Missing & Backfiring on Cold Start

[87GN&98VET]

Anyone ever experience this before: missing, bucking, and backfiring on a cold start condition. Runs like crap until it's warmed up about 5 or 10 minutes, then idle increases slightly, smooths out, and runs like a champ. All stock. Most of the ignition system has been replaced. Is this a sign of a bad computuer?

 

[Brian Mc]

I think it's a curse of the LC2 Buick engine.

 

[Granny 2]

Check the set up of your Cam sensor

 

[87GN&98VET]

I've checked the voltage from the cam sensor and it appears to be o.k. But if it was the cam sensor, wouldn't the problem still exist after the car is warmed up? For some reason this problem only exists while the car is cold. Isn't the car in open loop on a cold start, before the O2 sensor starts reading and supplying feedback to the ECM?

 

[jastrckl]

yes it's open loop on cold start, so you're not chasing an o2 problem. if it was cam sensor alignment or whatnot, I'd imagine it'd do it all of the time. I bet it's some problem in the spark system somewhere, coil, est, esc, etc.

 

[Nick Micale]

Originally posted by 87GN&98VET
.......... Runs like crap until it's warmed up about 5 or 10 minutes, then idle increases slightly, smooths out, and runs like a champ. All stock. Most of the ignition system has been replaced. Is this a sign of a bad computuer?

Few years ago I had a T-R with this problem and chased everything. A different ECM cured it.

 

[Chuck Leeper]

bad cold idle??

Could be a leaky inj that are loading the intake valves w/ fuel upon shutdown. Then when cold started, the plugs are wet, engine is real rich, the missing and backfires come about. Most likely backfiring out the tailpipe?? If so, a sign it's way rich.
How many miles on the injectors??
Does the FP stay up for some time after shut down?

HTH, Back under my rock

 

[Eric Stage I]

The BLM's are still being used when cold. Can you give some BLM readings when warmed up at idle and just off idle?

Regards,
Eric

 

[87GN&98VET]

I'll check the plugs to see if they are wet before I start it up. As for the BLM's, I do not have a scan tool but see if I can borrow one. Can the computer be checked at a parts store like Autozone, or does the whole vehicle have to go to the dealer?

 

[6=8]

Don't rule out sticky valves/weak springs if you have a few miles on this engine! This, combined with leaky inj. can lead to some nasty back-fires through the intake... And it may not happen every time.

Do you notice a "Spike" on the boost guage during start up?

My 140K stocker would do this regularly. On a hunch (And trusting that the electronics were sound) I tried topping my oil off with a bottle of that CD-2 "Frees up stick valves" stuff. During the next 500 miles of driving, I found the problem was reduced gradually and eventualy elliminated.

I then replaced my valve springs (and quit using Penzoil!) Don't know if the oil had anything to do with it, but more than one mechanic has recommended that I stay away from this particular brand.

For the last 18K miles, it has not done this even once!