Rough idle, no power when warm - no codes

[mjancola]

Ok, I give up. I've been searching the forums for hours and I can't seem to find anyone with a similar problem, so here goes.

94 Explorer Sport, manual trans, 196K. A few weeks ago it started missing and sometimes running rough. I checked spark and #5 was weak and did not follow the wire.
Plug didn't look bad but I swapped it out anyway - no improvement.

Since then it's gotten worse. Some mornings it will start and stall once. Restart and it runs fine until warmed up. Once warmed up (almost exactly 10 minutes of driving in 20-30 degree weather), the idle gets rough and when I accelerate it feels like it's running on 4 cyl.
I checked spark again when it was running rough and got very weak on #2 and #5, so I figured coil. Replaced it - no improvement.
I was thinking Fuel pump until I checked spark again tonight and got weak spark on most - only #1 or #3 seemed strong.
The most odd thing - no CEL... and yes, the light works because I ran my AutoXRay on it and nothing came up.

Speaking of the AutoXRay - the only observation was oscillating O2 (0.1-0.7) and EGR vacuum Regl (0.0-30.0). I tried plugging the EGR and no difference. I figure these are just side-effects of the problem.

Any suggestions on where to go from here? I'm tempted to do the Ignition Control Module, but I hate buying parts on a guess.

I want to test the Fuel pressure, but don't have a gauge. I'm not going to blow the $50 now cuz to me it seems electrical due to the weak spark.

I'm probably going to due the wires next, but they are only 1 year old and this problem seems to have come on rather quickly to be wires. Plus, it runs well when cold.

Any ideas appreciated!

 

[mjancola]

Spark Plug Wires!

I just remembered I never updated this post. I decided on a low-budget gamble and replaced the plug wires. To my surprise this resolved the issue!

 

[MrShorty]

Thanks for the update. Did you ever see any evidence of spark leak or anything? I recall once using extra cheap spark plug wires which developed severe spark leak after a few months. I always hate when new parts don't last like I think they should.

 

[mjancola]

I'm not sure what exactly spark leak is. The wires were probably mid grade (the same thing I bought this time, for about $25). They seemed to run fine until one morning. But I should clarify that my commute is very short (5 mi) so through the winter the underhood temps maybe never got that warm.

I checked them at night and looked for sparks/shorts but didn't see anything. I have a feeling one or two of the wires just began to fail in a manner that the electrical resistance increased enough to affect performance. Heat contributes to electrical resistance so the problem got significantly worse once warmed up.

 

[MrShorty]

I'm not sure what exactly spark leak is.

That's a term I've seen used for the under hood light show you were checking for.

It seems like my dad has had a similar situation on one of his trucks where the spark plug wires would sometimes get too hot and not conduct adequately.

Anyway, glad you got it figured out.