kennywayne28

ok use to when it would rain and only when it would rain my truck would buck real bad. my check engine light would flash and the whole truck would shake. now when I take off I can hear and feel a knock in my gas pedal only for about 10 sec then everything is fine until I get around 60mph my truck will start to shake badly and check engine light will flash. also when I increase speed it somewhat goes away (the shaking) but when I let off the accelerator it starts again meanwhile the check engine ligut is flashing the whole time also after passing someone or getting high rpm when it comes down the whole truck hits hard just a rough I dont know how to explain it and my mpg have gone down to about 10 I checked code changed plugs wires and oxygen sensors probkem still persist I dont know what to do ive cleaned maf or map sensor and changed cranckshaft sensor never had any major issues besides this with this truck it jas 230000 miles on it thank you any help will be appreciated

RLXXI

What I don't see is what year and what engine you have but what I do see is a ****load of miles on it and the first thing I would do on ANY engine with that many miles is a compression check and go from there.

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kennywayne28

it is a 2002 f150 with a v6 I think it is a 4.2 can I do the compression test or do I have to take it somewhere

RLXXI

You would have to buy a compression tester. Not knowing how to use it would be a good indication maybe you should bring it to someone that does.

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kennywayne28

yea just thought maybe I could figure it out im a motorman in the oilfield im not completely lost but thanks

RLXXI

To do a compression test is easy, pull out all the spark plugs, disconnect the coil pack feed wire, hold the throttle wide open and spin the engine over for a few seconds with the tester screwed into each of the spark plug holes 1 at a time. Note the reading from each cylinder.

You want all cylinders to be over 100psi and no more difference than 10-15% cylinder to cylinder.

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