Injuneer

Cross-firing is not limited to adjacent cylinders. It can happen anywhere two plug wires are close to each other.

tanmanski

GaryDoug or Injuneeer. Ok, I have all the pieces. ElmScan install was easy. GDScan enhanced GM parameters file downloaded, but resulted in no change to ElmScan menu, i.e "Enhanced GM parameters" is not present in menu yet. I suspect I've missed a step somewhere?

tanmanski

I understand your point Fred, but I don't think opposite bank wires cross anywhere do they? so at least it would be reasonable to suspect wires arcing to each other IF 1, 3 or 7 are misfiring with 5?
Anyway, I'm struggling to figure out why "enhanced GM parameters" has not appeared in the ElmScan menu now I've downloaded Gary's software? I must have missed a set up step?

Injuneer

Correct, wires run in separate banks. My point was not to suggest that cross-firing was possible across banks. It was simply to state that the cylinders do not have to be immediately adjacent to each other (1-3, 3-5, 5-7).... e.g. 1 & 7 might cross-fire if the wires were near each other. The factory setup has the guide grooves near the Opti, and spacers between wires in each bank. But, given the age of the car, who knows how the wires are currently routed.

Gary will have to answer the ELM question.

GaryDoug

You don't use the ELM menu. You run the GD-scan2a.exe file from the download.

tanmanski

I understand, thanks Fred

tanmanski

Hi Gary, sorry, I'm a bit of a computer dork....I need ultra KISS instructions!
I've unzipped the file and tried to run the exe but nothing seemed to happen?

OK, progress! I figured out where my laptop decided to hide the file and opened it from there and now I have the dashboard! Very cool, thank you!

So, you & Fred need to see a "log file for misfire count by cylinder correct"?
I'll try to capture one right now & post results within the hour!

thanks Gary

GaryDoug

You don't need to make a log file necessarily. Just copy the 8 misfire readings from the table.

tanmanski

very good, thanks Gary, data to follow shortly

tanmanski

or not...
Gary I sent you PM. laptop connects to car no prob, but im getting error msgs and no data

tanmanski

Yes! I finally have good data on which to base my actions! many thanks to Fred & GaryDoug for their help and patience (especially Gary)
I don't think there's any question what's going on here right? I'm guessing #5 wire is burned up and occasionally arcing to #7. I'm returning Opti and buying wires and plugs instead. Despite codes pointing to #5, I could never see or feel any problems with that wire, with engine running, so it must be where that I cant see or feel it.

What did I learn? Don't waste time and money replacing suspect parts. Get the data, it will (usually) point you in the right direction.

Thanks to all who contributed. I hope to post an "all clear" message tomorrow!

11a1 00 00 Engine run time 0
1206 00 Misfire Cyl#1 0
1205 00 Misfire Cyl#2 0
1207 00 Misfire Cyl#3 0
1208 00 Misfire Cyl#4 0
11ea 00 Misfire Cyl#5 0
11eb 00 Misfire Cyl#6 0
11ec 00 Misfire Cyl#7 0
11ed 00 Misfire Cyl#8 0
1201 00 00 Misfire History Cyl#1 0
1202 00 06 Misfire History Cyl#2 6
1203 00 00 Misfire History Cyl#3 0
1204 00 00 Misfire History Cyl#4 0
11f8 2C 61 Misfire History Cyl#5 11361
11f9 00 00 Misfire History Cyl#6 0
11fa 00 F1 Misfire History Cyl#7 241
11fb 00 00 Misfire History Cyl#8 0
114e Fuel tank pressure (V) 100197.4148
1297 Fuel tank pressure (inH2O) 8835.929
1172 IAC Position (count) NotSupported
1179 82 IAC Position (V6-96/97 count) 130
1143 22 Throttle Position (Volts) 0.6664
1234 00 02 Mileage since last code clear 6
1250 MAF Frequency (Hz) 2560149
1155 Fuel tank level (Volts) 109188.954
12c5 Fuel tank level (%) 129109

moparman

Yep, plugs and wires will probably clean up the problem. Number 5 had a few misfires, lol.

tanmanski

When I told the shop I wanted to have #1, 3, 5 & 7 plugs and wires replaced they looked at me like I was from outer space, lol. I finally agreed to do all 8, but $425 labor! Then again I've done plugs and wires on an LT1 before and its no fun. I'm hoping to post up "all clear" later today.

tanmanski

My love/hate relationship with the LT1 just hit a new low...

This game is breaking me, financially and mentally. Interface cable = $35. Code scanner (wasted, now I have interface cable & right software) = $70, 8 double platinum plugs & "model specific" wires = $80, labor to replace 8 plugs & wires = $425. Results to show for $600+? NADA!

Just got the car back from the shop, EXACTLY the same symptoms (I told them what I wanted done, not to try to diagnose it....they think I'm an idiot of course).

Finally got the scan software to work again (sorry Gary, didn't have time to move the file as you suggested, so that's my ineptness at personal computers)

Bottom line is cylinder 5 is virtually, but not totally, dead (misfire codes P0305 &/or P0300 and GM Enhanced parameter logs proving #5 rarely fires except at just perfect conditions (about 3k RPM with ~50% throttle & minimal load). Cylinder 7, which had been showing very occasional misfire, which I assumed was from #5 wire arcing, is currently firing virtually 100%

All 8 removed AC plugs looked worn (some erosion, fairly large gaps) but normal. They're could be OEM. I've never changed them. The car has 115k.

All 8 removed Packard plug wires look good to fair. I think I see a little age cracking on #8 (irrelevant to the symptoms by code). #5 & 7 look good, no burns, chaffes or corrosion.

So, other than drinking to alleviate the pain from my bloody forehead, what am I doing? Thinking dark, bad thoughts....

I'm going old school here, but could this be a worn cam lobe causing less than normal valve opening? I don't hear much more than "normal" LT1 rocker clatter when cold but maybe a slight "tick" at idle? Do a compression check? (Taking out the GD plugs AGAIN!)

Or am I back to the bane of our existence, the opti? Carbon tracking in the cap? hi volt terminal on #5 coming loose? Good thing I returned the one I bought LAST WEEK, when I bought plugs this morning

As always, really appreciate the advice I've received on this board, but I really need help now! In keeping my sanity amongst other things...

Thanks guys

tanmanski

Ok, after more (sober) thought, I think my plan is to go for Opti replacement after all. But I'd really like to hear other opinions

I admit I don't understand how the ECM detects individual cylinder misfires (is it simply looking for no spark energy discharged or is it looking at firing out of sequence/time), but I'm thinking a stuck valve, lifter or bad cam lobe would have other symptoms, like coughing and backfiring through the intake?

Since its basically a single cylinder misfiring, I cant see how it can be the ICM. Process of elimination is leading me straight back to Opti.

Is the Duralast Gold opti acceptable? I need an opti I can get today or tomorrow without waiting for one to be shipped to me.

thanks guys