Car doesn't yet have 50,000 miles on it so I sure hope it is not a timing chain!!!

Thanks for the suggestions, I'll get on them over the next couple days and report back.

Larry

 

An update, though I've not yet checked the plugs.


Pulled and reseated the connectors (3) on the computer modules under hood on passenger side. Ditto the sensor on the air filter cover. Ditto on the top of engine (coil pack?). But not on the throttle body (idle soln?).

Car drove on several short trips over two hours running fine, then symptoms returned and lasted a few miles (return trip), then all settled down and is now running fine!

OUCH!!!!

 

Larry_too,

Glad to hear you are not experiencing this concern now. If you do want your GM dealership to look into this, please let us know.

Erica Tiffany
Chevrolet Customer Care

 

What should the fuel pressure be? Should it be constant?

Larry

 

No thanks,

Car was obtained, used, at a "Dealer".

 

Yes it should be for the most part constant and steady and should not bleed off too quickly...it should be about 60psi

 

It remains intermittent.

It again ran several miles smoothly, then, when pulling up a drive, ran rough with a flashing check engine light. A mile later it again ran well but turned rough as it was being parked leaving the check engine light on solid.

Next day: Started, read codes.

The P0300 code was set, but when cleared, only posted "pending" codes as it alternated between open and closed loop. I removed the ignition pack and module , checking the connections which looked well and reinstalled. I also added a small flask of fuel "antifreeze" (methanol etc.), (recalling that the same had been done when the same symptoms were corrected last year). When restarted, after running a short while at 1500 rpm, it stopped running rough, closed the loop and ran smooth again!!!!!

In an earlier post it was suggested that cycling in and out of closed loop was a function of the O2 sensor yet there are no O2 sensor codes set. Could the O2 sensor be intermittent???

Larry

 

Thanks,

I'll have to find a gauge with the large threads to check that.

Larry

 

Too wet to work outside this wkend.

At least it is consistent, open loop and the shakes tend to occur after 10 miles of town driving. Then correct themselves.

Does anybody have the "SCANGUAGE II" "X-codes" for the Cobalt? I would like to look at the O2 sensors, fuel rail pressure, and the like. These would be the groups of four coding's (TXD RXF RXD MTH) for each function to be monitored.

Larry