Can't seem to diagnose issue at ~4500rpm and >85kpa
 

So i've recently put an MS3X into my NB8A, starts ok (still doing cold starts), idles great, drives fine at low loads, and cruises fine.

I have however had an issue that I cannot seem to track down the cause, and figured i'd ask here in case some extra eyes can spot something I'm missing.


Basically, when trying to do any pull, around 4500rpm and 85kpa or more, the car just hits a wall, Suddenly bucks, stops revving, etc.
AFR spikes to full lean as soon as it does it. Not too sure if it's actually lean, or if it's a misfire and the unburned fuel is causing a false lean on the AFR.

I've tried dumping fuel in those cells, same thing.
I've tried taking fuel out, same thing.

I've done a composite log, and it's not losing cam/crank sync.

So yeah, short of me just pulling more fuel in frustration and seeing what happens, any thoughts?




Specs:
99 NB8A (Aust spec)
MS3X
Flowforce LS coils
AEM X Series WB02 (mounted down near bellhousing)
GM IAT
OEM injectors


Log and tune attached.

Thanks all.

I'm away from my tuning laptop, so I can't open up your tune/log right now. It's possible your launch control is engaging by mistake. When I'm street tuning other cars and it hits a wall like that around 4-5k rpm it's usually launch control engaging. Try disabling it and go for a drive.

I'll give it a go over the weekend.

Just looking at the laptop, it does have Launch control/2 step etc active for some reason.


Although, it says "enable launch when TPS above 90%"
And I've been having this issue at a TPS as low as 45%ish (consistently at the 85kpa range though)

regardless, i'll turn off the launch control, since I wont be using it (no idea why it's active anyway)

Sounds like you're n/a, but check your "overboost protection" setting to make sure you've got ~20kpa of headroom there. Spark blowout also seems unlikely with LS coils, but I'd try closing the gap on the plugs to see if that helps as well. Those were the 2 things, along with disabling launch control, that have cleared up misfire issues under load for me in the past.

First change the accel enrich tpsdot threshold from 1000 to 25, zero accel above from 2500 to 6000, full accel rpm below from 600 to 1500 and test drive.
https://cimg9.ibsrv.net/gimg/www.mia...67802f853d.jpg

You can look at the status fields to know if you're going in and out of things like launch control, overboost protection, etc. It doesn't look like you're going in to anything that would cause a misfire. Your fueling and ignition settings seem reasonable and you don't have any wild changes around the problem area. An oxygen sensor reads oxygen not fuel. When the engine misfires you end up with a bunch of unburnt oxygen in the exhaust. Extra oxygen is going to show up as a lean condition because it's assumed that there wasn't enough fuel to combust with the oxygen. I would disable EGO correction until you can figure out your misfire.

I don't see an issue with the tune that would cause your problem. I would be looking at spark plug gap and doing resistance measurements on the ignition coils.

Long time between posts, but figured I'd update for anybody else having the issue.


After trying new coils, relocating IAT to reduce heat soak (even putting it outside the engine bay for a test)

The issue was finally found while talking with a mate who used to have an MS3

I was missing a single ground lead on the ms3x plug.

So under high injector load it was tripping the polyfuse.

A single lead from one of the 3x grounds to the power ground on my adapter board seems to have sorted it.