How to diagnose a DTC1222 injector control circuit problem on an OBDII LT1.
There is a loss of voltage to the PCM from an injector, which in turn means the PCM can't fire the injector(s).

The injectors are supplied with a constant 12 volts when the key is on. The other wire going to the injectors is supplied with ground potential when the PCM wants to fire the injector. When the PCM is not firing the injector, it is monitoring that control wire for the presence of 12 volts. There will be 12 volts on the control wire because the injector is just a simple coil like inside a solenoid. So if you put 12 volts on one side the coil, the other wire will have 12 volts until it's hooked to ground.

If the control line looses the 12 volts, it sets a 1222. The problem could be as simple as the injector connectors are warn out. Remember that.

You have to check all the injectors for the presence of 12 volts on all 16 wires. The pink wires going to the injectors are the supply of 12 volts. The injectors are nothing but coils so the 12 volts will show up on the other wires on each injector as long as the power is on but the engine is OFF. KOEO.

If you have any injectors that are missing the 12 volts on the pink wire, you have to trace the pink wire back to it's splice. On the passenger side, the pink wires all join at a splice approx 4cm from injector #6. On the driver side, all the pink wires join at a splice approx 13cm from injector #3.

If any of the injectors have 12 volts on the pink but 0 volts on the other wire, either the injector coil is bad and the injector has to be replaced OR the connector is not making good contact at the injector. Or the control wire is touching ground and burned out the injector. You should look at the connector mating surface for goofed up pins, maybe spread open. Sometimes they can be tightened up by hand. They should be replaced and replacements are available. With the RED PCM connector disconnected, measure the disconnected injector control wire to ground. Any reading OTHER than infinite (OL) on your volt meter, indicates you have a problem with the control line touching ground.

If all the injectors have 12 volts with KOEO on all 16 wires, then you have to ohm the connection from the injector signal(control) wire to the corresponding RED PCM connector contact pin. They are as follows:

List of injector control wires
Injector #1 Black wire to PCM RED connector pin #3
Injector #3 Pink/black stripe wire to PCM pin #21
Injector #5 Black/white stripe wire to PCM pin #20
Injector #7 Red/black stripe wire to PCM pin #6
Injector #2 Lt Green/black stripe wire to PCM pin #19
Injector #4 Lt blue/black stripe wire to PCM pin #4
Injector #6 Yellow/black stripe wire to PCM pin #5
Injector #8 Dk Blue/white stripe wire to PCM pin #22

It's ok to back probe the injector clips(connectors) while they are plugged in, but not at the RED PCM connector. Unplug the RED PCM connector before probing it from the PCM contact side.

One last thing, when back probing the injector clips, it is very hard sometimes to make contact. When you can't make contact like you should, it is real easy to falsely assume there is a problem. Remember that too.

It is preferable that you use either a probe made for "back probing" or at least a paper clip. Don't try to stuff in the fat meter lead and possibly damage the connector if it isn't already.

Hope that helps.

Dave

 

asqf

 

Thanks speedy, I checked a few of the injectors on the cyclinders that were bad and I had 12 volts on both wires and they all ohmed out. Also I know you said to check all 16 wires bot I only checked a few on the cyclinders that were having a problem, that OK?

Any other reason to throw a P1222 code? If we have rulled out that lack of fuel to the cyclinder what should I check next? Don't think it is mis adjusted valves because we have been driving the car.

Gonna trhow this out as an potential problem. Instead of buying o2 sensors extensions when we installed headers I went to a salvage and cut out some 02 sensor wires from another chevy and spiced them in. Could this have anything to do with the issues?

 

Fuel pressure was 47 psi while fuel pump was running and dropped to 40 once the fuel pump turned off. Held at 40.

 

What about my opti and how would I check it?

 

There's only one reason for setting a 1222. No voltage at the PCM. Has nothing to do with anything else.

When you said they ohmed out, what does that mean? Only measuring from the injector connector to the PCM connector will mean anything at this point.

Clear the codes and see if the 1222 returns. If it does, focus on that. Remember if it's throwing a 1222, it's not firing all the injectors. Get a noid light at that point and then you will have to ohm the control wire from that injector to the PCM.

I see by your thermal data, 3,4,5 and 7 were a problem. Focus on those for now.

 

Ok, thanks speedy. I'll have to get the scanner back from my brother tomorrow to see if it throws another code. The ohms I was talking about was between the PCM connector and the injector harness. I forget what the ohms were but they were all the same. Hopefully that was a old code or something. I pulled one of the dead cyclinder plugs and one that was firing, the good one looked normal and the other one didn't look like it had been firing. In the mean time I found a link on how to check opti, and all checked ok except the coil. It ohmed at 11,000. When you crank the engine it sure sounds like a ignition problem, back fires under the hood. Gonna replace coil tonight and will follow your advice on resetting code and tracking P1222 code tomorrow. Thanks again.

 

PS, Didn't see anthing on how to check the ICM.

 

Speedy, Prior to me checking for codes we had the engine running and un-connected the injector harness on each cyclinder, just to see check injectors. After reading what you wrote on what causes a P1222, wouldn't it be logical that it would throw a P1222 code if you pulled the injector plug off?

 

Yes. Clear the PCM and try again.

 

Is the car able to throw that code again if it wont start?

 

The PCM can diagnose many voltage related problems without the engine running.

 

Ok so the P1222 code is gone, I guess it erased itself last night when I unplugged the battery. Here is what I have checked.

Verified 12 volts on both injectors wires.
Checked ohms on red pcm connector with corrosponding injector. I forgot what the ohms were but all were the same.

Ohmed the coil, it ohmed 10K 0r 11K, so I bought a new one and replaced.

Verified the 2 wires from ICM to coil had 12 volts, and the other wire went to ground. I tested the white wire(control wire) turned meter to a/c and cranked engine it read over 1.5

Verified I had 10 volts on both "A" & "D" wires at the ICM, KOEO. Then switched meter to A/C and checked the B wire to ground whlie cranking, it read somewhere between 1-3.

Does this mean that my opti's screwed or did I miss something else?

 

So confirm dead cylinders and it's best from a dead cold start.

Pull the plugs and check for spark. Then put a known good plug on the wire and check it for spark.

Throw a compression tester on the cylinders in question.

If those 2 items check out, lift the fuel rails and watch the spray pattern for the dead cylinders while someone cranks it over compared to the good ones.

DO NOT CONTINUE to run engine with dead cylinders as you may be washing the cylinders walls (souping) and will destroy the pistons rings and cylinder walls.
That is if the injectors are squirting.

 

Compression was good, spark was a issue, for sure. The #1 cyclinder, which was one of the good ones fired like normal. The #3 cyclinder fired one time while turning the engine over 4-5 times. I'm convinced with all the testing the cheap as_ opti we installed already took a dump. What do you think, opti shot? The bad cyclinder is getting fuel it was covered in it, just nothing there to burn it off. So im thinking unless there is a timing chain problem, which I hardley doubt being since this engine only has a few hundred miles on it and the plugs and wires are all brand new it's got to be the dist. Any thoughts?