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Old 03-25-2011, 11:04 AM
eo273 eo273 is offline
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Default 89 ram 2500, fuel injector voltage

Hello all, I've been checking your site for some time now, usually found my answers without needing to post anything, but this time I'm stumped, hopefully you can offer some advice.

I have an 89 Dodge Ram 2500 (actually listed as a D250) with a 5.2, auto trans, 2 Wheel Drive setup.

The fuel pump recently went out, so me and my brother replaced it, along with the fuel lines where they needed it. We put it all back together and started it up and it worked! We let it idle for an hour or so as it had been sitting for a month with a bad pump... the next day we went to move it, and nothing. She wouldn't start. We checked everything...

Fuel is good, both sides of the throttle body have pressure...
We have spark, truck will start/run on starting fluid...

It turns out the injectors are not firing. They will squirt fuel if we apply 12 volts to the top of the injectors. They have good matching resistance across both top terminals. I checked the voltage at the wiring harness connecting the fuel injectors.

We have 1.5 volts at the injectors when cranking...

I have a good 12 volts when I probe the positive into the harness and the negative to a good ground, but only 1.5 volts when I probe the negative side of the injector harness.

I think the computer breaks / connects the ground side of the injectors to make them fire, is this correct?

I have traced the engine harness towards the passenger wheel well and checked the voltage here and it is the same... it sounds like a bad ground either in the harness or with the computer.

My questions are... the computer is located in the driver front fender, correct? Will a computer replacement correct this problem? Is this a common problem? Does anyone know the color or pin location where I can check the resistance from the computer to the injectors? I'm figguring it's either a bad connection (checked / wiggled all connectors) between the computer and the injectors, or the computer itself.

Thanks.
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Old 03-25-2011, 11:08 AM
eo273 eo273 is offline
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Just a quick extra note...

Occasionally, when the key is first inserted and turned, the injectors will fire for a split second. The truck will start for a second and die... this is completely random and only sometimes happens. I believe this is supposed to happen as it sort of "primes" the engine before starting.

No engine light codes...
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Old 03-25-2011, 11:15 AM
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You are correct. The injectors are ground controlled by the PCM. Since you have 12V on the positive side of the injector harness and resistences are equal, I suspect the PCM. Checking the resistence of the injector wiring wouldn't hurt but I think we both know what you'll likely find. You should verify the power and grounds to the PCM are good before replacing it.
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