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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum

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Old 09-05-2014, 09:22 AM   #51 (permalink)
Freddyack
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Quote:
Originally Posted by vanuatu chevy View Post
Codes yes 6 of them Po 251,370,380.4104,406 and 236 I think most relating to lack of fuel
P0236 Turbocharger Boost System
P0251 Injection Pump Cam System
P0370 Timing Reference High Resolution
P0380 Glow Plug Circuit Performance
P0406 EGR Sensor Circuit High Voltage

Not sure what "4104" is

Corrosion must be a problem where you live. Recommend you thoroughly clean your ground connections. See this: https://www.dieselplace.com/forum/63-...d-grounds.html. Cleaning your grounds may help get rid of some of these codes.

P0251 & P0370 are usually related to the injection pump Optic Sensor. Most likely dirty and needs a thorough cleaning by using heavy doses of "Sea Foam" or "Diesel Kleen" fuel additive.

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Old 09-05-2014, 03:21 PM   #52 (permalink)
HeavyChevy95
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Heres a very insightful and informative 6.5L Diagnostic Check List



Quote:
Originally Posted by racer55 View Post
For OBDII primary power for the LP is as shown in the diagram,the ECM activates the prime cycle through the relay and once it sees a running engine from OS/CPS signals activates the relay for constant run operation.
Should the relay circuit fail,the OPS is backup LP power-it also operates the LP after engine shutdown while oil pressure bleeds off.

P0231 Fuel Pump Feedback Circuit Low Voltage

Racer. Not that I dont believe you, but I want to see the OBD2 6.5L diesel specific "Fuel Pump Circuit Description" and "Diagnostic Chart" with "Test Description(s)" for myself. Copied directly from an authorized factory service manual, much like I routinely provide for OBD1 owners. Not some randumb internet source or someones "independent" studies..

Please. Can SOMEONE provide the applicable "Fuel Pump Relay Circuit Diagnosis Chart" with the "Circuit description" for OBD2 models that can confirm the info being provided is completely accurate. Thanks..

Everything I find about P0231 nearly confirms our current understanding of the OBD2 lift pump relay circuit description, only its applicable to gasoline engines. Cant find ANY specific to C/K 6.5 diesels (OBD2) from any FSMs.

Sorry Freddy but that "wiring schematic" isnt factory authorized...
Looks alot like this '94 Engine Schematic I found at autozone. Notice the LPR circuit,, oh pooh wheres the OPS represented at? Wait thats not right at all.
Stands to reason if that '94 schematic is inaccurate, I wouldnt put much stock in that '96-98 schematics accuracy, most likely came from the same source of misinformation...





Quote:
Originally Posted by racer55 View Post
To the OP:
Behind the underhood fusebox is a single red wire with a female spade terminal and a white or black insulator-this is the test lead for LP activation or priming a new fuel filter.
If you apply 12v to that red wire the LP should run through the normally closed contacts of the relay.

The OP might also need to check out the condition of the LP ground wire that should be located along the frame very near the LP-high resistance at the ground can cause excess amperage draw.
X2 Thankyou for articulating that point far better than I.
If theres a LP or LPR Circuit problem, regardless what is eventually found faulty. Take a few extra minutes and actually clean the grounds too..


Last edited by HeavyChevy95; 09-05-2014 at 03:23 PM.
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Old 09-05-2014, 03:27 PM   #53 (permalink)
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When time permits I will try to source that trouble tree from the 2000 3500HD manual I have.
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Old 09-05-2014, 04:28 PM   #54 (permalink)
Freddyack
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Quote:
Originally Posted by HeavyChevy95 View Post
Racer. Not that I dont believe you, but I want to see the OBD2 6.5L diesel specific "Fuel Pump Circuit Description" and "Diagnostic Chart" with "Test Description(s)" for myself. Copied directly from an authorized factory service manual, much like I routinely provide for OBD1 owners. Not some randumb internet source or someones "independent" studies..

Please. Can SOMEONE provide the applicable "Fuel Pump Relay Circuit Diagnosis Chart" with the "Circuit description" for OBD2 models that can confirm the info being provided is completely accurate. Thanks..
Quote:
Originally Posted by HeavyChevy95 View Post
Sorry Freddy but that "wiring schematic" isnt factory authorized... Looks alot like this '94 Engine Schematic I found at autozone. Notice the LPR circuit,, oh pooh wheres the OPS represented at? Wait thats not right at all. Stands to reason if that '94 schematic is inaccurate, I wouldnt put much stock in that '96-98 schematics accuracy, most likely came from the same source of misinformation...
No what I posted is not a factory wiring schematic.

I cannot verify these two are either, but at least page 2 has the OPS circuit(s). I swiped these from here: https://www.dieselplace.com/forum/63-...ml#post4469709
Attached Images
File Type: jpg 1996 Engine Controls Pg 1.jpg (101.6 KB, 185 views)
File Type: jpg 1996 Engine Controls Pg 2.jpg (73.7 KB, 147 views)
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Old 09-05-2014, 06:00 PM   #55 (permalink)
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Actually they both have the OPS in the circuit and ARE from the 2001 6.5 L65 3500HD manual.

Trouble tree to follow as requested for informational purposes only.
Attached Images
File Type: jpg fuel system diagnosis 1_0001.jpg (77.8 KB, 36 views)
File Type: jpg fuel system diagnosis 2.jpg (82.1 KB, 39 views)
File Type: jpg fuel system diagnosis 3.jpg (96.7 KB, 41 views)
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Last edited by racer55; 09-05-2014 at 06:26 PM.
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Old 09-05-2014, 07:21 PM   #56 (permalink)
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Originally Posted by racer55 View Post
Actually they both have the OPS in the circuit and ARE from the 2001 6.5 L65 3500HD manual.
I see the OPS circuits in both now. More than a bit under the weather today...
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Old 09-05-2014, 07:48 PM   #57 (permalink)
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where will I find the fuel pump test terminal ? Weather here is hot 30 just about to get the boat over to work on the truck have down loaded all the check info I could find and will go through it. fingers crossed cheers .if you ever need a holiday check out my place Beach house on private island - Home
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Old 09-05-2014, 11:08 PM   #58 (permalink)
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Quote:
Originally Posted by Freddyack View Post
Do you have any DTC codes from the truck's computer?

How much fuel is in the tank?

Do you have a voltmeter? If so,

1. Disconnect the electrical power to the lift pump.
2. Put transmission in D (drive)
3. Turn the ignition key to ON (not start)
4. Check for voltage at the the connector the lift pump plugs into.
5. Do you have power at the connector?
No power at connector.
I think I may have a faulty oil pressure switch is there a bypass I can do for now ? I also had a kink in the fuel line just in front of the sender unit. Straightened that a little .I ran power to the pump to prime the filter
.
Truck is running for now no fault codes see how it goes to town Monday. Off now for a swim
Thanks for the help
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Old 09-05-2014, 11:18 PM   #59 (permalink)
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Do you have a FSM diagnostic chart or trouble tree for DTC P0231?

Thats odd Racer.. Your "Circuit Description" nor "Diagnosis Chart" never mentions the OPS nor what role, if any, it plays in the Fuel Pump Electrical Circuit as shown in this schematic which appears to be significantly different than the schematic in post 47. so to eliminate any further misinformation, could everyone please limit there info to and provide the GM Title(s) and publication number(s) of any/all reference material.


Assuming this schematic is accurate.. Take note of the ECM-B power feed. Virtually a straight shot to and through the OPS before reaching the lp...
It appears to me the PCM D8 (?) connection is the glow/LP prime signal. Then once the OPS is HOT (engine "ON"), the PCM simply monitors the LPR circuit via PCM D5 connection.
The OPS wouldnt be in the loop if it didnt play some role... How do you explain OBD2 LPR circuit faults and/or inop LPs resulting from just a faulty OPS?
Not lookin for an argument, just ensure that we are passing on accurate info. That is all..




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Old 09-05-2014, 11:54 PM   #60 (permalink)
Freddyack
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Quote:
Originally Posted by HeavyChevy95 View Post
Assuming this schematic is accurate.. Take note of the ECM-B power feed. Virtually a straight shot to and through the OPS before reaching the lp... It appears to me the PCM D8 (?) connection is the glow/LP prime signal. Then once the OPS is HOT (engine "ON"), the PCM simply monitors the LPR circuit via PCM D5 connection.
The OPS wouldnt be in the loop if it didnt play some role... How do you explain OBD2 LPR circuit faults and/or inop LPs resulting from just a faulty OPS?
Not lookin for an argument, just ensure that we are passing on accurate info. That is all..
My thoughts:

1. GM didn't eliminate the safety role of the OPS. Loss of oil pressure shuts off lift pump.

2. PCM D8 seems to be designed to sense interruption in current flow from both the relay and the OPS. How does it do this....

The OP states he does not have voltage at the lift pump connector. So, if the OPS is active in LP operation, then a bad one could cause the ECM to cut the power to the lP. And/or the LP relay is bad. Should be able to test each gray wire going from the relay and OPS for 12v to figure out which is not working.

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