Cam to crank sensor correlation fault

[Tdean91491]

I always get my parts from the local car quest dealer. I usually use the BWD cap and button. As soon as I get home I’m going to put them on and see where I’m at.


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[Tdean91491]

Alright, new button & new cap. Still a constant miss on 1 & 8. I did notice that if I get it to around 2500 rpm and hold it for a second or two. A few other cylinders miss a couple of time. This is what I’m reading with my app. I also bought a lilse in-line spark tester.the number 1 & 8 plugs are sparking just like the rest of them. I’m wondering if it could be it doesn’t have fuel getting to those two cylinders?

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[east302]

I haven’t used an inline tester, as I had read that it will illuminate the light if any spark is present regardless of quality. Not knowing if that was true, I’ve used an adjustable one which lets you see the strength of the spark relative to the gap. It may be worth taking a look at just to confirm spark quality.

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The VCM grounds each injector, so each injector should have battery voltage with ignition on. Test by probing each positive to a ground (not the ground pin in the harness).

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I believe that a noid light would be used to see if each injector is getting a pulse. It’s a little light that jumpers the + and -, so if it pulses on and off when cranking then the ground connection to the VCM is correct.

The additional misfires may be a result of the crank rotation being thrown off by the ones at 1 and 8.

What brand plugs are these again? How do they look? Try swapping those two with two others and see if the misfire follows.

A compression check probably wouldn’t hurt, either.



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[Tdean91491]

Anyway you could possibly go a little in depth on exactly how to test them? I’ve never tested injectors before. They are the best ac delco that the truck calls for that my local carquest dealer carries. Luckily I use to work at the place & I still get my employee discount which means I get everything at cost.


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[east302]

Here’s a video someone did on the adjustable spark tester. His results were similar to what I had when I had a bad cap. The spark at the bad cylinders couldn’t jump the gap that the good ones could. I think mine was set to around 25 or 30kV but I don’t know what the correct open air gap spec would be. I’m not sure that it’s that critical if one cylinder is firing so poorly, so just compare the spark to one of the non misfiring cylinders.

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If you meant how to test the injectors, you’d pull the main harness from the injectors and test each cylinder’s positive feed for battery voltage with ignition on. See the pin diagram above for which one is which. It’s cavities ‘B’ and ‘K’ for cylinders 1 and 8.

I’ve never used a noid light to test for the VCM grounding correctly, but maybe someone can chime in. You may be able to just jumper the positive injector feed to the ground pin, crank it and see how your multimeter responds. It may be too quick, though, to get a voltage reading. An analog (dial) type may be better so you can watch the needle swing, but rigging up an LED bulb may be better. Sorry, that’s not much of an answer, lol.




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[Tdean91491]

Well I finally found my problem & fixed it. Went and bought the noid light set & got home pulled the plug for the injectors tested them & everything tested good. Went to plug it back up and I noticed something, one of the prongs on the plug for the injectors was bent over. Straightened it out bam no more miss fires. A few hundred dollars & countless hours of time later I finally learned what to check for first next time! I really do appreciate you for your help in figuring this deal out!


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[east302]

Glad you got it sorted out and that it was an easy fix. For my future reference, what’s the part number for the noid light set that you picked up?


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[Tdean91491]

Glad you got it sorted out and that it was an easy fix. For my future reference, what’s the part number for the noid light set that you picked up?


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This is the set I bought and I had to use the one labeled GM SCPI



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[east302]

Thanks, so it just jumpers across the + and - for each injector in the harness?


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[Tdean91491]

Thanks, so it just jumpers across the + and - for each injector in the harness?


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That’s the way I used it. You have to turn it over for it to send fire to the injector your testing, I’m assuming it sends it in the firing order. So it may take a second for it to light up.


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