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Old 05-12-2009, 05:16 AM   #1
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Desperately Need Help

I am trying to desperately get to Maryland for the Regional Qualifier in June. The only way we can go is if we have our RV running. There is a problem with it and I cannot figure it out. The RV is a 1989 John Deere, Pace Arrow Class A. The engine is a Ford 460 with a Holley 4bbl. It has an external (in front of the tank) fuel pump. The problem is when I try to drive at highway speeds the engine will start to stumble and “Pop” out the exhaust. Driving around town up and down hills it runs fine. Once on the highway it starts acting up. It doesn’t take long, about a ¼ mile. If I pull over and take off again it goes fine until it gets to highway speed then the same thing. I have changed the following. Cap, rotor, Distributor base cap, wires, plugs, fuel filter, rubber fuel lines. I have checked the following: vacuum at the distributor is 18” at idle. The vacuum advance will hold a vacuum and pulling a vacuum on it with a pump it will change the timing (you can hear and feel it) while its idling. I don’t know what to do next. PLEASE HELP!!!!! I cannot afford to put it into the shop, so this is not an option!!!! If I cannot get this running we will not be able to go and Spaz will be Heart Broken.

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Old 05-12-2009, 05:22 AM   #2
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Try loosening the gas cap. the cap may be bad and you are drawing a vacuum on the gas tank. It's worth a try!

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Old 05-12-2009, 05:27 AM   #3
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One other thought. Check the routing of the coil wire. I once had a Ford that had a similar problem and the coil wire was shorting out into the wire in the radiator hose.
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Old 05-12-2009, 06:04 AM   #4
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Sounds like the only thing you didn't change was the coil.Open hood at nite and see if maybe defective wire is arking.Check that you didn't confuse wireing order.Not a mechanic so these are things that I have done myself.
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Old 05-12-2009, 06:06 AM   #5
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Another possibility:

If the MH has been parked for a while maybe the gas is bad. It could be stale or even have some condensation or trash in it. You might be able to find a way to eliminate the possibility of bad gas causing the engine stumble.
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Old 05-12-2009, 06:26 AM   #6
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Did try the gas cap. I loosened it so it was only on 2 turns. I put 6 cans of dry gas/carb cleaner in it. It has about 50 gallons of new gas in it.
No light show that I could see under the hood.
I did check how the coil wire was routed and I didn't like it so I moved it. No luck :(
Keep the ideas coming please
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Old 05-12-2009, 06:33 AM   #7
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I had an 89 P30 with the 454 CID engine and it acted much like yours. I started the engine one night with the engine cover off and the hood open so that I could see the engine. With no lights I got some electrical arcing visible. Replace the full plug wre set and no problems.

Does that engine have two fuel pumps and two fuel filters? One at the tank and on at the engine? It may have an in-tank pump or filter.

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Old 05-12-2009, 06:50 AM   #8
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It sounds like a fuel delivery problem, vapor lock, dirty carburetor, low fuel pump flow or cracked rubber fuel lines on top of the fuel tank also could be a plugged fuel filter.
I had an 86 ford 460 in a Tioga mini, same problem after fixing the above conditions it ran great.
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Old 05-12-2009, 06:59 AM   #9
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Looks like you have changed all the normal failure items. At highway speed if you floor it does the MH accelarate without hesitatation or does it fall flat? How does it idle? When idling if you listen to the exhaust at the exhaust pipe outlet is it smooth, does it smell rich or normal?
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Old 05-12-2009, 07:07 AM   #10
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I am with you on avoiding shops. In addition to the things you have done, the spark plug wire suggestion sounds good although it usually just affects one wire and one cylinder. Bad fuel is a possibility. Check to be sure you don't have an in tank fuel pump. There is sometimes a screen in the fuel tank that can become clogged. To me it sounds like a fuel delivery problem.
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Old 05-12-2009, 07:56 AM   #11
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Check to be sure that you have located and changed ALL the fuel filters! Sometimes there is one in the line between the tank and the engine. There might also be one at the carb inlet. Good luck
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Old 05-12-2009, 07:59 AM   #12
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Without being able to see and examine your Ford 460, I would vote for a fuel starvation problem. The carburated versions are famous for this. Check the fuel pump, since you say the filter has been changed already. I used to "T" in a fuel pressure gauge before the carburetor, and secure the gauge somewhere out front so you can see it through the windshield, and drive until the problem occurs, bet you will find the pressure goes away under load. Also check to see if you have a mechanical fuel pump with a canister type filter screwed on to the bottom of it, in addition to an inline filter. Good luck to you.

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Old 05-12-2009, 08:11 AM   #13
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I'm not a mechanic and know NOTHING about that stuff, but I do know that my 1999 Itasca Suncruiser was doing the same thing and it was a bad "power" chip. I don't know if yours has a power chip or not. Mine was a Banks chip. It did the exact same thing that you are describing until the chip was removed and then it was fine. Good luck!
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Old 05-12-2009, 08:17 AM   #14
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This may be a very long shot but since you are desperate, I'll throw it out. I agree with JWalker that your symptoms sound like fuel delivery issues. If you truly can go to WOT at a lower speed climbing hills in town, however, that should rule out a fuel flow problem. In your place, I'd be tempted to see if I could simulate the highway condition at a lower road speed by running around town at about the same RPM but in a lower gear. What I'd be trying to eliminate is the effect of highway speed air flowing into the intake. I think examining the air intake carefully to make sure there are not obstructions or problems would be fairly easy to do. Something in the air intake, affected by hightway speed airflow, might cause your symptoms.

Like I said, it is long shot.

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