Rough acceleration - Little power

[Footlong70]

Hey guys, some help would be awesome. My explorer (91 4.0L Auto) went from running awesome to terrible while leaving it run to go in the store for 5 min. The idle is still decent, shakes a bit but rarely bogs down since the incident. In park while being reved it sounds strong and healthy with no hesitation or shakiness. But as soon as i put it in any drive gear and accelerate the engine is very rough with very little power to get the wheels spinning at any amount of throttle. It seems shakey as if it's not running on all cylinders at any speed. I was hoping for the check engine light so I could scan it but still nothing. I've put on brand new plugs, wires, oil w/ filter, temp sensor, coils, transmission, checked for leaking hoses and intake (all good), and re-cleaned my brand new MAF. I'm positive its not an Air/Spark issue. My guess is a plugged or malfuntioning injector, plugged fuel filter (only 2500km on it), or the fuel pump dying/plugged and cant keep up. Any ideas or tests I could do to try and isolate the problem is extremely helpful. What do you guys think?

 

[Otto]

My trucks doing this as well. I'm pretty sure it needs a new fuel filter. Showing thos symptoms as well, not much low end torque and all you can hear in 1st gear is the torque converter spinning around then clunks into 2nd. Pain in the rear and I dont even have 12 bucks right now to buy a new one! lol

 

[PickupMan04 FX4 L2]

do a fuel filter and maf cleaning..

 

[Footlong70]

been there done that... next?

 

[91rangerxlt]

my ranger had this problem. clogged air filter was the culprit

 

[Area 52]

Did you recently put gas in it?....bad gas??? Your symptom is indicative of crappy gas.

If not...
My guess is one of the plugs is not firing. Check boots to plugs; if okay then pull plugs until you find a wet one (unburned gas). I would not think a bad fuel pump would cause this symptom when it was running fine, then let it idle for 5 minutes and then running rough.

 

[Footlong70]

Actually I finally figured her out. I had an appiffany one day and went and bought a laser thermometer. With the engine idling i checked the temp on each header pipe right after each cylinder to find which ones were running cold (not igniting).... Sure enough 2 cylinders were half the temp as the others so I tried a couple tests on those two cylinders. My test with all the lights off found the problem. To my pissed off surprise, the spark plug wires were arcing from the boot to the head because the brand new plugs (1.5 weeks old) weren't grounding... They worked fine for the first few days I had them in there but failed after that which is why I was so puzzled with what was going on....No plug should fail after 3 days of use (especially the Bosch 4+ Fusion). But easy fix with a new pair now... Just a good example as to why we have to look at every aspect of diagnosing even when we just replaced a part....

 

[Sasquatch_Ryda]

Please toss those Plus 4's, they are absolute garbage.....

There are more missfire issues because of those plugs than anything else i've come across.

Go get a set of Motorcraft platinum plugs and be done with it.

 

[AZFX4]

I know this is an old thread but my truck is doing the same thing. I have not yet tried the plugs but im just curious as to why it runs fine when in park but putting it in gear causes the issue?