5.8 driving us crazy!!!!!!
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5.8 driving us crazy!!!!!!
hey guys. I have a 1990 F-150 2wdshortbed with a efi 5.8L. The truck will not rev past 3grand if you play with the timing alittle bit you can get up to 3800rpm. At first we thought it was a plugged cat or resonator to we pulled em off put hedman headers with hi flow cats and mufflers. With no difference. We have narrowed it down to a fuel starvation. The inside of the manifolds were white indicating a lean condition. We have had 2 fuel pressure regulators on it. Also the fuel filter was clean as a whistle but repaced anyways. Along with a brand new tank a month or 2 ago. Both fuel pumps are kicking on. When you pull the fuel filter or regulator off theres so much pressure built up it almost wants to blow it off. We have also changed the throtle positioning sensor. Its almost like the fuel isnt recirculating. What do u think? Its got three of us stumped and runnin out of ideas!
Lead Driver
Joined: Feb 2003
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From: Oak Harbor, OH
Test the fuel pressure with a GAUGE, don;t just throw parts at it. Test the parts. Buy haynes manual for the vehicle it's in, there are testing procedures in it for almost everything. It could be anything from a vacuum leak, to clogged fuel injectors. I'd check the return line and make sure it's pinched off somewhere. How old are the plugs, wires, cap and rotor? If they are original it's time to replace them. Is it MAF? (Has a sensor in the air cleaner inlet hose). That could be bad.. Like I said get a haynes, and test, test ,test.
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We have purchased a haynes Manual for it. But has lead us nowhere. It just had a tune up 2 months ago and was fine then plugs cap rotor wires the hole nine yards. There is no MAF on this truck. Testing the fuel pressure on the rail seemed to be alittle on the low side. thanks for the replys keep em comming!
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Joined: Aug 2004
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From: St Cloud/Orlando area, FL
Check coolant temp sensor and air inlet sensor. These help computer regulate amount of fuel injectors pump in. Checking the fuel pressure with a gauge (auto zone might loan you one) is a good start, too. Heard the question before, but no answer...did it happen all of a sudden or over time? Does it change from when its cold to when its hot? More info. And if you don't own a good multi-meter and know how to use it, fix that too.
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We have tested the coolent temp sensor, throttle body sensor and and they check out fine. It does not matter if its hot or cold. I do not have a guage for the top of the fuel rail but when u press down on it it squirts up like 3" and thats it. I will head out today and purchase one. Is it possible the fuel rail is plugged?
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Freshman User
Joined: Aug 2004
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From: St Cloud/Orlando area, FL
You didn't say anything about air inlet temp sensor, located on intake manifold in top center of engine. Also, have you pulled the codes and did it happen all of a sudden or over time...
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