'93 4.0 Intermittent stalling/missing/dying at idle

[lucasruble]

First off, I have noticed that when I fire it after cool down (such as the next day
), it will run slightly rough until I supply fuel, then allow the engine to regulate idle. I'm pretty sure this roughness is tied to my stalling/dying problem. Anyway, on to the main issue..CEL will come on intermittently and stay on for awhile, then shut off for awhile, then back on..etc.. When CEL is on, truck runs fine, but will intermittently die at idle. However, when CEL is off, while driving, it will intermittently miss, or lose power, at speed. It's a real quick miss and it doesn't happen consecutively, but will happen more than once, depending on how far I'm driving. Also, with CEL off and accelerating from a stop, it will sometimes lose power for a moment. After the quick power loss, it bounces right back and I can continue accelerating. I have tried a different TPS, cleaning the IAC & MAF, pulled some KOEO codes (KOER test won't initiate, so I can't get those codes), and checked a little for obvious vacuum issues. All to no avail. Any ideas?

 

[bmerr98]

Mr. Obvious here. Plugs and wires? Did it for me with similar symptoms. No CEL and idled fine, but had the miss under acceleration.

 

[lucasruble]

I can't rule plugs & wires out, but to try to be more accurate, I shouldn't say it's missing. It's a complete, momentary loss of power (when CEL is off) sorta like all the plugs cease fire for a second, then start firing again. It definitely seems to be electrical. When the CEL is on, it idles smoothly (unless it dies, of course) after idle regulates on initial cold start. This leads me to believe that it isn't plugs & wires.

 

[RonD]

Clean the MAF sensor first, Read here:
http://www.therangerstation.com/tech_library/CleanMAF.html

My '94 4.0l needs a shot of Seafoam in the fuel tank once a year to keep it from random misses.
320k now and purrs like a kitten 52 weeks a year, well an older kitten, lol.

 

[lucasruble]

That was one of the first things i did. Cleaned it with MAF cleaner. No change.

 

[lucasruble]

Any more ideas?

 

[RonD]

If you can't get any codes then it could be a computer issue.
CEL on could mean Open Loop which is making it run better.

I would check fuel pressure as well, could be filter, Fuel pump relay or pump itself
Should be 35psi to 42psi at the rail.

 

[lucasruble]

ECU had crossed my mind. I'll have a looky. I'll have to track down a fuel pressure gauge and test that as well, for good measure. Thanks for the pressure ratings RonD.