Idle and cylinder 4 problem help please! - Ranger-Forums - The Ultimate Ford Ranger Resource

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Old 01-11-2015
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Join Date: Jan 2015
Location: vancouver, bc
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Idle and cylinder 4 problem help please!

first time posting here but i really need help, ive bought an 02 ranger, 4L v6 and shortly after the check engine light came on with a cylinder #4 and 5 misfire and a really rough idle while stopped or at low rpm and higher speeds and rpm the truck seems to be good, so i thought may have been a vacuum leak or something to do with the fuel system, so i checked:

intake manifold put new gaskets in
vacuum leak test
injectors checked
new plugs
checked spark
checked compression
spark plug cables
coil pack and plugs
cleaned the iac
took the valve cover off everything seemed normal

any feedback or info would be greatly appreciated, i know i can't be the only person with this problem!
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Old 01-11-2015
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Location: Vancouver, BC
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If there is a rough idle then you do have a misfire.

Misfire is caused by:

You seem to have checked all 3 but missed something because those are the BIG 3.

A compression test needs to be done with all spark plugs removed and then test one cylinder at a time with at least 4 "compression hits".

Then you compare all the numbers
A one or two cylinder test doesn't tell you anything unless it comes up as 0psi

Spark can be tricky, best way is to use an old timing light on the effected cylinder and watch its pulse, you can see if spark is intermittent from coil.

Fuel is also hard to test because it is a mix with air, and the wrong mix causes the misfire.
A dirty injector can cause a lean mix misfire at idle but will pass enough fuel at higher RPMs for cylinder to fire.
Seafoam in the gas tank can clean injectors.
Or you can swap around injectors to see if the misfire moves with the injector.

#4 and #5 are adjacent so could be an intake leak there, leaning out both enough for a misfire at idle.
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