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Mike S.
Mike S., ASE Certified Technician
Category: Ford
Satisfied Customers: 7155
Experience:  ASE Certified Master Technician
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1995 f250: with a 5.8 liter v8 in it..real loses power

Customer Question

I have a 1995 f250 with a 5.8 liter v8 in it. my problem is that the truck has no power at take off and it is real sluggish. the engine revs up really good at idle but when in gear under normal load it loses power. it does not misfires. so far I have checked the fuel pressure good (35-39 psi), good spark at plugs, checked timing and it is good, check the exhaust system for back-pressure and found no back-pressure, check compression and it is good (125-130 psi all cylinders), tried a different ignition module and coil with rotor cap and rotor, checked for fault codes with no faults found, done a major tune-up on it. had a new transmisison installed on it and none of these repairs have done any good. any help will be appreciated. thanks guys.
Submitted: 5 years ago.
Category: Ford
Expert:  Mike S. replied 5 years ago.

Ok, first of all I read that you checked the timing. This either has the DuraSpark II Ignition System or the TFI-IV Ignition System. I am assuming it's the DuraSpark II Ignition System because on the TFI-IV Ignition System no ignition timing adjustment is possible and none should be attempted.
On the DuraSpark II Ignition System the distributor has a means to advance the timing of the spark as the engine speed increases. This is accomplished by centrifugal weights within the distributor and a vacuum diaphragm mounted on the side of the distributor.

So with that in mind hook up a timing light and check the operation of both advances.

Customer: replied 5 years ago.
I already check the timing and it was at 10 degrees at BTDC which is what the specs call for. I advanced it up to 20 degrees and drove it with no good results so I set back to where it was. thanks.
Expert:  Mike S. replied 5 years ago.
Thats the base timing. I said to check the operation of the centrifugal and vacuum advance. Hook up a timing light, unhook the vacuum and plug then rev the engine over a few thousand rpm and watch the timing mark and see how far it advances to check the mechanical advance, the while holding the throttle at a steady rpm, like 1,500rpm push on and pull off the vacuum hose and then watch the timing mark again.
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Expert:  Mike S. replied 5 years ago.
How did you check the exhaust for a restriction?
Customer: replied 5 years ago.

ok what happens is if the timing mark moves or stays where it is at after I do what you say???....I checked for exhaust restriction with my OTC exhaust backpressure gauge.

Expert:  Mike S. replied 5 years ago.
Ok, you should get both a mechanical and vacuum advance. If the vacuum advance don't work, light up a cigarette and blow smoke into the hose going to the vacuum advance and if smoke pours out all around the distributor cap, then the vacuum advance diaphragm is busted. If the mechanical advance don't work, or jerks or doesn't work enough, remove the distributor cap, rotor and check to make sure the mechanical advance weights are not worn out, that the springs didn't fall off and also make sure the little plastic bushings on the pins are ok, too.