arco777

Please help me! 1990 LX 5.0, AOD w/ 3000 stall. Ran fine but gradually got worse to this point. Starts and idles fine. When you accelerate from a stop the car shudders and has little torque, and acts like the fuel pump is bad or it is misfiring. Once RPM gets up to over 2000 it clears up and runs better. Problem occurs from cold and warm starts.

Since the problem began I have tried the following new parts, with no effect on the problem.

-New 155lph fuel pump
-New fuel filter
-New factory replacement MAF
-96 Explorer injectors with new seals
-New O2 sensors
-New upper intake manifold gasket
-New vacuum lines
-New ACT
-Tried a used MAP sensor with no luck
-New distributor pickup
-New plug wires, cap and rotor
-New evap system lines
-New TFI module
-10-pin connectors cleaned

Timing is set to 13 degrees BTDC, premium fuel. Fuel pressure is set at 39psi w/o vacuum. Modifications are the typical bolt ons. There are no catalytic converters. Can't find any vacuum leaks. EGR passages seem fine. Ignition is a Crane Cams HI-6S with LX-91 coil. Average cylinder compression is 150psi cold.

KOEO codes: none
KOER codes:
94: Thermactor Air Injection system inoperative (left side). [my air inj system is incomplete]
44:Thermactor Air Injection system inoperative (Right side). [my air inj system is incomplete]
13: Cannot control RPM during ER Self-Test [low/high] RPM check. [Idle is set higher than 750 for B303 cam.]
Cylinder Balance Test results: 90 - all cylinders contributing equally

Any help is greatly appreciated!

arco777

Fixed! After over a month of throwing parts at it - let this be a caution to anyone who thinks they can spend their way out of a problem!

I have GT40P headers from BBK so on cylinder #4, there is almost no clearance between the plug boot and the header. When I last changed the plug wires, instead of buying a plug wire insulator, I used aluminum tape and wrapped that around the spark plug boot. This caused two arcs, from the wire boot to the head and the block. Yanked the tape off and took it for a spin. Runs like a scalded dog.

I noticed the arcs by watching under the hood at night - I'm told a spray bottle of water helps too.

mattdel

please tell me you're trolling. you sank serious money throwing parts at a misfire caused by a burnt plug wire. You type way too intelligently to be that.... absent minded.

arco777

Not trolling. I knew from the beginning that throwing parts at the problem was the wrong way to go, but I did it anyways. You can tell I tried almost every test in the book, but there was only one test that would have revealed the issue, and it took looking under the hood at night.

I thoroughly searched various forums for answers first and kept ending up with threads that were never resolved. This one is, and hopefully someone finds it and is helped by it.

I don't mind the parts I replaced because it runs far smoother than it did before the arc issue began. But still it's a lesson not to throw parts at a problem - nothing I bought could have fixed the problem, not even new plug wires (I'd have taped it up again).

fl1a

Thanks for posting your solution, it'll help someone.

Flora62

Fixed! After over a month of throwing parts at it - let this be a caution to anyone who thinks they can spend their way out of a problem!

PRO50SC

I agree, how do you misdiagnose a simple misfire? Here's a tip, ALWAYS back to basics when trouble shooting. More times then not it's a simple issue.

mjr46

hey now..remember the amatuers are the experts/ pros

mattdel

Nice to see you back around, Pro.