Stalling
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Cross-Country
Joined: Apr 2003
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Stalling
I have a '86 Bronco fuel injected 5.0L with manual transmission. The engine runs fine with the tranny in neutral or the clutch pedal pushed in. I can rev up as high as I want. However, as soon as I start to let out the clutch, I lose fuel pressure (I put a gauge on the manifold schraeder valve) and the engine dies. This happens whether I go forward or backward. I have bypassed the fuel cutoff inertia switch. I don't see fuel pressure again until I cycle the key back to the "OFF" position and then back to "ON". I can then crank the engine and it starts right back up. Any ideas?
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Joined: Jan 2001
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From: Virginia
While watching the fuel pressure guage, pull the vacuum line off the fuel pressure regulator. When you pull the vacuum line off, it should be dry with no wet fuel in the line, and the fuel pressure on the guage should jump up.
Elder User
Joined: Feb 2005
Posts: 526
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From: Spokane, WA
You do realize how little fuel an engine uses when running without a load? Not much...so little it can run through a plugged filter, bad pressure regulator or even a weak pump.
Like the person said above...try disconnecting the line. If you have -0- difference, start with the fuel filter (you should be changing it anyway), if that doesn't cure it it will have to be a pump (frame rail high pressure or tank mounted low pressure). I don't know your setup but it can really only be those three things.
Kenny
Like the person said above...try disconnecting the line. If you have -0- difference, start with the fuel filter (you should be changing it anyway), if that doesn't cure it it will have to be a pump (frame rail high pressure or tank mounted low pressure). I don't know your setup but it can really only be those three things.
Kenny
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Cross-Country
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I'll check the regulator and replace the filter.
It is a two-pump setup (rail and tank). The really strange thing is that as soon as I start letting out the clutch, the fuel pressure drops. Even if I immediately push the clutch back in, the pressure does not recover. I would think that if it was initially running fine at no load with a clogged filter or bad regulator that the pressure would come back up when I push the clutch back in. It's almost as if the ECM is cutting off the fuel pumps. I'll monitor the voltage at the fuel pump cutoff relay to see if this is what's happening.
It is a two-pump setup (rail and tank). The really strange thing is that as soon as I start letting out the clutch, the fuel pressure drops. Even if I immediately push the clutch back in, the pressure does not recover. I would think that if it was initially running fine at no load with a clogged filter or bad regulator that the pressure would come back up when I push the clutch back in. It's almost as if the ECM is cutting off the fuel pumps. I'll monitor the voltage at the fuel pump cutoff relay to see if this is what's happening.
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Joined: Jan 2001
Posts: 56,999
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From: Virginia
The regulator "helps" the computer by raising the fuel pressure when the vacuum is low. That's why the pressure should go up when you pull the line off. The vacuum will drop when you open the throttle, and are pulling a hill.
What kind of pressure are you getting? It should be around 38psi.
What kind of pressure are you getting? It should be around 38psi.
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Joined: Nov 2004
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From: sunny fla sometimes windy
Gas line dryer!!! Do not do anything else Just 4 bottles or so(each bottle treats ten gals but double up) of Dedicated gas line dryer/antifreeze on whatever is in the tank. Run it until almost empty then fill up with fresh gas from a popular station that hasn't had a tanker truck visit it that day!! When you put a load on the motor it is pulling more fuel swirling up what water is in the lines, filter, fuel rail and gas tank. Since water has a higher surface tension then fuel it blocks up the small orfices in the fuel system(Injectors,partially clogged filter,Etc) Water builds in your tank from condensation, it forms in the tanker truck overnight that brought the fuel to the station, it forms in the tanks at the station and at the suppliers tanks, Then they sell it to us! After your truck is running like you can't believe get back and let us know how much fuel was in the tank and how much gas line dryer you used! Always update your posts so people that search can find out what solved your problem!!!
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Cross-Country
Joined: Apr 2003
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I replaced the fuel filter and added Heet and IsoHeet, ran tank low and refilled. No change. Looks like a fuel pump. Any easy way to tell whether it's the rail-mounted one or the in-tank one that's failing?
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