1999 Mazda B2500 SE, random cylinder 4 skip.....HELP

[BAPorterfield]

Truck sits and idles great, as soon as you try to drive it around the block it starts skipping on cylinder 4. Started with EGR valve, it was clogged all the way through to the intake, so I cleaned it out. No difference. Checked fuel pressure, 64 steady, checked compression, all fine. noid light flashes, and can hear fuel injector firing with stethoscope while skipping. So has fuel, and checked fire while skipping, it's fine as well. Mechanic talked me into a new head, made no difference. New coils, new plugs and wires, no difference. Am thinking maybe crank sensor or ECM. if it's firing and has fuel, maybe computer is glitching and doing right thing at wrong time? also replaced injector on cylinder 4, and still no difference, except about a grand chasing this issue from my wallet. I replaced timing belt, tensioner, water pump, thermostat and all that good stuff while I was in there doing the head. The skip is only on cylinder 4, which leads me to believe electrical. I plan on trying ECM next and Crank sensor. Also trying to find out if this model has a cam sensor as well. Thanks for any help anyone may offer.

 

[RangerX]

Welcome, BA!
I moved your post into the Ranger forum, since your engine is specific to Rangers and B-Series.
Hopefully someone smarter than me can help.

 

[Tbars4]

..Only two things I can think of real quick to test..

Go ahead and move both plugs and wires from cylinder 4 to another cylinder (swap) and see if the problem moves. I know you put new stuff on but give it a try.

Also, in the dark try and check for any arcing from coil packs, wires, and plug locations....

 

[Red FX4]

Check both spark plugs for any evidence of tracking (arcing along the insulator). I had a similar problem with a V6 Cougar. I got tired of trying to find the problem and took it to a Ford dealer for diagnostics. They found a problem with one of the spark plugs and replaced it, problem gone.

Apparently a piece of lint or something got in the boot when I replaced the spark plugs and wires. After 500 miles of the spark plug firing, that lint carbonized and became a path for the current to partially bypass the spark plug and cause a misfire. I could not see it because it was happening inside the boot.

 

[BAPorterfield]

Check both spark plugs for any evidence of tracking (arcing along the insulator). I had a similar problem with a V6 Cougar. I got tired of trying to find the problem and took it to a Ford dealer for diagnostics. They found a problem with one of the spark plugs and replaced it, problem gone.

Apparently a piece of lint or something got in the boot when I replaced the spark plugs and wires. After 500 miles of the spark plug firing, that lint carbonized and became a path for the current to partially bypass the spark plug and cause a misfire. I could not see it because it was happening inside the boot.

I have replaced plugs, wires and one coil, and have swapped all around various ways and gotten same situation.

 

[BAPorterfield]

Noid light tested and firing when skipping, and replaced injector to be safe, but was fine. Thinking maybe something is telling it to fire at wrong time or stroke??? Crank sensor or ECM maybe???

 

[Tbars4]

Do not rely on a noid for testing..

Since you never have received any codes for this problem I would still do the "arc in the dark" test and a compression test as well as a code test.

Bring your results back here and lets see if we can better assist you..

 

[BAPorterfield]

Do not rely on a noid for testing..

Since you never have received any codes for this problem I would still do the "arc in the dark" test and a compression test as well as a code test.

Bring your results back here and lets see if we can better assist you..

I just checked, no arc in the dark. Compression I checked day before yesterday after putting the new head on. As for code test if you mean check engine codes, their are none. I have found on a vacuum test the vacuum fluctates very very little and drops a couple PSI every few seconds. Tester says carb issue, but I don't think that is it. Can a bad fuel pressure regulater or EGR valve effect just one cylinder? I'm really stumped. Checked fuel pressure at idle and when holding idle up a little and maintains 64. Though it should fluctuate when you remove the vacuum from fuel regulator and it doesn't. Mechanic said was ok as long as pressure maintained.

 

[Tbars4]

How many miles on the vehicle and what were your comp numbers?

...and no and no...

 

[BAPorterfield]

vehicle has 186,ooo miles. Don't know the compression, but mechanic checked it when he did the new head and said all was fine. didn't actually do it myself.Before we did the head compression was fine too, just thought maybe had a valve issue. That was $800 down the drain.

 

[Tbars4]

vehicle has 186,ooo miles. Don't know the compression, but mechanic checked it when he did the new head and said all was fine. didn't actually do it myself.Before we did the head compression was fine too, just thought maybe had a valve issue. That was $800 down the drain.

I replaced timing belt, tensioner, water pump, thermostat and all that good stuff while I was in there doing the head.

..:scratch:..Who replaced the head and was it from Ford or somewhere else? we can only guess from what information you tell us and if it changes, well..

..With no code, how was it determined it is cylinder #4 ? There has to be an intermittent code if it is one cylinder or even a code for a random misfire.

Did the mechanic ever work on the vehicle before the mis started happening?

..I only ask these questions because if you are relying on this mechanic and can not verify these things yourself, I would suggest another mechanic to verify unless you are capable of verifying the work yourself...

..I am not trying to be harsh but this sounds like a common scenario which we've seen many times.

It could very well still be plug or wire related from wrong plugs to or even perhaps they were never changed..The previous or even new compression numbers per each cylinder can say a lot.

We are really trying to help you here but maybe we should start way back at the very beginning (after answering the above questions please)..Was any work done on the vehicle before this started? How long ago did this problem start and what were the first symptoms?