Hey everyone, sorry to bother everyone im just trying to get a feel or understanding for my problem i do better with these things when its more directed towards my problem and not something similar but slightly different or sounds similar but is completeley different.

Anyways i've had this problem for awhile now, but with life events gettting somewhat hectic i had to park my car and put it off for the time being. The problem is a misfire which i know can be so many things. This misfire DOESN'T happen at idle or freely reving. It happens with the car in any gear(m6), i have yet to try reverse, between clutch release and 3000rpms.... Its like a sputter which is highly more noticable in higher gear at lower rpms and then bam around like 3k rpms bam its like vtec kicked in and everything clears up. I had a fuel gauge on it and besides dropping pressure on prime fuel pressure seemed decent mid 30s around town driving and such, 43 at idle/ that was back in early october. I then had to move and had a lot going on so i parked my car and would go out and start it on the ocassion. Well about 2 weeks ago i went to go for a start and click click battery dead jumped it charged it took it for a little drive still had the issue.... and the battery wouldnt hold a charge. Battery was still under warranty so i replaced it and just put it in yesterday. Replaced my positive battery terminal scrapped some corrosion off of the positive terminal for it was slightly gunked on there and hooked it back up. Started the car up and took it for a cruise to the pep boys down the street to get coolant for my grocery getter.

While driving i noticed that the sputtering was still there but seemed noticably weaker like it was almost diminished. But then once we left it got worse again still not as bad as it was before i parked it. My question is could corrosion really be that bad it cause a misfire only under 3k rpms. Thats the part i don't understand it clears up and im curious why and what all i need to check. I really wanted to spend my tax returns working on the chassis of my car but its looking more and more like i have to take it to a shop because i don't feel like dealing with this.

I replaced the plugs originally when the problem started also. Need to check my spark plug wires but im looking for the logical reason for something like this to happen. Also i noticed extreme timing advance when its sputtering like 40 some odd degrees and split fuel trims long term. My scanner does not show knock count or air fuel ratio though, o2 sensors seem to be operating efficiently not hanging up around a certain area. Car runs extremley rich like enough to burn you eyes.

mods are
280xfi comp cam 230/236 113lsa
le2 heads with ported intake and 58mm throttle body
36lb injectors
pacesetter no emissions header and ory
madz28 mail order tune

withint at least 2k miles or less i've replaced opti, waterpump, spark plugs wires.

driving me nuts i'm hoping to get this running right soon so i can get it dyno tuned around march....

 

sorry for the long post wanted to give good back story and description


also heres a video i shot back at the end of october beggining november.... pardon my wife haha talking in the video, and you can somehwat here it clear up and at one point im in 5th gear and car has some loud afterfire out the exhaust like gun shots before i put it down a gear

 

Do you know what codes you are throwing? If my ears are not deceiving me it actually sounds like you have a dead cylinder, as in one that is not firing at all, however being OBDII and if your crank position sensor is in working order you should receive a flashing SES.
What I would suggest is to start the car and then pull each injector clip off one at a time. Pull it, listen to see if the idle changes. If not, plug clip back in and move to the next injector. If you pull one where the idle doesn't change then you've just found your dead cylinder. I'd also get the codes read which can be done at any parts store for free. When it's dark, open the hood, start the car and give the engine a few revs using the throttle body linkage and see if any plugs are grounding out on the headers/manifolds/block. I'm thinking your problem is downstream of the opti. When is the last time the plug wires have been changed?

 

wires were changed in july, plugs i did when this all started, at idle and above 3k rpms it seems pretty good it clears and and idle is relativley smooth but i will try the injector clips, i have a code reader thats how i get most of my data its just not gm specific so no knock counts. I get the flashing ses light ocassionally but lower the gear raise rpms and it usually goes away , no codes are thrown but i had my misfire code deleted for it was giving me issues, was going to have it re enable when i went to get it dyno tuned.... i thank you for the help and at some point today i will try and check the fuel injector clips. I have at night looked for spark jumping havent seen any but i will look again tonight after i leave class.

 

Also, make sure all plugs are on their boots securely. Both on the plug side and opti side. They can be finicky sometimes. My guess is one or more plug wires are damaged and are grounding out. Your plug wires cannot come into contact with the exhaust at all. Doing so they will burn out in a hurry.

 

i learned that on my first batch of wires and tryed harder to keep them out of the way, i just ahd the car running though and i think cylinder 8 fuel injector is probably bad, only one that didn't seem to have any real affect on idle, but i will still check wires and such tonight, i plan on otvc set eventually but at the time of putting the car together and everything i was extremley strappped for time... also i have extremeley split fuel trims, what would cause this, it measures in percent and not blms though, lt im at like 25% bank 2 and im usually real low sometimes in the negatives long term bank 1?

 

Highly doubt the injector is bad. It's more likely the plug/wire is/are bad. You can either get an auto stethascope or even a broom handle and butt it up against the injector to see if you can hear it actuating.

 

i'll give it a try like i said im going to check all my wires later, just want this thing to start running right so i can enjoy it on some liesure cruises this summer haha, thanks for all the help ill post what i find out.

 

hey back again, went to school tonight before hand i checked plugs, wiggled them a bit and they were all on snugg, looked for arcing, only reved engine maybe 2500 rpms when i was looking no body tends to like the sound my car makes around here, haha, no arcing that i could see from up top, listened to fuel injectors all ticking like they should be, i really am stumped..... what a pain in the *** this has been

 

anybody else got any ideas?

 

I would look at your wires again. Especially #8.

 

Is there any way possible to get a hold of a scanner that can monitor misfires while you are driving or when it is missing? This would really help.

 

its a plug wire. The reason it idles fine is because there is a lot less pressure inside the cylinder. When the pressure increases, the resistance between the electrode and ground strap also increases. Electricity will find the least resistant path. The distance between the burnt place on the wire and where it is arcing to ground is probably three times the distance of your plug gap. This causes the current to go to the plug under light engine loads, but starting jumping when a higher load occurs.

 

well i guess ill be overlooking wires again, im glad everyone cleared it up logically to me and i thank everyone for your help, i'll report back with what i find either tomorrow or thursday. Again i really appreciate all the answer i get on these forums, no body has to go out of there way to help educate someone they don't know on the forums thanks.

 

What wires are you running? Check the porcelains for cracks too.

 

they're cheap wires i needed them semi quick, i was in the process of getting ready to move accross country, was hoping they'd last a little longer oh well

 

hey guys just an update, figitted my wires around a little tryed to look at them the best i could, more off feel then sight though no access to get the car up and i have them routed real funky. They are prime suspect for sure, after moving them and unplugging and re plugging them making sure they weren't really touching anything i went for a test drive, car ran freaking great for like a minute haha, little sputter letting off the clutch but cruised real nice down about 2 roads then it startd acting up, so they're prime suspect that and my ignition control module. Needless to say im going to taking the ICM off and have it tested, also what is the best way to do otvc setup with msd wires, anyone sell a kit still pre cut or should i try cutting and crimping myself?

 

The ICM works or it doesnt period there is no in between. Pull the wires and resistance check them and see if they are within spec. Chances are you are in need of a new set of wires. Buy heat protection boots and a pack of zip ties and go to town securing them away from your headers and be done with it. Let us know how you make out.

 

misfire/stumble at low RPM UNDER LOAD often indicates a spark issue.

I went through this and replaced wires, plugs, opti, ICM, coil, PCM (had all these as spare parts)...same thing. Yes I looked carefully in the dark for any arching and sprayed water to see if I could find something...nada

when I was under the car while engine was running with laptop hooked up banging all kinds of stuff to see if somwething was causing knock retard....BINGO I looked up and could see #7 plug boot arching against the boot heat shield

Yeah I felt stupid for replacing all the parts and assumeing everything was on right but glad to see the hard fact of the arc

pulled the heat boot...made sure the boot was settled on plug and no problem now

My point is even though you think you check your shiat out...Really, I mean really confirm you have seen every angle of every plug wire to determine if there is arching going on

 

i read on corvette forums that icm was cause of some of there misfires, either way spark plugs are my main culprit right now, waiting for pay day or taxes to come back whichever happens first and i'll be ordering a set of msds and some protectives for it, there is still snow all over the ground so i didn't bother jacking the car up and laying all over the snow haha.... but i do have 2 metal boots on my plugs might have to check that haha