Badly misfiring 85 318i

[redhotchilipepper]

My car misfires often, and abruptly, on the highway. It will misfire about 9 times in 10 seconds. Some of these are fairly jolting on the car, and sometimes it feels like the car has stopped accelerating all together for a few seconds. I have been playing around with it while driving in the last couple weeks and this is what I have found:

1. I can replicate the symptoms (misfiring) in all gears but symptoms are the worst in the higher gears.
2. If I shift early, keeping the rpm's down, the car seems to do much better, not missing as much. And when it does, it doesn't jarr the car too much.
3. On the highway going normal speeds (60-75mph) the car will misfire less if under heavy acceleration (flooring it) and misfire even more under slow deceleration (slowly letting back on the pedal). The car really bucks when peaking a hill and easing a tad off the pedal. However, if I *quickly* get off the pedal it seems to decelerate okay without the car bucking too much.
4. Symptoms are present when the engine is hot or cold.
5. The car is definitely running rich, the mileage is terrible and I've even seen a couples flames shooting out the tailpipe when it misfires on the highway real bad.
6. I thought it was fuel starvation so I replaced the in-tank pump, the outer in-line pump, and the fuel filter.
7. After that I thought it might be spark so I put in a new ignition coil, cap, and rotor. (All 3 pretty much due for replacement). I looked at each spark plug and wire and they all looked pretty good but fairly black from running rich. Dropped in a new air filter at this time as well.

Nothing has solved this so far. Any ideas??

[Smelser]

play with timing maybe? might be a bit retarded, try an advance and see what happens, if it gets worse, go in the other direction.

just a guess. assuming wires are all in correct position.

[E30_Pare]

I've had this problem before.

Check & clean the ground on top of the intake manifold. Listen for the fuel pump relay in the engine bay. Located in a black box next to the air box. It's probably tripping out

[redhotchilipepper]

I cleaned up both ends of both contacts on the braided ground cable on top of the intake manifold. Also checked the resistance of it and all seems good. Drove it around and it seems to have made no difference. I will get a another fuel pump relay and try that.

[nwwonka]

Check for vacuum leaks and make sure you afm isn't stuck. Replace that fuel pump relay and see if any of your plugs are in the wrong order. A brand new afm is around 100$. I was having the exact same problems. Took it to a buddy and that's What he fixed, car runs legit now. Also check the little round cylinder on top of your intake manifold, mine was bad so I replaced it with an open close PVC valve from the hardware store, works great.

[redhotchilipepper]

Since last post, I have replaced the spark plugs, checked the afm using the Bentley resistance check, and drove for a while with the TPS unplugged. No changes resulted. Only thing left to replace in the ignition system is the plug wires, but they look good and all resistances check out okay.

However, in running through a series of fuel pressure tests (off, idle, FPR vacuum on/off, w/throttle, and while driving) I noticed that while the fuel pressure is consistent, it is consistently 36.5 psi instead of between 40.6 and 46.4 psi as suggested by the Bentley. Does this reveal anything?

I discovered a new symptom a couple days ago. The car stalled while I was accelerating down the road at 30mph. When I attempted to turn it back on, the fuel pump ran and DID NOT STOP, and it wouldn't click or crank or anything. Usually it primes for a couple of seconds and then stops. I checked the battery, was fine. The car would not stop this "indefinite priming" until it had sat for several hours, at which point it started up like nothing was wrong at all.

nwwonka: Does the "little round cylinder" = idle control valve? I put a new unit on a month ago.

Apparently these old-skool 7 pin fuel pump relays are $45ea and I don't think the symptoms sound like the relay is malfunctioning. Can anyone chime in - does this sound like a relay issue?

I'm about to give up and go to a $mechanic$ and ask them to do a smoke test or whatever else necessary to discover the culprit.

[thebutterson]

I had that same long fuel pump prime and no start, then I cleaned the grounds and all was fine. Clean the grounds on the intake manifold, valve cover to body, and oil pan to body.

[redhotchilipepper]

I cleaned all 3 major grounds nicely. I also replaced the fuel pressure regulator, and the fuel pressure is back up where it should be! And...the car still randomly misfires once you hit 1500rpm or higher. However, I have noticed something huge: the problem is gone while the car is cold. Only once the car has warmed up does it start to misfire. Surely this narrows it down, right??

[ruizl300]

I had a similar issue and it turned out to be the Fuel pump relay. It would work at cold and then as it warmed up would start giving out randomly like a missfire. After about a week of this it finally gave out and the car wouldnt start.

[redhotchilipepper]

Solved! As I was fiddling around under the hood while the car idled, I bumped the ICV and noticed a jump of about 1000rpm. I checked the connector, and one of the wires had almost frayed itself completely off. After putting on a new connector, the car runs waaaay better: smooth idle and no more misfiring!

[skillet318]

Where did you find or get a connector for the ICV? I am having similar issues.