Check Engine Light

My '99 Expedition flashes the check engine light when I accelerate uphill at highway speeds. It goes off when I decelerate and the dealer said that there was no code stored in the computer for that. It also seems to hesitate shifting to a lower gear at freeway speeds unless I give it quite a bit of gas. I changed the MAF sensor a few months back, which seemed to help, but it didn't fix the problem. Anyone have any ideas???

Thanks!

Nate

possably fuel injecters a bit dirty? try running some cleaner thru the system for a couple tanks of gas, and how long since the spark plugs have been changed as well? sounds like maybe an engine performance issue?
how about it "way2old"? the guru have any suggestions? hehe!
Rick, Ore

How long has it been since the last tune up? Those are classic signs of the plugs or boots breaking down. If it does it under light load, like going up a small hill and trying to maintain speed, then look to the ignition system. We run into that daily on the 4.6 and 5.4 engine. Also look at number 4 plug to be sure antifreeze is not leaking from the heater hose down on plug boot. Also check the throttle positioning sensor for the shifting problem.

I replaced the plugs recenty (less than 5k miles) but didn't replace the wires. I can't see a leak into the #4 cylinder, but I imagine it could be happening intermitently. I will change out the plug wires, what do you think about changing out the coils too? Which should I change first?

Thanks for the help!!!

Nate

If you have the 4.6 with wires, I would replace the wires first. If you have the 5.4 with COP, pull the coils and look at the boots closely for any sign of arcing through to the block. Most of the coil packs were fairly reliable and I would not change them unless absolutely necessary. If it has COP, they are more suspect to failure. This needs to be diagnosed to the individual cylinder as the coils can be expensive. If you know anyone that has a scanner that can read the PIDS, have tham hook it up and go for a ride and make tha vehicle act up. Look at the information and it will point you to the right place. Good luck. It seems strange to me that a code is not stored however. These will have a pending and an active code for a problem. Might run it by Autozone, Advance or other chain parts store. They will read codes for free. DO NOT BUY PARTS YET!! These stores make money by selling parts. See if there is a code number and post the EXACT code number back here. You may need to go by there before you shut the engine off, but usually not. OBDII is sophisticated enough that it will store all the information. Post back with findings.

way2old-

First off, thanks for the all of the help so far!

A little history since the last post. The check engine light stays on now (before it would turn off when I stopped accelerating). The light stayed on a year or so ago and cleared by itself after I put a few tanks of fuel injector cleaner through it.
I went to Autozone and got the code read. It was P0308 (cylinder 8 misfire detected). I drove around with the reader attached and tried to make it flash again, but it wouldn't. I repeated what had caused it in the past (freeway speed acceleration), but it never flashed, just stayed on. I cleared the code to see if it would come in again. It didn't. At least not on the trip home from the store. I have the 4.6l V8 4WD. What do you think?
Also, if it is the plug wires, what brand do you recommend? I can get the Autozone Duralast for $50 or Bosch for $85. Napa also has their standard for $50 and their premium for $85. Which ones do you suggest?

Thanks again for your help,
Nate

What is the price of Motorcraft? I am a firm believer in original equipment ignition componets. If you have other than Motorcraft plugs in it, I would also change them.

Most check engine lights come on when an engine miss is detected. Before you go spending money on parts, try a bottle of Techron - it is one of the few over the counter cleaners that work.

Ron