engine swap/cracked spark plugs now

Did an engine swap this summer on my 91 Ranger 3.0L. My manufacture date was 2/91.... the engine I swapped was from a 8/91 truck... ended up being the same engine except for the newer one was a roller cam engine.... Since running the engine I continue to seem to have plug issues.

Initially after starting, I had a miss..... soooo, went through the plugs and found one cracked... ok, seemed to remember possibly hearing something when I tightened that one down... so changed it and had about a week of good running (50-100miles) before it was "missing" again... ran back through plugs and found another cracked... hmmmmm, don't think that was my fault as everything seemed good for a week... but ok, maybe it was just at the verge and the heat got it? soooo, two plugs changed now... different cylinders.... truck seemed to work fine for a week or two and then I start getting the "missing" AGAIN!!! SOB! what now!? sooo, checking around and find a wire that has a crack in the boot... ok, so maybe from the pulling off and on I was a little rough on that one? The wires, plugs, cap, rotor all are new! Replaced the bad wire, all plugs seem fine, go for about another couple weeks (maybe 100-200) miles and here in the present, I seem to be having another missing issue! grrrrr

question - my owners manual for the truck suggests platinum plugs. is it possible that the 8/91 engine uses standard copper for some strange reason? Going to the local Autozone, their recommendation is copper for a 91 Ranger 3.0... had to bring in my owners manual to prove to one guy once that yes, it actually calls for platinum on the 3.0L whereas the others (2.9L & 4.0L for that year) called for copper per my manual...

just wondering if this upgrade from the non-roller cam also made some kind of difference in which spark plug is needed and possibly the difference is causing problems that seem to appear possibly engine/heat related? obviously, possibly just continued stoopid errors by me but it's sure seeming to be a little more than coincidence at this point... have yet to figure the current miss but I'm guessing it's a plug again! Drives just fine for about 1-2 weeks... also from what I can recollect, it seems to initially appear after a highway trip (and I'm not nice to the throttle entering the highway, I believe in being UP TO THE SPEED LIMIT by the time I'm merging! and this truck sure can seem to be a "dog" and not get out of it's own way at times... lol)... Currently with the miss issue it isn't noticable until the truck is up to normal operating temp.. then the missing starts..... I've never had these issues before changing plugs.... grrr

ideas?

ok, will answer my own question... hahaha.... went checking the driver side plugs and wires again, since this seems to be the culprit side.... once again I have #6 wire with an issue.... before it was cracked and looked like maybe I wiggled it on to rough or something.... or pulled on it too hard.... well, this time it looked bubbled... ok, so that seems to be a problem with heat! coming from the exhaust manifold I figured.... I do have a slight tick that I figured is coming from that side so I took some snips and moved some of the exposed gasket that seemed to be possibly tunneling escaped gases up towards the wire.... after replacing the wire and driving on the highway for 20 miles, I AGAIN started getting a miss.... argh!

sooo, after taking a closer look at cyl #6 @ manifold, I figured there must be something wrong.... it's been making that slight tick for years even before the engine swap... took off the manifold and yep, the gasket is blown... and probably because it seems the manifold is not totally square so I'm taking the manifold to the machine shop in the morning and getting it machined and hopefully cure my problem.... amen!

what are you gapping the plugs to? too large a gap will fry the ignition system and cause high RPM/load misfires, too small will foul the plug and cause misfires at low speeds

We need a little PLUG GAP 101 here

BRUTUS_T_HOG said:

what are you gapping the plugs to? too large a gap will fry the ignition system and cause high RPM/load misfires, too small will foul the plug and cause misfires at low speeds

Click to expand...

Why has the gap in spark plugs changed of=ver the years and from engine to engine (you should be asking)!

Doesn't have anything to do with the plugs themselves!
What is it then, you may be thinking?

Well it's all about lighting the fuel mixture. Back when gas was cheap vehicles didn't give a hoot about economy. So it was simple.. gap the plugs to whatever would work...and be on your way.

Then economy got to the head of the list! As the mixture became leaner and leaner the gap had to be increased to ALLOW enough of this lean mixture INSIDE the gap or there would be no fire and the engine would miss..

This required a much stronger coil to make the spark in the wider gap! Also much better wires to HOLD the lectricity inside all the way to the plug.

As for the gap itself.. smaller is better..if it will still light the fire without missing. Too small will simply miss, too large will do the zact same.

If plugs foul it is another mechanical problem.. or perhaps the WRONG (too cold) plug has been installed.

Big JIm

my thoughts/experience is that when spark plug gap is set too wide the coil obviously builds up more voltage and heat than its supposed to and IF electricity can find a path with less resistance..say from the spark plug boot to the nut of the spark plug it will create a carbon track that looks like a crack on the porcelain. the high voltage could burn through any weak spots in the wires as well and create a short to ground. and i've seen one on a ford explorer where it melted a spark plug electrodes

like you said. smaller plug gap is better up to a certain point, too small and the engine won't idle smoothly and might miss at low speed/load conditions

i personally like to set my plug gap a little wider than spec to get a smooth idle and haven't had any problems, but i've seen people just get crazy with it and setting the gap at over .090" and of course the coil, wires, and plugs were destroyed from heat/shorts

It might be related, but for my '88 4.0L, i haven't had any more issues for the last 3 years with cracked spark plug porcelin since i changed out my thermostat. It was cracking one every 2-3 months, both the #6 and the #1 cylinder. I had and continue to use Bosch Platinum+4, and i didn't switch to a different one in the hope that the 4 electrodes kept the cracked porcelin from falling into the pistons. I had noticed that from a cold start the temp gage would sit at cold for a long time, and around 10 minutes later it would have "popped" up to mid-temperature. After changing the thermostat, it the temperature would rise nice and slow as you would expect, so i think it was overheating the plugs and then thermo-shocking them back down.
Maybe this can help.

Been a while since I posted to this one but exhaust manifold was warped on driver's side.... machined it flat and put new gasket in and no more escaped gasses melting my plug wire.... BUT, still getting an occasional cracked plug... I've been suspecting something along the lines of the heat this engine gets to during very hot days (mainly with A/C) running and I think I do have a 190 thermostat possibly in it.... you might be onto something knucklescraper... intend to check that thermostat if I have another plug crack.... at first I just thought maybe I was torquing em down too hard but it's happened more than just 2x now and I'm starting to think something else is at play