Engine trouble - Engine Troubleshooting


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Engine trouble

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Auto Repair Home>> Automotive Repair>> Engine Troubleshooting

clemjr
Novice

Aug 14, 2006, 6:13 PM

Post #1 of 5 (1907 views)

Engine trouble	Sign In

Hi: I have 89 F-150 Ford with 300-6cylinder eng. Just recently the engine started loping when idleing. It goes from 500 to 900 constantly on the tach. The exhaust is black that tells me it is getting to much gas. Any idea of what went wrong recently? Truck has 51 thous. actual miles.

DanD
Veteran / Moderator
DanD profile image

Aug 15, 2006, 1:21 AM

Post #2 of 5 (1898 views)

Re: Engine trouble	Sign In

I’m not saying this is the problem but it was a common one back in 89. Check the vacuum line that’s connected to the fuel pressure regulator. What would happen is that the diaphragm in the regulator would rupture allowing fuel to pass through the regulator down the vacuum line and into the engine without a sign of leakage. It sure would make the engine run rough and rich as hell.
So any sign of fuel in the vacuum line replace the regulator. Be careful if you start the engine with the line off; I’ve seen fuel spray out of the vacuum line spigot of the regulator and it’s under a fair amount of pressure if the diaphragm has gone bad.
Dan.

Canadian "EH"

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Aug 15, 2006, 4:50 PM

Post #3 of 5 (1890 views)

Re: Engine trouble	Sign In

Just to add: A total vacuum test would be nice and a book to describe.

Note: Some of the 300 six engines around then had problems with stretched head bolts and the only fix was new ones not just tighten them up agian. If so the diagnosis could be tough. Head gaskets can make a whole assortment of different problems. FORD did not own up to that TMK. Just bad luck and that has not happened to all of them, T

clemjr
Novice

Aug 15, 2006, 7:32 PM

Post #4 of 5 (1886 views)

Re: Engine trouble	Sign In

When I take the vacuum line off fuel pressure regulator & start engine gas shoots out of spigot. Does this mean diaphgram is shot. Also to replace regulator does one have to remove the top part of the manifold on top of engine. Thank you.

DanD
Veteran / Moderator
DanD profile image

Aug 16, 2006, 3:29 AM

Post #5 of 5 (1883 views)

Re: Engine trouble	Sign In

Yes if gas is coming out of the spigot then the regulator is NFG. (No Further Good)
As for replacing the reg do what you have to, to get at the retaining bolts? It may mean removing the upper plenum it may not and I can’t remember on this year of three hundreds whether you do.
Maybe get the replacement reg before you begin; that way you know what fastens it to the fuel rail and you wont be removing things you don’t have to.
Dan.

Canadian "EH"

(This post was edited by DanD on Aug 16, 2006, 3:31 AM)

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