Stumble and stutter- sensors or fuel system on '86 2.3?
 

Hello, folks,

I am at wit’s end here, hoping someone can give me some ideas.
My truck is an ’86 2WD 2.3L EFI, one of the early versions with two fuel pumps and the IAC on the air filter housing. The whole engine was rebuilt about 60,000 miles ago.

Back in the fall, I had a stall problem that ended up being a bad electrical ground. During the hunt for this problem, I replaced most of the ignition system (coil, plugs, plug wires, TFI module, distributor pickup, distributor cap, rotor button). I also replaced the in-tank fuel pump and the fuel filter, fuel pressure regulator, and the fuel pump relay.

I have now developed a stumble/stutter/miss symptom that seems like a general fuel (?) issue, rather than just one missing cylinder. Under more than half throttle under load (climbing a hill or coming out of a curve), there is an intermittent stumble. It acts like a carbureted engine that is cold and doesn’t have the choke set right. It used to only do this when the engine was cold, so I suspected a coolant temp. sensor and replaced it to no avail. Now the truck is doing it once in a while even when it is warmed up. I have also replaced the air filter, although it looked fine. I replaced the fuel filter again, which looked fine, and had no water in the bowl (this is the tuna-can shaped, frame-mounted filter). We have had E10 ethanol fuel here for about three years now.

I have tested the fuel pressure, and it holds about 35 psi even at high rpm. The EGR valve vacuum line was disconnected and capped off several years ago. My Actron code reader shows nothing with the engine off, and only an “010” code running, which it says is a manufacturer-specific code, but I cannot figure out what this is (it comes right before the 011 code, which it says signifies the test is completed). I cannot find any vacuum leaks anywhere.

I am at a loss as to what to check next. I am thinking it must be MAP sensor, intake air temp. sensor, throttle position sensor, or something else? I put a can of injector cleaner in today, just to see if that helped, but it really seems to be more than just one cylinder missing. I am looking for ideas, folks, and hate to spend more money unnecessarily. Any input would be greatly appreciated!

Hope y'all have a great weekend!
Regan