Injector Harness Issue

[87chrisss]

Im having an issue with a friends car im helping him fix the problem. This is an 87 setup by the way, so first of all it sounds like a cylinder isn't working. I started pulling plugs to see if there was spark in all cylinders one was very weak almost no spark i changed the coil pack ign module. Still gave the same symptom, i started pulling injector plugs to see if all injectors are working. One had no change in idle nor engine characteristic so i thought well it either has to be this injecor plug or injector. So i did not have a probe to check the injector, but i did have a multimeter. So i checked the injector plug and the plug wasn't receiving any voltage. Now behind the injector plug (wires that lead into plug) its receiving over 6 volts. I checked every other injector plug and they were only receiving half a volt .50-.61 volts and only that injector plug was giving me 6+ volts??? Any ideas? I cut the plug and im going to try to adapt another plug n there or i might just tell him to buy a caspers injector harness new.. I want to know if i should be looking elsewhere as well? My uncle told me it could have a bad ecm or a resistor that has been shorted. Need some assistance this car has been kicking are butt.

BTW the injector harness had a spliced wire to run a blackjack anti theft security alarm its running off the same plug thats giving me the issue im thinking the fellow who checked for injector pulse short circuited that plug or harness you think the ecm could also have been damaged?

 

[mikestertwo]

How are you measuring the voltage...to ground or across the connector? You should read 12 volts to ground on one side. The computer supplies the ground on the other side to fire the injector. If you are reading 6 volts across the connector there is a path to ground somewhere. Disconnect the blackjack wire and see what you get. Either the blackjack is causing the problem or you may have blown the injector driver in the ECM.

 

[87chrisss]

How are you measuring the voltage...to ground or across the connector? You should read 12 volts to ground on one side. The computer supplies the ground on the other side to fire the injector. If you are reading 6 volts across the connector there is a path to ground somewhere. Disconnect the blackjack wire and see what you get. Either the blackjack is causing the problem or you may have blown the injector driver in the ECM.

Im just using + and - from my multimeter on the actual connector .. the car turns on fine, just that one cylinder is giving me problems.. so i ruled out the ecm? would the ecm just blow 1 injector driver?

 

[mikestertwo]

You have to measure each wire to ground. You should see +12v on one wire. The other wire goes back to the computer to the driver transistor. You shouldn't see any voltage on that lead or very little. The transistor grounds that lead to fire the injector. It is very possible to blow one driver. The fact that you saw 6 volts across the one connector says you have a high resistance to ground which is most likely from the blackjack. Like I said above, disconnect the blackjack from that injector to see if your problem goes away. If not replace the computer.

 

[87chrisss]

ok thanks, i just checked my personal car i check one lead on the connector and yes it had 12+ actually 13 volts i grounded the multimeter to a engine bracket, im going to try and swap computer and see what happens on my buddy's car..hopefully it'll stock acting up

 

[87chrisss]

has anyone else ever had a bad harness? What where the symptoms? I really need to buy a power probe and check the injector and see if maybe the injector is faulty. Does anyone know what the resistance (ohm) should read on a multimeter be on a 42.5 pound injector ? Between what number is it in tolerance or faulty?

 

[RmvBfrFlght]

A standard high impedance injector will be between 12 & 16 ohms. The injector harnesses do go bad. If the car has a lot of miles on it the more likely that the wires are breaking where they enter the connector.

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