What could cause a truck (2005 5.4) to drive-out of a severe misfire, backfire and hesitation condition? Over the weekend I passed a car on the highway and briefly opened up the throttle, running approximately 4-5,000 rpm's for perhaps 15 seconds. A short time after that the truck developed a severe hesitation and backfire, I couldn't go over about 30mph. CEL was flashing indicating a misfire but my scangauge couldn't pick up any codes. Drove like this for approximately 5 miles until I could find a safe place to pull off, truck died as I was pulling off. Let is sit for a few min - looked under the hood and didn't see anything obvious. Tried to start it and it did start after cranking a bit longer than usual and full power was restored. Drove the the truck another 20miles home at highway speeds with no repeat...though I never opened up it up again. No lights or codes, at least that I can see w/ a scangauge.

A similar situation happened to me last year though not quite so severe. In that case, the truck drove out of it again after one very loud backfire. The dealer finally diagnosed 2 loose sparkplugs (plugs had been replaced w/ autolites prior to me buying it, don't know if they were torqed to spec.) Tech tightened them up and truck had been great since. I didn't necessarily buy the 2 loose sparkplugs as I couldn't understand why it would drive out of it. I surmised I had a clogged cat and the loud backfire blew the guts out of it, thus relieving the back pressure. I never questioned it further as the truck seemed to drive fine ever since.

So here we are today. Any ideas - fuel problem perhaps? Or was the tech right and can loose spark plugs do that?

 

Did the CEL go away? You have a scanner that can do pending codes?

 

Water on the COPs?

 

No, my scangauge only reads existing codes. I suppose I need to take it in but I wanted to get some ideas beforehand.

I suppose water on the COP's is possible, I did drive through a puddle a few days before...but it was 105 that day and I'd already driven 120 miles at highway speed before it happened so I would think any water would have long since dried out.

 

You don't have clogged cats. If they were starting to plug up you'd notice decreased power at high RPMs under full throttle because that's when your engine draws the most air. It would behave like having a plugged air filter, meaning it would just lack power. It would not cause a misfire.

I suspect it's something electrical, but that's not going to be easy to find unless you get a better code reader.

 

Still not sure what happened to the CEL that was set. Did it go away when you restarted your truck after the incident? Like Crazy said without some codes to go by it will be hard to determine what it is.

 

Had a similar situation in a 08 mustang I was driving on a trip passed a guy in a super duty doing like 30 in a 55 and it went in to limp mode. No missing or backfiring it would just idle pedal on the floor and it might get to 1200 rpm in neutral. Pulled over looked at everything nothing obvious under the hood or car. Shut off and restarted longer than normal crank and it started. Turned out to the throttle body.

 

Tom, Sorry I should have explained better. I didn't think clogged cats was the issue in this case, but I thought it was a possibility when it happened last year...but from what you're saying it probably wasn't. In that case I had been getting a p0420 code for a couple months prior to that, but didn't really have any symptoms. Before that I had a stuck injector which was fixed under the 2005 injector warranty and I thought that may have fouled the cat causing the 0420 code. I had been fighting w/ Ford trying to get it covered under the injector warranty so I didn't fix it. Then after the first episode of severe hesitation w/ the single loud backfire it was cured and I haven't ever gotten the 420 code since. In that case I thought the cat may have been the problem and the backfire blew the guts out of it. I didn't realize the cat couldn't cause a hesitation at lower rpm's - thanks.

Mike, There was never a solid steady light so I don't know as one was set. It was flashing indicating a misfire...I would assume that would set code but I guess I don't know that. There are no lights right now.

Thanks, it certainly sounds similar, though mine never went into limp mode that I know of. Doesn't the message center say limp mode?? I'll keep the throttle body in mind.



Does anybody think the intake manifold runner control could cause something like that? I've had that code set in the computer ever since I bought the truck 4 years ago - never had a light for it, but the dealer brings it up every time I'm in. The tech didn't think it was the problem last time since it was stuck open, and said I honestly probably wouldn't ever notice a problem with it. Only the service writer said I should change it.

 

**Update: I finally got a code reader that can read pending codes, it did bring up one - P0191 (Fuel Rail Pressure Sensor Circuit Range/Performance). First off, what is that, and second could it be related?? I'm amazed there weren't any pending codes for misfires as bad as it was.**

 

Yes it can be related. Your fuel rail pressure sensor tells the PCM how much pressure is reaching your injectors, and the PCM uses this to adjust injector pulse width to get the mixture correct. If your mixture is jacked up the truck won't run right, and this could cause a misfire.

This does NOT necessarily mean that you have a bad sensor. Just that there is something wrong somewhere between the PCM and the sensor. Time for some diagnosis!

 

Thanks! Next question, can anyone tell me first off where it is so I can start tracing wires or vacuum lines? Fuel pressure is reading 40psi at idle, I think that's within specs?