Truck started acting up on Saturday. It was failing consistently around the 2k rpm area during acceleration. The engine was not generating any trouble codes.
I pulled the plugs and found that #3 had oil all over it. I assume a valve cover seal leak to be the cause of oil. Since I already had plugs out, I checked compression on all 4 cylinders. They ranged from 210 to 220 across the board.

Installed 4 new plugs. Reinstalled plug wires and went for a test drive. The failure was still there. Came back home and sat in drive way and revved engine off an on and it finally generated a code. It indicated a misfire at cyl 3 (P0303).

Swapped plug wires positions 2 & 3, cleared the code and went for another test drive. It still failed the same way. Came back to driveway and tried revving engine again and again to see if, but couldn't get it to generate another code to confirm whether the problem had moved to cyl 2. I have driven it again to see if code will throw, but no luck. I pulled the plugs wires off the coil and checked Ohm readings across secondaries 1-4 and 2-3 and got infinity?

I plan to ohm all the plug wires tomorrow to see if there is any variation. If nothing obvious jumps out, I plan to see if my plug wires on my Miata match the Ranger wires and if they do, I will swap out the suspect wire to see if it eliminates the issue.

Assuming it is an ignition issue, I figure I am down to the plug wires or the coil pack. Am I missing anything or does anyone have further suggestions?

Thanks,
Bernie

 

im having a similar issue in my 08, it runs fine at idle but under a load it acts like it hits the limiter a few times throughout the acceleration, it also does it down low when i bog it. I just checked the airbox but pulled some data with my HPTuners scanner today but have not dug in yet. Just started doing it Friday of last week, this truck has never given me any issues but i was thinking maybe some bad gas but seems to be only on one cylinder and i typically run ethanol free gas.

 

Yeah, your description of the symptoms may be better than mine. I just changed the plug wires with no help. I now have new plugs and wires, but same fault. I went ahead and changed these since these are normal maintenance items. I may be wrong, but if it was a coil, I would think it would be good or bad and wouldn't run properly across the range.

I have a simple OBDII scan gauge, but I have only used it for collecting codes. Don't know if it can do any meaningful data collection.

I forgot to mention that the truck has 247k miles on it and I was told the engine is not original, but have no idea how miles it has run.

 

im right at 150k miles with almost no maintenace other than oil changes ,brakes and one tune up.

i did a clutch once too but it wasnt bad, i had a rear break locked up due to broken spring that mimiked a clutch slipping.

 

I'm trying to decide whether I should order a coil pack. I may need to bring it somewhere for them to perform a diagnostic inspection. The possibilities are endless. It could be a bad injector, a bad sensor of some sort, a vacuum leak....who knows. I don't even have a tool to check the fuel rail pressure.

I replaced both O2 sensors, replace fuel filter, cleaned the MAF sensor and cleaned the idle air control valve around a year ago for different issue.

I'm an amateur mechanic, so please update the forum if/when you find your root cause. I will do the same.

 

Not a bad sensor, for sure, that couldn't cause a single cylinder mis-fire

If compression was OK, 200's seems high, 175-185psi is expected in a 9.7:1 compression ratio engine, so could just be the gauge or you tested with engine warmed up, but as long as 2 and 3 were within 10% of 1 and 4 all is well

If you can get an "old fashion" timing light, lol......you could test rhythm of #3 spark when REVing, see if its missing a few beats compared to the other 3, indicating a coil pack issue

Yes, certainly possible for an injector to fail, not common but possible

Could even be Computer issue, very uncommon but possible

 

i may order a coil pack to throw at it just out of laziness, may do plugs and wires at the same time since its an extra $30

 

I went ahead and ordered the coil pack. It gave me a Thursday delivery estimate. If it doesn't do the trick, I will have to decide how to proceed. I think I will have eliminated the ignition side of things (plugs, wires and coils).

By the way, I unplugged the TPS, started up the engine and sprayed some starting fluid around the intake manifold. I didn't hear any changes in rpm. I didn't get crazy with it, but I think a vacuum leak is unlikely. I would also think a vacuum leak would show up at idle anyway and idle is solid and steady.

 

The coil appears to have addressed it. No misses during a quick test drive following replacement.

 

Awesome! ill order one for sure then

 

Found my issue, it was a valve cover gasket leak, filled the spark plug hole to the top.

 

Wow........your leak is obviously worse than mine. I plan to monitor mine and put it off for as long as possible.

Happy to hear you got it resolved.

 

i got the valve cover gasket replaced, took about 3 hours in my yard, ive never had to fix one in the primitive conditions and it went well, my dad was a mechanic so i always had a shop full of tools but this time i was dreading it as everwhere online said it would take about 6 hours but this went way smoother than anticipated.

 

Good to know. I will still monitor mine and if it looks to be bad enough, I will plan to replace it when it gets cooler.