random/multiple cyl missfire

[JerzLT1]

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.

[Camvill]

ill give you 2500 for it

[deadtrend1]

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.

[JSPERFORMANCE]

-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.

[JL8Jeff]

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.

[JSPERFORMANCE]

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..

[JL8Jeff]

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.

[WildBillyT]

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?

[JerzLT1]

-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.

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

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

[WildBillyT]

my new one which would be strange at 6k miles but still possible


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.

[JerzLT1]

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

[ar0ck]

http://img.photobucket.com/albums/v215/FistFullOfDinero/Myspace/optiavatar.gif

[JerzLT1]

http://img.photobucket.com/albums/v215/FistFullOfDinero/Myspace/optiavatar.gif

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

[ar0ck]

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:

[JerzLT1]

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

[JerzLT1]

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?

[bubba428]

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

[JSPERFORMANCE]

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

[JSPERFORMANCE]

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?

[IROCdan330]

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.

[JerzLT1]

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

[bubba428]

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

[JerzLT1]

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

[JSPERFORMANCE]

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

[IROCdan330]

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

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?

[98tadriver]

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?

It seemed like after idling or cruising at low rpm, it would misfire a bit. As soon as you open her up, it runs like a raped ape! and then seemed fine after that. josh (86formula) also noticed it was smelling a bit rich as well. possibly fouled
plugs?

[JerzLT1]

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?

well the day it ran fine i ran a vette and walked him which is good and it feels stronger then before. at this point i still need to get the crank position sensor in it to see if that clears anything up then im just throwing a new opti in it. and it ran fine all day till i hit a spot in the road where alot of water was running across and it started acting up again. 6k on an opti would suck but i just want her fixed at this point. and now even when its running ok its still got a misfire that i can hear which im pretty sure is fouled plugs so im going to pull all of them tomorrow cause its supposed to be nice out. this is turning into such a project lol

[98tadriver]

think, youll be walking more vettes when its fixed!

[IROCdan330]

i feel bad seeing you go through this man...sucks when its on the internet because all we can really say is "try this part." Throwing parts at it generally will fix the problem eventually but only after a good bit of money is spent, unless you get really lucky and get it on the first or second shot. New defective parts suck, too, because you have it dead set in your head that "i just replaced that part, it cant be bad." I have gone through it a bunch of times.

If you hit water and it started acting funny...i would think maybe there is a hairline crack in something that you cant see and its allowing water in, causing the spark to find its way to another cylinder, path of least resistance...

As far as the rich smell, I wouldnt condemn the plugs so quickly...these cars generally have an ignition that could clean a plug off relatively fast if everything is working up to par...depending on quality of said plug and all...
If i recall you dont have cats, and you are taking a lot more air into the engine than before...and on a stock tune it may run a little more fat...next time you scan it check out the Block learn multiplier values (aka long term fuel trim) and see where its at...

[JSPERFORMANCE]

I would still pull the plugs and inspect them for cracks in the porcelan and possible fouling.. When you are looking at them a magnifying glass will help or of you are in doubt just replace them..

[98tadriver]

i can plug in hp tuners and do a basic scan and see the LT and ST fuel trims if that holds accurate

[Stevoone]

Have you checked for any vacuum leaks? From what i have seen with crank sensors is when there bad the car will not run or when they get hot the car will stall and not start till it cools down. Not so much with the Pontiac's but we get a lot of Caddy's with sensor problems. Do you know what your MAP and BARO sensor readings are?

[JerzLT1]

Have you checked for any vacuum leaks? From what i have seen with crank sensors is when there bad the car will not run or when they get hot the car will stall and not start till it cools down. Not so much with the Pontiac's but we get a lot of Caddy's with sensor problems. Do you know what your MAP and BARO sensor readings are?

no i havent checked for Vacuum leaks but this seems much more like ignition, over the next couple weeks all of the ignition is getting replaced down to the opti, some of its due anyway, and i will check the plugs as you said Josh. just have to wait till a little more money comes in. christmas did me in a little bit. thanx for all of the info guys. do you have HP Tuners Dan? i have the log file saved that has all of that on there

[IROCdan330]

no i havent checked for Vacuum leaks but this seems much more like ignition, over the next couple weeks all of the ignition is getting replaced down to the opti, some of its due anyway, and i will check the plugs as you said Josh. just have to wait till a little more money comes in. christmas did me in a little bit. thanx for all of the info guys. do you have HP Tuners Dan? i have the log file saved that has all of that on there

Nah man, no HP Tuners for me at this time.

[JerzLT1]

ill give you a call and see when you can stop by bestbuy, ill just bring my laptop with me and let you check it out

[JSPERFORMANCE]

Vacuum leaks are usually not intermittent. Also definately check the injectors, if one was getting weak it could hang open once it has cycled for a while and make the car run rich and have a big miss at low rpm's.

[JerzLT1]

where 2 of the plugs were arching i believe.
http://i36.photobucket.com/albums/e29/BeanieBamf/IMG_0561.jpg
http://i36.photobucket.com/albums/e29/BeanieBamf/IMG_0563.jpg
but the tips look fine, not fouled or anything
http://i36.photobucket.com/albums/e29/BeanieBamf/IMG_0562.jpg
http://i36.photobucket.com/albums/e29/BeanieBamf/IMG_0564.jpg
http://i36.photobucket.com/albums/e29/BeanieBamf/IMG_0565.jpg
http://i36.photobucket.com/albums/e29/BeanieBamf/IMG_0566.jpg
my guess is that moisture got in at the plugs and became the path of least resistance so it was arching there rather then on the tip. seems to be running much better now with the new plugs but well see how long that lasts.

[JSPERFORMANCE]

Not sure if I can see an arc track but the plug tips look damn good, I am impressed that they arent way off since you have a stock tune.

[JerzLT1]

well putting all new plugs in actually cleared up the problem, im going to inspect them more to see if i can find any cracks in the old ones but it runs alot smoother and all and no missfire.

[JL8Jeff]

In that first picture it looks like that black streak through the 'R' could be a crack. Do you wipe it off and look at it closer? Good to hear it's running better. Gotta love the simple and inexpensive repairs.

[JerzLT1]

In that first picture it looks like that black streak through the 'R' could be a crack. Do you wipe it off and look at it closer? Good to hear it's running better. Gotta love the simple and inexpensive repairs.

that would be anti seize. ok i was wrong, its still missing but not like before. only at low RPMs and it probably wouldnt be noticeable if i didnt drive the car every day. i can hear it in the exhaust and its causing a vibration in the car as well. next paycheck im probably replacing all of my ignition parts other then the plugs obviously cause theyre brand new. but other then the low RPMs she runs GREAT

[JSPERFORMANCE]

now its missing at low r's? I know you were careful but are you sure you got them all in properly and undamaged? Gapped correctly? Its strange that the symptom changed with new plugs. That does tell me that you are on the right track..

[JerzLT1]

yeah i checked and double checked all of the gaps (.050) and didnt drop any of the plugs. could it have been a combination of plugs and wires?? im thinking maybe it was the plugs and something else that was causing it so im gonna start replacing some cheap things and see where it takes me.

[WildBillyT]

that would be anti seize. ok i was wrong, its still missing but not like before. only at low RPMs and it probably wouldnt be noticeable if i didnt drive the car every day. i can hear it in the exhaust and its causing a vibration in the car as well. next paycheck im probably replacing all of my ignition parts other then the plugs obviously cause theyre brand new. but other then the low RPMs she runs GREAT

You used a very light coat of anti-sieze, only on the first few threads- right?

[JerzLT1]

ask josh, he reinstalled my plugs when he had the car lol looked like there was a generous amount on there

[JSPERFORMANCE]

When I install plugs in alu inum heads I always use anti sieze on the threads. Dosent matter where you put it, it will spread around as they are threaded in.

Did you ever get around to replacing the coil wire?

[JerzLT1]

When I install plugs in alu inum heads I always use anti sieze on the threads. Dosent matter where you put it, it will spread around as they are threaded in.

Did you ever get around to replacing the coil wire?

yup did that almost right away.

[WildBillyT]

ask josh, he reinstalled my plugs when he had the car lol looked like there was a generous amount on there

Eh, I'm really just throwing it out there as a random possibility. I tracked down a misfire once that ended up being a smearing of copper anti-seize on electrodes, but I can't imagine either one of you being that messy.

[JSPERFORMANCE]

alright, I got a plan for you.

Get then car in a garage and make it as dark as you can in there.

Get a windex bottle and fill it with water and set it on the mist setting.

Go to the car, start it and start spraying down the ignition system while the car is running (do not put your hands near spinning objects) when you hit the weak spot in the insulation it will studder and make blue arcs that you should be able to see very easily.

[BonzoHansen]

alright, I got a plan for you.

Get then car in a garage and make it as dark as you can in there.

Get a windex bottle and fill it with water and set it on the mist setting.

Go to the car, start it and start spraying down the ignition system while the car is running (do not put your hands near spinning objects) when you hit the weak spot in the insulation it will studder and make blue arcs that you should be able to see very easily.

How old skool of you. I have a spray bottle of water in the garge for that. :)

[JerzLT1]

new symptom, took the car to the car wash (she was dirty) and was pretty careful not to get the engine bay wet. so i took it down a back road to dry the car off and it started missing (like it has been since it started after it sits for about 10-15 mins when its at operating temp) the difference this time is that my airbag light started blinking for about 10 second and shut off. could it be a short? and why would it only happen when its at operating temp and shut off for 10-15 mins?

[Pampered-Z]

How old are your wires and what brand? I don't see anyone mentioning replacing the wires other then the coil, which is a common problem with corrosion. I had a few cases of wires going bad, after markets that don't fit in the stock holders can easily be cut through trying to force then unti the holders or by the belt or pullies where they run behind the PS pump, or even just damaged from the headers. I chased a freaken problem with the car shuddering badly after it went into closed loop and the engine was up to operating temp. Chased it for weeks and found out the #6 wire burnt just slightly on the header and was arcing to the knock module and it never threw a code!

Make sure the wires are run so they aren't near anything or against each other.

Are you running the stock heat range on the plugs? If the car is that rich maybe the colder plugs are adding to the problem?

If you think it's injector related, I have a set of stock 24lbs you could borrow.

It's very, very rare on the newer cars, but on the 93-94s there were also some cases of the harness on the top of the engine being bad causing intermittent problems with injectors not firing - actually pairs of injectors not firing ( batch fire back then and wired in pairs). With your car running poke around at the wires, wiggle the harnesses and such and see if anything happens.

Moister may not be getting to the opti but maybe leaking or sitting back by the ECM harness? I would look at that wiring as well.

JB

[JerzLT1]

How old are your wires and what brand? I don't see anyone mentioning replacing the wires other then the coil, which is a common problem with corrosion. I had a few cases of wires going bad, after markets that don't fit in the stock holders can easily be cut through trying to force then unti the holders or by the belt or pullies where they run behind the PS pump, or even just damaged from the headers. I chased a freaken problem with the car shuddering badly after it went into closed loop and the engine was up to operating temp. Chased it for weeks and found out the #6 wire burnt just slightly on the header and was arcing to the knock module and it never threw a code!

Make sure the wires are run so they aren't near anything or against each other.

Are you running the stock heat range on the plugs? If the car is that rich maybe the colder plugs are adding to the problem?

If you think it's injector related, I have a set of stock 24lbs you could borrow.

It's very, very rare on the newer cars, but on the 93-94s there were also some cases of the harness on the top of the engine being bad causing intermittent problems with injectors not firing - actually pairs of injectors not firing ( batch fire back then and wired in pairs). with your car running poke around at the wires, wiggle the harnesses and such and see if anything happens.

Moister may not be getting to the opti but maybe leaking or sitting back by the ECM harness? I would look at that wiring as well.

JB

my wire are 7k miles old and about 4 months, theyre Taylor custom cut wires, theyre not run near theyre not running that close to anything and theyres no damage to any of them, i checked when it started doing it again, if it was plugs why would it be so intermittent? i would think it would do it all tthe time if it was that.

ill check out the harness near the ecm and also check the injectors, still kinda curious as to why my airbag light would go off....

[Pampered-Z]

Plug wires can do odd things once heat gets to them. If you had to cut them and put the clips on them you should double check them.

[98tadriver]

i figured out my mom's blazers misfire problem. time actually mightve helped me lol. it stopped saying random/multiple cylinder misfire and said cyl 5 misfire. i changed the plugs, cyl 5 looked crappy. after the plugs were installed, i put the wires back on. i used the cyl 5 wire for cyl 3 (i didnt cross them) and cleared the codes. cyl 3 misfire. ripped the wire out of there and sure enough, it was burnt! lol. so i bought new wires and its fine now :)

[oh one ls1 SS]

im going threw this **** right now man.. its sssoooo aannooyyinggg!!!!!!

[JerzLT1]

yeah fortunatly my ignition system isnt all that expensive except for the opti which i have a plan for, im going to replace all of it and if that solves it ill switch to the Delteq system and i shouldnt really have to worry about my opti at that point.

[JerzLT1]

seems like my problem is fixed, replaced the MAF and had Brian from PCM4less tune it as per Josh and its a totally different, now the only light thats on on my dash is the low traction light :)

[IROCdan330]

seems like my problem is fixed, replaced the MAF and had Brian from PCM4less tune it as per Josh and its a totally different, now the only light thats on on my dash is the low traction light :)

Did he dyno tune it for you, or did you just go ahead with the mail order? I remember Josh saying something about Brian being in the area which is why i ask.

[JSPERFORMANCE]

Nah since Josh's car only has bolt on mods there was no need to strap it to the dyno. Brian has so much data on LT1s that there would only be a minimal difference.


Oh yeah Dan,,,,,,311rwhp for Dads ride..

[JerzLT1]

oh and the car is fine even in the rain, and after sitting for 10 mins and firing it back up. seems like the problem is sloved.... still curious about that airbag light though

[98tadriver]

oh and the car is fine even in the rain, and after sitting for 10 mins and firing it back up. seems like the problem is sloved.... still curious about that airbag light though

thats awesome to see that shes running great again!! as for the airbags, TAKE EM OUT!! lol or pull the fuse so they dont go off

[JerzLT1]

back to the drawing board, no missfire code or anything and no check engine light, wont idle unless i blip the throttle then it will for a second and the idle starts getting choppy. wont maintain RPMs at anything below 3k. IAC or TPS?

[98tadriver]

hmmm thats what I would think, but im no LT1 expert lol. check vaccum lines and such?

[JerzLT1]

car is being dropped off at JSPerformance today. while its still acting up. just dont have time to diagnose the problem :(

[98tadriver]

werd. i hear that dude!

[oh one ls1 SS]

ever find out what was wrong with it?

[JerzLT1]

O2 extensions, water was getting in em. car is GREAT now :) thanks again to Josh lol