..............

 

ttt.... any help?

 

Does the HP go up after 5000 rpm?

What about injectors?

 

Check the thread again.

At 5000rpm it starts misfiring and loses hp.
I also have new injectors.

 

I had a similar problem but it was off of idle. Turned out to be injectors but maybe you got a bad set or one?

 

Many times it is the coil pack wiring harness. Have you tried switching them out to known good ones?

 

Another thought, I 'assume' when you had your cam installed, a CKP Variation Learn was performed?

http://www.seattleautomotive.com/ckpdoc.htm


Required when chaning a cam, so the PCM knows how to detect a real misfire.

When my cam was installed, the tech did not perform the re-learn, and just like clock work, I would get the blinking SES light between 3000-4000rpms!

You'll need to find a shop with a Tach 2 scanner, even the dealer can do it if you want to pay thier price tag....or I think HP tuners can also do the re-learn.

 

I had the problem before i got the new injectors so it couldnt be the injectors.

I switched out coil packs and plug wires from another camaro that is running good and it didnt change a thing... still misfiring.

Yep i had all of that taken care of when the cam was installed.


Thanks for trying guys... keep the ideas coming. The shop that specializes in LSX cars is lost and so am i. They have never seen this kind of problem before and neither have I. TSP didnt have any suggestions either. SO IM LOOKING FOR ANY IDEAS NO MATTER HOW CRAZY THEY SOUND.

Thanks

 

I did read the thread. In the past, some guys have had misfires at high RPM and then power came back afterwards. I was trying to help you by asking if this was the case with you.

 

A few things come to mind:

1) Are you sure that you have the correct length pushrods for your new heads?

2) Are you sure that the lifter preload was set correctly?

3) Make sure that all of the coil pack connectors are snapped in all the way (been there, done that)

4) Are you using stock rocker arms? There had been some instances were aftermarket rocker arms have puked out after 5,000 rpms.

5) Are you sure that the cam was dot-to-dot (could be a tooth off).

6) Only other thing I can think of is the tune might be off.

 

1. Yes these are the ones that TSP recommends for the LS6 stage 1 heads.

2.Im sure the connectors are snapped in all the way... cause they have been put on and removed at least a dozen times with no changes.

3. yes im sure the rockers are stock. The car was bone stock with i bought it.


4. I dont think it could be that. Cause it ran good for a while and then all of a sudden the misfire started and we have tried everything to get it to go away.


I misunderstood your question... my bad. The car never recovers from the misfire. Once it starts misfiring at 5000rpm it just keeps misfiring.

This is one hell of a mystery.


Thanks for the replys.

 

I'm assuming with your new heads you had all new valves/keepers as well... When you bent the valve did you perform a compression check on all the cylinders to make sure it didn't screw anything up internally? If it drops off that quickly it sounds like oil could be getting past a ring (or rings) and causing detonation. At least that's the only thing I can think of off the top of my head right now.

 

Yep i did a compression test and everything was good. I think my compresssion in most of my cylinders was around 168 with a small percentage difference in a couple of the cylinders. This is what it showed even with my bent valves... i guess my dual valve springs were strong enough to make it sill to give it a good compression reading. Either way i know this is not my problem.

Plus i dont think it could possibly be that consistant.... you can lay the dyno graphs on top of each other and they are identical... 5000rpm misfire everytime and continues to misfire all the way to redline.

 

bump...

 

try changing the fuel filter if you haven't and clean your fuel rail and check the screen's on the top of the injector's to see if there is any dirt getting in them. it all may sound stupid but I've have had similair problem's with a fuel system that wasn't clean. had a bad filter and clogged injector. when I swapped out the other injectors and such I failed to clean the rail's and problem cam right back. btw put a wide band o2 on the car and check your reading's that will verafie if you have a fuel problem for sure.

 

Yeah when you tested fuel preasure did you watch the gauge as you ran the rpm's up on the dyno. You could be running out of fuel up top. The only other thing I can think of is when a buddy of mine had his computer(accel gen6) setup for the wrong number of injectors by accel and that caused a miss at higher rpms.

 

That was my best guess, my dad had a miss last year that was bad and we found out the fuel pressure was dropping off at the other end of the track. Not sure if that's your problem here just a guess.

Good luck man, I hate mystery problems like this.

 

I changed the fuel filter about 5 months ago so i doubt its that. The old one that i took out even looked pretty clean. I can change it again for the hell of it and maybe check my fuel rails but i dont know if it will change anything.

Im assuming the shop watched the gauge when they ran the rpms up but im not sure. Ill ask. I know they saw the a/f on the dyno and it looked fine... so i dont know if its even fuel related.

There is a couple of things that i want to check with the fuel to see if it makes a difference. I hope it does.

 

bump......

 

Maybe a few of your lifters are starting to fail and as your rpms increase the lifters just bleed off and the valves are not opening fully or staying open the degrees they should, causing the misfires.I know it's alot of work, but if you've tried everything else and nothing has changed, buy a new set of lifters and see what happens. Good luck!