Two weeks ago, my 98 Ford ranger (Which I have had for four years and am really fond of) with 2.5 L started running really rough. CEL said codes PO300, PO301, PO302. The engine would start, run rough and on acceleration, ping or bang as if it had marbles inside it. So, I began researching the possible causes.
I did not do a compression check because I couldn't imagine how two cylinders could lose compression so quickly at the same time.

As time went on, I did the following:
Changed both oxygen sensors
Changed fuel filter
Checked fuel pressure twice (60-62 PSI)
Replaced MAF
Cleaned throttle body and intake ports (was really dirty after 250,000)
I decided to replace timing belt, water pump and tensioner pulley since didn't know when they were changed if ever.
Checked catalytic convertor - ok
Replaced serpentine belt because it was cracked.
Found one Autolight plug with broken ceramic, replaced all plugs with Motorcraft.
Replaced both coil packs plus ignition wires.
Checked EGR valve and DPFE sensor - ok.
Installed new PCV valve and new thermostat which I already had.
Bench checked all four injectors, and eventually swapped them out for some from junk yard.
Replaced IAC (Idle Air control) valve.
Replaced ECM computer with one from junkyard.
Removed valve cover and checked for integrity of valve rockers - everything fine.
Checked all fuses and relays for ignition - all fine.
Finally, I read that a head gasket could blow between the cylinders and that there would be no other indication than loss of power and misfiring. So, I did a compression check. Cylinders 3 and 4 were about 120 pounds each, and 2 was 30, and 1 was zero or possibly 10 psi. Now, I knew I had a serious problem. Yesterday afternoon, I pulled the head and "voila", I found that there was about a half inch passageway blown between cylinders 1 and 2, and the gasket was about to blow between 2 and 3. Fortunately, there were no cylinder or head cracks. Now, I have it almost all reassembled and tomorrow morning I hope to finish and drive it around the block on all four cylinders.
I suspect that the previous owner ( who apparently took pretty good care of it), must have gotten it very overheated at some point ( some other signs like new radiator, and rust trails down the fan shroud), and that weakened the gasket. I haven't been driving it hard, and never had it overheat for me.
So, praise the Lord, I finally found what was causing the problem. Murphy was there helping me all the way as I broke two of three tools I borrowed from Autozone, and had a lot of other crazy things happen on this job.
Count it all joy when you encounter various trials, knowing that the testing of your faith produces endurance.

 

Welcome to the forum


Good post
And good work on tracking down the problem

The 3 things that allow a gasoline engine to run correctly are:
1. Spark, at the right time
2. Fuel, in the right mix with air
3. Compression, higher than 100psi to vaporize gasoline enough to be ignited by a spark

Spark and fuel can be intermittent issues, so can be hard to eliminate as a problem

Compression is directly mechanical so is either above 100psi or is not above 100psi, black and white, and it won't be intermittent.

Quick testing of spark and fuel, i.e. is there spark(spark tester or spark plug) and is there fuel(wet spark plug tip after cranking engine a few times) is enough to move on to compression and take it off the table as possible cause or confirm it is the problem.


But you have almost a new engine, so loads more miles left on your Ranger

Good work