Sputtering, Bucking, Sneezing(!?) 3.2

[Mex]

I've read a lot of old threads on sputtering problems but none seem to describe what I'm experiencing. It's an intermittent problem, but when it occurs it's very noticeable and renders the car extremely difficult to drive. When both accelerating and cruising at a constant speed, the engine will stick at a certain amount of revs (usually between 2300 and 1300), and quite often will also drop down incrementally. If I keep my foot down, it'll usually jump up incrementally by a few hundred revs, each time often accompanied by a very odd "Choo" sound coming from the passenger side rear. A fairly significant bucking can sometimes accompany both the drops and the jumps. Then it'll disappear for a bit, only to come back just as bad anywhere from seconds to minutes later.

I've never tried to see if the car will eventually stall, but quickly engaging and disengaging the clutch seems to sometimes temporarily stop the problem, as does pushing the accelerator to the floor. I've never noticed the problem from cold, the only two times it's happened it occurred after the engine had some time to warm up, with several trouble-free drives between the two.

I've decided to winterize and garage it for the rest of the winter until I can get a handle on what's wrong and how many body parts I'll have to sell to fix it. I had initially thought it could be a fuel system issue, but a trip to my local garage for another unrelated problem turned up a potentially broken head stud or studs. Could a vacuum leak cause such severe symptoms? I haven't had a chance to check out the flywheel sensors that many other threads have talked about (it's a little cold up here), but from what I've read a sneezing noise isn't associated with their failure.

Another possibility I've kicked around is the result of an embarrassing newbie moment (documented on this board for my eternal shame ), in which I dumped an extra quart of oil into the tank based on the gauge in the dash without checking the dipstick (though the car was warm and level...I swear). Still, I have a hard time believing that one quart would cause such dramatic symptoms.

Hopefully all that makes some sense. Has anybody experienced a similar issue or have an idea as to what I'm experiencing? Any help would be awesome.

[Fly911]

I had a similar problem on my 3.2 Carrera. It turned out to be the RPM sensor. I got a kit with the RPM and TDC sensors here on Pelican, and that cured the problem!

[Mex]

Originally Posted by Fly911

I had a similar problem on my 3.2 Carrera. It turned out to be the RPM sensor. I got a kit with the RPM and TDC sensors here on Pelican, and that cured the problem!

Ok, I'll check that out once it warms up around here. It drives perfectly when it's not experiencing the problem, so I'm reasonably hopeful it's sensors and not actual engine damage. I'd tackle it this week but I head back north for my last semester on Wednesday

[Mex]

Anybody else have an idea?

[ischmitz]

Can be as simple as the DME relay about to fail (intermittent loss of fuel pressure) or the speed sensor on the engine. Get the spare DME relay in any case. And the sensor is only around 90$.

To answer your other questions.

- a quart of oil is very unlikely to cause what you are seeing. The dipstick from lowest to highest mark is at least 2 - 3 quarts and overfilling has other symptoms (once you suck oil into the intake you blow a lot of smoke)

- a snapped head stud doesn't do much. Many drive around with these for a long time and don't even notice it. So I doubt that is your issue.

So no body parts (yet)

[Mex]

Originally Posted by ischmitz

Can be as simple as the DME relay about to fail (intermittent loss of fuel pressure) or the speed sensor on the engine. Get the spare DME relay in any case. And the sensor is only around 90$.

To answer your other questions.

- a quart of oil is very unlikely to cause what you are seeing. The dipstick from lowest to highest mark is at least 2 - 3 quarts and overfilling has other symptoms (once you suck oil into the intake you blow a lot of smoke)

- a snapped head stud doesn't do much. Many drive around with these for a long time and don't even notice it. So I doubt that is your issue.

So no body parts (yet)

Good, I can put the bone saw away for a few months ...

I've had a fresh DME Relay in my glovebox for months, just never thought to try it. I'll try those sensors too, if they're anything like the rest of the electrics I'm sure they're in a bit of a state.

Just so I'm clear though, you're talking about the two flywheel sensors (911-606-215-01-M14), correct? Seems like everyone has a different name for them.

[ischmitz]

Yes Taylor,

correct on the flywheel sensors. There are two identical (part number wise) sensors. One is called the engine speed sensor and looks at the fine toothed area of the flywheel. The other one is the reference sensor. It looks at the single metal pin on the flywheel.

If one is bad it's a good idea to replace both. However, it's the speed sensor could cause your symptoms. An intermittent reference sensor is by far less obvious because it is only used at certain conditions.

If you search the forum there is a BMW replacement part for about half the price of the Porsche part. They are the same item so get the BMW version and safe some cash.

ingo

[Mex]

Originally Posted by ischmitz

Yes Taylor,

correct on the flywheel sensors. There are two identical (part number wise) sensors. One is called the engine speed sensor and looks at the fine toothed area of the flywheel. The other one is the reference sensor. It looks at the single metal pin on the flywheel.

If one is bad it's a good idea to replace both. However, it's the speed sensor could cause your symptoms. An intermittent reference sensor is by far less obvious because it is only used at certain conditions.

If you search the forum there is a BMW replacement part for about half the price of the Porsche part. They are the same item so get the BMW version and safe some cash.

ingo

Ok, perfect. And I had heard about the BMW alternative. Both for the price of a single Porsche sender? No brainer as far as I'm concerned. Thanks Ingo

[SiberianDVM]

If you're going to replace the 2 reference senders (as I did 3 months ago when my 84 died at the track), I recommend you also replace the cylinder head temperature sensor, while you're in there. It's a fiddly place to work, and all 3 wires end up having to go through the same grommets.

[MConn]

I've used these BMW parts for the speed and reference sensors. They are a direct replacement.

Pelican Parts - Product Information: 12-14-1-708-619-M14

Mike

[mnez]

Subcribed - let us how how it works out.

[Tippy]

Read my horror story called something like "running my Carrera3.2 off a cliff". Same symptoms I never figured out after 6 months of testing every component in the EFI chain........most more than a couple of times......

[Nathans_Dad]

Sputtering, bucking, sneezing??

Sounds like a Journey song.

[Mex]

Originally Posted by SiberianDVM

If you're going to replace the 2 reference senders (as I did 3 months ago when my 84 died at the track), I recommend you also replace the cylinder head temperature sensor, while you're in there. It's a fiddly place to work, and all 3 wires end up having to go through the same grommets.

I'll do that. I've got a feeling all the insulation is shot on the wires for all three. If the sensors themselves died completely I would think the engine would also die. If the wires leading to the sensors are shorting, though, to my mind at least it seems more likely that I'd get the sort of symptoms I'm experiencing.

Originally Posted by mnez

Subcribed - let us how how it works out.

It'll be at least a month until I can get down to it, but I'll update when I do. Thanks for the interest.

Originally Posted by Tippy

Read my horror story called something like "running my Carrera3.2 off a cliff". Same symptoms I never figured out after 6 months of testing every component in the EFI chain........most more than a couple of times......

I'm looking through it now, ouch. Did you ever find the issue?

Originally Posted by Nathans_Dad

Sputtering, bucking, sneezing??

Sounds like a Journey song.

Now I've got Lovin' Touchin' Squeezin' stuck in my head...thanks

[Joe Bob]

Sensors, check threads on compatible BMW sensors for the 3.2....they be 1/2 price. John Walker has the part numbers.

The bucking could also be a fuel filter.

[scarceller]

Could also be bad/cracked solder joints within the DME usually near the coil drive transistor. I've repaired dozens of these DMEs in this area and often it causes erratic coil signal.

Bad Ref and Speed sensors usually cause no start issues, simple test for these is resistance/ohm testing them for 1000ohms +/- 10%.

Other sensor is the AFM carbon track wears out this can be tested in car with DC volt meter, search around and you'll find a writeup on howto do this.

My suggestion is replace the DME relay then if possible lend your DME to someone with a 84-89 3.2L to have them test it in a known good car.

[JessL]

When my '89 3.2 did this, it was an intermittent bad temp sensor.
Cheers,
Jess

[Mex]

Originally Posted by scarceller

Could also be bad/cracked solder joints within the DME usually near the coil drive transistor. I've repaired dozens of these DMEs in this area and often it causes erratic coil signal.

Bad Ref and Speed sensors usually cause no start issues, simple test for these is resistance/ohm testing them for 1000ohms +/- 10%.

Other sensor is the AFM carbon track wears out this can be tested in car with DC volt meter, search around and you'll find a writeup on howto do this.

My suggestion is replace the DME relay then if possible lend your DME to someone with a 84-89 3.2L to have them test it in a known good car.

Good call, thanks. I found some info on that AFM procedure in another thread. So far I'm planning on replacing both flywheel sensors, the CHT sensor, the fuel and air filters, and the DME relay. If that doesn't work I'll check out the AFM and DME. If it comes to that I'll most likely PM you with more detailed questions.

[Joe Bob]

Unless you are made of money.....throwing parts at it can get pricey. The parts can be tested.....

[DCinVA]

Check the idle microswitch. Procedure is in the workshop manual.