I will give you some direction on this tonight.

George

 

Thank you, I’ll be on standby.

 

Was the new purge solenoid the only change before the new codes?

My first thought is a disturbed wiring harness so I would inspect the connectors and wires going into these sensors.

The next thing I thought about was a common ref voltage circuit but the CKP uses a 12V ref and 5V ref on the EGR. They both have their own low ref wires back to the PCM. IOW they have nothing in common except wiring harnesses and the PCM. Of course coincident failures is possible but not likely. Check your main grounds at the back of the engine heads, the radiator support and the ER walls.

The CKP issue has to be intermittent because the truck wont run with a hard failure. The EGR can be messed up and the truck will still run. Both of these can be a challenge, especially without a high end scanner.

I would start with measuring the reference voltages back probed at the connectors all plugged in. On the crank sensor its lt green and purple. On the EGR its gray and black.

George

 

Yes the purge solenoid was the only new part. Had a shop do the relearn on the crank sensor. The tachometer had smoothed down like normal till about 10 minutes in the test drive the starting bouncing again. The harness has always had a rough spot where it rests on the AC box, I called myself doing a through inspection for about a foot length a while back. The transmission guy did suggest that I had a commutation issue after the rebuild when a month later it was doing the same acting up. Maybe source another harness from my local pull a part? Is it worth completely changing the whole harness or just splicing in these two sensors at the ECM connection? Thank you again for your help.

 

I will also check those voltage inputs first thing Saturday morning, let you know what I find.

 

I would not change the harness. If the voltages are ok we can test the signal wires. Have you ever cleaned or replaced the EGR valve?

Grorge

 

Okay today’s results. EGR reference was 5.0 volts. CPS was only 10.89 volts. I got switch on. CPS wires look brittle at the plug, one wire has exposed wire. I cleaned it all off with cleaner and straighten the wires.
I captured some live data, first 3 are at just cranked. Next 3 are at 2500 rpm’s. Also some graphic pics of the 3 O2 sensor voltage. B1S2 the white one seems to not act like the other two.
There are several pics of data collected during a deep scan. LTFT for bank 2 is always at 99.5%, how is that possible? Bank 2 STFT is mostly in the negative range, what does that mean?
I removed the EGR valve again to check it, plunger moves in/ out when pushed, never got any movement with the switch on but not sure if it’s supposed to move.
Rpm’s constantly moving up/down, steadys then starts moving again,not much only couple hundreds but never really settle’s down, all this while hooked to the scanner, unhooked it’s normal.
Having issues uploading pics,will sent as soon as possible.

 

I understand now that the 99.2% fuel trim is a general one for the after cat sensor so not a contributor to my issue.
I did check the ground from the ECM to the EGR and it was battery voltage.
Im not sure how to do the same for the CPS sensor though.
Will pressurize the exhaust system with my shop vac today to check for any leaks.

 

There is a lot to unpack here so lets get started:

O2 sensors: You have three sensors, 2 before the cat (B1S1 and B2S1) and one after the CAT (B1S2, B1S3 on some years). The front sensors switch back and forth from around 0.15v to 0.85v at around once per second at idle with rise and fall times around 100ms. Typical graph attached (idle and 2500). The rear O2 sensor is almost steady at between 0.5 and 0.7v. If this rear sensor is also switching, there is a problem. All of this on a warm engine at temp.

Fuel trims: Always have to be reported together (LTFT1, STFT1, LTFT2, STFT2). The fuel delivery on a given bank is the combination of the 2 for that bank. The most useful is all four numbers at idle and again at 2500, all in park, engine at temp. A fuel trim of 99.5% is a major failure that needs to be addressed. Any failure with a sensor in the circuit can be a proper sensor reporting a bad set of real conditions, a bad sensor reporting crap, bad power, bad ground, bad signal wire or bad PCM.

EGR: The EGR is a tough device to diagnose without a proper bidirectional scanner because the control on white and red is a pulse width modulated (PWM) signal from the PCM, not a varying DC voltage. A high end scanner can commend the PCM to move the valve to monitor for proper function. A shade tree mechanic can at least check the continuity of these two wires. The sensor and its output on the other three wires is a little easier. You can measure for proper net reference voltage (back probe) on Gray and Black (not frame/battery) ground and the can monitor the voltage output on brown while moving the pintle by hand.

Unhooked scanner: So the truck stops rpm hunting as soon as the scanner is unhooked?

CPS: Assuming this is the crank sensor, this one is also tough to completely diagnose without some better gear but we can do a first order check that involves rotating the crank by hand and measuring the pulses on the yellow wire. This first measurement however is back probe the ref net voltage (lo ref not battery/frame ground) on purple and lt green.

This should keep us busy for a while.

George

 

Wish I had at least spent money on a basic bidirectional. I believe some of you guys use a pc based software, what is the cost of these? I had no success uploading the data ofro my last scan, any chance I can email you these for your review?