High RPM Stumble/Cutoff - Running out of Ideas

[JIMBOkye]

Car: 1989 325is

So I've been having this problem for maybe 2.5 months now, it started all of a sudden one day. Car was running great up until then.

Symptoms:
Car will stumble/cutoff at some point between 4500 and red line. the RPM seems to depend on both engine temperature and load. Runs great up until then.

By Stumble/cutoff I mean the motor will all of a sudden start missing, or maybe cutting fuel or spark, loss of all power. If you stay on the throttle, it will continue to go up in jumps, and it struggles (continues to miss/cutoff/stumble). Sort of like the motor is turning on and off and on and off...

When the motor is COLD, I can run it up all the way to redline no problem (which I hate doing cold). Once hot, and sitting there (no load) it happens around 5700-6200 RPM. If hot and under heavy load (going up a hill) it happens near 4500 RPM.

Modifications to the car: This car does have a Miller Mass Airflow meter.


What I've tried so far:
1. Replaced CPS
2. Replaced and tested TPS
3. Replaced spark plug wires
4. Checked with a timing gun and it stayed lit the whole time during the stumble (not sure if this is truly a valid test...)
5. Cleaned C191 connector (it looked fine either way)
6. Checked fuses for continuity
7. Fuel Pressure is good, (also, pump/filter/regulator recently replaced)
8. Checked function of coolant sensor and switch

The distributor and coil have been replaced in the last 1000 miles...

The next thing I'm going to try is to replace the ECU and Flowmeter back to the original, but I would be very surprised if this changes anything.

Any ideas, suggestions would be greatly appreciated as I'm running out. Let me know if any questions....

[JIMBOkye]

Forgot to mention I pulled the plugs and they all looked good/gap was okay.

[DesertBMW]

put the stock chip and AFM back in there and see if you still have the problem

[TobyB]

AFM, methinks.

t

[MrBurgundy]

There may be a dead spot on the AFM track.

Also, pull EACH plug and make sure they're okay.

[sert57]

sounds kind of similar to the issue iv'e been having, but not exactly the same.

Does the problem happen at any throttle position or only WOT?

Are your engine grounds clean and all that?

[JIMBOkye]

Update
Yes, happens at any throttle position, not just WOT
What I've done today
1.Removed grounds, cleaned and replaced. No difference
2. Disconnected o2 sensor while running (to force rich), no difference
3. Swapped old dme and afm on, no difference.
4. Stomp test on either computer was 1444-no fault
5. Voltage is 13.7 while the car is running, don't think battery or alternator is the issue.

Not sure what to do next.

[sert57]

https://www.r3vlimited.com/board/showthread.php?t=365368

Heres a useful thread I found a month or so ago, post #12 is a nice summary of how most think the motoronic operates. However, this does not have any of the logic for the Limited Operation Strategy - an early limp mode. I am suspect I am going into this with my car and it sounds like you also may be.

found this pdf with some interesting info on the LOS from an E32 site - may have some good ideas to look at, i just found it so haven't examined it yet.

https://www.meeknet.co.uk/E32/DME_1.1_1.3.pdf

[Kershaw]

Switch to megasquirt.

https://www.r3vlimited.com/board/showthread.php?t=372569

[Bimmer_Baron]

Could you be running lean? You could have a clog in your injector inlet filters that's making the car run lean, it'll run worse the warmer the motor gets. Clogged fuel injectors won't effect your fuel pressure at the rail, so you'd have to pull them off the rail to check their condition. They'd have to be really clogged to cause a lean condition, since the DME will overcompensate by dumping in fuel if there's a mild to moderate clog, causing a rich condition. It doesn't seem like this would be the problem, but basically everything else I can think of, you've checked already. When's the last time the injectors were replaced / rebuilt?

[JIMBOkye]

I replaced the injectors about 3500 miles ago with rebuilt ones. BUT since then I had to do the filter, pump and fuel regulator, AND fuel tank as the issue was a ton of rust in the tank. did that about 1500 miles ago, so the injectors saw 2000 miles of potentially bad gas. I will take a look at them, good idea.

I think I'll also swap out the Temp Sensor, that link you posted, sert57, to Som's table is pretty interesting.

Kershaw, your story is not confidence inspiring... One thing I don't think I've noted here is that my car will do this sitting there, does not NEED to be under load to happen. If it is just parked in the garage it stumbles around 6000.

[Reichart12]

Not much to add but make sure your CPS is properly gapped. Too far away can cause this problem.

[JIMBOkye]

Is there a way to adjust the cps gap?

[sert57]

yeah the cps bracket can be adjusted

[Reichart12]

You basically loosen the bracket to the block and adjust it with a feeler gauge before tightening back down.