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1990 Sun Clipper Back Fire David 3-22-13  
I recently purchased a 1990 Gulf Stream SunClipper with the Ford 460. The RV had sat for a whilebefore I bought it. The person I purchased the RV from had recently cleaned the fuel tank and changed the fuel pump with a Motorcraft PFS-48.
When he changed the fuel pump he connected the fuel line for the generator to the fuel pump but not to the generator. He simply plugged the hose on the generator end. I removed the plug expecting fuel to come out. That didn't happen. I started the 460 to get the fuel pump pumping, and still no fuel was coming out of the generator fuel line. I put a syringe to the generator's fuel line and pulled a vacuum to try to get some fuel, but never could get fuel out of that line.
The next time I put the RV on the road it started back firing when you push the gas pedal down. If you push the gas pedal about a quarter of the way down it will back fire. As long as you barely press the gas pedal you can get up to about 25MPH. You can rev the engine in Park or Neutral, but it backfires under load. When we drove it home after purchase it ran fine.
Please advise me on how to get it running well again.
Re: 1990 Sun Clipper Back Fire Phil Feinstein 3-22-13  
The first question I have is: "Where do you hear the backfire?" Backfire out of the tailpipe is a fuel problem, backfire under the hood is an ignition problem.

I suspect, since you have to feather the accelerator, that you have a fuel problem or a possible vacuum leak. 1990 was when Ford started to sell the 460 with fuel injection. Is your rig fuel injected or does it have a carb? If your rig is EFI, it is possible that you have a problem with a muffler blocking the exhaust or the catalytic converter collapsing. Is the backfire a "bang" or a sputter?

That should be enough to get started.

Hope that helps!
Re: 1990 Sun Clipper Back Fire Phil Feinstein 3-22-13  
Something else:

I looked up that fuel pump number and it appears to be an EFI fuel pump for the F-super duty chassis, but has the note "FIELD FIX QSF-97002" associated with it. This appears to be a "Jumper harness" but information is very vague. A wiring problem to the fuel pump could explain your backfire.
Re: 1990 Sun Clipper Back Fire David 3-22-13  
The rig is Fuel injected.

The back fire is coming from the breather line that runs from behind the grill to the intake.

It sounds like a oud bang.

Thanks for the response.
Re: 1990 Sun Clipper Back Fire Phil Feinstein 3-22-13  
Backfire is from under the hood and indicates an ignition problem; your timing has slipped or you have cross firing between spark plug wires or you have an ignition coil that is failing.

If you plug wires are more than 4 years old or age unknown, they need to be replaced. Cap and rotor are in order as well as new plugs. Inspect and test the ignition coil and replace if questionable (they fail regularly on the bigger V8s of this vintage). Set timing to correct value.

Hope that helps!
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