puffing out the exhaust or if it's puffing out the intake that's a strong indicator of the cam timing being off. Firing too soon or too late, with the ECU not having a clue as to what's going on, knowing something is wrong, and going all hairbrained.

Thanks for the feedback TurboJake. I'm not familiar with the term VAF, is that the same thing as the AFM? I've tested the AFM for resistance variation at the ECU connector as I move the flap and it behaves correctly per the Bentley. What other tests should I be doing?

As far as checking the timing; do I have to pull everything off the front of the motor to check this? Or is there an easier way?

It is backfiring through the exhaust, I can definitely hear it pop via the tailpipe. So if that isn't technically a backfire I'm not sure what to call it but it isn't through the intake.

[RoDo]

Verify the plug wires are attached in the right order. After a friend's second 24v swap, he had a weird backfire issue similar to this, and two of the coilpacks were switched. Once that was fixed, the backfire disappeared. I know the M20's ignition system is completely different, but it's easy enough to check for.

Verified.

[ncrmtrsprtsE30]

HOLY SHIT you are having the same issue i have/had, except for mine is eta. and now mine does not run at all, and i am still trying to figure it out..

did it sound like this when you were driving??

https://www.youtube.com/watch?v=kSRYMTR3ygw&feature=youtu.be

and this..

https://www.youtube.com/watch?v=Xh4yWowEpgg

edit: when i was in the paddock, i would hold my throttle at ~1/4 throttle and it would run very rough and backfire through the exhaust and intake and my MPG need would bounce as well as the temp gauge a tiny bit. but mine would EITHER idle smooth and only sputter when throttle was given, or surge idle randomly.

[RoDo]

HOLY SHIT you are having the same issue i have/had, except for mine is eta. and now mine does not run at all, and i am still trying to figure it out..

did it sound like this when you were driving??

https://www.youtube.com/watch?v=kSRYMTR3ygw&feature=youtu.be

and this..

https://www.youtube.com/watch?v=Xh4yWowEpgg

Hard to tell exactly from the video but yeah it seems like the same thing. Mine will always start, just runs horribly. Maybe 1 out of 10 times it will idle smoothly and then once I give it any gas it stumbles bad and won't go back to a smooth idle. Super frustrating.

I believe it is an electrical issue given the MPG gauge behavior and jlevie's posts but I can't say for sure. Everything tests out okay so I don't know where to go from here.

[TurboJake]

Thanks for the feedback TurboJake. I'm not familiar with the term VAF, is that the same thing as the AFM? I've tested the AFM for resistance variation at the ECU connector as I move the flap and it behaves correctly per the Bentley. What other tests should I be doing?

As far as checking the timing; do I have to pull everything off the front of the motor to check this? Or is there an easier way?

It is backfiring through the exhaust, I can definitely hear it pop via the tailpipe. So if that isn't technically a backfire I'm not sure what to call it but it isn't through the intake.

Yeah, the VAF is is the AFM. They're a Vane Air Flow Meter. Two terminologies for the same thing, but it tested out okay @ the DME so that's all good.

There's no need to tear it down and inspect, but it will give the definitive answer as to if it's in time if you do. They easy button would be that it does run, at all, to have a timing gun and check the timing on the crank pulley. But if it doesn't run at all, yeah, you'll have to take off the front pieces to get at the timing belt, which if you're that far you might as well do anyways.

[ncrmtrsprtsE30]

check all these pinouts of the DME connection without the DME plugged in.
(undo battery before undoing DME)

check you TPS.. I just found out mine was soaked in oil from the throttle body.

[RoDo]

check all these pinouts of the DME connection without the DME plugged in.
(undo battery before undoing DME)

check you TPS.. I just found out mine was soaked in oil from the throttle body.

Thanks. I have actually done that already and everything passes. TPS was just replaced as well.

[RoDo]

Yeah, the VAF is is the AFM. They're a Vane Air Flow Meter. Two terminologies for the same thing, but it tested out okay @ the DME so that's all good.

There's no need to tear it down and inspect, but it will give the definitive answer as to if it's in time if you do. They easy button would be that it does run, at all, to have a timing gun and check the timing on the crank pulley. But if it doesn't run at all, yeah, you'll have to take off the front pieces to get at the timing belt, which if you're that far you might as well do anyways.

Got it, thanks. It does start and run (just really poorly) every time so a timing light would work.

I'm towing it into a local shop that has a good reputation on old BMWs tomorrow morning to have them see if they can sort it out. I've kind of had it with the car at this point.