Cold weather break up
 

Ok i've noticed since the weather is getting cooler that my car will tend to misfire. It only happens at night, which i suspect is because it's colder at night. It will run great until i get to around 5K rpm, and then it'll misfire slightly, but enough to make you now wanna accelerate anymore. My plug gap is around 20-25 thousandths, so i really don't want to close it anymore, and i'm running one step colder plugs.

I'm wondering if the coldness has something to do with the atomization of the fuel? Or maybe it's more probable that my IAT is overcompensating fuel when it's really cold, and that's ------- me up. It's tuned to about 12 AFR @ 5K so i wouldn't expect that to have an effect on it, so i figure i have some ignition breakup for some reason. Should i switch to stock plugs? Maybe upgrade the ignition system or timing? ideas?

Re: Cold weather break up
 

is it tuned for part throttle or just wot and boost?

Re: Cold weather break up
 

Slap a wideband on there and see what's going on. I doubt its too much fuel. Most likely too little if I had to make a guess. I've touched more than a few cars running rich(10's AFR) and they didn't have issues with misfiring.

Re: Cold weather break up
 

I know on my carb setup the AF ratio was at 11.8 to 1 on the chassis dyno (70 degrees) Then I would bring it out ice racing and it would be about 12.2 to 12.4 to 1 in cold weather. I don't know how the computer deals with this.

Randy

Re: Cold weather break up
 

Yeah i didn't think it woulld be too much fuel either because i used to run a 10 to 1 afr when i was running my VAFC :8. But if it were too lean wouldn't i be hearing detonation instead of misfiring? I can definately tell it's a type A misfire, and it's kind of intermittent, it's not like totally awful, but it needs to be fixed. Also, i would expect the IAT sensor to adjust the fuel trim accordingly for the weather, unless for some reason my IAT compensation map in crome is messed up, but i didn't even touch it. I'm wondering if maybe i need to gap the plugs a little more and put a better ground on the engine, and try another IAT sensor with better wiring in case mine is skewed. I want to get a wideband on it but i dont have one and i can't get ahlod of anyone with one. It is tuned for part throttle, but not perfectly tuned. But when it's part throttle, no misfire. Only at WOT, it starts to break up, which would make me think. too much fuel, too much compression; puts the spark out. I need this fixed. ------ a.

Re: Cold weather break up
 

Do you have a chip burner? Go into the IAT compensation table and increase the multiplier a touch. If you don't have a wideband, but can datalog, it would be great to know what your IATs are at during the misfire vs what they are when the misfire doesn't occur. Then you would know basically which cell to increase in the IAT modifier table. It really wouldn't be a terrible idea to buy a LC-1 diagnose your problem and sell it for a couple bucks less than you bought it. If you have to spend $20-30 to diagnose your problem, thats pretty cheap.

Re: Cold weather break up
 

yeah i need to get a wideband bad, but i believe i fixed the problem. I had another IAT lying around, so i threw that in, and i re-did my wiring to it (it had to be extended), because i think the wiring may have had excessive resistance. Plus i gapped my plugs down to .025 and it appears to be gone. Seems like it's running better overall, we'll see what the wideband says when i can borrow a buddy's and, even still i'll probably go in and change the IAT compensation.