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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 04-07-2015, 01:11 PM   #11 (permalink)
Glagulator
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#8 is the CPS.
Look where the wires enter the sensor for missing insulation/short.
If the CPS is bad there should be a code 19 and you will be in limp mode.
It will be harder to start than normal.
Unplug the CPS and see if anything changes.
If not, plug the CPS back in, then unplug the OS and if it will not start then the CPS may be bad.
Search GM 12557046 to see what the CPS looks like.

CPS01.jpg

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96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine & main harness, converted to OBD2, PMD to bumper...
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Old 04-11-2015, 12:26 AM   #12 (permalink)
hkusamdoc
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Thanks for all the help. The timing cover is off. Would this cause a CPS fault code ? Would a faulty CPS cause starting problems but then allow engine, once started, to run normally ? This doesn't make sense to me.

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94 GMC 2500 TD Not mine yet. Has starting problem. Told that error code is crankshaft sensor and needs a new wiring harness. I am beginning my research before spending $ on what may not fix.
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Old 04-11-2015, 12:58 AM   #13 (permalink)
hkusamdoc
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Thanks for the diagram and advice. I didn't see that there was a page 2 of my thread. If I follow your suggestion, a bad CPS may cause starting problems, so if I unplug there should be no change. I don't know what OS is, but bad CPS and OS unplugged results in no start. Does this mean that good CPS and unplugged OS may still start ?
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94 GMC 2500 TD Not mine yet. Has starting problem. Told that error code is crankshaft sensor and needs a new wiring harness. I am beginning my research before spending $ on what may not fix.
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Old 04-11-2015, 01:16 AM   #14 (permalink)
Glagulator
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OS is the optical sensor on top of the injection pump (6 pin connector). The OS has 2 engine speed sensors for IP control and combined with the CPS the computer keeps things running.
Either the CPS or the OS can quit and the other will keep the engine running but the computer will go into a limp mode, set codes, and be harder to start, long cranking times.
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99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine & main harness, converted to OBD2, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 04-11-2015, 01:21 AM   #15 (permalink)
quadstar87
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I can't stress enough how cheap GMTD scan software and a DIY cable are compared to time spent guessing. You can figure out your issues with the free version.

If it shows any missed cam or crank references, then you know what to fix. Pending codes and live data make troubleshooting a breeze.

Did you say your timing cover is removed but you are still running it??

Last edited by quadstar87; 04-11-2015 at 01:24 AM.
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Old 04-11-2015, 12:15 PM   #16 (permalink)
hkusamdoc
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No, the truck is not mine yet and timing cover was removed as part of the troubleshooting. Two shops told the owner about the CPS fault code and one recommended a new wiring harness. The owner is gifting the truck, but I don't want to own a lemon. I have learned a lot from this thread in case I do own a GM diesel. Thank all of you very much. Now I am working on a Zetor tractor and will not bother you again about this truck unless I bring it home and start working on it myself.
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Old 12-15-2017, 02:34 AM   #17 (permalink)
Iraqvet
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Quote:
Originally Posted by quadstar87 View Post
I can't stress enough how cheap GMTD scan software and a DIY cable are compared to time spent guessing. You can figure out your issues with the free version.

If it shows any missed cam or crank references, then you know what to fix. Pending codes and live data make troubleshooting a breeze.

Did you say your timing cover is removed but you are still running it??
Are you saying a free programs to read the pcm. Also, what about this dyi cable?
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Old 12-16-2017, 11:07 AM   #18 (permalink)
Okiebenz
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Quote:
Originally Posted by Iraqvet View Post
Are you saying a free programs to read the pcm. Also, what about this dyi cable?
Yes I would love to hear about this myself
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