evilstuie

Hi Guys,


My 0411 swap is giving me the ***** in a big way.
After endless troubles and trying to get everything to even fit, and bricking 2 PCMs with faulty flash software, I'm at my wits end.


My build is a 400SBC, with AFR heavily ported heads, XR270HR cam, HSR intake, 10.4:1 compression and 4L60E transmission, with a 0411PCM running a mafless tune from a LS1 HSV Holden Commodore.


When I crank the car, it sounds like it might almost start, but then backfires and coughs and splutters.


I've set the vortec dizzy about 5 times now, and yesterday I took the hood off the car so I could stand in the engine bay and make sure the alignment was perfect and get the oil pump shaft lined up properly as well.


Everything has power that should, crank signal is coming out fine, no DTC codes are shown, although the commodore tunes have a lot of stuff turned off. No crank relearn DTC, nothing.


Fuel pressure is on 48psi, I've tried adjusting from there up to 58 and still nothing.


I've triple checked the harness pins are correct for the change in firing order, the PCM tune has VATS removed, cylinder bank assignments adjusted, and still doesn't want to fire up.


How many degrees out does the timing have to be for the car to not start?
And how many degrees out to cause backfiring?


The last two things I can think of is the fuel injectors need cleaning as LX_SS has suggested, or one or more coils are bad.

How can I test these to confirm all are working, or can someone suggest another cause for this issue?

LX_SS

When i checked my LS injectors, i removed the fuel rail from the manifold, put a plastic bottle(cut down 2L) under neath one, and connected only that injector (wiring). Then cranked the engine. You could see if the spray pattern was there or it was simply dripping.

Coils = Have a spare spark plug, just take each lead one at a time, plug in the spare plug and test.

These two points are more likely to cause bad running/non running issues.

However the fact that when yours tries to fire, it backfires seems its a timing issue but it wouldn't hurt you to check those items anyway.

I remember when i was tuning an aftermarket ecu on a turbo 4 cylinder years ago, the ecu timing was locked static @ 0 degrees. This made it hard to start, poor idle, and sound very flat. Soon as it was changed and set to base timing of 10 tdc it was running perfectly.
Point is timing can make a huge difference.

Another example i remember from a 202 Holden 6 engine that i had years ago in a torana, ditched the shitty points system of the mallory dizzy and went to a proper electric dizzy. When i put the new dizzy in i accidentally put it in 180 degrees out and it caused a whole lot of backfiring. Rotated the engine 180 degree, put the dizzy back in and spot on.

Since yours is a conversion, can you manually crank the engine so piston 1 is tdc, then check where the ecu thinks the engine is at ?

evilstuie

Hey LX_SS,


Yeah I suspected it was in at 180degrees off to start with, but I removed the valve cover and confirmed it was at TDC on #1 on the compression stroke and could turn the pushrods with my fingers, so that was definitely right. I also lined the "8" marking with the triangle on the vortec dizzy, slid it in and checked the movement matched what the youtube videos did.


I'm going to check the injectors and coil pins for the 4th time, but I'm pretty sure they're all right. The one thing that could possibly be off is the harness could actually be flipped, and right side is firing when the left should be...
Highly doubtful...but possible.

LX_SS

That harness issue would cause the backfiring like your saying.

When you had it at TDC in the ecu did the crank/cam sensors show the same ???

evilstuie

Not sure, I didn't see. The scanner I'm pretty sure said 0 degrees advance when it was cranking, but I was able to see the crank and cam signal data itself.


Just had a quick look at a VX and realised the TB IAC and TPS are on the other side of the TB on the LS1. Logic may have made me put the harness then the other way around, I'll have to check this afternoon.