Week spark after long drive

[belize1334]

I noticed this issue on a long hot drive back from Salt Lake City this weekend. The car breaks up under load but the severity of the condition is strongly dependent on how long the engine has been running and how hard it's working. For instance, if I take it out, warm it up, and get on the freeway it runs really strong up till about 10psi and 4500 rpm and then it starts breaking up. But, if I've been driving it for hours and I'm pulling a hill it will break up at 0psi and 3000 rpm. At that point, if I crest the hill and let it coast down the back side then it'll get better but then the next time I'm pulling a hill it's bad again.

So the question is this... what could cause a misfire and be aggravated by excessive load (or possibly heat). Plugs are new. Cables are new. Coil-pack and igniter are original. Fuel pump is Evo IX. I'm leaning toward spark and not fuel cause I don't get any knock until after it starts breaking up and it seams like a lean condition would cause knock long before misfire. I'm also thinking it may be an alternator issue. Long exposure to heat could cause the alternator to run weak and lower the voltage at the igniter. Possible? Maybe.

Chime in if you have an idea...

 

[vr4play]

What brand are your spark plug cables. I spent hours looking for a problem similar and it ended up being my new MSD wires where junk out of the box. What are the plugs gapped to?

 

[James]

If the coil and power pack are original I would be testing them.

 

[mitsuturbo]

Week.. 7 days

That's a whole lot of spark!


I would suggest you tear open your ECU and check the caps. Nearly every failing ecu i've encountered behaved similar to the way you are describing.

 

[belize1334]

Week = my spelling. Cables are NGK. Plugs are gapped to 28. ECU was recapped about a decade ago, though it's probably worth checking. I just can't see why the ECU would care whether the engine was working hard or not... I'll check the specs on the coil and igniter, double check the resistance on the cables and replace the plugs.

I also realized that my igniter doesn't have much of a heat sink where it's mounted so it could just need to be remounted where it won't be prone to overheating. The weird thing is that on the way to Park City I pulled the whole 10 mile 6% grade in fifth gear with passengers and the car acted like a CHAMPION. And then on the return trip I get issues.

 

[slugsgomoo]

do you have a log of the car when it's doing this? DSMlink/mmcd/etc?

Be curious to see what the temps are and what the injectors & afr's are doing when it happens.

 

[JNR]

I was going to suggest the ignitor and its bracket to be sure its secured properly...also I cannot recall if the ign touches the bracket for the heatsink effect but if it does perhaps some of that hs compound you use for cpu processors would help. I couldnt believe the difference on my processor between not using it and using it.

The breaking up sounds like an ignitor issue thoug so if it only does it after getting hot it sounds likes its overheating...the other things like plugs and wires would seem like they either work or dont work all the time and not intermenent.

 

[belize1334]

^^ Agreed. No logs right now 'cause I have to figure out how to emulate TMOLogger.exe now that I don't have a windows laptop anymore. Too bad that MMCdroid app was never set up to work with a USB connection -- that'd be the sh*t.

 

[JNR]

Wish my palm tungsten t5 would work for logging so I can use it and get rid of the archaic m125 or whatever model I was using.

Be nice if you had a known good ignitor to test, but I was able to pick up a nice brand from rock auto for good price although it may have been a closeout. I personaly wouldnt trust a used one though given a choice (for testing or replacement).

Dumb question but did you burn thru your tank of gas to eliminate that as a possibility? unlikely but to eliminate something.