Ford 460 Missing out... Mechanics puzzled?

Hello All. Thanks for taking a few minutes to look at this post.

My 96 Itasca Suncruiser has this strange "quirk" that started a few months ago. When we are on a trip, and get off the interstate it starts "missing out" when I start accelerating. It clears up once the RPMs get over 2500. It is worst when I have been traveling and get to a park and try to back it up...then it starts missing and backfiring. it idles just fine though?????? Only does it when you push the accelerator.

One mechanic told me to drive it until it fails... and the other thinks it "may" be the fuel pump. Personally...from a logical point of view...I am wondering if it is the EGR valve sticking open (letting too much burnt gas back in). Any ideas?

Thanks for your time... I am in panic mode trying to get this thing fixed before a big trip next weekend to Myrtle Beach (15th anniversary).
Re: Ford 460 Missing out... Mechanics puzzled?

Replace your fuel filter, and change your spark plugs & wires if you haven't done so yet. Some motorhomes have more than one fuel filter. Check along the frame for and in-line and in the engine compartment. Could also be a dirty pickup on the cam shaft sensor but this should give a fault code on the computer(if your chassis is a 1996 or newer). EGR failure will cause a fault code as well. Fault codes will cause your check engine light to come on. Miss firing should also give a fault code. Maybe your computer is failing. :(
Re: Ford 460 Missing out... Mechanics puzzled?

I don't think I would go back to the mechanic that told you to keep driving until it fails. He's not the one that would be stranded in the middle of nowhere is he?

If the above suggestions don't help, cleaning the fuel injectors and a fuel pressure test could rule out fuel delivery and you could turn your attention to spark.

C Nash

Senior Member
Re: Ford 460 Missing out... Mechanics puzzled?

If it was the EGR valve it would probably not idle. Sounds more like an ignition problem. I would start with the above advice but don't think it will be filter problems although if they have not been changed do so. Coil, wires, plugs would be my guess. keep us posted
RE: Ford 460 Missing out... Mechanics puzzled?

Thanks for all the replys above... tmarrs: Believe me when I say that I wont be taking it back to the mechanic that said "drive it til it fails." That did not set real well with me either.

OK, more info...
- I have changed the main fuel filter back in April, however, I will have to see if I have a second one up by the engine. Thanks for that tip.
- I put new Bosche platinums in it back in February and the wires looked OK, but... I think that I will replace the wires just in case.

Another thing that I maybe did not clarify real well is that this ONLY happens when I get off of the interstate... I can start it up from cold and drive this thing all over town and this "missing" out symptom will not happen. The second mechanic let it sit running for two hours with a fuel pressure monitor on it... he only noted that the pressure was "about 5psi low, but it was consistant and not fluctuating."

I talked to the second mechanic about the EGR theory and he came over and tested it by manipulating the vacuum line... It started missing and backfiring at idle, which you would expect, so we know that the EGR system is at least somewhat functioning. So, for the interim, he has capped the vacuum line for today's trip as a test. I will know if that is it when I get off the interstate today... If not, I will put the vacuum line back on.

Believe it or not, the only reason I am suspecting the EGR is because our 2001 Honda Odyssee had a similar would be fine at idle, but at low RPM would begin missing out. The EGR was not at idle, it was fully closed, but when accelerating, it would go to fully open instead of partially opening. This was causing too much burnt gas back into the mixture. The motor would not die, only missing out incosistantly on the cylinders, so the computer never sent any codes to kick the "check engine" light.

I have the 100,000 mile warranty and went round and round with the local Honda Dealer on it because the "check-engine" light would not come on.... after having to pay diagnosis fees and losing my cool with the manager over it (because it was not fixed), I sent a complaint letter to Honda Motor Cars along with a copy of the complaint to the dealer in Tampa where I purchased it. Next day, the Tampa dealership calls me and tells me to bring it in, because they may know what it is. Whalah...faulty EGR valve. Six months later...Whalah, Honda Technical bulletin on a faulty batch of EGR valves.

Well...the trip is set for today. Thanks again for your replys. I am taking a copy of all of them with me and will reply with the outcome when I return.
RE: Ford 460 Missing out... Mechanics puzzled?

Hello All... Just got back from our trip. Made it all the way to the Georgia State line and pulled off the road to take a break and it started missing again...with the EGR unplugged. So, I can rule that out.

We found an open mechanic with a scanner, so he plugged it in...and on que, NO CODES. He was baffled. We could rev the motor and hear it missing and backfiring, but no error codes. I asked him to run the scanner on it while running, but he indicated it would not tell him anything...I think that he did not know how to use it personally.

I then proceeded to put on a new rotor, cap and wires...this seemed to help, but it was still missing at the lower RPMs. The difference was now it was "consistant," and I could work with it and still drive it to a campground. I then biked to a NAPA that next Monday and obtained some Motorcraft OEM plugs. This even improved it more and all of these seemed to help...she is still sluggish and hesitates when we pull off the road, but it is not missing out and backfiring.

I also noted a realtively large header manifold leak by cylinder #8...I think this is where the backfiring is originating...

Well, its back to square one on this...thanks to all for the replys. If anyone has any more ideas, please relpy to the post.

Re: Ford 460 Missing out... Mechanics puzzled?

Since you found the bad header, do a compression check on all 8 cylinders. If you have had the leak for a long time, there is a possibility of a burnt valve. It would also cause miss firing ect.
Re: Ford 460 Missing out... Mechanics puzzled?

Thanks for that reply on the valves...sounds like a painful repair, but thats a new lead and opportunity. Thanks again. I will post the results when I am able to get er done.
Re: Ford 460 Missing out... Mechanics puzzled?

Cant say for sure but I had an old Ford pick up once that wouldnt untrack itself with out spitting and back fireing. After spending time and money I hit on the problem. Timing chain streched and was fixing to go. New timing chain and gears and you couldnt ask for a better running pickup. Ran like new. Don't know about yours bit might be something to run by a mechanic.
Good Luck
Re: Ford 460 Missing out... Mechanics puzzled?

Well...I think that we finally cured it. We had the fuel pump replaced and had the exhaust leak fixed. Once the new fuel pump was in it seemed like a new coach...with the broken manifold stud fixed, it was even better.