the number one issue with fuel sync off will be backfiring out of throttle body, especially at part throttle, but, if your running a cheap crank sensor, that will also make it do funny things, I've been having misfires and stumbles for almost a year now, only,to find out my cheap advanced auto crank sensor was intermittently losing its signal, finally replaced it with a Delphi sensor and cured everything...

 

The only sensors i changed were the pre cat o2 sensor and the engine coolant temp sensor. The ect sensor is from napa. I don't know if that would be the problem but i noticed the temp is about a needle width higher then before. Still about 2 needle widths below the middle mark. I don't think that would cause it to run rich, more lean if anything

 

Hi, i'm reviving this thread as my truck still isn't running properly, i was busy with work so i let the truck be for a few months.

The truck is no longer misfiring however it still runs rich. I changed the plug wires to msd ignition 8.5mm, and plugs to ngk v power gapped at .035". The truck runs good for about 15 mins, idling, normal driving and WOT. After that it begins to sputter and idle rough, idling between 300-600 rpm and it will stall if i don't feather the pedal. Taking off from a stop it sputters and wants to die unless i'm feathering the gas. When it does stall it'll fire right back up. I tried unplugging the front o2 sensor and that didn't help. Fuel pressure is at 48-49 psi idling, when i shut the truck off it immediately drops to 40-43psi and stays there. Is that normal?

Since changing the intake manifold to the air gap i have replaced:
Spark plugs (Ngk v power)
Spark plug wires (msd ignition 8.5mm)
Cap and rotor
Pre cat o2 sensor (NTK)
ECT sensor (napa echlin)

The only code its showing is P0132(pre cat o2 sensor high voltage).

Anyone have any suggestions? Thanks.

 

If you reset the codes, does the 02 code come back?

 

Yes they come back after 5-10 mins of driving

 

What about post cat 02? Almost sounds like it's stumbling once it reaches the point where is in closed loop.

 

I haven't replaced the post cat o2 sensor. I agree it seems like the problems are in closed loop. Would the post cat o2 sensor be enough to cause the engine to stall?

 

If it's leaning out your fuel trim it's possible

 

I have figured out the main problem with my truck, the o2 sensor connectors weren't hooked up properly, it isn't setting rich codes anymore. However there is still a random misfire at idle. It'll set codes for misfires and i'll clear them to see if it'll misfire on the same cylinders, but it usually doesn't. Last time i drove it i would load the engine up a little at intersections, around a 1000rpm and it wouldn't misfire and check engine light stayed off. I've cleaned the throttle body and sprayed the Iac with carb cleaner. Could the iac be bad without setting a code?

 

Check fuel pressure.