random/multiple cyl missfire
 

ruled out fuel by replacing the fuel filter and testing my fuel pressure when it starts stumbling, replaced ignition control module, and ignition coil, opti is only 3 months old. it started doing it when it was snowing, let it sit for a day and cleared codes (and put on new fuel filter) and it was fine. rained the following day and it started doing it again. pulled off the opti and theres no moisture or anything of that sort. loctited the rotor screws even though they werent loose and cleaned the opti with electrical cleaner, still the same exact symptoms. i have a HPTuners log file from when i scanned it and its reading -26ish degrees of timing at idle and it goes more into the negative as the RPMs go up. id be more then willing to send the file to someone if they want to take a look at it but im stumped at this point. any help would be greatly appreciated.

ill give you 2500 for it

I don't know if hp tuners has a fix for it, but the negative timing on my scanner is actually advanced. Just reversed for some reason.

-26 like tim said is normal, advance is actually a negative reading. The computer is pulling timing as the number gets more to the positive. Have you pulled the plugs yet? How do they look? Is it possible you got bad gas?? The more it think of it it actually could be a possibility.. Did you get gas at a different or shady place last time? If you do suspect bad gas, pull the fuel filter off and try not to spill any gas, then empty the fuel filter into a clear container and let it sit for a little while. If there is water or anything that is not gas in there it will separate and stay on the bottom. The reason I think that it could be contaminated fuel is that the fuel filter will catch the water until it goes past the opening in the side, and you said that when you changed the filter it cleared up for a while, while this could just be coincidence, it could also be a clue.

Sorry if I gave you alot if things to check but with a problem like this I always try the easiest/cheapest things first then go from there.

Have you take out the crank position sensor and cleaned it? That's worth a try since it could be sending bad information to the computer.

Very true, the crank sensor also fits the critera for the symptoms. As the crank sensor gets hotter they can fail just like any ignition part..

My old 96 SS ran great and would show a P0300 code every once in a while for no apparent reason. The car would be idling great and suddenly the SES light would start blinking. I never fully solved that problem and the guy who bought the car had it pop up a month or 2 later. The 96's are a little more touchy with the P0300 I think because they were the first year with that crank sensor setup. But it sounds like you have a real issue. The rain makes me think water is getting into something.

JS has a good point- it could very well be bad gas. Where did you fill last time?

Also, when you replaced your ignition parts, did you replace them with aftermarket or GM parts? If aftermarket, who is the manufacturer?

havent pulled the plugs yet, i was workin on it late lastnight getting everything back together after throwing the rear, etc back in Rons car. ill check that next time i work on the car and also check the gas. ive gotten gas from all of the same places that i always do. there 1 sunoco and 2 wawas that i get gas from. and i believe i would have burned all of the gas anyway on sunday night when she was running great. no appology needed i appreciate that your not having me buy a new opti lol. i may have my old opti laying around that was still working great that i can throw in there just to see if its the optical sensor going bad in my new one which would be strange at 6k miles but still possible

i never mentioned selling my car.. that was something you were resorting to... btw ill race you for that 2500 :)

Absolutely. I had a set of brand new Accel coil packs go bad on my GTP after 120 miles. Yes, one hundred and twenty. I pulled them off and put on my stockers and the misfire went away.

im gonna try to find my old one that still ran great. throw it on and see how everything goes. this will be after i check the crank sensor and the gas

if it is infact the opti... there will be a video of me blowing it up with a very large amount of fireworks shortly after the new one is installed. but im shooting for it being the crank sensor or the gas

Don't you have a shooting range on your base? That would be much cooler :mrgreen:

no but theres one around the corner from my house... would a 12 gauge slug be to your liking?

ok so no bad gas and after sitting a few days its running fine again which points even more to moisture. Crank sensor is fine (no corrosion or anything noticable) im lost as far as what to check next. any more ideas?

ignition module maybe? cam sensor? possibly the timing chain.

Its not the ignition module, the cam sensor is in the opti, and there is no way it could be the timing chain..

If the damn crank sensor wasnt $135 I would say to toss one in... Maybe someone with another 96 wouldnt mind letting you borrow one to help diagnose this issue?

crank sensors generally aren't a matter of how they "look" its about resistance values...when cold it has low resistance but when you get it hot thats when the resistance could spike which would cause the faulty or lack of a signal. They generally don't throw a code either, but at the same time when they get hot normally the car will stall, and not restart until the sensor cools...but, I'm with Josh...trying couldn't hurt...

You never mentioned what the deal was with the opti...you said you would check with your old one, but never got back to us on that, unless i missed it somewhere.

gotta try to find the old opti but its running good again lol its hard to diagnose the problem when it only happens form moisture. i have a decent paycheck coming up soon so i may throw a crank sensor in there just because and see if it does it next time it rains. just sucks when it happens on my way to work lol

maybe a crack in the crank sensor? maybe when there's a lot of moisture in the air it messes with the resistance :shrug:

... didnt i say i was checking that? and replacing it?

when it runs ok how has it been pulling? better than before I hope.. And dont forget to re-check those header bolts!

do you have any idea how things on a car work or do you just blurt random things out?

when thinking about it man i think that opti is suspect...did it run like crap yesterday when it was raining?