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6.5L Turbo Diesel 1992-00 6.5L Turbo Diesel - Welcome to the Internet's first discussion forum for the 6.5L diesel engine. Tips on performance, cooling, fuel economy, troubleshooting and more.

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  #1  
Old 06-14-2018, 08:48 PM
jerry598 jerry598 is offline
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Posts: 188
Default Sudden Change in Glow Plug Cycle

Glow plug cycling has been perfect on start-up for years now. Suddenly it changed. When key is turned on, glow light cycle on dash lasts only a second or less. After several attempts, I can get a long enough cycle barely enough to start the engine and then it will cycle normally for a couple times after starting up.

Would this be related primarily to the glow plug relay? Or, could it be the PCM? I do have a spare, brand new GPR that I plan to put in tomorrow. Other than the GPR or the PCM, are there any other possibilities except maybe the ignition switch or something like that? There are no codes set.

I see on some posts that a faulty or failing temp sensor might be a possible suspect, but my temp guage seems to be operating normally.
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Black 95 6.5 929 block, 146k miles, 43k on IP, 22k miles on engine rebuild done myself in '09, 6 L&S Full-torque inserts in the outer main crank bolt holes, Clearwater heads, Fluidamper, rebuilt NV4500, 3" downpipe, 4" exhaust, no cat, dual T-stats, 9 blade fan, 180 degree clutch, Heath hi-flow spin-on water pump w/ restricted orifice, turbomaster, PMD relocated, OPS relay mod, Heath PROM upgrade (great performance boost, especially startups). Now us semi-syn Lucas 2-cycle oil in every tank which fixed a DTC 35 code.

Last edited by jerry598; 06-14-2018 at 11:22 PM.
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Old 06-15-2018, 05:32 AM
Robyn's Avatar
Robyn Robyn is offline
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Default

Hi

The glow plug relay/controller is likely the culprit.

The coolant temp sensor does not run the gauge.

Gauge is controlled by a separate sender on the LH head near the front.

Tossing in a new Coolant temp sensor in the water crossover is not going top hurt a thing and are not costly.

The PCM does act upon the entire system, but the glow relay is most likely the issue and is causing the goofy operation.


You can check the coolant temp sensor by unplugging it after the engine is warmed up..

Unplugging the sensor should cause the engine to speed up a bit a the engine should rattle a lot sharper with the sensor unplugged.

If nothing changes then the sensor is not working properly


A failed sensor thats failed in the WARM/HOT mode will not allow the cold advance and can also limit the glow cycle too....


Both items can cause issues.


Before you spend $$$

on a cold engine..

Try turning the key on and if glow cycle is short ...turn off key and unplug coolant temp sensor then turn key back on and see if glow cycle is propper.


If glow cycle is correct then replace sensor.

If cycle is still too fast then replace the glow controller.

Good luck
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Old 06-15-2018, 08:21 AM
jerry598 jerry598 is offline
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Thanks Robyn! Glad you are still a regular contributor. Your advice is always my favorite and easiest to follow. That said, I tried disconnecting the two temp sensors while the engine was cold this morning and there was no change is symptoms. Took 3 tries to get a normal 5+ second glow cycle and then she fired fine. I will replace the glow relay today and let you know the outcome. Thanks again! I do love my truck. With the Heath Performance prom and turbo master and his cooling system upgrade I installed about 5 years ago, I've never had a better running truck. This one will be with me forever.
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Black 95 6.5 929 block, 146k miles, 43k on IP, 22k miles on engine rebuild done myself in '09, 6 L&S Full-torque inserts in the outer main crank bolt holes, Clearwater heads, Fluidamper, rebuilt NV4500, 3" downpipe, 4" exhaust, no cat, dual T-stats, 9 blade fan, 180 degree clutch, Heath hi-flow spin-on water pump w/ restricted orifice, turbomaster, PMD relocated, OPS relay mod, Heath PROM upgrade (great performance boost, especially startups). Now us semi-syn Lucas 2-cycle oil in every tank which fixed a DTC 35 code.
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Old 06-15-2018, 06:28 PM
jerry598 jerry598 is offline
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Thanks Robyn, it worked. Simple fix. Just a new glow plug relay was all it needed.
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Black 95 6.5 929 block, 146k miles, 43k on IP, 22k miles on engine rebuild done myself in '09, 6 L&S Full-torque inserts in the outer main crank bolt holes, Clearwater heads, Fluidamper, rebuilt NV4500, 3" downpipe, 4" exhaust, no cat, dual T-stats, 9 blade fan, 180 degree clutch, Heath hi-flow spin-on water pump w/ restricted orifice, turbomaster, PMD relocated, OPS relay mod, Heath PROM upgrade (great performance boost, especially startups). Now us semi-syn Lucas 2-cycle oil in every tank which fixed a DTC 35 code.
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