Gimp98TNT

iTrader: (21)

I would think the PCM was bad like you said, just for the simple fact that you've tried everything else, but then again i'm no expert.

The couple times I welded on my car I never unhooked the PCM, but i have always unhooked the battery.

Did you try hooking up a old spark plug to #6 to see if you are getting any spark? Thats one of the first things i would have tried.

<small>[ February 16, 2003, 01:11 PM: Message edited by: Gimp98TNT ]</small>

BluVette

Todd,

Are you thinking that the injector pulse width is too great on cylinder #6 because of a faulty PCM?
Do you have the means of measuring the injector pulse width to see if cylinder #6 is longer than the other cylinders?
If it were running rich on cylinder #6 then would you see the upstream oxygen sensor on that side run richer than the other side?
Did you do a compression test or a leak down test?

It sounds like you are doing an excellent job of swapping parts (coil packs, spark plugs, injectors, etc.) from one cylinder to another to isolate the bad part.

Good luck!

Country Boy

iTrader: (24)

Do you have spark to the plug??? Pull the wire off the plug, put a screwdriver in the end, hold it near a ground and turn it over and watch for spark. You said you have compression in that cylinder, right? What about heads? Any problems before uninstall? How about the valve springs, how many miles? I had my subs welded on and didnt disconnect anything.

LS1derfull

Although not impossible, it seems unlikely damage to pCM would be isolated to poor control of #6 cyl. Usually damaged pcm will not communicate or would affect all cylinders perf.Could you have damage to crank reluctor wheel? How bad does it idle? What is your leak down in that cylinder? Did you pinch any wiring with intake swaps? Do you have aftermarket Crank pulley? Is plug oiling, and did you swap it to other cylinder to see if problem moves?

rich

I am leaning toward the reluctor wheel or crank sensor. can you run the car and do a snap shot and record all the diagnostic info while the problem exsists.

wrencher

iTrader: (2)

You need to determain what this cylinder is lacking, fuel ,spark or compresion. If it is fuel or spark, then check those out >I.E. pcm, cam &crank input to pcm etc. No damaged wiring harnesses. You gotta get a compression gauge, leak down tester & a spark tester. If it's the inputs of cam or crank have seen before (many diff. engines) with a digital storage lab scope. But the only people who use them (on cars) are profesional auto tech's & skilled ones at that. The reason I'm leaning this way is you say 6 is a dead miss & adjacent cylinders in firing order are affected. Sound familair w/ alot of stuff I see in every day vehicle's now & then. Can't count how many opti-spark I "scoped" when there problems first cropped up. This is what some of the opti- cars would do. Ls1 are alot different though, they have p/m pick ups . If it,s pcm causing the miss either it's garbage goin in to pcm from crank/cam sensors or the logic end of pcm or the output side coils/injectors, or wiring harness. This does not sound like the kind of problem to be chased down with no tools. You need to aproch this 1 step at a time , is there a local shop you can trust that can do diagnostic's? Is your car a stock bottom end? Sorry so long hope it helps.

cantdrv65

iTrader: (3)

You have to check the basics as has been mentioned. Spark? Compression? Fuel? It's one of those three <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> . Good luck!

kp

iTrader: (34)

A longshot but I have had this happen to a few cars, under the coil pack the wires get pinched on the valve cover boss - hard to see but once you look at the wiring under them you will see what I am talking about, it drove several people I know crazy until I found it by going through the wiring. If you had your coil brackets off during the install (if you have 99+ heads) that may be your problem.

Did you leak it down or do a compression test before you took it apart? You could have a broken ring/crushed ring land and the cylinder wall will still look OK sometimes..

Like wrencher said take one thing at a time, you need fuel, compression and spark for that cylinder to work - one is obviously missing..

BYBYC5

i had a similar problem on #5, you use n2o right? i metled a ring or 2 but didnt even see or could tell till i pulled the piston out. my wallwere nor scrated or anything but i pulled it cuz i had a gut feeling and sure enuff, the looked awfull

Reckless

iTrader: (9)

OK guys...I appreciate the replies! Think I have isolated the problem. I started thinking after this post (along the lines of what LS1derful said). Was thinking it didn't make sense for only #6 to misfire if the PCM was flaking out.

Since I used a NOID to test the injector signal, I thought all was well with the wiring. Just for the hell of it, I used the OHM meter today to check for continuity, and guess what? Intermittent on #6 injector feed.

So I made a few nicks in the wire to probe for discontinuity and voila! Wire was broken internally about a half-inch up from the injector plug on #6. Damn was I happy <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Won't fire it up until tomorrow, but she's mostly back together, except for the intake. I am pretty sure this will cure my woes.

<img border="0" alt="[gruffy cottonball]" title="" src="graemlins/gr_gruffy.gif" />

Todd

Jason99T/A

iTrader: (21)

Great to hear Todd! <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> Electrical problems SUCK! lol

GeorgeC

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Reckless:
<strong>Wire was broken internally about a half-inch up from the injector plug on #6. Damn was I happy <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Don't you just hate problems like that???

I had a rare intermittent problem last year. Once in a great while, the car would just feel like it was laying down a bit for a split second during a WOT run... It ended up being the connector that plugs into the MAF!

Glad you found the problem. Too bad you tore the motor down as far as you did. <img border="0" title="" alt="[Frown]" src="gr_sad.gif" />

Jason99T/A

iTrader: (21)

Todd, I forgot to mention. You can order a new injector pigtail from GM for around $10 or so. It comes with a new connector and wires already attached. Just cut and splice, and you are good to go.

I have had to do this for the Veh. speed sensor and the oil level sensor.

Jason

<small>[ February 16, 2003, 09:41 PM: Message edited by: Jason99T/A ]</small>

Reckless

iTrader: (9)

Been battling a misfire issue with my #6 cylinder for over a week now. Until today, I have tried everything short of pulling the head. Well I did that today to inspect the hardware further. Still can't find any sign of a hardawre issue anywhere. I thought perhaps a cracked ring land, but the piston and walls are near perfect:

<img src="http://www.cofba.org/users/reckless/misfire1.jpg" alt=" - " />

Well, maybe it's a valve spring or bent valve? But the valves all seat great and the springs were fine when I took them off for inspection. I also pulled the lifters out and they show no signs of foul play. The pushrods are perfect. All I found was 3 carbonated, but dry exhaust ports, and one grimey exhaust port (#6). Doesn't really seem oily though, more like wet carbon from raw gas.

<img src="http://www.cofba.org/users/reckless/misfire2.jpg" alt=" - " />

<img src="http://www.cofba.org/users/reckless/misfire3.jpg" alt=" - " />

On the intake ports, 2,4,& 8 all show signs of life with some grimey, oily substance in there, but the #6 intake port is clean as if nothing is happening in there, or at least abnormal (no pic).

The cam is fine and the rockers all check out fine, and I have been through all the wiring. I swapped coil packs, noid tested the injectors plugs and swapped injectors to different cylinders, and swapped around plug wires. I even installed the stock intake, but still get consistent misfires on #6...with intermittent misfires on #2 (fires right before #6) and #5 (fires right after #6).

All of this started with the car in the garage for a direct port installation. I thought the problem was the Holley intake not sealing and causing the misfires, but the misfires persist with the stock LS1 intake on the car.

The heads were assembled by TEA and have less than 500 miles on them. Even if a guide was bad, it would just burn oil right? Not cause a noticeable misfire and poor performance? The head gasket (Cometic) is perfect. Basically no sign of a hardware failure anywhere.

That leads me to my personal diagnosis, the PCM. Why? I was an *** and didn't disconnect the battery and/or computer when I welded a bracket onto the front bumper support as part of my direct port install (relocated my radiator overflow). I suspect the PCM got zapped when I welded, and now is amuck.

ATAP and LS1 Edit still work fine, but the #6 cylinder is having misfire issues. So basically, no signs of hardware or wiring issues. Why would there be? I was simply removing the intake and installing the instake several times.

Sorry this is so long, but I want some other opinions from you techies out there. I plan on sending the PCM out Monday morning unless you guys give me a reason not to.

Louis

iTrader: (7)

<img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" />

Reckless

iTrader: (9)

Thanks Jason..you don't happen to have the part number for that do you? If not, that's cool. I can call GM and get it.

I agree though...electrical gremilins suck *** <img border="0" alt="[bang head]" title="" src="graemlins/gr_banghead.gif" />

Todd