Stalling, Backfiring, Sputtering... oh, my!
 

This AM, I had to drive the 928 in slow moving, heavy traffic through a downpour to get to work-- about 15 miles in ~45 minutes (welcome to NYC). The car ran great right up until the point when I pulled into the parking garage. Just as I did, the engine suddenly started running rough and would barely rev when given throttle. As I let off, it backfired and stalled. I restarted... it ran long enough to get me into a space (no power) rattled a bit, and died.

At lunch, I took a quick look. Again, it started reluctantly and just barely ran (only if I gave it throttle; if I released it, the engine stalled.) If I gave it constant part throttle up to about 3k RPM, it would hold for a few seconds, then suddenly drop down with a backfire or two...then jump back up... hold for a second, then sputter hard again.

Under the hood, the coil wires are still secure as are the plug wires at the caps (didn't have time to check each one.) There didn't appear to be any water in the oil. Didn't see any obvious vacuum lines off, but only checked for a minute. Couldn't see any arcing but the engine died before I can get out of the car to check.

The car was below 1/4 tank of fuel and has not had the fuel filter changed in 4+ years (it's due).

So, I'm wondering what happened. Could something just be wet (cap/rotor)? Is the fuel filter clogged? What can I check next?

Thanks everyone,
Mark

It is an 86 5 spd car.

Do you have a fuel pressure gauge on the fuel rail ??? if your car is an 86.5, as Jim B says it is, you have a fitting on the fuel rail to mount a fuel pressure gauge. The symptoms you are describing are definitely indicative of a loss of fuel pressure, which "could"... indicate a clogged fuel filter, or a failing fuel pump...or a fuel leak.. either at the filter to engine fuel line..the fuel rail, the dampers, or the pressure regulator, or perhaps an individual injector "O"ring...a fuel pressure guage would be most beneficial in determining whether the problem is at the pump-filter-fuel delivery line...or at the fuel rail-injector end of the system...good luck. :burnout:

could the fuel pressure regulator have failed causing a massive amount of fuel to flood the cylinders?

It is indeed an '86 5-speed as Jim said. I thought that was in my .sig. Wonder what happened to that.... anyway.

I don't have a pressure gauge on the rail (was planning on it, but not yet). I may have one to try, though.

Odd that it was so sudden, though, no?

Would fuel flooding by the FPR give that kind of weird pulsing of engine speed as I hold the throttle position constant??

Wet cap and rotor? If the symptoms were still there at lunch, I'd be thinking about other things. My guess is that the post-shutdown, morning-to-lunch heat soak in the garage probably would have dried out anything that was wet.

Quick update: Just ran down to the garage to have another quick look (still supposed to be working so couldn't linger). It's still doing the same thing -- I'm guessing, along with Will, that it would have dried out in the intervening 11hrs if it had been merely some moisture somewhere where it didn't belong. Drat.

-Mark
'86 928S, 5-speed manual

wouldn't hurt to do distributor caps, rotors and ignition wires as a start.

I suppose you're right about caps, rotors, and wires. However, the caps (and plugs) are new as of about 6 weeks ago and the rotors and wires were checked pretty thoroughly then.

might be a fuel delivery issue then. I've heard weird things also when a fuel damper fails on some cars.

Is it possible there's an issue with the fuel pump or the pickup? Would the low fuel level contribute here (it's low but the low fuel light wasn't on)...

Is my 1st step to try to check fuel pressure at the rail?

Hey Mark I gave this some thought and consulted with another Rennlister to exchange thoughts...it sounds like your ignition system got wet. For one thing if your plug wires are old; it would be a good idea to change them. Second, pull your cap and rotor to ensure there is no water in them. If there is, let it air dry and apply di-electric grease on all brass/copper grounds and pieces exposed where the rotor comes in contact to optimize the arc.

Thanks again for all the advice.

I certainly like the "ignition system got wet" idea. Any thoughts on what, in particular, might be wet? The caps are up pretty high, though it's possible I suppose. Any particularly vulnerable connections I should be checking? What about the computer?

Anyway, I checked on the car this AM. Still doing it. With all the backfiring and fuel smell the idea of a lack of spark seems appealing. Going to try to get down there during lunch with a screwdriver and flashlight to at least open up the caps. The wires are only about 3yrs old and looked good upon inspection when I did the caps and rotors 6 weeks ago.

Wish me luck.

-Mark
'86 928S 5-sp.

Hi Mark - I'm having similar problems, did you find a solution?

Barry
'89 S4

Hi, everyone-
Meant to post this over the weekend but got sidetracked, sorry.

The problem is solved. Turns out that the drivers' side coil wire had come loose (it appeared that the black plastic cover had worked its way free and pulled on the wire itself). Because of the cover being loose and the separation being on the bottom part, this wasn't immediately obvious until I started methodically checking all the connections. Cleaned things up with some electrical contact cleaner, reassembled, and it started right up.

The most important thing in this case was a decent light so I could see what had happened!

This did raise a question for me- how often do the coils need replacing in our cars? I've never done mine. The connection looked OK (better with cleaning and some dielectric grease), but not perfect.

Moral of the story is to check out all the electrical connections before going into full panic mode. Good luck, Barry.

'86 928S