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Cold Start Backfire

1019 Views 5 Replies 5 Participants Last post by  SUBTLT
This is starting to bug me, and I'm sure it's not good for the car either. ugh

For the last few weeks my GN has consistently backfired when starting up in the morning. 4 out of 5 times it'll start right up afterwards and run fine, 1/5 it'll run like it's on 5 cyls for a minute till it clears up. FWIW, it seemed to start when the temp dropped into the 50s from the 70s.

I've dug through the archives with little success. I did find a recommendation to check the CPS, so I reset the clearance on that to .025, but no joy (stopped the ticking though! :) )

From what I've read, either the coolant temp sensor is sending a temp that's way off, I have a sticky valve, a leaking injector, or some combination of the above.

I'll throw T-link on it tomorrow morning to check the temp sensor, try some "valve unstick" additive, but if that doesn't work, what's next? :confused: I had the injectors cleaned a year ago, so they SHOULD be OK.

Anything else I should check?
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If the crank sensor was hitting before you reset it then it's garbage now. Replace it with a new GM or Delco one. This may or may not solve your problem, But will be causing one soon... Check your cam sensor it may be on the edge of proper adjustment.
i,ll have to go with the the cam sensor, i had a similar situation.check the play in the shaft of
the drive also.
I bet it's the IAC.
I'm no expert but I had the same thing happen this morning (40 outside) and the other day I noticed my IAC reading was 01 at idle. Coincidence??

How do you check your IAC to see if it is good??

Threw T-link on this am and the coolant sensor is sending valid info, so that's not it. I'll reset the cam sensor this weekend (finally get to try my caspers gizmo :D ) and see if that helps.

Confused on the IAC recommendation though - how would that affect cold start ignition? I understood it to meter air at idle once the car is running - which it isn't when the backfire occurs. Just confused - what's the reasoning? dunno

If I do just a quick hit to the starter (and I mean quick, like just a fraction of a second) I can get the car to start "on the backfire", sort of an instant start feature. Weird.

Thanks for the advice!
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