I really notice the problem while driving about 25 mph and stomping on the gas pedal. The engine sounds like marbles in a spray can or really bad timing. I dont have a laptop (only a desktop) so i cant see that data while driving. While parked i rev the engine and sometimes hear something but almost always the datamaster program picks up spark retard of up to 8 degrees max. Only happens if i rev the engine quickly. Usually happens around 2000 rpm. Doesn't matter what temp the engine is but it gets worse as the engine warms up. Running 91 octane gas.

Other than this problem the car runs awesome.

This is what i have done to try to fix it...
Swapped KM, pcms, MAF from another LT1. Put in new knock sensor. Programmed in original tune, still doing this.

 

how many miles on it?

age of the O2 sensor?

fuel pressure?

exhaust smell odd at all?

 

Fuel Pressue is good (42-44psi).

Lt1 has about 100K miles

The exhaust smells weird at full throttle but i have the egr and charcol canister removed and everything capped.

I know nothing about the age of the O2s. They are probably the originals.

This is also my last problem to fix in my engine swap. I have new plugs, new wires. Have replaced intake manifold gasket, valve cover gaskets also.

 

hmm...

let me think about it


also, the marbles you are hearing IS spark knock, so do not drive it until it is fixed, prolonged knock destroys pistons

 

If you can hear knock, then most definitely your sensor should pick it up. Use some higher octane gas.

 

about how many gallons of high octane gas would i need? I have about a 3/4 tank of 91 octane in right now. I think i can get some 100 or 110 octane locally.

 

fill it up with 110 unleaded if you can, or at least the highest octane unleaded you can find

 

If you do find that higher octane gas locally let me know where you got it because I need some.

 

What gear are you in when you floor it at 25mph?

 

25 is where i notice it the most. As long as i'm just crusing and then gun it, sometimes it will do it between 25-50mph.

I've done it in 3rd and 2nd. When in 1st the rpms are too high. I thought it was the torque convertor before so i swapped that with a spare convertor, still did the same thing.

I can get it too make the marble sound (barely can hear it) while in park but only when its warmed up all the way and by quickly stomping on the accelerator.

Another thing i did notice was that i dont have a ground strap or the copper braided strap that goes from the ground on the coil to the chassis like the stock LT1 cars do. Think this would cause a problem?

I have a spare used opti I could put on. Do you think the opti is a possiblility?
My Lt1 came out of a wrecked car with front end damage so it could have rained on the opti before i got it.

 

since it happens it open loop, it can't be the O2 sensors then, right??

I think this is the 3rd batch of gas i've had it on, so not the gas.

My suspects are the opti, fuel injectors. I've tested the coil with a meter and it was within spec.

Unless something is actually wrong inside the engine.

 

I've swapped plugs, fixed a header leak(hopefully), checked fuel pressure reg and injectors. Ran datamaster to see whats going on now.

At idle - For BLMs i'm seeing 108 on both sides when fully warmed up. The IAC slowly falls to zero and reaches zero when the engine warms up to about 175 degrees. Tried adjusting the throttle stop, nothing changing the IAC.

So, Vacuum leak or bad IAC???? IAC does change value (increases) when i press on the throttle.

 

vacuum leak, the IAC at 0 at idle is the giveaway, it means that the computer can't control idle speed any lower, because the IAC is closed

 

Ya can get 100 unlead or 110 leaded in 5 gal lots delivered from VP fuel. Try it and see.

 

The 108 BLM's indicate the PCM thinks its running rich, and has bottomed out the long term fuel corrections, trying to solve what it thinks is the problem. If it really isn't running rich, the BLM's might be pulling out fuel when they aren't supposed to, and causing it to run lean. You need to find out why the BLM's are so screwed up.