Hello again. I'm making progress on getting my $300 91 B2200 (Regular cab, 4 Cylinder - carbed, Auto Transmission) back on the road and need help diagnosing a problem. When the engine is started cold it puffs a bit of smoke out the tailpipe which is most likely from worn valve stem seals. After it runs for a while it really starts smoking. On most occasions, after its good and warmed up, if I shut it off then restart it the smoking goes away - totally. I replaced the PCV valve thinking that might be the problem but it didn't change the symptom.
I'm suspecting maybe the vacuum modululator on the automatic tranmission. Does this sound reasonable? How much of a job is it to replace that module? Thanks in advance.

 

I had a '92 that did this, a very white smoke, and only when very cold outside. The colder it was the longer it would smoke. In MY case it turned out to be a cracked cylinder head, which was found by the machine shop after removal for a valve job. I had no idea. They fixed it right up (somehow?), and no more problems. I think they may have pressure checked the head in order to find this, but I'm not sure. They may have just known where all to look.

Extra note: I had been noticing coolant losses in the reservoir, having to top off about every other week. So that's where the coolant was going. Up in smoke!

 

Well, I confirmed my suspicion about a faulty modulator valve today. When I disconnected the vacuum line at the valve, transmission fluid was dripping out of it which is a tell tale sign of a bad valve. Fortunately earlier this week I had purchased a new modulator valve on Ebay for $3.99. I installed it this morning and the smoking problem is history! It still puffs a little bit of smoke on a cold start but its minor compared to the smoking from the bad modulator valve.