Misfiring at 40-50 mph+ (Ford Tech here's a challenge...)

This is most likely an ignition problem. I'm guessing that it happens under light/moderate throttle, right? If you give it enough to gear down or unlock the converter, it goes away, right?

I don't remember if you have COP or not, but I doubt it. If you have plug wires, I'd suspect the wires first. If not, plugs are most likely.

There is an issue on some Ford V-8's of misfiring due to bleedover between plugwires that are misrouted. I forget which two, but there are two adjacent cylinders that fire sequentially and often the wires for them are run side by side. If that's the case, there is some bleedover between the two wires resulting in misfiring and weak spark. I may be thinking about the 5.0 tho... I'm just an amateur who has a decent amount of Ford experience. Someone else will be able confirm or correct that.

It's theoretically possible that you have a TPS issue, but since the problem seems more related to speed than throttle position, I'd suspect ignition first.

CJB

Yeah when the problem starts to kick in I almost feel like i could apply a fair amount of gas with no response...I have to REALLY lay it down for a further response from the engine. WHen I give it a ton of juice accelerating out of 1st, 2nd, or third no problems at all.

I tend to agree with what you're saying.

Look at your plug wires and distributor area late at night, and you may be able to spot the bleedover. I'm not really clear how a 98 F150 could have a

5.8, so I'm assuming it 's really an F250. I have had several episodes of misfiring in my truck in 4th gear, and it's just plug wires I think. It doesn't happen in the lower gears.

Ok the 5.8L V8 is bogus if its a 98. Ford doesnt list the 5.8 in 98 F-150 PC/ED (thats the Powertrain Control/Engine Diagnostics manual). So I would say you have a 5.4L. In that case, I would be willing to bet you have problem with COP going bad on a cylinder or two. It is possible it could be a PCM issue as that controls which COP is firing at that time. It could be a bad crank sensor, as that is what the PCM uses to keep time. Could be a bad TPS sensor and it could be "skipping". The list here is ENDLESS. Does it only happen in a certain gear? Can you hit the "OD off" switch and make it stop?

Your best bet is to have someone run a stress test on the COP system, that is depending on which engine you have. A stress test will tell if you have a bad coil. I suggest you raise the hood and look at the EPA sticker under the hood. If you see 5.4 or 5.8 anywhere that is the engine size. Its usually listed in the "Engine Family" area on the sticker. Then check back here to verify the engine size.

The best thing to do at this point, is that I know that WDS or IDS has the ability to watch TPS, cylinder firing and watch sensors as you are driving. I would take it to the dealer and have them hook it up and take it for a test drive. That way they can see exactly what is going on at the time of the problem.

Check back and let us know.

Will do. Thanks again...

I had a similar problem right after the transmission was rebuilt. I changed everything related to the engine but the problem did not go away. I strongly suspected that there was a some kind of slippage/grabbing somewhere in the torque converter or band somewhere. The problem only occurred when climbing a grade. I live in the mountains. I just lived with it as nothing could be proved one way or the other. As time when on it seemed to be less of a problem.

Sounds like your truck just had to "relearn" the shift pattern for your driving habits. It's common when you do a trans rebuild or reset the PCM as is commonly done in a trans rebuild as well as other times. It will not shift normally until you drive it a certain distance and allow it to relearn your driving habits.

Perhaps. But it went on for 20,000 miles

: > I had a similar problem right after the transmission was rebuilt. I : > changed everything related to the engine but the problem did not go : > away. I strongly suspected that there was a some kind of : > slippage/grabbing somewhere in the torque converter or band somewhere. : > The problem only occurred when climbing a grade. I live in the : > mountains. I just lived with it as nothing could be proved one way or : > the other. As time when on it seemed to be less of a problem. : >

: : Sounds like your truck just had to "relearn" the shift pattern for your : driving habits. It's common when you do a trans rebuild or reset the PCM as : is commonly done in a trans rebuild as well as other times. It will not : shift normally until you drive it a certain distance and allow it to relearn : your driving habits. : :

Sounds like a bad rebuild then to me.. Should only shift rough for the first (at most) 20mi. As for the band slippage that would be impossible for speeds above 10-20mph cause only manual low and reverse use a band anymore. Low gear uses a 1-way clutch, and all other gears use a series of clutches and a ravigneau gear set (thats a dual planetary gear set that uses the same sun gear. Has 2 rings and 2 pinion sets.). Some tranny's use 2 ravigneau gear sets, good examples would be the Corvette 6 speed auto.

The transmission was an E4OD out of a '92 Bronco.

: > Perhaps. But it went on for 20,000 miles : : Sounds like a bad rebuild then to me.. Should only shift rough for the first : (at most) 20mi. As for the band slippage that would be impossible for speeds : above 10-20mph cause only manual low and reverse use a band anymore. Low : gear uses a 1-way clutch, and all other gears use a series of clutches and a : ravigneau gear set (thats a dual planetary gear set that uses the same sun : gear. Has 2 rings and 2 pinion sets.). Some tranny's use 2 ravigneau gear : sets, good examples would be the Corvette 6 speed auto. : : : : :