I am new here and in desperate need of some help.. I have an 89 Iroc 5.7 That is getting no impulse signal to the injectors. It will turn over and start on starting fluid But will not start on its own. It turns over and has spark to the plugs. And the injectors ohm out as being good At 14 .1 to14.3.So it is not the vats system. If anyone knows anything for me to try I would greatly appreciate any help I could get.. Thanks

 

How does the ohm value of the coil in the injector let you come to the conclusion its not the Vats system? The first question is what are you missing power or ground at the injector? How is your fuel pressure? Any stored codes in the ECM? Even low fuel pressure can cause a no start condition. The manual will have a step by step trouble tree for this condition. Compared to today this is not a complicated system. Assuming my memory still works Positive power is supplied to injector by fused wires. ( I don't remember even a relay) ground is supply by the ECM which gets its signal from the distributor. Back in the day if you had spark 90% of the time it was Vats or fuel pressure. ECM errors normally have codes in the 50's.

To check power to the injectors:
You may want to start with a noid light because they are designed to not draw too much power. If you have a good volt meter you can check for +/- voltage. You will get funny numbers since its a square wave signal. A digital volt meter will average the reported voltage. DO NOT USE A TEST LIGHT OR CHEAP VOLTMETER. They can draw more power then the ECM can handle and fry the quad driver in the ECM. Also note that is one injector is bad, internal grounded, none of the injectors will fire. If the noid light will not light you can unplug all the injectors, if it lights then, then just plug in one injector at a time to find the bad one.

 

Hello, is there an update to this situation? I have exact same problem and would love to continue this thread until there can be a resolution. I have 12 bolts to my injector harness, no flicker at the blue and green wires the go to each side of the V6. I had a 46 code “VATS” but it has been cleared and bypassed. It will just crank and crank
please help

 

No ground or no power?

 

No flicker at the blue and green wires that head to the opposite sides of the motor at ignition start.
the greeen and blue wires that are in the main harness that plug into each injector

how can I test for ground to an injector ?

 

You can use a high impedance volt meter. which means not a house type old school volt meter. Any modern voltmeter.


The only thing I saw in this video I did not like was the use of a test like to confirm ground pulse at the firewall. A high quality test light may be ok for this but most test lights a DYI would have would just have a regular blub inside. That could draw too much power and cause the Quad driver in the PCM to fail. Just use the volt meter, you will not see a pulse but you will see low voltage because of the pulse. No Voltage or full voltage would be bad.

 

Thanks for the video, I think I’ve watched it before but I will test continuity and test again for pulse.
if I have continuity (no breaks in the wire) then could it be the ECm?
another question is could VATS still be engaged even though there is no code and the security light is off?

 

Have you verified you are getting power to the injector? Without power the ground would do nothing. There is a fuse and a relay involved.

Yes it could be ECM. The ground to the ECM could be the problem. In fact If I was working on this issue at the dealer the first thing tech support would have had me do was to run temporary grounds to the ECM and the Engine. The ECM could have fried its Quad driver also the ECM may have another issue internally. If you want to try a ECM you can just go by the part number on the ECM then use your PROM. I have seen several ECM that issues on the diagnoses side of the ECM. It would not post a error code. You cannot put limits on what a failed ECM can do. The best you can do is make sure nothing on the outside of the ECM is working as it should. With out a higher end scan tool you can not really diagnose the ECM itself. At the dealer we had the GM CAMs system and could test input and outputs and it could verify the ECM was working. Even back then it was 30K tool

 

Yes I have 12 volts to the injectors. Two wires one pink and one pink and black. Each of those wires have 12 bolts with the key on. At crank no voltage is to my green and blue wires. and my understanding is that the blue and green wires are the wires that send the “pulse” from the ECM to the injectors signaling them to fire.
I do have a new ECM but when I switched the prom from my old unit to the new unit and installed it…
Here’s what I got
noid on 2,4,6 cylinders.
Then the engine was making a clicking sound near the battery with the key off so I stopped

 

Do you have a manual? I do not have the trouble tree memorized. You should be able to follow step by step till you find the issue. I have never done what you are doing without a scan tool. Using a schematic or knowledge of a circuit requires a high level of understanding of how the system works as a whole then using a trouble tree. A large part of the GM certification tests was whether you could use a trouble tree and the manual in general. Your ASE certification is more about automotive knowledge.

I am sure it is semantics, but I do not think of it as a pulse from the ECM as much as you are sending power to it, and it grounds it.

The drivers that ground the injectors are called quad drivers. Meaning each driver can ground up to 4 things. If a quad driver fails, it would be normal to see 4 injectors stop getting grounded. Also, it is common that is all 8 cylinders stop pulsing that it is not a quad driver issue, it is more likely an issue with another part of the system. The issue with these electronics is "assuming" is what normally causes a car to be un-repairable. If a 12 volt wire has crossed a 5 volt wire and worn through and sometimes it makes contact sending 12 volts into a 5 volt system. OR you are sure the issue is on the output side of the ECM but it is really on the trigger side. An ECM ground that has built up some resistance can play all kinds of games with the ECM it will also adds to the stress of the quad driver. I read a history on a new cars back in the 80s that had 11 ECMs installed in it. Truns out it was a bad crimp on the ground wire to the ECM.