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Old 05-18-2011, 10:26 AM   #1
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99 V10 "Weak" Fuel Pump?

Hi, This problem started over a year and a half ago with my 99 Suncruiser on a Ford V10 chassis. It began to have a hard start issue where it took 2 tries to start the engine. At approx the same time I started getting intermittant P0171 and P0174 lean codes and the CEL coming on. I bought a Scanguage to reset the light and read the codes, cleaned the MAF and then bought a new one. Had the engine tuned with new plugs and checked for vacuum leaks. None of this worked except that now I get codes of P0171 (no P0174 yet) and P0304 (misfire).

We have continued to use the MH on several trips in the meantime and put several thousand miles on it. No driveability issues at all even back and forth to Florida a couple of times except for having to turn the key twice to start which points to fuel pressure.

My mechanic checked the fuel pressure at the fuel rail, no leakdown of pressure while off, and no effect at idle when the fuel regulator is disconnected (and no gas leaking from it either).

Here's where it gets interesting: My mechanic and I then took it for a ride last week with his scanner and fuel pressure guage attached (that engine is loud with the doghouse cover off...). While at idle or while cruising at 40-50 mph the fuel pressure is approx 30-32, but when accelerating from a stop it drops down to as low as 21-22! (still drove fine tho...)

At the same time the scanner indicates that the computer is trying to compensate by calling for a richer mix but it hits its max settings and "runs out of fuel" according to him. (but no misses or stumbling...)

So before I try and find a full size shop that can handle dropping the tank, is this something modern fuel pumps can do or is it a blocked uptake screen or something else? I have never heard of a pump being "weak" like this for so long and not failing entirely.

Thanks for the help.
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Old 05-18-2011, 01:16 PM   #2
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Check all fuel fittings for fuel leaks or air leaks into the system from engine all the way back to the tank. Any rubber hose portion should be changed due to age.
I believe there may be a rubber hose at tank to chasis that can't be reached entirely to the tank and that is one reason fuel tank needs to be dropped. If it is the fuel pump in tank then you could DIY by draining tank first.

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Old 05-18-2011, 01:39 PM   #3
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Hi Steve (Avatab),

I assume your tune up included a new fuel filter. If not, that is the first thing to do.

Fuel line pressure, even under acceleration should be high 30's and certainly never down into the 20's.

Possible causes:
There is a strainer screen, or "sock" at the pump inlet (in the tank) that could be plugged up. Not common but possible.
Fuel pressure regulator is faulty. Cheap and easy to replace.
Fuel pump is weak.

Now, having said all that, I'm not sure that fuel pressure is causing your starting problems - but you are certainly having some issues in that department so get it right and then go from there.

Good Luck!
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Old 05-18-2011, 02:12 PM   #4
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I just went through getting a new fuel pump installed on a Ford 460. The fuel line pressure with the old fuel pump was in the 20's, hard to start and missing. Changed the fuel filter, plug wires, plugs and no change. The technician at the repair facility, where I took it, told me the fuel pressure should be about 50. Oh, did I mention I had a full tank of fuel! Changed the fuel pump and it made all the difference in the world. Now all you have to do is touch the key and it fires right up.
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Old 05-18-2011, 02:14 PM   #5
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And you DID replace the FUEL FILTER I assume
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Old 05-18-2011, 05:07 PM   #6
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Thanks for the replies. I did have the fuel filter changed, but will look at the new one again as well. No signs (or smells) of any fuel leaks.

My mechanic did say that the strainer in the tank might be clogged, but the tank must be dropped to access it.

He says the fuel regulator appears to be ok. We ran it with the hose off and no fuel came out and no difference in the pressure readings.

I was mistaken tho about the fuel rail pressure. He says it did drop while key off/engine off. So that points to fuel pump or a leak as well...

I guess I am trying to avoid the inevitable here and will have to take it somewhere to have the tank dropped and the pump replaced. Not something I can do, especially since Winnebago installed the rear hydraulic jack braces and lines under the tank....
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