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740 No Pulse to Injectors, Has Spark

bmdubya1198

Active member
Joined
Aug 24, 2016
Location
Charlotte, NC
I ended up replacing the EZK module in my '88 Turbo, and I finally have spark and the fuel pump engages when it's supposed to. The only thing keeping my car from starting at this point are the injectors. For some reason, the ECU isn't grounding them.
The injectors have power when checked between the terminals and a ground.

What can be preventing the injectors from getting a pulse? It's not the power stage, ballast resistor, or radio suppression relay. I already changed the power stage (plus if it was bad, it would not get spark) and the other two being bad would most likely prevent them from getting constant power.
I also bypassed the boost over pressure switch, so that's not the problem.

There is continuity between the injector connector and pin 13 on the ECU.
I have also changed the LH ECU, but I guess it is a possibility that it's another bad one (assuming my original ECU is bad?).
 
You've tried the boost pressure over pressure switch. How good are the connections at the radio suppression relay?
 
No pulse/weak pulse to injectors can be caused by bad CPS, RSR, corroded resistor pack, bad ecu, and some other things. Does the vehicle start on starting fluid?

If you are certain your injector grounds are clean, you should remove the connector for the resistor pack and file the spades clean down to bare metal. Being corroded caused a no start on my 940t. Do you feel the RSR click in KP2? You can bypass the relay temporarily by removing it and jumping the 12v wire (should be red) to whatever wire gives power to the injectors. I believe it’s striped. You’ll have to look at a wiring diagram though.

As lummert mentioned, RSR connections can be gross. When I looked at them on the 740 the plastic was so old and rotted that it was booger consistency. I ended up cutting the harness and splicing in a Bosch style 4 post relay. All good now.
 
No pulse/weak pulse to injectors can be caused by bad CPS, RSR, corroded resistor pack, bad ecu, and some other things. Does the vehicle start on starting fluid?

If you are certain your injector grounds are clean, you should remove the connector for the resistor pack and file the spades clean down to bare metal. Being corroded caused a no start on my 940t. Do you feel the RSR click in KP2? You can bypass the relay temporarily by removing it and jumping the 12v wire (should be red) to whatever wire gives power to the injectors. I believe it?s striped. You?ll have to look at a wiring diagram though.

As lummert mentioned, RSR connections can be gross. When I looked at them on the 740 the plastic was so old and rotted that it was booger consistency. I ended up cutting the harness and splicing in a Bosch style 4 post relay. All good now.

No CPS on a 2.2 car, just hall effect in the dizzy. Since he has spark, that rules out the hall effect.

OP is right, in that the RSR /should/ prevent power from getting to the injectors if it fails, but if he's got a spare, it takes 10 seconds to swap. I'd suspect the fuel pump relay before the ECU or wiring, since 88 has the decent wiring, and the fuel pump relay controls both the pumps and the injection.

A noid light will be your best friend on injection diagnosis, though.
 
No CPS on a 2.2 car, just hall effect in the dizzy. Since he has spark, that rules out the hall effect.

OP is right, in that the RSR /should/ prevent power from getting to the injectors if it fails, but if he's got a spare, it takes 10 seconds to swap. I'd suspect the fuel pump relay before the ECU or wiring, since 88 has the decent wiring, and the fuel pump relay controls both the pumps and the injection.

A noid light will be your best friend on injection diagnosis, though.

is the RSR the same as the A/C fan relay on those cars? may be an easy way to test it.
 
You've tried the boost pressure over pressure switch. How good are the connections at the radio suppression relay?
The connections are good at the RSR. I just soldered some sh***y looking splice connectors and cleaned them up, but still no difference.
No pulse/weak pulse to injectors can be caused by bad CPS, RSR, corroded resistor pack, bad ecu, and some other things. Does the vehicle start on starting fluid?

If you are certain your injector grounds are clean, you should remove the connector for the resistor pack and file the spades clean down to bare metal. Being corroded caused a no start on my 940t. Do you feel the RSR click in KP2? You can bypass the relay temporarily by removing it and jumping the 12v wire (should be red) to whatever wire gives power to the injectors. I believe it?s striped. You?ll have to look at a wiring diagram though.

As lummert mentioned, RSR connections can be gross. When I looked at them on the 740 the plastic was so old and rotted that it was booger consistency. I ended up cutting the harness and splicing in a Bosch style 4 post relay. All good now.
Last I checked, it ran on starting fluid. But not since I replaced the EZK module, but I haven't exactly tried either.
No CPS on a 2.2 car, just hall effect in the dizzy. Since he has spark, that rules out the hall effect.

OP is right, in that the RSR /should/ prevent power from getting to the injectors if it fails, but if he's got a spare, it takes 10 seconds to swap. I'd suspect the fuel pump relay before the ECU or wiring, since 88 has the decent wiring, and the fuel pump relay controls both the pumps and the injection.

A noid light will be your best friend on injection diagnosis, though.

Yes, already replaced the hall sensor. The fuel pump relay is kicking on when it should. The injector side clicks on with the key on and stays until I turn the key off, and the pump side clicks on while cranking and holds until shortly after. And it sounds like it's clicking on and off while cranking... is that normal behavior?

I'll have to pick up a set of noid lights today just to be sure. No point in fiddling with the test light anymore.
 
Picked up a set of noid lights earlier this afternoon and tested the injector connectors again. The injectors are definitely not getting a pulse signal.
 
I will check those things tomorrow. Where are the injectors grounded other than through the ECU? The ECU grounds are all good as well.
I’m 100% sure I have spark. My spark tester shows a signal. I have yet to try the starting flud again because it’s a bit of a pain doing that without help. I’ll give that another try tomorrow as well.
 
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