How many misfire threads to we need? 1 more.... Calling the guru's. SOLVED!

[TurboJake]

Well guys. Here's the spiel.
89 325i. M20. No overheats. No problems. Runs great except for that the car has been giving me a high RPM misfire. Around 5300 ish, but not always in that area. Only "Usually"
Sometimes it won't do it at all.
Some days it will do it every time.
Only happens under load.

Temperature does not seem to be a factor.

It's pretty much like the motor is hitting a brick wall. It stops accelerating (Much like an ignition cut, or those that know. Boost cut where it falls flat on it's face), and then I can keep going on my merry way. If I try to stay through it, it turns into a bucking bronco and It's probably taken 3 years off my transmissions life from the two times I tried it.

Things that are NEW, Since the problem has manifested.
Miller MAF conversion and war chip. My AFM was pretty borked, in cold it would stick. This did NOT solve it. Currently running a bog standard miller tune on my WAR chip. So this has been on 2 different chips now.
02 sensor. Replaced last year
Cap and rotor. Look great. Replaced them last year, along with plugs.
Water pump, Timing belt, tensioner, and tensioner spring. Replaced last feb
Engine ground wire. Replaced 2 weeks ago.
Battery ground wire. Replaced 1 year ago.
Fuel filter. Did it Just in case a couple months ago.

I have NOT replaced my wires. as this isn't symptomatic of it. It's not one or to cylinders dropping. It's all of them. At once. Like a bowling ball hitting the ground, with your foot inbetween.

Couple weeks ago, it pulled a 1261 for fuel pump relay. I replaced the relay, and fuse #9 for shits and grins. Nothing changed.

Couple days ago the check engine light came on. 1251. Perfect. This explains NOTHING to the misfire and complete shutoff of the motor. All this explains to me as that it's no longer running in batch fire...

I looked at the harness plug. No corrosion. Zip, zilch, nada. Probably a bad injector. Get some of those on the way. Car idles and drives perfect when not hooning on it.. NO loss of MPG's (24ish city, 27 highway)

I've looked at the CPS. It tests out A-OK at 527 ohms. NO rubbing, fraying, or anything to lead me to it being a problem. And it is properly gapped to the trigger wheel.

Valve adjustment? Did it. That's just fine.

No vacuum leaks.

TPS? Fine and dandy. Stomp test even works.

Coil tests out okay.

Cat's not an issue. It doesn't exist. Food grade stainless steel single pipe from the stainless headers to the tail.

Here's a video where you can see it. As I approach it the CEL light comes on, Power goes away completely. CEL turns off. Like nothing ever happened. That pop that you hear when I lunge forward because of the loss of power is fire coming out of my tailpipe. Good old fashioned backfire.

I'm at a loss. There's nothing to explain exactly what's going on. And at this point I'm going to end up throwing money/parts at it with no real positive leads. So some insight is very welcome.

Could it possibly be running lean and the ECU goes into a "FFFFFFFFFFFFUUUUUUUUUUUUUUUUUUUUUUUUU" moment? Killing ignition? Seems a bit too intuitive for M1.3, and not throwing a permanent 1222

Shaky camera work warning. I'm sorry.

[jlevie]

Based on the description and video I'd first suspect a fuel delivery issue. It could be a problem with power to the pump (or the pump itself), the injector wiring, or even the DME.

The first thing to do would be to tee in a pressure gauge and see what the rail pressure is when a cut occurs. You can zip-tie the gauge to the windshield wiper where you can see it. If pressure is good I'd next replace the CPS and if that doesn't help, the DME. If neither of those help I'd replace the engine & injector harness.

Getting diagnostic information from this is difficult, hence the parts swaps. You just about have to have the ability to log data from the engine management system during an event. In the past when hunting down similar problems in my race car I have used the logging capabilities of my IQ3 dash and a battery powered storage scope to gather diagnostic data

[JayDee916]

any update on this?

[TurboJake]

Swapped ECU's. No change. Actually dropped down to a consistent 5k when the event happens.
No fuel pressure change during an event.
No more check engine lights. New ECU reads code 1444.

Still thinking it's ECU related somehow. Sometimes when it happens the Tach goes all kinds of crazy.

Starting to lean towards CPS. Maybe the ECU isn't getting the indexing signal from the crank trigger wheel. It would make sense that if it can't see it. Freaks the fuck out. Killing ignition, but maintaining injector pulses for a brief moment after it all comes back.

Worth a shot, anyway.

[scrowner]

Just stating the obvious here....isn't that the rev limit point of your model? My 40hp smaller engine, 325e, rev limits a bit lower, I think around 4750. I moved the rev limit in another 325e to be around 5300 with a chip change. Your issue sounds a bit different than what I know about how the 325 rev limits - but maybe the ECU is not properly controlling it due to some intermittent issue.

[jlevie]

Still thinking it's ECU related somehow. Sometimes when it happens the Tach goes all kinds of crazy.

Starting to lean towards CPS. Maybe the ECU isn't getting the indexing signal from the crank trigger wheel. It would make sense that if it can't see it. Freaks the fuck out. Killing ignition, but maintaining injector pulses for a brief moment after it all comes back.

Seeing the tach drop during an event means that the DME stopped producing the tach signal, which is generated from the CPS data. That can be caused by a bad CPS, bad harmonic balancer, bad engine harness, or a bad DME. At one point or another I've experienced all of those failures.

I'd suggest that you start by replacing the CPS with a new BMW OE part. Also check to see if the harmonic balancer wobbles when you rev the engine and replace it it does. Since two different DME's have slightly different manifestations of the problem, I'n not inclined to suspect the DME itself, but a bad fusible link in the DME power cable could be a cause. Replace it with 60-80A fuse. I use a 60A lug type fuse bolted to the DME power point in the engine bay and splice out the fusible link.

If the problem persists after all that, replace the engine harness.

[SpecM]

^ also a bad main relay can cause a tach drop

[Cabriolet]

Seeing the tach drop during an event means that the DME stopped producing the tach signal, which is generated from the CPS data. That can be caused by a bad CPS, bad harmonic balancer, bad engine harness, or a bad DME.

is the tach signal not pulled from plug wire 6? and not the CPS?

[TurboJake]

Just stating the obvious here....isn't that the rev limit point of your model? My 40hp smaller engine, 325e, rev limits a bit lower, I think around 4750. I moved the rev limit in another 325e to be around 5300 with a chip change. Your issue sounds a bit different than what I know about how the 325 rev limits - but maybe the ECU is not properly controlling it due to some intermittent issue.

No. The 89 325i has a 6500 RPM rev limit. I also have the magical war chip, and it's raised up to 7100 RPM. 6 months ago this time I could take it up to it all day long, only occasionally getting the ECU cutout. I won't take it farther than that for obvious stock rocker reasons.

^ also a bad main relay can cause a tach drop

Without a doubt. But I checked that. Replaced it with one of the many I have. No wires going to it have any issues that I could see. I don't think it's the issue as it ONLY happens in higher RPM.

I have yet to find a corroded wire on my car. Even my injector harness was shiny like new inside and out of the C191...

is the tach signal not pulled from plug wire 6? and not the CPS?

If my understanding is correct, It's pulled from the coil negative terminal. Not the CPS... But it goes to the DME and is then sent over to the cluster. Should be Pin 1 on the ECU plug. And Pin 6 is the output to the cluster.

What your thinking of is the cylinder ID sensor. That's to allow the ECU to run the injectors in batch fire. Without the CID sensor, it will just fire all the injectors at once.

Either way. If it's getting a smeared signal from the CPS, I could see it being a problem. If only I had a fluke I could take a look at it.

Sigh... Seriously debating on picking up a Zeitronix ZT-2

Oh. Also. I'm gonna try swiping the coil from my woman's E30 tonight. I'm curious that with the tach signal being wonky it could be that. Like maybe it's internally grounding when it's in the higher RPM's.... Worth a free shot, because her car does not do this. Might just trade the CPS too while I'm at it.

EDIT: It also needs to be noted, I already looked at the harmonic balancer and trigger wheel. It's dead on, and doesn't wobble at all.

[jlevie]

^ also a bad main relay can cause a tach drop

True, but the CEL light will also come on with no fault codes stored.

If my understanding is correct, It's pulled from the coil negative terminal. Not the CPS... But it goes to the DME and is then sent over to the cluster. Should be Pin 1 on the ECU plug. And Pin 6 is the output to the cluster.

Not correct. The tach signal is generated by the DME from the CPS data

[TurboJake]

Not correct. The tach signal is generated by the DME from the CPS data

Durr.. Momentary lapse in judgement. If the ETA requires the peg on the flywheel for the tach signal, and the reference sensor. Why would they change that in the 325i when using what is pretty much the same Programming and hardware?

Thanks for the slap to the back of the head. I deserved it...

CPS is next on the list.

[Aahj]

Any update? Have same issue on mine.

Thanks!
AJ

[TurboJake]

I'll have a CPS here within two weeks. Already paid for it. Just needs to be shipped and installed.

If it's happening to you, I've been driving it for 4-5 months like this.... Haven't had any drive ability issues. Just hoonability issues.

[accident]

Had the same issue, never fixed it. It just kinda worked itself out except for very occasionally. Sold the car before I found out what was wrong. Curious to see what the outcome here is

[TurboJake]

Well... The new CPS is on it's way. Should be here monday or tuesday. Installed on wednesday. Will post an update then.

Also, I picked up a whole car that runs. So if that doesn't fix it. New harness time.
(Even though I already have another harness.................. Fuck I have too many parts)