Part Throttle Misfire Troubleshooting help - Tuner-Junction

njn63 · #1 (**permalink**) January 31st, 2009, 04:18 PM

I think I know what is wrong, but I want some second opinions.

My beater HF has been running weird the last week. It runs fine when cold but when it starts to warm up it misfires as part throttle when a decent load is put on it (uphill, higher gears at low rpm, etc.). Car runs fine if you give it more gas and idles perfectly fine when warm.

Last night I started by pulling the plugs (well, 2 of them*) and pulled the dizzy apart. Distributor looks fresh inside, pretty sure the cap/rotor were replaced recently. Plug wires are really old (they came off my Si so... over 7 years old) and I couldn't get a good reading with my multimeter so I ordered new ones this morning. Am I on the right track that this is probably an ignition issue?

Also, the bottom part of the boot on the spark plug wires separated and is stuck in the tube. Any suggestions for removal with limited tools? I think we have a long pair of needlenose pliers at work so I might try that at lunch time on monday. Never really cared because the plug wire still went in fine, but with new ones I need to get that out.

*1 spark plug I'm pretty sure is cross threaded so I left it alone (I have to go to work on Monday and it still runs, only car I have here). I fucking hate people that work on cars when they shouldn't. Other spark plug has a piece of the boot separated and stuck in the tube.

jadkar · #2 (**permalink**) January 31st, 2009, 07:53 PM

I would definitely start with the plug wires. Report back after that, but I would that's the best guess. Also, long needle nose and a lot of patience. I've had that happen to me before on another car and it sucks trying to pull that thing off down there.

ATISTANG · #3 (**permalink**) February 1st, 2009, 11:01 AM

typically misfire under a load is ignition and based on what you found i would say that is probably it

now on my dx i had something similar. i have a 15 min drive to town from my house, I work in town also. if i drove my dx to work and back only i never had a problem, but if i went to the post office or something before work, or if i went into town for groceries or went to a friends house it would act up. If i drove the car and got it hot, then let it sit for a few mins to a few hours then started it back up, it would start fine, but when i went to take off it would miss. then once you got around 3500-4000 rpms if would clear up, you could floor it and it would pull fine until you got back down into lower rpms. It was a funny sounding miss too. Rapid sounding if that makes since. Anyways the only thing i could figure was when i would shut it off it wasn't getting as much air moving around under the hood so the dizzy would sit there and heat soak. Based on my experience of distributors in hondas i figured it was a good guess and just went ahead and ordered a use dizzy from ebay. And that turned out to be the problem.

But it was similar to what you describe, because sometimes if you gave it WOT it would quit missing even in lower rpms

njn63 · #4 (**permalink**) February 2nd, 2009, 03:21 PM

Yeah, very similar. I figure I'll start with the wires and if that doesn't fix it I'll test everything in the distributor. Something else I didn't consider was that the resistance in a wire goes up slightly with heat and part throttle is the hardest mixture to light because it's leaner than full throttle. Both are factors that would lean towards a ignition problem.