Getting frustrated...Need Help!!!

[Mr. Luos]

Set-up....
LQ9 402, Patriot Stage III LS6 62cc, TSP 248/254 629/622 113, FAST 90/90, Morel (lunati) lifters, Kooks 1 7/8.
Bunch of other stuff, but you get the idea.
Pistons are -12 Mahle's, plenty of clearance. Not the problem though.


I got a base tune on it. Basicly a break-in tune.
Replaced O2's, cleaned MAF, can't find any vacuum leaks.
Car starts up right away after reseting the computer OR after it sits for a while. Otherwise...it takes the pedal to the floor to fire.
It will idle when it first starts for about 30 seconds...then it starts getting lower and lower until it dies.
Backfires through exhaust when the idle starts to decrease under 900.

The one thing I checked over and over again was the timing set. Made sure it was perfect. Rotated the motor over...still good. Did this a couple times then put the cover on.

If I try to drive it, it stumbles anything under 3500 RPM's pretty badly. Fighting to accelerate, and backfiring.
Above 3500, it seems to go fine.

Tune??
Something mechanical??
Ideas welcome!!
I am coming very close to giving in and taking it to a shop. I have done the work myself to this point and I just want my car running again.

[Bombguy99Z28]

What pushrods / rockers are you using? The Morels have a different height.

[Mr. Luos]

Pushrods are 7.400. Stock rockers.

Are the Lunati/Morel lifters shorter or taller than the stockers?? I would guess taller.

[RainMan]

It will idle when it first starts for about 30 seconds...then it starts getting lower and lower until it dies.

Next time you fire it up have friend monitor the engine vacuum, until it dies, let us know what you see. Then check your pushrod length, with the Morels you may be holding the valves slightly off the seats at TDC.

For the following suggestion:
Before you flame me for being an idiot let my explain my thinking. . . .Bombguy99Z28 has a valid point. . . . .This can be a possibility if your pushrods are now too long due to increased Hyd lifter height with the LSX non-adjustable valvetrain. When the engine is off and sets for a while, the lifters will bleed down, especially if there is excessive preload (pressure) on them. That would explain why the engine will start and run. But as the lifters "pump up" the change in the rocker geometry will cause the lifter to go into hydraulic lock and cause the valve to eventually lift off the seat, especially if the hyd plunger in the lifter tries to bottom out. It will feel like you have a massive vacuum leak and will backfire. Just depends on whether the Intake or exhaust valves are being held off seat as to where your backfire will occur (Intake/Exhaust). Your intake vacuum will drop drastically as this happens.

Go beg, borrow, steal, or buy a push rod length checker tool or an adjustable pushrod for the LSX engines. If you have to buy one then follow the directions included. Otherwise. . .Pull off the driver side rocker cover, manually rotate #1 to TDC compression (Both valves should be fully seated and closed). Remove #1 Exhaust push rod. Adjust checker a little shorter than your pushrod, and install. Reinstall and torque to spec's the rocker, then adjust checker for 0 lash at rocker, and tighten it. Remove rocker, then checker, compare with regular pushrod you initially removed, if Hyd lifters then add about ..030"-050" to compensate for Hyd lifter preload with the non-adjustable LSX valvetrain. If the difference is excessive, you will need custom length pushrods.

Forgive the stupid question but, . . Did the Hyd lifters specify shorter pushrods? The Cam? With the aggressive lift you are running, the base circle that was ground into the cam, coupled with possibility of a taller hydraulic lifter plunger height can have a dramatic impact on the required pushrod length.

If none of the above is an issue then. . .
Did you degree the Cam? What are the Spec's on the Cam Card? I/E Open / Close, LSA, Cam ground advanced or straight up, installed advanced or straight up? If all else fails you may want to consider the possibility of a bad grind!

When you say:

The one thing I checked over and over again was the timing set. Made sure it was perfect. Rotated the motor over...still good. Did this a couple times then put the cover on.

You are obviously referring to the timing chain & Gear set! Correct.

If you throw your hands up and relent to an engine shop, have them degree the Cam & verify the Cam Card.

As I said, it's an off the wall suggestion, but what can it hurt. It's something else to check and verify. Remember, valvetrain geometry is very critical, and is sometimes overlooked as a potential source of problems.

http://www.carcraft.com/techarticles/116_0401_push/

http://www.holley.com/data/TechServi...20Geometry.pdf

http://www.grapeaperacing.com/tech/valvetrain.pdf


PM Sarge, he is building a nasty LQ9 402, may have some other suggestions/idea's.

Keep us posted. Curious to find out what the problem is.

[Mr. Luos]

It seems the the pushrod length is off.
My problems are exact to anothers. Backfiring and not running.

His pushrods were roughly .075 too long and holding the valves open. Sputters and doesn't want to run.
Seems mine are just the same. About .075 too long.
Cam is installed dot-dot. Straight up.

I will check out your ideas later this week. Too much going on tonight...plus I am looking for new pushrods ASAP. Of course...I want to know what I need length wise. Betting on 7.325".

[Bombguy99Z28]

I know from experience... I ran morels, checked the pushrod length with a checker, but could only get pushrods locally in .050 increments, mine fell about dead middle. Did a lot of trial and error, instead of getting a custom pushrod made, I raised the rocker shaft with a .020 shim that I made from some sheetmetal stock. That probably would have worked, except dicking around I managed to tap all the valves and destroy the lifters... ooops. So I slapped another set of heads on there that I had laying around and put some stock lifters back in. I was out basically a set of morel lifters and fuggered up all the valves on my AFR heads.

But I learned a lot... lol...

I'd ask around and see if a shim would work... probably be a lot cheaper than new pushrods. But don't do it because I tried it, I'm just a driveway mechanic.

[Mr. Luos]

I figure I can sell the 7.400's that are in it now.
The 7.300's should be here tomorrow.

[Bombguy99Z28]

Cool. you think you banged any of the valves?

[Mr. Luos]

Naw.
Pretty deep reliefs in a already dished piston.

Probably find out soon though. Took the old 7.400's out last night. Cylinders that should have had both valves closed even had the springs come up ever so slightly.
I will report back later tonight as long as the pushrods show today.

[BIG D's SS]

Man I hope that fixed your problem. That is gonna be a badass mofo when its done.

[Mr. Luos]

TSP did me VERY well. Overnighted them from Manley for me.
Pushrods are here...will get at it here in a few.

[Mr. Luos]

That was the problem.

Finally heard this car running properly for the first time.

I have wood.

[RainMan]

Sweeeeeeeeeeet!

Glad to hear it wasn't something terminal! Get that beast on a Dyno tune and let us know what Warp factor you hit!

[Mr. Luos]

Will do.
Hell...the daily driver probably isn't going to see much drive time anytime soon.

[Mr. Luos]

Idle is set at 1150 RPM's. WAY too high. When I get a chance...I will drop it to about 1000 RPM's.
http://home.comcast.net/~mrluos/thirdstart.wmv

[Bombguy99Z28]

Hot. Glad everything worked out and nothing was damaged.