My car runs like crap when it warms up, it misses, idles like crap, and at part throttle surges and pulls ALOT of timing only when the car warms up. When the car is cold the car will pull 0 timing and run like a champ.

I have a scanmaster, when the coolant temp reaches around 180 the car acts up it seems.

I've changed MANY things including o2 sensors, opti, plugs, wires, ICM, coil, blocked off EGR, new PCM, reprogramed PCM to disable knock retard, etc etc. Tested vacuum, fuel pressure, replaced PCV valve, so many things it sickens me.

I've ran the car with the IAT disconnected and the MAF disconnected, same thing happens runs bad when warmed up.

I also disconnected the crank position sensor no dice.

What can I do to force the car to open loop at all times, or what should I be looking at?? Is the temperature reported on the scanmaster from the coolant sensor by the water pump or is it using the one for the guage, can my coolant temp sensor be defective, could the PCM think the car is overheating and pull timing??

Thanks, I've been troubleshooting this problem for a year, any help would be great.

Brian

 

I am having pretty close to the same problem, the way I forced open loop was by disconnecting both o2's. I am not planning on really driving it that way, but it does run okay with them disconnected.

 

You can get it programmed for open loop operation or you can disconnect the o2 sensors, but it will set codes and a service engine light.

 

ok, thanks for the replies.

What exactly does the computer do differently in closed vs. open loop, is it just the o2 sensors?? Any other sensors that the computer uses in closed that it doesn't in open?? And, how does the computer know to go to closed loop, is it just the coolant temp sensor and/or 02 temp?? An answer to these questions would help me find where to look, thanks again.

 

Ion, what would be the performance effect of programming the car to run open loop, will the PCM still use the o2's?? This may be a last resort.