Thomas Owen

The problem is rich/smoke running after about a 1 minutes warm up.

I bought this early ’91 engine with 52k miles already out of the car, so did not hear it run in a proper environment. Needed top end due to leaking cylinder to head.

I did the top end with new pistons cylinders and machined heads to accept newer gasket. All new valve and guides.

Engine starts right up, idles perfectly.

After about 1 minute it begins to get more and more rough and then begins to smoke.
I have a spare/new of almost everything on this engine. AFM, fuel pressure reg, wires, coils, distributor caps, and it is the same problem!

Fuel injectors were sent out and cleaned/tested perfect.
Have a second ECU and also same problem.
Stock chip or Steve Wong chip - same symptom

Has B&B headers with O sensor.
proper personality jumper

I have verified wiring and connectors – all ok.

I do have the diagnostic scan tool where I can monitor ‘Actual values’ while engine is running.

Intake air temp – 80F
AFM – 1.4V
CHT - climbs up normally
Idle – 900
Inj time – 2.8ms
Ign time - 6.5deg

I took a big leap outside my thinking on this… on my engine stand I have an oil tank for a ’70. What if the suction side of the oil pump was pulling in oil and the outlet side was not able to move it back to the tank (fast enough)?

I am not sure the smoke after a minute is oil or fuel, so is it possible that the block is filling up with oil and causing a problem with the cylinder/plugs which results in the rough running and smoke?

I appreciate any and all advice! Really want to get this resolved before it goes in my car.

Here is a video, but does not show the problem:


Thomas

cajonfan

Doesn't the motronic system switch from "open loop" (no dependence on oxygen sensor input) to "closed loop" (using oxygen sensor signal) operation after about 60 seconds?

If that's your problem you need to read or measure the oxygen sensor signal. I sort of remember 0.5 Volts being the target number.

Good luck,
Michael

Thomas Owen

Michael,

The output from the O sensor does indeed oscillate as it should, and the signal is getting all the way back to the ECU.

I am leaning more and more towards a situation similar to an oil overfill.
I will make a video of the startup and problem development today and post it.

Thomas

Thomas Owen

OK everyone, here is a video showing the problem. The engine runs perfect up to 1:20 and then the smoke begins.

A prize to the person that can diagnose this because I am at my wits end.

Earlydays

If the rings are all new, they have not yet properly seated and you're burning some oil when the engine begins to warm up.....

ras62

Change the O2 sensor and recheck.

J richard

^yup

And that is not the way to break in a fresh build. Put it in the car and run it in. Excessively idling a fresh build will do more harm than good. It needs to be run in properly under load and at rpm to seat the rings, at idle you can glaze the cylinder wall and not get a good seal.

Odds are without being broken in it starts clean and starts to build up crankcase pressure (ring blow by) and starts to smoke...take the cap off the oil tank and see if it's over pressuring the tank to confirm.

Put it in and break it in, then if it smokes you have an issue...

dlpalumbo

If you're not using it already, I suggest using 'dino' oil for break-in. Synthetic oil will delay a good breakin.

I just had my engine rebuilt and it smoked initially. I didn't think anything of it. 1000 mi on dino oil then valve adjust and switch to synth. Its fine now.

me61ic

I had a similar problem but with a '90 C2 that had been sitting for 16 years, it run perfectly when stored and now after changing all the spark plugs, oils, filters and belts, it was running great after about that minute, minute and a half when it started burning oil, little at the beginning and then crazyly to the point of not being able to see around.

I was told the car only needed a good run, the oil had made it's way to the exhaust system through all those years and it was full of oil, it was smoking as soon as the exhaust was getting hot at around that time. At the end we had it running for some 15-20 mins and the smoke went away. In our case it was running great with no iddle issues.

All this happened last month, I'll try to upload a video, my neighbours thought the car catch fire

Michael D'Silva

Did you solve the issue??