My car smokes after 2 cold starts in a row

[Dale_K]

Thanks for the replies. No other symptoms. I've been having trouble with a fuel trim CEL and the car was running rich at low load and lean at high load (didn't make any sense) and a new MAF sensor cured it per the Durametric readings and subsequently I've been totally free of CELs. It did the same kind of smoking before changing the MAF sensor.

I suspect the cold start enrichment might be the culprit but I have no idea how it works. My car acts like the first start is OK but then it uses that value as the starting point for the second start and enrichens it again, sort of doubling up on enrichment. That might not really be what's happening - you know how owners get an idea about something that's totally off base.

It's hard to see how oil migration could be different. I mean the oil has a full day to drain back down to the sump.

[shlim8]

I noticed a similar pattern on my 2001 2.7 Tip...

If I drive my car out from its usual parking spot to down the driveway to wash (total of about 20ft), it will throw out a huge cloud of smoke the next morning, almost guaranteed (if I don't go for a looong drive after the wash, I usually just drive around the block to dry the brakes and that isn't long enough).

Other than that, it only smokes once in a fairly long while.

The car used to throw out smoke once every 8 to 10 cold starts regardless, but I discovered that it was the brand of oil I was using - voltronic. It was a blast as the power was good, but it clatters on cold starts and the car used to throw out smoke more often.... changed to elf and almost reduced all the clatter, and greatly reduced the frequency of the start up smoke (but not the "morning after the car wash smoke").

I've always assumed that my car is normal after I had post about the smoking issue previously...

[BYprodriver]

Originally Posted by Dale_K

Thanks for the replies. No other symptoms. I've been having trouble with a fuel trim CEL and the car was running rich at low load and lean at high load (didn't make any sense) and a new MAF sensor cured it per the Durametric readings and subsequently I've been totally free of CELs. It did the same kind of smoking before changing the MAF sensor.

I suspect the cold start enrichment might be the culprit but I have no idea how it works. My car acts like the first start is OK but then it uses that value as the starting point for the second start and enrichens it again, sort of doubling up on enrichment. That might not really be what's happening - you know how owners get an idea about something that's totally off base.

It's hard to see how oil migration could be different. I mean the oil has a full day to drain back down to the sump.

Horizontially opposed cylinders don't drain down very well. The worst normal operation you can do to any engine is start it & not allow it to fully warm up to normal operating temp. With over 100,000 miles on your engine I would assume your cylinder walls are worn & possibly out of round.

[thstone]

Here is my best understanding of the start up fuel injection control sequence:

The DME controls cold start using engine temp and rpm as the critical signals that regulate injector pluse time and ignition timing. Normally, the injectors will pluse longer to enrich the mixture along with maintaining the timing at near TDC to get a clean and smooth start.

If the engine fails to immediately start (as sensed by low rpm), then the ignition timing is advanced and the mixture further enriched to get the engine to start but not to the point where the engine would flood with fuel.

Once the engine starts, the DME will keep the mixture enriched for 5-30 seconds and continue to adjust the timing based mostly on engine temp. This enrichment is gradually reduced as the post start timer (time since engine start) reaches the 30-sec mark.

After post-start, the DME transitions to the warm-up phase where the engine is controlled by the stored map control feedback loop.

Of course, this is all happening in a closed-loop feedback system designed to start the engine smoothly and then maintain a smooth post-start idle.

If you were to stop the engine 10-20 seconds after start, then upon re-start it would begin this process all over. However, with the engine shut off in a somewhat rich condition, this should improve the re-start (since the mixture is already rich) but then the engine could run slightly "over rich" for 10-20 more seconds until the post start timer reaches 30-sec mark because the DME hasn't transitioned to using the O2 feeback system to maintain the mixture until the warm-up phase.

However, the amount of fuel that is injected to enrich the mixture at startup is only a teeny tiny amount more than normal and even a slightly over-enriched mix would still only contain slightly more fuel than a perfect mixture. Plus, a rich fuel mixture rarely (ever?) causes an engine to smoke.

Engine smoke is almost always related to oil in some way.