Intermittent engine bogging/turning off problem

[kronus]

Allright, this is weird. This problem started today, and I don't know what could be happening.

When the car is warm, it will occasionally, randomly turn off. This usually happens if I am at a low speed in 1st or 2nd gear, like accelerating from a streetlight. When it turns off, I can restart it instantly, but it will run for maybe 2-3 seconds and then turn off again. If I try to rev it when I restart it, engine speed will climb as it should, but after a similar period of time as when not trying to rev it, revs will hit a brick wall (at around 3-3.5K RPM) and the engine will turn off.

The odd thing is that after several tries of restarting it and having it die no matter what I do (keeping the throttle pegged will not prevent the engine from shutting off), I would start it and it would work perfectly fine. This happened maybe 3 or 4 times today, at almost regular intervals. After I got it work again, there was a distinct smell of gasoline, although I think that was from the FI system dumping fuel into the engine to start it repeatedly.

Any tips/ideas on what I should check? Car is a 1987 325e.

[bryant.cw]

My '85 325e does the same thing, very frustrating.

[kronus]

Anyone? I'm thinking there's an electrical short that temporarily kills the fuel pump, but I'm not sure how to check it.

[kronus]

Plugs look good, engine ground cleaned.

Should there be a relay floating around in the driver side wiring mess behind the bolster?

[Farbin Kaiber]

Did you check the engine harness connectors? IIRC the m20's have an intrnmit issue there.

[kronus]

Which connectors?

There's the main round connector clipped to the firewall that feels good and tight, I don't know the locations of any other connectors offhand.

Going to go do a stomp test and see if the engine thinks anything is wrong.

EDIT hurr lol nevermind motronic 1.1 doesn't have stomp test

[kronus]

Ok, the problem is back. I was paying attention and have a bit more information this time.

Maybe 20 seconds before the car shut off as I slowed to a red light, I was still in gear and going at a respectable speed. Then, for about a second, it felt like the engine just shut off or someone applied the brakes. Since it was in gear and moving, the car in effect restarted the engine after the second of braking. It didn't feel like sudden loss of power, because the car would have just kept coasting (since I wasn't accelerating), it actually felt like something was actively slowing it down.

Then, I came to the light, put the clutch in, and it died.

So, I still need help with this :(

[jmc1590]

'87 eta, that should be a "super-eta", right?

I have had similar issues with engine "dying" while driving. In my case it turned out to be two fold. 1) The Engine Speed (or crank position, I'm not sure which...) sensor in the bellhousing had started to fail. 2) the ECU had developed bad solder joints which effectively removed power and ground everytime I hit a bump in the road!

After it dies and goes through the no start syndrom, does the tach move while you're turning the engine over? If not, I'd start with the Bentley tests for the sensor...

Likewise, do you have access to another ECU you can test with? If so, that's a quick and easy operation.

As far as testing the fuel pump, I believe there are two pins on the diagnostic connector that if you connect them, the fuel pump will run. I believe that sends the same signal that the ECU does for pump operation.

[kronus]

super-etas are only 1988.

I'm going to go pull the ECU and look it over for bad solder joints. I also have a stock chip that I'll use for a while and see if the problem persists.

The tach works properly when I turn the engine over.

Another symptom that I just now realized probably is related to this: my MPG sucks. It's a chipped eta, but it gets worse mileage than stock i's. Maybe 20 average suburb, 25 highway. My friend said he had a similar problem on his e36, turned out to be his gas cap, which was not sealing and depressurizing the gas tank.

[jmc1590]

You had mentioned Motronic 1.1 earlier. If so, then it is a "super-eta." (All of the "eta"s use Motronic 1.0 Basic.)

If you're inspecting the ECU, look by the voltage regulators. (Large components on side/edge of board.) This has been where I've found the problem on 2 027 ECU's.

[kronus]

Will do, thanks.

And yes, that was my mistake. Motronic 1.0.

[kronus]

Ok, tore into it.

What's the small black box in the middle of this photo? (below and in front of the airbox)

The harness that plugs into it is sleeved together with the AFM harness.

Took out the airbox, afm. The intake boot is intact. I also tried cleaning off the engine muck a bit, but it was fruitless:


Why, hello there! This hose connects to the intake boot and goes to the ICV.


I think I need a new one. Urgently, as I am supposed to leave on a road trip on Monday.

[jmc1590]

Ok, tore into it.

What's the small black box in the middle of this photo? (below and in front of the airbox)

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I think I need a new one. Urgently, as I am supposed to leave on a road trip on Monday.

If I remember correctly, the small black box is a barometric sensor. I have the same on my '86, but my '82 (both eta's) doesn't. I don't think it does much, other than compensating for altitude.

The cracked idle air line may be your culprit. Depending on engine vibration, you could very easily change from a minor vacuum leak, to a huge one, resulting in a very lean condition! Replacing it is the best option, but in a pinch, a couple of other options are available.

1) Cut the cracked portion off, and reseat.

2) Create some form of air tight seal over / around it. (I had an intake boot rip in the middle of a cross country trip. Ended up using a Wal-Mart bag and electrical tape to get to my destination!) If you go this route, put a worm clamp over the end to keep everything in place.

Best of luck!

[kronus]

Yep, it's e-taped now. I'm going to a show right now, so I will see if anything has changed. I don't have a worm clamp handy, but I'm going to the dealer tomorrow to see if they have any new ones. (and of course begging and crying in the Wanted section ;))

I can't cut it, though. it's a shaped hose, and won't reach the intake boot if I cut it.

[mikegar]

kronus did you ever get your problem figured out? im having a similar problem. in a very similar car. 87 325, no chip tho.