Open/Closed Loop transition?

[iansane]

I recently picked up an '84 325e and I'm in the process of fixing some of the things left neglected by the previous owners. The car starts fine 99% of the time. However, after a few minutes driving it will barely run. I'm used to GM ecms/programming so to me it feels like when the car is going from open loop to closed loop. The temp gauge reads between 1/4 to just above and the car just runs rich as all hell. I have to mat it just to keep it running and it pours rich smoke. If I shut it off I will not be able to start it up. This is the weird part, if I just wait a minute it will crank and fire off perfectly fine and run for however long I need it to. I've gone on a few 100+ miles drives and it never gives me any issue after that (from what I can tell, as long as the coolant temp is up to normal).

Now with GM coolant temp sensors a typical failure is going full open and they then tell the ECM it's something like -270* and it DUMPS fuel. Is it similar to e30s? My feeling is that there is a dead spot or something in the CTS that happens to be right about 1/4-3/16 on the gauge and when the car is sitting it heat soaks enough to get above that point and goes back to normal. Does that seem logical? If so, which is the CTS for the ECM? There are so many! I replaced one already. A two pin right down near the head with a Bosch fuel injector style clip but that just seemed to smooth out the gauge reading.

Any help would be appreciated, it sucks getting stuck in traffic...

[jlevie]

I'd be more suspicious of the time/temperature switch and cold start valve. As best as I can determine, the crossover to closed loop operation occurs at 60C.

[iansane]

I'd be more suspicious of the time/temperature switch and cold start valve. As best as I can determine, the crossover to closed loop operation occurs at 60C.

Which one/where is that?

Does the cold start valve function at any other time then cold cranking?

[jlevie]

The cold start valve and associated controls only operate on a cold start. See the Bentely for details.

[iansane]

Then I would presume the cold start valve isn't an issue because the car starts fine...?

[HR2L]

I'd wager your ECT is bad, your issue is almost what I'm seeing, yet I don't have an early model e30 (mines a 90). The ECT Sensor with the brown end housing is the one the gauge uses, the blue (or possibly whitish/clear if its not a genuine bosch ect) is the one the DME uses. You'd be amazed at simply changing the ECT that the DME uses will do for idle, fuel economy, transitions between open loop/closed loop. I'm going to be swapping mine out tomorrow as I'm not sure when the previous owner did it last (or if they ever did it).

[iansane]

That's the sensor I replaced the day before yesterday and still had the issue on the way to work. Will the ecm have to relearn that transition?

[iansane]

So I live crazy close to my work. At night when I go to leave I never even get the car into closed loop so I never have the issue. Well tonight I just sat in the driveway idling until it happened. The R's dropped and shuddered, I punched the throttle, hopped out and started messing with things. The cover for the AFM was loose so I pulled that off. Forcing the pivot towards the back of the car, it wanted to die even more and pushing towards the front of the car it smoothed out and idled fine from then on. If the ECM sees a hugely erroneous reading with it eventually ignore a sensor? (IE, if the motor is getting a ton more air because of a vacuum leak or something with it ignore the AFM after a set period of time? Or if the O2 is toast and showing a huge lean or rich situation will it default back to open loop after a set time?)

[jlevie]

Fiddling with the AFM and getting a better idle suggests that that there is a abnormal idle A/F ratio, but we had other evidence of that. On this car the first thing I'd do would be to to check all of the parts of the cold start valve. Then I'd run a smoke test of the intake & crank case and replace the O2 sensor if it has 100k on it or is of unknown age.