LSGunZ28

iTrader: (8)

Im having issues on the dyno and I dont know what it is!! I need help, I took my car to get dyno tunes on Dec 3 , wed... and I put it on the dyno, its a Land & Sea dynamometer...

I keep having spark issues around 4000rpms...

2002 Camaro Z28 M6

SLP lid, K&N, FAST 92 with PTM 95mm Tb... 402 LS2 stroker, 238/244 cam, PRC 5.3 stage 2.5 heads (862 castings)pacesetter 1 3/4 LTs, ORy , magnaflow catback... LS7 clutch, Aluminum FW, built T56, Moser 12 bolt 3.73s... 25%udp...36# injectors...

91 octane, at around 11.1 or so C/R

I have NGK TR55 spark plugs, gapped at .045", we checked and saw that the #2 cyl spark plug had a crack on the porcelin, so we replaced the plugs... No luck, replaced the spark plug wires, and checked if the coil pack connections were good, but no luck... So I drove it home from the dyno shop and today we tried to fix other poetential issues, because the alternator was getting old... we replaced the alternator and no luck, we replaced the spark plug wires again and no luck, lastly we replaced the coil packs and no luck!!

What could it be?

The power is climbing up strong til 4000 or so RPMs and then falling on its face... The Air fuel ratio is around 12.9-13.0, if im not mistaken.... The timing is pretty far back at around 23 or 26 or something like that(again Im unsure of these #s)....

I made 330RWHP @ 3900rpms and my torque at 38xxrpm was right at 440s o 440... The power is there, but spark or something is getting cut off at 4000rpms or higher, until I fix this problem I wont take it to get dynoed... Oh and it seems its more under load that this problem occurs, for example in 4th gear at 4000rpms, in 5th maybe as early as 3600rpms... under WOT...


could it be my PCM??

again the car idles smooth (but once in a while it is idling too high and sometimes falling short and stalling(but that will be fixed, because I left the dyno shop before my tuner worked on that issue)... and it has good power over 1400 til 4000 (or a couple hunder rpms less) it has good solid, smooth acceleration, but I dont know what is happening after that... I mean, the tuner said everything looks good, but that is something we are all trying to figure out...

If anyone knows what could be a potential issue, PLEASE I need your assistance...

LSGunZ28

iTrader: (8)

added info if it helps at all:

It had a previous speed density tune and it IS being tuned right now on speed density...

It does have a new 85mm MAF in there, but its unplugged, However I will be removing the MAF, when I get a straight bellow or whatever from the lid to the TB....

could it be my TPS?? ( I doubt it!!)... But I dunno, im just so lost...

12secSS

iTrader: (30)

What happens to the spark at 4000 rpms? Does the spark advance just take a dive? Is it retarding timing, can you be more specific or at least post a log of the issue?

LSGunZ28

iTrader: (8)

Im not sure, the engine misfires (I think) Ive heard detonation before and It sounds like a metallic sound, this just sounds distorted...

I spoke with my tuner and he should post here tonight or tomorrow morning...

How do I change the thread title, Im not sure he is gonna find this thread...

SweetS10V8

iTrader: (4)

I came across a similar sounding issue on a L92 engine. It would run great right to 4000 RPM on the dyno then everything would go haywire. I tried everything I knew, called LSx experts, and after a few days I found a ground was loose. Go figure.....

I would check your grounds, starting with the one to your PCM.

LSGunZ28

iTrader: (8)

I believe we checked all grounds, but I will check them again...

But if it was a ground, why only at higher RPMs, under heavier loads?? shouldnt it be the same???

SweetS10V8

iTrader: (4)

I have no answer to that one, its still a mystery to me.

elky489

iTrader: (1)

You could have maybe a marginal ignition system,and at 4k your going to make your most tq/cylinder pressure,you could be blowing the spark out,this is a easy quick check,take the plugs and gap them at .030 then do another pull.if this cures your problem you have weak coil packs.

elky489

iTrader: (1)

Also if the ground on the back side of the driver head is loose it will cause the same problem.

LSGunZ28

iTrader: (8)

im pretty sure its not, but ill recheck when i get a chance..

also we changed teh coil packs as I said and it didnt work... what are the odds if the 2 sets of coil packs are weak?

BuffJoeyD

iTrader: (2)

Get your tuner to post your tune, post a log file from the dyno pass, and post a sheet from the dyno.

Had a car die outta no where at 4500 rpm once. Came to me for tuning and saw it previously tuned before the owner had purchased it, PE was set to come in at 4450 rpm and that the commanded afr was 16.0 . Easy fix.

Just cause your tuner says it looks fine doesnt mean anything. Everyone tunes differently -

gold98Z28

iTrader: (7)

if the engine really changes its sound, and its already busted the porcelin on one or more plugs then i would look at a mechanical issue. are you sure of the CR? did you cc the heads? could the valve springs not be up to snuff?........

elky489

iTrader: (1)

Ya i always set it to go into pe at 100 rpm with 80% or higher throttle,with a nailed down ve table and a nailed down maff transfer function.

LSGunZ28

iTrader: (8)

mechanically it sounds fine... the cam is a mild cam for a 402... The heads have been milled .003 the most, from stock which were the TSP 5.3 heads... The pistons are -10cc dished!! I DOUBT I will run into PTV issues, even if I go with a Huge cam... Btw, my heads were checked at a professional machine shop for any bent valves and the springs are set right...

DaddySS

We need the tune and the log from the dyno run - otherwise we don't have much data to go on.

LSGunZ28

iTrader: (8)

Well My tuner should respond to this thread ASAP, I emailed him and linked him this thread..... So keep an eye out...

Frost

iTrader: (45)

you doubt you will run into issues? So you are saying that you didn't check it...

LSGunZ28

iTrader: (8)

There is NO PTV issues!

Haans249

iTrader: (24)

Can you post up the complete specs of your cam/springs(brand)/install heights?

Also, have the tune file and data log yet? We're all eager to help you out!

Random thought, how long did the gas sit in the tank while you were working the car over? Check your fuel pressure? Replace fuel filter?

dan@masportspeedshop

iTrader: (6)

Try checking crankshaft end-play. I had a similar problem before. Chased that bastard-of-a-problem for four days only to discover that the crank thrust bearing wasn't clearanced properly (newly built engine). Higher rpm (also around 4K rpm) and load would cause the car to literally die out and detonate heavily as the crank walked slightly causing the crank sensor to read the adjacent reluctor wheel and throw timing way off. In my 20 years of futzing with cars, I never would have guessed, and yet there it was. Crappy problem that caused someone a ton of money and me a ton of gray hair (I was beautiful once!)