91 running rough

[rocket7824]

I have a 91 ex that seems to have a bad miss. I swapped bodys from my stock ex onto my crawler.(tranny was out on the stock one and i needed a daily driver)anyways. I was coming home from my parents house after i did the swap and about 70 miles into my ride it just loss tons of power and shook like heck when the converter locks up(when the motor is under the most load i think). I thought it was an electrical problem so i started with plugs and wires even though they were not that old. Did not help. Now here is a list of what has been done since. Plugs, wires, coil pack, ignition module, mass air meter, computer, wiring harness. Well after all this still the same problem. So i thought i would check the compression. All cylinders were very close except for the middle one on the drivers side which was down about 15 lbs less. I thought it may be a head gasket but thats the last thing i want to try. I also checked the fuel pressure and it was fine.
The engine is under alot of strain from turning over 35's but it has 488's in it so i thought it would be fine. so an suggestions would be greatly appreciated.
thanks Randall

 

[BrooklynBay]

Check for a broken or unplugged vacuum line. Did you see a check engine light when it started to run rough?

 

[rocket7824]

checked all vacume lines and the ecu came up with a few things but it was old stuff. cleared it and nothing comes up now
thanks randall

 

[BrooklynBay]

I know that you've already checked the fuel pressure, but how long ago did you replace the fuel filter? Did you clean the IAC?

 

[rocket7824]

bout 2000 on the fuel filter. iac? which one is that?

 

[BrooklynBay]

The idle air control. This thread should help you: http://www.explorerforum.com/forums/showthread.php?t=84220

 

[Clarke]

i have a 93 x and it did the same thing turned out i had to replace the intake gaskets, 3 hour job, and learn from my mistake make sure you lube up your o-rings on the injecters.
I figured this out by spraying some brake cleaner around the intake gaskets, the idle will increase when you find the leak.

 

[Cobraguy]

The IAC should be out of play when you get very far off idle.

You said one cylinder was down 15 lbs. Down from what number? For example...if they were all 100 psi except the one at 85, that could possibly be your miss. 100 psi could fire where 85 psi may not. But that should show up on your spark plugs. Look at them all and see if one looks dark.

If it's a vacuum leak, bad enough to miss like that, you should be getting a lean code.