Chris,

Glad to hear a new opti did help somewhat.

Good luck on your further tests....

 

ok-have you checked the alternator while running to see if its producing any ac voltage? 300mv and above is too much. throws noise down the line where it shouldnt be. that practice of pulling the cable off the battery while the car is running has the potential to cause problems exactly like what you are going thru now. thats a huge old nono where do you think the spike goes when that cable comes off the terminal? that practice was incorrect decades ago when all ya had to blow were diodes-now you name it itll send the electrical componentry into a tailspin-problem is that the spike dosnt usually kill the component-it just makes it behave in some really oddball ways-sound familiar? if the component that was spiked, died, you would know what to fix.

 

I've been having a somewhat similar problem still. My SES light will not go away and it flickers like crazy when i acclerate at higher speeds (70-80 mph) I've changed the optispark, coil, and wires, and even the crankshaft position sensor. i put the car under my mechanics scope and everything seemed normal. we even tried using a lower resistance wire and that seemed to help a lil bit but not much.

when they scan the car while driving all cylinders go way off the charts as far as misfires, but the car is running smooth as ever and you cant feel anything so its obviously electrical.sometimes cylinder 7 will show tons of misfires then the next time it shows no misfires at all. so everything is inconsistent. my car is not cutting out or anything and runs fine. but im trying to sell it and do not want the potential buyer thinking something is wrong with the car when they see the light. the next thing im gonna do is to gap the plugs higher and change 02 sensors...if that doesnt work what should i do????? please help

 

can anyone help me?

 

You'd get more replies with a NEW thread since this one is about my ongoing issues. Most aren't even going to look in here if they've already read this thread before.

Personally, if the scope read OK and the components, opti, coil etc. are fine, then its probably NOT electrical/ignition. The crank sensor could be picking up vibrations that are too minute for you to see/feel. Has a compression check been done? What about checking for broken valvesprings or misadjusted valves? Fuel system? Fuel filter new? What about fuel pressure or injectors?

If you read through this mammoth thread you'd get every suggestion you ever wanted for fixing a missfire.

 

Just from experenice in working in a dealership you sound like you have a bad PCM. You may want to check conuity on the wire and also voltages. I seen stuff like this all the time and it usually is a bad brain. I seen them do the same thing when you reflash them. you may want to check into this a little further.

 

the autoshop did put a new PCM in, but when they scanned it all cylinders were still showing random misfires everwhere you cant feel anything. so i just put back in the old pcm so i wouldnt pay for a new one that didnt help. if the O2's and gapping the plugs for higher spark, the guy said he wouldnt know what to do after that...he's pretty stumped himself and he knows his ****.

 

Chris,

I know you and I were in somewhat of the same boat, so I've got to ask. Have you done a compression and leakdown test?? That turned out to be my problem. Just food for thought.

 

Leakdown, no, but compression yes, look at my posts from Saturday.

I am working this evening on it. Going to lean up #7 cylinder using cyl balance tables in LT1 Edit and see if I can get it running as hot as the other 7 cylinders. Hoping that if I can acheive that the vibration will go away at least somewhat and the fuel trims will balance right to left.

 

Ah, sorry, forgot about that. Did you ever get to the passenger side??

The #7 could be suspect with the 195, but not that bad. When I was seeing how choppy your dyno graph was, that looks like it "should" be something electrical.

 

Update:

Finally have some good news. PUt the car on the dyno yesterday.

First pull...NO CUTTING OUT!!!!! But only 343hp. But you have to remember I have my cats in right now for emissions testing. It was real rich too, 11.8-12.0:1. Second pull I leaned it up some and made 346 still only like 12.2.

THird pull I left it in overdrive and completely wasted the pull.

4th pull I leaned it up a little at part throttle and then a tad at WOT and made 353...I think that's within range considering the cats....362 was my best last year with the offroad pipes in.

So no ignition problems. It did fuss and buck a tad at 72mph while waiting to go WOT but we figured out its because I'm getting way too much timing, 47* !

So I just need to work on the part throttle timing and pull a couple of degrees there. I think the vibration I'm getting is part cam and part the #7 cylinder being down on compression. But clearly no ignition issues whatsoever. I'm borrowing a leakdown gauge so I'll test #7 this afternoon.

I tried friday night adjusting the cylinder balance on #7 to lean it out and get it hot like the other cylinders but even -3% didn't seem to help.

I think part of the cutting out may have been where they put the dyno's inductive pickup last time. The day it was running so poorly they clamped onto the coil wire that goes to the opti rather than the #1 plug wire. I thought it was odd but they said it was common practice on the LT1 (every time I've ever dynoed before then its been on #1). Well yesterday he cliped it to the feed wire that goes to the coil from the ICM..said he gets a much cleaner signal. I have a wierd suspicion I have been chasing ignition demons for 6 mos that weren't really there, and its all really been about the #7 cylinder and whatever's going on there mechanically.

 

Man, good luck there. I'll keep my fingers crossed that you don't have a serious leakdown problem on your hands. Glad to hear you're getting it narrowed down though.

 

Good to hear Chris!

Sounds like you are really starting to narrow the problem down, which is #7.

Let us know what you find out!

 

I feel your pain, Chris, and we're with you with our fingers crossed!
Keep us updated!

 

Am I an idiot or just mislead by wierd circumstances? You make the call.

According to the leakdown there's nothing wrong with cylinder #7. Results were the same as #1 both held the psi very well.

Took it to a friends house to use his compressor, a fellow Fbody owner (94NOTOPZ on this board, 11 sec procharger powered 355 camaro convertible). After looking at all the evidence, he seems to think I've just got a case of good ole cam lope. He did agree the idle vibration was a little wierd but nothing too out of ordinary considering the size of the cam.

#7 plug wasn't so rich anymore either, its good and brownish-white like #1.

Maybe I was a victim of circumstances all this time? I had a wierd lope/vibration that I ignored for a long time. Then I get the car on the dyno and its cutting out and missing so we think there's an ignition problem that I think it was really dyno operator error in terms of placement of the inductive pickup where it disrupted the spark.

In trying to fix that problem I put an autozone opti on the car, and I get a new problem, the car dies on me after it heats up. I misinterpreted that as the "miss" getting worse. After finally figuring out they are different problems, I replace the opti and now the car runs w/o dying....then I get on the dyno and discover its not cutting out anymore either, and then a leakdown test shows nothing out of the ordinary on #7 cylinder and its not running painfully rich anymore either.

Everything but the funky vibration seems to have been taken care of or proved false.

I bought a cheap infrared pyrometer today that I'm going to use to fine tune the cylinder balance at idle...hopefully will get that #7 cylinder good and hot like the others and maybe even out my split fuel trims too.

I'm going to drop in a set of 3.73 gears this spring and shoot for 11s. Might as well drive the crap out of it at this point.

Thanks everyone for your suggestions and support...though now I feel like I've wasted everyones time on this adventure.