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sgm11155, ASE Master tech
Category: Ford
Satisfied Customers: 589
Experience:  I have worked in the automotive feld for over 20 years
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Ford F150 Pickup 4x4: I have a 1984 Ford F150 pickup truck

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I have a 1984 Ford F150 pickup truck with the 4.9 litre 6 cylinder gas engine and a 4 speed transmission. we bought it brand new and it has been a dandy. sometimes, after the engine warms up, i put it into gear, press the accelerator and the truck will go to a certain speed and then start bucking and trying to throttle down, if i continue to "put my foot" into the accelerator, it will increase speed and then do the same thing. I shift gears and it will do the same thing, reach a certain speed and then start this jerky motion. Most of the time, after it has been driven for a little while, and is running at operating temperature, it will quit and the truck runs smooth like silk.
it hasn't been tuned up in years, i am going to do plugs, wires, dist cap, rotor, ignition module this weekend and set timing.
the truck has 158,000 miles on it but still passes emissions. I have been thinking that the catylitic converter and muffler could be plugged up, they are original equipment. what do you think??

sgm11155 :

hi i am shannon i will help on this issue

sgm11155 :

the tune up sound like a good idea

sgm11155 :

i would add a new ignition coil to that too

sgm11155 :

as far as the cat converter being blocked you can test for that with a engine vacuum gauge

sgm11155 :

i will post a video and a vacuum chart.

sgm11155 :

hear is an inexpensive gauge

sgm11155 :

i hope this answer,s all your questions. if not please post back any question on this issue you need

Customer: replied 4 years ago.

I appreciate your informative and timely reponse. your suggestion about testing engine vacuum to determine the condition of the exhaust system may save me $750 bucks. i even think i have a vacuum testing gauge. What do i need to do to insure that you are paid the $59 bucks.

i am thinking that if i have additional questions regarding this same issue, i can continue to post those questions using this procedure. thank you again.

when doing the vacuum test be sure to hold the engine speed at 2000 rpm in park . the vacuum should not drop below 15.hg. if it goes below 10. hg. and stays there at 2000 rpm . you got a exhaust blockage.
yes you can always post to this thread just go to (MY QUESTIONS ) at the top then click on this question .then post a question on this issue any time you want .
i will get a Email and answer as soon as i see it. for me to get credit click on 3 to 5 happy faces i will be paid .thanks Shannon
sgm11155 and 2 other Ford Specialists are ready to help you
Customer: replied 4 years ago.

I am going to continue to pester you for information, if i can get it for the fee i have already paid ;-)


i did a compression test on the engine and came up with 110 PSI for all the cylinders, i was tickled. i have done some research and cannot find an actual specification for that. I think the fact that all the readings were exactly the same says a lot. anywho, if you can give me the actual specifications for a nominal compression test for the 4.9 liter ford 6 cylinder, i would be thrilled

i am thanking you ahead of time

be sure to let me know what you find. thanks shannon
i do not have a spec. for compression. but you are right all reading the same is good. how did the vacuum test come out?
Customer: replied 4 years ago.

there has been nothing new to report
i have followed your directions and suggestions and the truck project is kind of at a standstill right now.
i can only spend so much time and money trying to restore my old pick'em up trucky
thank you again

no problem just post a question or results of testing when you are ready