leaman griffin

montecarlo... i think i have ruled out airflow because I have cranked the engine with both valve covers off and watched the valvesprings function correctly...

leaman griffin

also i can hear sucking through my intake when the truck is "idling" haha..

sicksspeed

iTrader: (2)

And I assume you verified that there isn't a over fuel condition as in pull those plugs and they are not soaked. How about ruptured fuel pressure regulator diaphragm. Just passing thoughts.

leaman griffin

yes i checked the regulator.... seems to be fine.. not leaking through to my vacuum hose. as far as the overfuel, hard to tell because my plugs seem a little black but not soaked... which could be caused by multiple problems like firing at the wrong time and the air movement in the cylinder is blowing out the spark....

leaman griffin

thank you everyone for all of the suggestions....

sicksspeed

iTrader: (2)

Here is another way to check compression, cylinder sealing. Hook up compresion gauge like normal and fire the motor up. Preasure will be lower than regular test but you can watch it under normal conditions and release the preasure repeatedly and watch it build then swap to a good cylinder and watch how it acts. I found a problem this way before that regular compresion test missed but a leak down test was also was questioned.

Iam Broke

Since the PCM was from a different engine ect. verify the correct firing order in the tune if you haven't.

S8ER95Z

iTrader: (3)

Can you post up the tune file?

Old Geezer

iTrader: (3)

"Any thoughts before I start pouring money into the car. "

Maybe, start your own thread??

aknovaman

iTrader: (7)

Pm me your email and I can send you a config to use with hp tuners to see exactly which cylinders are mis- firing. It's pretty easy.

CattleAc

iTrader: (7)

I have to ask...did you change intake manifold??? Gaskets???

Every 1999-2006 5.3L I had come through the shop this winter with any kind of mileage on them needed intake gaskets...

Lots of P0300 codes, lean codes, poor idle, high idle.

S8ER95Z

iTrader: (3)

Wrong thread? Did I miss a post?

1FastBrick

iTrader: (16)

You did. There was another post above but it was deleted by the user.

Since Old Geezer didn't quote it properly in his reply, it can't be seen.

The part in parentheses is part of the quote from the deleted post.

S8ER95Z

iTrader: (3)

That makes way more sense...I even searched the page to make sure I wasn't going crazy. haha thanks!

NJ 666

Was thinking this reading the thread. Maybe those 2 cylinders are firing on the exhaust stroke Maybe the coils are wired to the ECM incorrectly. .

joecar

Looks like you should obtain a wiring diagram and verify the correctness of all the wires/connectors.

95wannabe

iTrader: (20)

Soon as read your original post, I thought of the 4/7 firing order swap from SBC days. I'm not familiar with tuning software...do you tell the PCM what the firing order is?
If old school SBC guy put it in, it may be why 2 & 3 were wrong also. If memory serves...didn't the LS firing order swap 4/7 & 2/3 from SBC firing order?

joecar

Ls1: 1-8-7-2-6-5-4-3
sbc: 1-8-4-3-6-5-7-2

RENE'S RAGE

iTrader: (96)

cracked or broken valve spring.
Need to pull the springs on those 2 cylinders.
Can't tell by looking at them installed.

Stormed_Norm

iTrader: (10)

Any progress on this? Curious as to what the problem was.