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New here. The issue, my Autel MZ808S while doing an Injection Balance Test, says injector command for 2 is pulsing number 3 and 3 is pulsing 2. And the same for 4 and 7. I have the intake off and have the spider connected to the fuel lines and connector. On the pcm, these pairs are right next to each other. The wires ohm out correctly, even the colors are correct all the way to the big spider harness to pcm, but the Autel is telling my different. And can watch what injector is spraying. I don't know if the computer has been modded. So which to believe the wiring or the scanner? Thanks for any input.
History: 5.7 vortec in 2000 blazer. Engine out of a 2002 express van with the 0411 computer and updated MFI spider injection and wiring. Got everything fixed except p0300 and the lean bank codes popped once (0701 and 0704). The STFT high right away, LTFT would max out after a long drive. Easy money, went for the intake gaskets, but they looked really good, almost new felpro 98000T (engine rebuilt 2018ish). No sealant on the intake bolts, noticed everything had a light coat of engine oil (inside intake, ports etc) Just to get it running pretty good, replaced the plugs and wires, distributor, fuel pump (60psi, 50ish pulsing injectors) and ignition module with gm parts.
This may very well be a scan tool issue, wouldn't be surprised at all. You could try another scanner if available.
With a scope you can verify where the injection pulse takes place in the cylinder during the 4 stroke cycle. Using the secodary ignition as a reference for TDC from the cylinder under test the injector should fire around the end of the exhaust stroke./beginning of the intake. You also can compare this to another cylinder that's not suspicious.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
I'm inclined to believe to believe the wiring. But first, do you have the vehicle identified correctly in your Autel?
Asking because the firing order for the 5.7L out of the '02 Express is 1-8-4-3-6-5-7-2. However, other GM V8's used an alternate firing order, 1-8-7-2-6-5-4-3. It just so happens that 2/3 and 4/7 are companion cylinders, and are the cylinder numbers that get reversed between the two firing orders.
That's kinda why I suspect a scanner problem. The PCM is probably doing what it's told, but the scanner software has the cylinder assignments wrong.
Great catch. Did not know or remember the firing order was different between the vortec and ls based engines. I put the firing order over each other, I can see that the scanner is firing the LS pattern, so it commands 7 and 4 pulses, command 3 and 2 pulses etc. And I was using the vin reader on the scanner, says 2002 gmc express 1500 and they only came with the old school sbc vortecs. I'll try late 90's truck pre LS on the scanner see if that works. Worse case I was going to put it all back together and re-pin pcm and see if it got better/worse. Thank you very much.
Was going to try 1998, but remembered it's a different computer/wiring. Tried a couple different 2001 2002 gm trucks and vans that used the 0411 pcm, still defaults to the LS firing. Tried 5.0 no pulse. Maybe try 2002 4.3l just to see. But at least I know what's going on. Thanks again.
Was going to try 1998, but remembered it's a different computer/wiring. Tried a couple different 2001 2002 gm trucks and vans that used the 0411 pcm, still defaults to the LS firing. Tried 5.0 no pulse. Maybe try 2002 4.3l just to see. But at least I know what's going on. Thanks again.
Interesting! Thank you for experimenting with that.
To be honest, I can't say I've ever actually checked that the injector I'm commanding is the one that's actually firing.
On Vortec engines, anyway. If one injector had a failing/questionable result, I just recommended replacing them all.
Now I'm wondering which scan tools are balancing in the right order... Or if they all default to the LS order like you found.
The 0411 computer is such a popular swap, I'm surprised this hasn't come up before. But it could just be the Autel and most of the swaps are ls. I even manual entered diffenent trucks/vans, the Autel has the correct years and L31 engine code (vortec), but still deflauts to ls order. I gave up on the spider and going to ramjet with conventional injectors you can actually see. Bonus it looks way cooler.
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On Vortec engines, anyway. If one injector had a failing/questionable result, I just recommended replacing them all.