P0200- Injector Circuit Problem....help me sort it out !

[OldSkool69]

I post this in another forum, I guess I can get better help here....

It all started couple of days b4 intake swap (Edelbrock intake, Aarons elbow, Wilson TB, etc)
SES came on and I scanned it with my android. Infamous P0200- Injector Circuit. The truck had a rough idle and misfired when driven. I erased the code with my android and things went back to normal…so I thought.
The day I was letting it in the shop for the intake swap it started again, this time with heavy fuel smell. We trace the fuel leak to the #8 piston….it was flooding that chamber with fuel. We disconnected that injector and idle was better and engine resume some “normal behavior”.

My first thought, Injector damage. So I took all the injectors out and send them to test and clean. Injectors where perfect. So I installed them again but this time I changed position to the one that was in #8 piston.
Turn the truck on and same issue. Injector #8 stayed wide open.

I consulted some known Gurus around here and told me my ECM injector driver was doom. So I have to replace the ECM.
Well, that sound easy, but I will have to spend $200 in HP tuner credits. I refuse that yet. I start looking for ECMs to test in my truck. All locked or wrong year. So I took another approach. I got mine reflashed and tested in a friend’s 2002 Tahoe.
It worked perfect for the 3 days test. So At this point I ruled out my ECM as the problem !

Those 3 day testing gave me time to swap intake. So the swap is done. I took my ECM, write entire again with my tune. And VOILA!!! It idle perfect. No roughness. No code, no nothing. So I start tuning my idle.

Went for a spin to test the truck and a few blocks away from the shop SES came on…monstrous P0200 attack again. Rough truck behavior now. Try to erase it with HPtuners and came back on in a minute. Took the truck to the shop and let it there sit for a while. Try to start it again and almost hydrolock. I called a day.

Now I know for a fact that when my ignition is on, the #8 injector work like all others. They all pressurize and turn off until cranking. Once the truck is running #8 stays wide open!!!

Now I hit the wall and don’t know what to do.
So guys, If you have any other test procedure, any other part I should look at, fuses, wiring (wiring was check 50% and rerouted because of intake swap), etc, let me know.

[mcfarlnd]

Got any logs while this is happening?

[OldSkool69]

here is a log....

The truck starts fine. No gode....couples of blocks and Code sets and rough idle and drive.

[Ricardo]

If the PCM checked OK in another vehicle and the injectors too upon swapping them around it could be the wiring harness.
Your #8 injector return line to the PCM could be damged and is being grounded randomly.

[planethax]

Remove Inj#8 control ckt from pcm connector.
Use a noid light in Inj connector and crank start engine.
If the light is on it is shorted to a ground, if noid light flashes it is shorted to another inj control ckt.

[blownbluez06]

Remove Inj#8 control ckt from pcm connector.
Use a noid light in Inj connector and crank start engine.
If the light is on it is shorted to a ground, if noid light flashes it is shorted to another inj control ckt.

If you don't care to buy a noid light, get a meter and measure continuity from your negative trigger side to ground with the PCM unplugged. The positive side will be hot with the key on and you'll obviously be checking the opposite pin. While checking for the short to ground, feel free to move the harness around while watching your meter. Also carefully inspect your harness for chaffing. Sometimes even the metal support brackets that are bolted to bell housings and cylinder heads from the factory are the culprit.

[OldSkool69]

Thanks guys.

Today we tested with the Noid light.

It was working good, and I started moving the harness from back to front. As soon I reached the nearest part of the harness to the pcm the noid stayed on....I moved that part of the harness and the fail come and go.

Now I know where to start looking for the shorted wire.

Again, that you very much guys.

[planethax]

Thanks guys.

Today we tested with the Noid light.

It was working good, and I started moving the harness from back to front. As soon I reached the nearest part of the harness to the pcm the noid stayed on....I moved that part of the harness and the fail come and go.

Now I know where to start looking for the shorted wire.

Again, that you very much guys.

Glad to hear you found out where fault is!