Intermittent roughness/power loss

[t_marat]

I had this thread on this issue before
http://www.bimmer.info/forum/showthread.php?t=33143&page=4&highlight=idle+rough

Well I changed the O2 sensor to a new original BMW one (sensor is a siemens one, my car has an MS40 siemens ECU, that wasn't exported to USA). Unfortunately I still have this issue.

When I first start the engine it runs normal. After a while it starts running rough with black smoke coming out of the exhaust. Taking for a drive and keeping revs at about 2500-3000 level makes engine run normal again. If I stop and idle for say a minute or so, then roughness and black smoke are back. Holding the revs at 2500-3000 for a minute is enough to bring the engine back to normal. I can also say that this behavior seems pretty much irrespective of engine temp, be it cold or warmed up. All this made me think the heating element in O2 sensor is gone bad, so I replaced it. But the problem is still there, exactly as before.
I thought maybe the heater voltage wasn't coming to the O2 sensor. checked at the connector and a 5V signal and 12V heater voltage are there, so an O2 sensor is now ruled out.

What else could be causing this problem? Injectors? Coils? TPS?

[t_marat]

Tried disconnecting TPS. Issue is still there.
Tried disconnecting MAF. At first engine runs normal, but then it starts wobling, rpm rising and falling, coming to near stall. The moment I reconnect it returns to more or less normal (black smoke).

[Jeff N.]

Black smoke is too much fuel. You may have a bad ECU engine temp sensor causing the ECU to keep the car on the cold run cycle. Or, a stuck thermostat so it never warms up.

Does this car have codes? Do a stomp test and get the codes. Work it from there.

[t_marat]

Thermostat is working, as the engine warms up.
The stomp test won't work on my car.

It could be the temp sensor, but would it depend on rpm? As long as I keep driving/rpm higher than 2000, then no black smoke.

[Morgenster]

Thermostat is working, as the engine warms up.
The stomp test won't work on my car.

It could be the temp sensor, but would it depend on rpm? As long as I keep driving/rpm higher than 2000, then no black smoke.

Sounds logical: higher RPM means higher temperatures and better combustion as well as better cat functioning. It's probably still running very rich. Only way to know is have the exhaust gases analysed and look at condition of plugs. I'd have thought that the fixed O2 sensor would correct for this when warmed up though. Apparently not. If the resistance of the temp sensor is higher than normal that means the DME gets the idea that the engine is cold, but If you really have that much smoke I'd also look at injectors or FPR?
Looking at your plugs and seeing one or two fouled plugs could quickly point to the injectors.

[Ross]

X2 what Jeff N says.

[t_marat]

I disconnected the intake manifold temp sensor. Still had the same problem. After a while engine would start running rich.
When I just start it, it runs normal. It takes a minute or so (shorter if fully warmed up) to start running rich. Raise the rpm to about 2500 for about 30 seconds, and its all normal. Leave idling, and it goes rich again.

So now things left to check are injectors and FPR? How can I check the FPR is working correctly? If the pressure in the fuel system is normal, then FPR is OK?

Could this be injectors? Or coil packs?

Another thing. I read that Siemens ECU can control the O2 heater. I understand this as its ability to turn off the O2 heater. Also there seems to be no heater relay. Could it be the ECU is going mad?

[Morgenster]

I disconnected the intake manifold temp sensor. Still had the same problem. After a while engine would start running rich.
When I just start it, it runs normal. It takes a minute or so (shorter if fully warmed up) to start running rich. Raise the rpm to about 2500 for about 30 seconds, and its all normal. Leave idling, and it goes rich again.

So now things left to check are injectors and FPR? How can I check the FPR is working correctly? If the pressure in the fuel system is normal, then FPR is OK?

Could this be injectors? Or coil packs?

Another thing. I read that Siemens ECU can control the O2 heater. I understand this as its ability to turn off the O2 heater. Also there seems to be no heater relay. Could it be the ECU is going mad?

I don't think the manifold temperature sensor has the same impact as the engine temp sensor and I don't know if disconnecting these sensors one by one will yield good diagnostic info.
Any ECU can go mad.
I'm just thinking logically here and not speaking out of experience, but if the FPR is failing It would let fuel pressure build up in the fuel rail in idle since the FPR is operated by the level of vacuum in the manifold. Normally more vacuum means more fuel is bypassed to recirculation and less pressure. What I don't know is if that would ultimately result in an over-rich condition because injector timing is pretty sharp and fluids can only be injected up to a certain limit. If the injectors were designed to be dependent of the FPR for metering the amount of fuel I'd definitely check it out, if not I'd look at the injectors.
But I could just as well be talking BS since I have only my logic and an idea of how these engines manage themselves. It's best to listen to the real engine gurus here.

[t_marat]

How engine determines timing for the injectors? Using the crankshaft sensor?

[t_marat]

Had the car scanned. At first the following errors were read:
98: Idle Speed Control Valve
161: Unkown. Absolutely no info anywhere.
100: Self diagnostics error of ECU
Errors were erased and after 5 minutes of driving only error 98 reappeared.
As I wrote above my main problem is that if I idle a couple of minutes engine starts running really rich with black smoke from exhaust. This actually happened during the second scan. Right at the same time as engine started running rough and rich another error code popped up
97: Tank Ventilation
After a pressing the gas couple of times engine returned to normal condition and ran for about 5-6 minutes fine. Final third scan revealed only error 98 (ICV), error 97 dissapeared by itself (no reset after second scan).

I don't think such a rich running condition can be caused by some vacuum leak. Is it possible? Engine runs really rich, you can smell it.
What is tank ventilation? Evap purge valve?

[Morgenster]

How 's the fuel pressure?
BTW: didn't you change out the ICV?
I'm thinking tank ventilation is related to the purge system but I wonder how the ECU determines there to be a problem with it. I don't know of any sensors on that system so I think your ECU is just guessing. Could still be broken FPR. After all, it is part of the recirculation of fuel. If the FPR is stuck closed fuel pressure should be higher than normal.

[t_marat]

I did change the ICV last year with another used one. Problem that I was having last year was due to the dead MAF, car would stall. It wasn't related with ICV but I changed it anyway, the new (used) ICV looked cleaner and better.
I will try to measure the fuel pressure tomorrow. Intake manifold will also be taken out again to see if there is any vacuum leaks, plus ICV swap to the old one.

Today tried disconnecting the purge valve right at the time the car was smoking black. Didn't make any difference. But it did make a difference when I disconnected the hose from the valve, letting it suck air. Revs increased, stabilizing after a while. No matter how long I waited the car did not run rich again (it was sucking in a lot of air). In this regard, I am thinking maybe ICV is going dead? jamming from time to time in a near closed position. Revs go down and ECU tries to compensate by increasing voltage to ICV and increasing the fuel feed (injector timing). Is this plausible? But that won't explain why it still runs rich when you press the gas.

edit: did I write that after the errors were erased by the scanner idle acted funny? it would oscillate between 1400-1500rpm before settling down slowly.

[t_marat]

Today had the ICV swapped with my old one. Unfortunately there was no difference at all. So then went for a fuel pressure check. The guy connected the hoses and manometer to the fuel rails and asked me to start the engine. The moment I started the engine he started shouting "switch it off, switch it off!!". His gauge was capable of reading pressure up to 6 atmosphere, that makes about 85psi. Pressure in the car's fuel system was higher than that, the gauge maxed out immediately. He said he barely held the setup in one piece, hoses wanted to shoot out. Return hose was checked and it wasn't blocked. So it was the FPR..
Got a "new" used one and had it installed. No longer any black smoke from the car :)

So Morgenster, you were correct about the FPR.

[Morgenster]

Awesome!
I'm real happy to have finally made a serious contribution!