4.2 Cylinder 3 misfire
 

i got 97 f150 with 4.2 in it i been having trouble trying figure out the why i keep getting a misfire on cylinder 3 it first started missing between 45 and 55 mph replaced the spark plugs then the coil pack drove it a few miles drove fine then i decided to open it up a bit made it to 60 the miss was back so i replaced the wires did the same thing went for a good drive opened it up made it to 65 then the miss was back at this point im stumped before all this happened maybe a week before this started i was setting in walgreens parking lot had a misfire on cylinder 6 put new spark plugs in cleared it up but the plug in 6 was horrible it was gunked up on the tip when i got the truck in febuary its always had the egr code insuffcient flow im starting to think the ports are egr clogged up causeing it to dump into cylinder 3 has anyone else had this problem or any ideas thanks

Early 97-98 model year trucks were plagued with bad intake gaskets allowing coolant to get into the cylinders.

How is your coolant levels?

How many miles are on the truck? What the the codes you are getting?

ive done some research on the intake gaskets before getting the truck and been keeping and eye on it its stayed normal the truck has 139,000 ive gotten codes p0303 p0306 p0401 but i fixed the p0306 code with new plugs

Fix the EGR issue.

What brand plugs, wires, and coil did you use?

Try putting some Techron in the gas to clean the injectors.

Did you do a compression test when you had the plugs out?

i dont remember what brand the coil and wires were but the spark plugs were motocraft and no i didnt do a compression test how do u do that? im in the proccess of figuring out the egr problem ive replaced the egr and i aint had the p0401 code since my truck started misfiring

Compression test- Disable the fuel pump. Screw in a gauge into the spark plug hole and spin the engine with the starter. Check all six and compare compression readings. they should be close together.

Cheap aftermarket wires might possibly cause it, but check compression next.

done the compression test everything was close together the only time itll start missing is when its under load going up hill or trying to go 65 or 70 its a pain in the ass ever since i got the truck its a had a real slight shutter at idle i appreciate all the feedback fellas

Well, you probably have one of the following problems:

Bad plug
Bad plug wire
Bad coil
Bad fuel injector

im gonna try to replace the injector see what happens ive replaced the other 3 you listed i got the egr code P0401 ( insufficient flow) ive been gettin it since i got the truck im gonna try replacing DPFE sensor i already replaced egr and im gettin suction from the little green hose on top of the egr and where it meets the red hose to go into what im thinkin is the egr solenoid when i take both hoses of there i got a strong suction

Before you buy an injector, just swap it with another cylinder, clear the codes, and see if the miss moves or not.

The egr passages may need to be cleaned out.

are the injectors pretty easy to get out what all needs to be removed to get to them?? are the egr passages behind the egr or under the intake or are they in both spots

You may need to take it to a mechanic.

i got a mechanic goin to take a look in the morning hopefully they find the problem