Ducman82

So over the last year i have been chasing this "stumble" or "cut out" that happens under a WOT/full load run at about 5200 rpm. it has this event about 2-3 times, then clears up around 6k. for the longest time i figured it was the MSD coils I'm using for my mega squirt system. swapped them out and nope, not the coils. the one thing i could get to change was if i messed with the Dwell of the coils, say go from 4.5 to 3.5ms, i could get the "hiccup" to move around, and past 6k.

well with the newer standard LS2 coils i have the coils settings back to stock.

the part that gets me is the hiccup does not happen all the time... only some times. i can floor it and have it not happen, then that the nest light ill try again, and there it is...

So i took this screen shot from my data logger. you can see my knock sensors showed some activity at about the same time as i feel the stumble. now they are the standard 928 sensors, and i have the calculations for the resonance pretty well sorted (bore diameter etc). so being that it is sensing something going on (knock, detonation).... and i run 91 octane.......... and its erratic... maybe timing?

BC

The coils double spark if you don't drop the ground cleanly, right? I can obviously be wrong, and am often, but I recall reading that the ls2 coils only want a specific dwell, and outside of that will not like it.

That could match the knock sensing as well, as if the spark happens at the wrong time, it could be igniting residual mix.

Ducman82

i have it set to factory LS2 coil settings. hmmmmmmmm

Tom. M

I'm watching this thread.

My megasquirt setup has a similar issue..for mine usually around 4k to 4.5 k rpm and some load... It just drops right out and then recovers. My aftermarket tach will drop to zero during this and then recover..and sometimes not even recover...and like yours, it didn't happen all the time.
I'm running the edis8 setup and no knock sensors...

BC

Have you guys provided logs on the megasquirt forums?

Ducman82

i have data logs for the MS peeps. they are not sure as well. after doing some digging on the MS boards, i am going to try some Dwell Battery Correction chart changes. make them match the stock GM coding.

Tom, are you getting any sync loss? have you added any resistors to the crank sensor (clean up the signal), use the tooth logger, or are you running full sequential?

jeff spahn

Subscribed for my MS install.

Tom. M

Not sure on the sync loss. I did check the spacing of the VR sensor and wheel to make sure it was optimal.

The interior of the car has been disassembled so I can't fire it up at the moment, but will look through my old logs to see if the tooth logger data is there... Not running full sequential at the moment..

yardpro

K... So my question in this thread is.... Is there any reason to convert to ms or vems if your ignition is working OK?

Ducman82

it all depends on what you want to do with the car, and how much you want to be able to control. later cars you can shark tune, early cars.. no so much.

toofast928

Duc can you monitor the injector time? Maybe acceleration enrichment is too rich. Also the TPS signal is smooth when the stumble occurs? Possible signal drop out.

And watch the AIT sensor. Could be leaning out the mixture after a heat soaking.

Ducman82

i check for TPS and IAT issues. nothing there. I'm pretty sure its a coil setting. the only odd part is it is not consistent every time, which makes me think temp/timing could be involved. but so far so good.

i plan to get the car out and run her hard in the next few days (when fam is out of town) and see how the Battery Dwell setting changes work