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MK 5 (Gen V) 454 big block SOLVED! THANKS FOR THE HELP

nmxhustla

nmxhustla

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so my buddies been working on swapping a mkV big block into a 91 suburban. He did the whole painless wiring harness and its all basically ready to go except the injectors on cylinders 1 and 8 aren't pulsing. He replaced them and still no pulse. The good injectors are getting 12v with the key on and 9v while cranking. The 1 and 8 cylinders are getting 6v key on and 4v while cranking. Any ideas?
 
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No experience with that vintage stuff, but I wouldnt be surprised if those injectors share a power lead. How are they run? 12V ignition, and the PCM(ECM?) grounds the injector to fire? Sequential injection?

If that's how they are wired, and you dont get 12V with ignition on, then the power feed is the issue. In the past I want to think four injectors share a fused ignition 12V circuit. Which would make low voltage at only two injectors odd.

Voltage is being measured using a good ground, not across the connector, right?
 
I'm thinking that its ground to fire because the good injectors start at 12v and drop as they pulse
 
Just not familiar enough with these to know for sure.

On OBD1, the injector voltage needs to be measured to ground. And on those you need to use a test light to check pulse, as it happens too fast for a digital multimeter to read accurately.
 
That's okay we appreciate your guidance so far, we used your method to identify that the PCM is actually fine we originally thought it was bad so now we are sure the issue is after the PCM
 
That's an L29 setup. OBD2. The injectors all share a common power source from the ECM 1 fuse. They each have a separate ground that is at the ECM.

If the injectors aren't working on 1 & 8 it would be worth wile to check the circuits out. There is a pink wire going to each injector, that's the common power source. Check with a voltmeter between the pink wire terminal on the harness and a good ground with the key on. It should read at battery voltage. If 1 & 8 don't have the battery voltage at the injector connector, go back to the main injector harness connector and check for power on the engine harness side at terminals J & K. If you got power at that point you most likely have a break in a wire leading to injectors 1 & 8.

If you have power at J & K then you need to look at the control side of the circuit. For #1 it is the black wire and #8 is the blue/white wire. Check continuity from the injector connector back to the injector harness connector at the back of the intake. #1 is terminal A, #8 is terminal B.

It's highly probable that the injector harness is cooked. The harness is in a space that does trap heat and will make the wiring brittle. The best bet is to get a new harness which are still available from GM.
 
ZooMad75 said:
That's an L29 setup. OBD2. The injectors all share a common power source from the ECM 1 fuse. They each have a separate ground that is at the ECM.

If the injectors aren't working on 1 & 8 it would be worth wile to check the circuits out. There is a pink wire going to each injector, that's the common power source. Check with a voltmeter between the pink wire terminal on the harness and a good ground with the key on. It should read at battery voltage. If 1 & 8 don't have the battery voltage at the injector connector, go back to the main injector harness connector and check for power on the engine harness side at terminals J & K. If you got power at that point you most likely have a break in a wire leading to injectors 1 & 8.

If you have power at J & K then you need to look at the control side of the circuit. For #1 it is the black wire and #8 is the blue/white wire. Check continuity from the injector connector back to the injector harness connector at the back of the intake. #1 is terminal A, #8 is terminal B.

It's highly probable that the injector harness is cooked. The harness is in a space that does trap heat and will make the wiring brittle. The best bet is to get a new harness which are still available from GM.
Click to expand...

Wow thank you very much for the info, we will go ahead and try that out now, we did notice how the wires felt brittle and are in a place like you say would probably trap ALL the heat.
 
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