1986 3.2 started backfiring then stuttered then stalled

[Jp-oh]

Hi out running errands and got caught in a big rain. The car started backfiring and bogged then stalled. This got worse over the course of about 1 minute and now the car wont start. I popped the engine cover and its bone assed dry in there so not likely distributor (i guess?)

Car turns over but wont catch.

Any thoughts?

Edit. Tried the car after about 5 mins and bam! Its alive and running normally. What the hell?

[ischmitz]

The first though coming to mind is always the DME relay in a case like yours. It's under the drivers' seat and known to fail intermittently. You should carry a spare in your glove box so it's time to order one and swap it out. The sputtering is because the DME relay when it turns off shuts down the fuel pump. And as the engine continues to run fuel pressure gradually goes down and as a result the mixture gets leaner and leaner to the point where the engine stalls.

Next, sensors on the flywheel do fail intermittent, too. Harder to replace but very common these days as these cars age gracefully. But that cuts fuel, spark and the engine dies completely. Normally no sputtering

Cheers,
Ingo

[Jp-oh]

Dme is 3 years old. I have a spare in the car.

[ischmitz]

I'm assuming you mean the DME relay and not the DME itself. Very different things.

Be aware there is lots of talk about even brand-new DME relays sometimes failing out-of-the-box. So age really isn't a good measure to determine if yours is good or bad. Unfortunately, only a swap test with long enough observation time will tell if this is the culprit.

There can be many more reasons for intermittent running. I for example had what turned out to be a marginal fuel pump. It would run fine and then all of a sudden fail to start. After lots of tinkering another couple of weeks of perfect running only to come back at the most inconvenient of times. This process repeated itself over month. Not easy to diagnose but it was the pump after all. Once that was swapped all is good again.

Good luck,
Ingo

[Jp-oh]

Yup. Meant relay.

I am not much of a believer in coincidence and the fact that these symptoms occurred immediately after a short but torrential rain makes me suspicious it was related.

[ischmitz]

Oh, good point and I missed the rain thing:

Another issue could be failing ignition wires. Do a spray test: Get a plant spray bottle, fire the car up in the dark and then mist into the engine bay. If you see "weather lights" or "northern lights" appearing around your ignition wires you know your wires are marginal.

And then there is the old "water into the distributor cap" thing, it also will prevent proper running and especially if the cap is a little older could be the issue. I believe the cap on the 3.2 is the same as on the 3.6 and it's secured by two screws. Maybe pop it off the next time it's rain that makes it fail.

And last but not least if water got to the speed sensor harness it could have shorted it intermittently. For the most part these sensors have old cracked outer sheathing from years of heat-cycling. Once water gets in there it'll short the shield to one of the signal wires and the sensor quits until it dries out.

I guess you need to observe if your issue really correlates with rain and take it from there.

[Jp-oh]

The wires and dist rotor are all less than 2 years old and when i poped the cover it was BONE dry in there. Wet dizzy was my first guess

[ischmitz]

What's the age of the speed sensor?

[Jp-oh]

Originally Posted by ischmitz

What's the age of the speed sensor?

I assume 30 years.

[Jp-oh]

After doing some reading the speed sensor does seem a likely culprit. Further evidence is at 3000ish rpm at a constant speed I can feel the car is just a little off. Ill look into how anoying it is to replace ( I suspect fairly anoying given the location).

[wrxnofx]

Best to replace both at the same time. Do a search on here and get the BMW sensors instead or the Porsche ones to save a couple hundred bucks.

[jlex]

If you're going to fiddle with the speed and reference sensors, do the CHT (cylinder head temp) sensor at the same time. All three feed thru the same grommet. Your car may also be running the older, non-grounded type so it's best to upgrade now.

[kyngfish]

Having done the CHT a week or so ago, can confirm that it might be best to do all three at once. All that said, the Speed and Ref Sensor are 150 each, and the CHT is another 90. I think you can get the Speed/Ref sensor for around 90 if you use a BMW part number.

It's not like it's SO hard to change 1 at a time, that you necessarily want to do all at once, but if you haven't ever done any of them, well, it's an afternoon's work. Maybe.

There are a bunch of threads on here about how best to change out the sensors. The ref and speed sensors are pretty easy. The CHT can be a mission to thread and tighten properly. There are a dozen threads and I spent hours cutting up a deep socket only to find it wasn't deep enough. So I took a box wrench and cut a small hole on the ring side of the wrench. Easy peasy.

[Dubbin']

Originally Posted by ischmitz

The first though coming to mind is always the DME relay in a case like yours. It's under the drivers' seat and known to fail intermittently. You should carry a spare in your glove box so it's time to order one and swap it out. The sputtering is because the DME relay when it turns off shuts down the fuel pump. And as the engine continues to run fuel pressure gradually goes down and as a result the mixture gets leaner and leaner to the point where the engine stalls.

Next, sensors on the flywheel do fail intermittent, too. Harder to replace but very common these days as these cars age gracefully. But that cuts fuel, spark and the engine dies completely. Normally no sputtering

Cheers,
Ingo

The speed and Reference sensors can be your issue. I went through the entire car replacing almost every culprit part to find that my intermittent hesitation was caused by these sensors. If you are interested I had created a long thread with lots of information last year.

Check the wires in the driver's side rear fender well. My car started running like crap after I washed it and hosed down the fenders wells. the wire insulation on both sensors was very brittle and was exposing the internal wire. Both sensors checked out fine when tested for voltage and OHMS. It was an intermittent issue that was real fun to find. Once I replaced both sensors, the car ran as if it were new. I used BMW sensors that were much cheaper than the Porsche replacements. Part numbers are in my thread from last year.

If those sensors are going bad they could DEFINETLY create a no start and hesitation problems. Good thing to check especially if your sensors are aged. Check your CHT and make sure it's the 2 wire version. the single wire version often creates intermittent issues.

Thanks,
Mark

[kyngfish]

Please don't just take my word for it, double check with some of these more experienced gents, but I believe this is the interchangeable BMW part.

Link