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Returnless fuel system issues...

ranger7ltr

Elite Explorer
Joined
November 17, 2001
Messages
1,305
Reaction score
18
City, State
Great State of Texas
Year, Model & Trim Level
1999 Sport
I have a 99 Explorer Sport that has had some fuel delivery issues since I got it..I finally installed an electric fuel pressure gauge to monitor what is happening..

At start-up, the fuel system primes to 65 or 70 psi...Start the engine and the pressure stays right there... There is very little pressure change...Start to drive and as I accelerate harder I can see the pressure drop and the more I open the throttle, the lower the fuel pressure gets..

If I hold the throttle open, the pressure will start to cycle from 70 down to 0 and then come back to 70!!! If I back off the throttle as the pressure drops, fuel pressure will stop dropping, hold at the current level and then start to climb back to static pressures...

Correct me if I am wrong but this truck has the mechanical returnless system which is supposed to keep the pressure at 65 or 70 psi...I am seeing no change in fuel pump voltage at the interia switch wiring to the pump...And since I do see proper pressures, I can rule out the tank mounted regulator I believe...

I have replaced the pump, strainer on the pump, system filter under the truck, and installed a fuel pressure gauge...I am about to drop the tank and see if there is a layer of crap in there to stop the pump from being supplied with fuel during running conditions...

Tank is half full right now so amount of fuel should not be a problem...This vehicle sat for at least 2 years with fuel in it and I drained that mess out before starting it up but I wonder if there could be a fuel starvation issue with a new pump and old tank...

http://www.aa1car.com/library/returnless_efi.htm

Any ideas? Comments? Am I missing something?
 
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ranger7ltr

Elite Explorer
Joined
November 17, 2001
Messages
1,305
Reaction score
18
City, State
Great State of Texas
Year, Model & Trim Level
1999 Sport
Update to this problem...

The beast has been exorcised...The tank was the problem after all...

This truck had years of varnish and dirt from sitting and the last straw was the tank of water and rust with the gasoline I bought last Monday...I could actually grab handfuls of garbage loose in the tank after removing the sending unit...

I pulled the tank and drained the remainder of the fuel from it that looked like rust....The sending unit/fuel pump strainer looked like it was covered with rust/varnish/some type of caked on crap ... And this was only a week old...

Time for major chemical intervention...After draining the fuel, I used a high pressure hose and a couple of gallons of muriatic acid and a caustic cleaner to eat away at this tank...I let the acid sit in the tank for an hour or so then drained , flushed with water, and added 2.5 gallons of Purple Power full strength into the tank.. I let this stay in the tank for 2 hours, shaking the tank every 5-10 mins....

After washing all the cleaner out of the tank I used some MEK as a final rinse before drying the tank with air if needed...I sprayed a gallon of MEK into the tank and it loosened more garbage and displaced any water still in the tank...

Now I have a clean tank that I can add my new pump, new strainer, new fuel filter and fresh fuel in and go drive it...

Results... Fuel pressure NEVER dropped below 65 psi and the engine pulled hard to 110 mph and it would appear that the tank was holding the trash that was stopping the fuel pump from delivering... Not any more!!!
 
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