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!!!!Time out!!!!

You said, the truck may have algae contaminated fuel?
How did you clean it.
Even if you put a Algae-cide, the dead organism needs to be thrown out.
Unless you pump the fuel out, it is still there.
That will contaminate the IP, hopefully, the filter catch it but it does not have that much capacity.
At the least the filter will be clogged.
 

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Discussion Starter #23
ECT, IAT, MAP/BOOST, and CPS all share a ground that is spliced in the engine harness,
under the intake. They are actually eng. ground but through the PCM.
"D" & "F" on the OS are also PCM sensor grounds.
Have you replaced the CPS? If not, have you inspected it?
An OEM 94 sensor will usually have the insulation missing where the 3 wires are molded into the sensor.

Thank you Glagulator. I just found the shared grounds studying the sensor wiring diagrams.

We did have the intake off, maybe that ground got over looked when reinstalling the intake. Can you confirm exact location under the intake? So far I can only see that they are part of circuit 452 and end at D6 of the PCM.
What do you mean by "D" & "F" on the OS are PCM grounds? do you mean terminals D & F on the optical sensor/ fuel temp sensor? Terminal D of the optical sensor is part of ckt 987 and grounds at D14 of the PCM. Terminal F of the FTS (fuel temp sensor) ties into ckt 987.
Yes there was a new CPS (crank position sensor) on the engine when we got it. I have only inspected it as to 0 miscounts at idle RPM. I thought that was strange, but it is a 6.5L normal reading. I do believe it is an AutoZone part...
 

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Discussion Starter #24
Might be wise to add a ground to the block to eliminate any stray voltages
He added two ground to the engine, 1 battery ground and 1 harness from the left rear of the motor at the back of the head to a stud at the intake manifold.
 

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Discussion Starter #25
!!!!Time out!!!!

You said, the truck may have algae contaminated fuel?
How did you clean it.
Even if you put a Algae-cide, the dead organism needs to be thrown out.
Unless you pump the fuel out, it is still there.
That will contaminate the IP, hopefully, the filter catch it but it does not have that much capacity.
At the least the filter will be clogged.

My son added 16 oz. of Seafoam after pulling the fuel from the tank. he then added 20 gals of fresh fuel to the tank. I don't believe the filter is clogged at this point. He has two inline glass filters at both fuel returns and you can watch flow...
 

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The sensor grounds splice under the intake then a single wire runs to "D6" PCM. There are no bolt down grounds under the intake. You have the OS grounds correct. The source of the PCM grounds are 1- 18ga black and 1- 18ga. tan wires at the rear of the pass. side head. Time for a GM CPS.
12557046 - ACDelco 213337
 

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I was suggesting adding another ground to the wires going to the sensors.... Aftermarket crank sensors on a 6.5 typically cause problems and are in my opinion junk.> Hope someone can prove it some day with screen shots off a high end scanner. I would almost bet the crank sensor wave form is inconsistent.
REPLACE with ACDelco
 

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Discussion Starter #28
The sensor grounds splice under the intake then a single wire runs to "D6" PCM. There are no bolt down grounds under the intake. You have the OS grounds correct. The source of the PCM grounds are 1- 18ga black and 1- 18ga. tan wires at the rear of the pass. side head. Time for a GM CPS.
12557046 - ACDelco 213337
Thank you for your expertise & thanks for the clarification on those grounds. I will confirm that they are connected and do a voltage drop test as well.
FYI we pulled a GM sensor out of it. So it seems the other owner that changed it used ACDelco... I'm posting pictures of the GM sensor made in mexico.
20200413_193504.jpg

I would have had to wait 3-days for a GM sensor. So I used a BWD, it looked identical and it actually had the same made in mexico. The area were the delco part # was stamped on the original GM is ground off on the BWD. As a parts guy myself. I know GM stopped making their own parts several years ago. they have been out sourcing since then.
But here was no change in the idle... so as I stated earlier off the the power and ground curcuits
 

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Discussion Starter #29
Another thought is; How important is the OS filter? Is there a way to tell if it is bad? Is it required on a 94-95 ALDL OBD1 set up? I did run the truck without it and there was no change to the idle.
 

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Discussion Starter #32
ACDelco is the only one to use. Been there done that.
It had an ACDelco in it. if it was unplugged it ran fine, plugged in it ran bad. BWD plugged in runs bad, unplugged runs good. New ACDelco is on the way... Gonna try a different one anyway. Beauty of working for a parts store. Damn BWD part is defective...LOL;)
 

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ACDelco won't have wires. It will have a ribbon with wires imbedded in it. Part number >213-337
Does the aftermarket have a ribbon on it?
 

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Grins and giggles > Might also try a re-boot. Disconnect batteries and turn the key on. Let it sit for 1/2 hour, turn off key and re-connect batteries.
 

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Just a shot in the dark, plug in a CPS not installed (in your hand) and see how it runs.
Should trigger some codes also.
Toss the noise filter.
 

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Another grins and giggles> Do you know how to check the sensor air gap? Watch a Master Tech do it >
Have no idea what it should be but the gap can be critical to proper performance.
 

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Discussion Starter #40
Grins and giggles > Might also try a re-boot. Disconnect batteries and turn the key on. Let it sit for 1/2 hour, turn off key and re-connect batteries.
Tried the reboot no change in the idle.
 
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