3.2 Bucking when cold - fine otherwise

[tadink]

Does not happen all the time - but some days on startup and before fully warmed up - there is a severe bucking at around 3k RPM - almost worried that she'll shut down completely....

but when warmed up - no issues save a slight stumble or hesitation under WOT when doing the Italian TuneUP at around 4k....then clears and is fine.

anyone ever seen this?

thx

td
1989 3.2, smogged in CA

[stlrj]

Sounds like an ignition or mixture problem. I would have it checked.

[tadink]

Is there a good Indy in Beverley Hills or nearby? I'm far from home down here - normally in Napa!

[88911coupe]

Not BH but Ottos has a good rep...down in Venice though. BTW, I had a similar issue with my 3.2 and it ended up being due to some broken solder joints in the DME circuit board that would cause issues as the moved due to temp changes. There are some threads here on how to fix it but I just sent it to ischmitz here on the board. Fixed it up in no time and has run perfectly ever since. He's in Santa Barbara IIRC.

[ischmitz]

If it's only happening with the engine cold the first thing coming to mind it the CHT (cylinder head temperature) sensor. It richens up mixture until you get the engine up to operating temperatures. If it is faulty it can cause poor running when cold.

The DME could be a factor because it also heats up and that could make a difference. Worth a look once the other things have been checked. The other component is the DME relay. It gets fairly warm, too and is known to fail with age. You should have a spare and this is a good opportunity to order one, swap it and see if it makes a difference. If yes, problem solved, if not you have a spare.

Then one test to differentiate between cold engine and cold DME/DME relay would be: Get the engine up to temperature by driving at least 30 minutes. Then shut it down for maybe 10 - 15 minutes (this will bring the DME back to ambient while the engine will still be close to running temps). If it happens in that condition the DME is more a more likely culprit.

Another test is to knock onto the DME and DME relay with a screwdriver handle when it happens and see if that makes any difference. If yes then the DME needs rework or DME relay needs to be replaced.

Ingo

[cgarr]

I had this problem, I think it was my O2 sensor not up to temp yet, I checked it by unplugging it and it was fine when cold, maybe try that and see if it's better when cold?


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