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740 No Pulse to Injectors, Has Spark

Well you could directly test the ECU itself with a scope. Or like I told you, with a test light.

One could connect one end of a test light to a positive source and then the other end of the test light to the injector control terminal, backprobed, at the ecu. Crank. Blink? =ECU inkector control circuit IS functioning.
 
Have you ever played Magic 8 ball?

^ so what do you think his problem is?



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Rather than doing your fancy electric test on the resistor pack, can just take it off and clean the spade connectors? Or have you already done this. Volvos are so picky sometimes. It doesn’t hurt to try.

After 5-10 seconds of cranking, are the plugs dry completely?

Sometimes it’s those rudimentary tests that give the most conclusive results the fastest.
 
The terminals on the resistor pack are clean. I'm afraid to take the terminals off the resistor pack itself in case it would break like my old one.

Last I checked the plugs, they were totally dry.

I'm really leaning towards the injectors.
 
Repeat: Test light to a positive source, then other end to your injector control wire. Crank. Blink?

Or....... "Ho! Man ye rusty parts cannon!"
 
Repeat: Test light to a positive source, then other end to your injector control wire. Crank. Blink?

Or....... "Ho! Man ye rusty parts cannon!"

I'll give it a try tomorrow just to check. Hopefully I can just get some new injectors and call it a day... and get this thing running once and for all.
 
Just tested it, it blinks. It’s not a REALLY bright light, but it’s bright enough to know for sure that it’s blinking. With the key off, it’s bright and solid, once the key is on it turns off, then blinks while cranking.
 
Is it supposed to light up with key off? They’re switched ground, so applying a constant 12v to one side of the noid light and then the injector harness to the other, shouldn’t it stay off?
 
That was tested at LH pin 13 with a test light with the clamp on the battery positive, not a noid light. The injectors won’t have power unless the key is on.
 
That was tested at LH pin 13 with a test light with the clamp on the battery positive, not a noid light. The injectors won?t have power unless the key is on.

Okay makes more sense. So you?re getting a pulse, but no fuel is coming from the injectors? My guess is either insufficient fuel pressure or dead injectors :e-shrug:
 
Mmmmm.....light shouldn't illuminate key off. Just blink while cranking. That sounds like your wiring is shorted to ground on that injector ground circuit. Remember that converstion???? I recall you saying you found bare wiring. Whatever happened with that!?

Replacing components when the circuit is no good is a bad move.

Current takes the path of least resistance. If you have a short to ground before the computer, most of the current will go thru the short instead of the ecu.
 
Okay makes more sense. So you?re getting a pulse, but no fuel is coming from the injectors? My guess is either insufficient fuel pressure or dead injectors :e-shrug:
Yup. I checked the plugs too, bone dry, no fuel smell. I take it the injectors are dead. Went ahead and bought a set for cheap, those should be here in the next few days.
Mmmmm.....light shouldn't illuminate key off. Just blink while cranking. That sounds like your wiring is shorted to ground on that injector ground circuit. Remember that converstion???? I recall you saying you found bare wiring. Whatever happened with that!?

Replacing components when the circuit is no good is a bad move.

Current takes the path of least resistance. If you have a short to ground before the computer, most of the current will go thru the short instead of the ecu.

The joint where all of the ground wires from the injectors come together was peeled away, but I already taped it all up and made sure it was not making any contact with anything else. The rest of that wire was good.

What could cause the terminal to ground out with the key off?
 
A short to ground in the wiring or the ECU. Unplug the ECU and see if it goes away.

Measure restsiamce between njector ground terminal and a good ground. It should be in the kilo ohms range. If its 0 ohms or anything lowish you have a short.
 
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