Popping Under boost at 3800.

[lethlz]

Hi Gentlemen,

I am new here just recently buying a ms3 extra. I originally had a hawk c12 control the engine.
In the brief it is a early 350 Chev stroked to a 383 with bowtie heads and forged bottom end 10.5;1 it has a procharger D1SC with a 7 inch on the crank and a 3 inch on the charge. Manifold is a victor jnr E with 95 pound injectors and 4 barrel like throttle body.
Transplanted dizzy from what I think is a late commodore, it has two hall effects one triggering 8 times every two revolutions of the crack and the other triggering once every two for the home signal.
It has two bosch 044 pumps and a BG fuel regulator. I am running full sequential and ls1 Coils.
The problem I have is that when the car hits 6 pounds of boost at around 3800 it starts to pop from the exhaust.
This I have done is lower the VE, Raise the VE, changes plug gaps, changed to 4 prong plugs, Added a ground from the coils to each head, then I lowered the dwell from 4 to 2 and it hardly pops now and has hit about 8 pounds of boost at around 4200.
I was wondering if anyone can explain why the improvement from lowering the dwell. I think I might be masking the real problem. I have attached a log of the last drive. In this log i was adjusting the dwell and even though it shows timming error with 2 as the dwell it significantly fixed the issue.

I would really appreciate some help.
Thanks
Marco

[Matt Cramer]

What sort of ignition module are you using?

[lethlz]

Hi Matt,

I am using LS1 coils directly out of the msextra, they have a igniter built in and connected straight to the second db37

[Matt Cramer]

Some LS coils will trigger early if you overdwell them; that would account for why lowering the dwell improved the running.

[lethlz]

I had the dwell set to the reccomended 4.
If I let off the throttle at 3500 until 4500 and put the boot into it, the popping was not there.
If they fired early would that be more advanced and ping or pop through the intake?
What does the timing error indicate in my log?
Thanks

[Matt Cramer]

The timing error is how far off the trigger teeth are vs their predicted position, but right now it's not a very useful value as it literally changes every time you see a tooth on the crank, and the sampling rate is very slow compared to that. They've discussed finding a way to calculate something more useful for future code revisions.

[lethlz]

Ahh thanks, so I still have the problem, hopefully someone can suggest what to look at next.

[Matt Cramer]

First question - are you sure it needs 34 degrees of advance at 7 psi? That sounds like a bit much. It also seems to have TPSdot AE false triggering a bit under full throttle.

[lethlz]

I have tryed lowering and raising the timing and no difference. I am not sure what tpsdot is. Ill have a read. I still have the problem. I changed my Procharger pulley and took it for a
Test. I obviously had less power so I changed the dwell back to the recommended 4ms. It felt better but after a wide open throttle I lost number 6 coil. Maybe this was the issue the whole time. I will replace it tomorrow and post then.

Thanks

[lethlz]

No luck!! Changed the coil but still have the popping. I have now dropped the dwell to 2ms and it is nearly not there now but not sure if I am loosing power this with lower dwell.
Is there something I can try to identify what it is or can it be that the dwell of 4ms is just too much?

[Matt Cramer]

TPSDot threshold is in the Acceleration Wizard. It is the minimum rate of TPS change, in % throttle opening per second, that triggers the acceleration enrichment. Increasing the number makes it less sensitive to noise.

[S.Bretz]

Does the code add dwell for accel enrichments? It might be seeing manifold pressure change to quickly hand ramp the dwell back up temporarily to a value that is causing you issues.

Hmmm.... there used to be a dwell catagory in the log viewer and I don't see it.


Are you spark plugs a cold enough range? I was having issues with plugs around 18psi with heat range 7 (NGK) plugs and nothing helped until I put in heat range 8's (one step colder).

[jesse408]

If you find the cause, please post!
I'm having the same issue and can barely get over 50% throttle before what sounds like a lean pop/backfire.

[wasted income]

If you find the cause, please post!
I'm having the same issue and can barely get over 50% throttle before what sounds like a lean pop/backfire.

Ditto, I'm having the same problem. Turbo 6.0L LQ4. My brother and I are about at our wit's end.

[Matt Cramer]

Those with similar issues, please post your own data logs and MSQs - you may not actually have the same problem.

[lethlz]

Just realized I didn't post the found issue. The pin on the distributor was damaged.. I put a trigger wheel and fixed everything.