Hello my 2002 ford ranger 3.0 4x4 is missfireing bad on cylinder one but for the life of me I cannot figure it out all the plugs and wires are brand new the coil pack was changed about six months ago I don't seem seem to have a problem with the coil pack but I haven't checked it because it still grabs spark , I don't believe I have any vacuum leaks and I have also changed that injector and the fuel rail is in good shape but I still can't figure it out and at times it seems that the missfire disappears and comes back in a day or two but still in that time frame I don't have the power that it should be having if I would floor it, it would accelerate like if it would be quater way on the throttle any suggestions would be great it's just costing me so much on gas and I'm currently trying to build up the truck and its delaying me on everything

 

To take it off the table I would get/rent a compression test gauge.
A cylinder needs 3 things to fire
1. spark, at the right time
2. fuel, mixed with the right amount of air
3. Compression

Spark and fuel issues can be intermittent, compression is either good or bad, very very rarely can it be intermittent, so once tested it can be taken off the table of possible problems or it is the problem.

Remove all spark plugs FIRST
Then test each cylinder's compression, write down results
Throttle needs to be propped open, foot on the gas pedal when cranking engine

170-180psi would be expected for 3.0l at sea level
But that isn't the point of a compression test
Since there are variables in the test procedure the point of the test is the comparison of all cylinders to establish an average and if any cylinder is more than 10% away from that average, higher or lower.
To average, don't use the highest or lowest cylinders, add up the 4 remaining numbers and divide by 4, that's the average compression, say it is 175, then 17.5 is the 10%, so 10% range would be 157.5 to 192.5, cylinder falling outside that range would indicate a problem

If one or two cylinders are lower by more than 10% then retest them but add a teaspoon of oil to each, via spark plug hole, and then test.
The compression number will go up, but by how much will tell you if it is the Rings or the Valves that are the issue.

If #1 has a compression issue then you can stop wasting time on other issues, i.e. spark and fuel.

Also have a read here: http://www.therangerstation.com/foru...96#post1510596
3.0l TSB is posted there about misfires

 

I had done the compression test and all seemed to be in order

 

Then check fuel pressure, '02 should be 65-70psi running, and 55-65psi engine off and it should hold that pressure for a few months, so no slow drop should be seen.
Poor MPG means very rich air/fuel mix or a leak, test will tell you if there is a leak.

After that you are down to the computer, and what is telling it to run rich.
If you have a misfire then you should be getting the misfires code P0301 because you know it is #1 misfiring.
Any other codes present?

 

97skull, did you find the problem? I am having this same issue. P0301 and P0316 codes. New wires, plugs, and #1 injector replaced. Will check compression and fuel pressure next. Seems to run fine at lower rpm's sometimes, but alway stumbles above 3000 rpm. Put a strobe light on #1 and shows firing.