Ms2 Engine exhaust popping

[ttbrendan]

I have a 70chevelle twin turbo 383 sbc, ls2 cop, 83# low injectors, AEM dual signal distributor.relay board.
I built the ms2 years ago before ms3 and

I cant get the engine from popping out the exhaust . Sometimes you can find a sweet spot where there is little to no popping but as soon as you give it gas violent popping starts. This has never run and 1st time for ms2. I have had the AFR's low and high also tried fixed timing but that hasn't solved the popping. Checked timing without car running and was spot on, but once running don't get a good reading with timing light.
Wondering if the pwm circuit can be making some kind of noise?
I know I have lots more tuning on the start up,warm up, cranking but don't like to run motor much more with the popping.

Thanks for any help
Brendan

[benckj]

Not sure if this will help but I had a similar issue and I tracked it down to my intake cam gear being off by 1 tooth. Did the same as you with checking & changing VE plus spark table with some improvements but wasn't until I re-positioned cam belt it all came right.

jim

[mjhillen]

How many Ignition outputs are you using? How many Injector outputs are you using?

The first thing i notice is that you have fuel set to batch fire with 8 injectors, If you are using a "Waste Spark" ignition setting then i think you are fueling on the exhaust stroke too.....thus the boom in the exhaust. I'm no pro with the MS systems but i think that's where your problem is.

[ttbrendan]

I'm using 8 injectors 4 on each bank.
8 coils 2 on each output.

[jsmcortina]

How many Ignition outputs are you using? How many Injector outputs are you using?

The first thing i notice is that you have fuel set to batch fire with 8 injectors, If you are using a "Waste Spark" ignition setting then i think you are fueling on the exhaust stroke too.....thus the boom in the exhaust.

There's an inlet valve that stops that being a problem.

James

[5.0Thunder]

Coils wired correctly?

[rickb794]

Popping in the exhaust can be caused by a number of things.

Spark at the wrong time

Fouled spark plugs

Intake valve not opening

Exhaust valve not closing

Cam timing (note - cam timing will affect all cylinders if it is a good correct cam for the motor)

[ttbrendan]

New spark plugs.
Checked base timing while engine was cranking.
Checked and double checked coils paired and ms2 spark matched.

But running can't get good timing to check
Like something is randomly adding in extra coil fires

May have to check for bent push rods.

[grom_e30]

what coils and how exactly are they wired to the ecu?

[ttbrendan]

The coils are LS2 truck coils. Used 18436572 firing order. Pair spark A(1,6) B(8,5) C(4,7) D(3,2). I used the factory harness that was in the van I got coils from. Ecu signal wires are going throught the relay board. Coils are grounded to block and to same location as the ecu.

The motor was assembled by a professional shop,not to say they didn't make a mistake. Cam is a custom ground for my application.

[rickb794]

Are you over dwelling those coils at 5.5ms?

[mjhillen]

Are you over dwelling those coils at 5.5ms?

Im running those coils with 3.5ms dwell,.5ms spark and no issues ever. i have read that 4-4.5ms TOTAL time is max safe setting.

[ttbrendan]

I will try changing dwell. And report back.

[ttbrendan]

New log and tune.
I couldn't even get all cylinders to run. There is either electrical noise or ?
You can see I was losing signal constantly. I don't know how it can be so inconstant. I have put so much time into this not sure where to go from here.

[rickb794]

Non-resistor plugs?

Low resistance plug wires?

Grounding see Section 3.2 of the fine manual?

[grom_e30]

and how exactly are you driving the coils of the ecu via the resistor method or by the fet method? and are 2 coils being driven of each output?

edit: your rpm signal is all messed up may need to take a comp log of it

[rickb794]

Low impedance injectors need the MS2 well grounded. Pins 15-19 should go to the motor. In extreme cases there is s board mod to route the injector ground current off the board.

Sensors should ground to the ms not to the car see section 3.2

[rickb794]

Is the distributor VR or hall/optical? Dual sensor?
So that is like a CAS for a Chevy?

[ttbrendan]

Distributor has dual hall/optical. I did ground the engine wrong and maybe others I will try to fix and report back.
All help has been appreciated.
Brendan

[ttbrendan]

Should I keep the relay board or discard it?
Brendan