old66tiger

OK...I have been chasing this for awhile and I am hoping that someone here can lend some support/ideas.

Specs:
525 HP GMPP crate motor 1000 miles on engine
Dougs Headers 3" exhaust with X-pipe. Graphite exhaust gaskets.
Spectre Intake with the MAF mounted per GM spec
Speartech custom harness and E38 ECM - base tune to start with several iterations of tune
The harness is made to 85" in length from the drivers side head to the ECM. The ECM is located behind the drivers side headlight.
I have a Innovate LM-2 dual band O2 monitoring O2 on both banks
Fuel supplied by Ricks fuel tank, 255 lph pump, corvette regulator/filter mounted back by the tank. -6an TFE hose everywhere.

So, the base tune from speartech was used to get 500 miles on the motor before I started playing with the tune. The base tune popped P0300 codes everytime that it started cold and the guy that is doing the tune massaged the P0300 code out with the tune and I am not seeing any more codes. He is located 120 miles from me and we have been e-mailing tunes back and fourth trying multiple things.

Main issue:
The car has a constant RPM stumble between 1500 and 3000 rpms. Less noticeable at a higher RPM but it is still there. If I get on it and I am in open loop, the engine pulls decent and the pull is smooth and the O2 appears to be steady. When cruising in closed loop between the subject RPMS, the LM-2 shows a swing in O2 readings with more variance on the right side than the left side. The O2 on the left side might vary between 14.2 and 15.0 where the right side it varies between 13.8 and 15.5 or better. The right side variance is more erratic where the left side is smoother and more controlled.

Thinking that I had a problem on the right side I have tried the following:
A new set of plugs, wires and a different set of coils with no change.
I swapped injectors left to right one-for-one in the cylinder order and there was no change.
I swapped O2 sensors left to right with no change.
I did find that the intake was loose from the factory so I pulled the intake and inspected gaskets and re-torqued to spec with no change.
I used a scantech 2 to monitor misfires and while a few were detected, there is no smoking gun here. No codes showing misfires

All grounds are tight and the system voltage is constant and steady. Before I go any further with tuning, I want to swap fuel pressure regulators to see if I have a faulty regulator. I am thinking about doing a leak down test on the motor to verify that there is nothing wrong with the motor.

I am running out of ideas and getting pretty frustrated. Speartech tells me that there is little to no chance that it is the harness or the ECM. I think that it is odd that I am seeing variance on one side and the stumble is occurring at the same time I see the O2 swings.

Getting close to sending this thing down the road.

jimmyg

Check fuel pressure . If using corvette filter reg , only use a wix or gm

Jimbo1367

Old66tiger,
Very well wrtten. Best of luck

jcvett56

Those fuel trims number seem high, but the variances you see between them are normal. The 525 motor has a pretty aggressive CAM and it's not uncommon for people to have some of these issues really. I've heard of shops removing the CAM from these and go to a less aggressive cam. This alleviates the bad running issues. Hopefully the leakdown may reveal something but unfortunately it may just be the 525 LS3 acting normal.

Suck you are having this issue but those cams are just crazy and not to streetable.

Old Geezer

iTrader: (3)

You state that you and tuner are "trading" tunes. If so, and you have the tuning tools, can you post the tune and the data log[s]?

old66tiger

All leakdown numbers looked good. Most were 1-2% with #7 being as high as 7%. Nothing there scares me.

Can I attach the EFI live tune file to a post? We will be doing data logs this week when we get the dashboard configured properly. This is a real interesting deal. I am not a tuner so I am at the mercy of the guy that knows this better than me.

Project GatTagO

iTrader: (7)

The ASA cam is perfectly streetable. I have one in my 5.3L and it purrs like a kitten. The difference is that I have a Holley Dominator ECU which uses dual wideband sensors for feedback in closed loop. An ASA cammed engine is just not very happy at the 14.7 commanded AFR that the GM computers and narrow band O2s work best with.

Bob and I hung out on Sunday and his GTO is super sweet. Real nice driver and it RIPS! However, there is a slight surge at light loads which I suspect is caused by a slightly lean condition. I don't know enough about tuning the OEM computers, but if Bob's tuner can figure out how to make it slightly richer at cruise, then the surge will be gone.

Andrew