98 Expedition running very rough

[cvpi71]

Hi Folks

I just recently acquired a 98 Expedition 5.4 2WD. It had a misfire in Cyl #1 , #5 .It has 195k miles, I did a tune up using Ford spark plugs lugs and replaced all the boots and springs on the coil and replaced 2 bad COP. It runs great when it been sitting for a while or cold and after about 10 minutes of driving it feels like it's stumbling and misfiring running really rough feels like running on 6 or 7 cylinder. No CEL or flashing CEL. Once it's warmed up when you come to a stop and have to step on the gas it feels like you are on the rumble strips, it feels like this every time the gas is depressed. I am running out of ideas. When it's cold it runs flawless, no stumbling or shaking from the engine. Thanx

[RickMN]

Welcome to the Ford Coil club. If you've only replaced 2 bad coils, you only qualify as a Junior member. Bad coils are a VERY common problem, especially if they've gotten wet. Also check the heater hose to make sure it's not dripping on the coils (also common). I've seen several of these that had to replace all 8 coils. I told a friend that and he refused to believe me and replace them all at once. So he ended up replacing them all--but one at a time as each one went out. Cost him a fortune at the shop since they charged him minimum labor each time. He's a slow learner.

BTW, most coils fail when they're hot and under load--exactly what you're describing here.

[cvpi71]

so when the engine is cold the COPS aren't effected but when it gets hot and at operating temperature and under load especially stepping on the gas they go bad, but how come the CEL is not on or flashing a codes? Thanx, any one have anymore ideas or options. I'll double check all he connections making sure the IAC, MAF, etc... are all connected.

[RickMN]

The short answer is yes. A coil can run ok when it's cold and fail under load once it heats up. That's not a rare failure pattern at all. As for the CEL light, I think you misunderstand how they work. They don't go on "instantly" in the case of a bad coil. The computer has to complete a "drive cycle" first. It has to see X number of misfires before it sets a code. A drive cycle varies for each particular code, but it's X number of starts, driven at X mph, for X amount of distance, etc.

In the case of a misfire, the computer looks at the crank sensor to see RPMs. It knows when it asked each cylinder to fire and so it expects to see that cylinder's contribution to the RPM. If it sees the crank slow down, it calculates backwards to see when each cylinder fired so it can find out which one isn't pulling it's weight. It also looks at data from the pre and post cat O2 sensors. If it sees a rich mixture that coincides with a calculated misfire, it adds that into the mix. Then, it starts accumulating misfire data as it goes through the drive cycle. If, at the end of the drive cycle, the misfire count exceeds a factory limit for a cylinder, that's when it flips the CEL light.

If you have a scan tool that's capable of reading live Mode $06 data, you can peer into the computer's memory and see how many misfires it has recorded and how far along it is in its drive cycle. (Although, back in '98, computers were far less sophisticated, especially Ford computers).

[cvpi71]

well I unplugged the battery, change the fuel filter, added a bottle of octane booster, connect the battery after 30 minutes and everything is fine now, runs smooth and powerful. Jump on the highway and put on about 120 miles. No CEL or stumbles or miss. Thanx everyone for their help.