Help please ? 6.5 td lift pump problems - Diesel Bombers



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Old 02-21-2015, 11:54 AM
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Default Help please ? 6.5 td lift pump problems

I have a 95 6.5 td k2500 suburban , now I have been having a ton of problems with this thing lately. I had replaced " with new " the injectors , the filter , injector pump " three times " , pmd , fuel pump relay, fly by wire throttle sensor, fuel tank , parts of the fuel lines that were rusted , crank shaft position sensor , .. Here are some things still clearly wrong with it.. The vacuum pump stopped working so I temporarily wired the waste gate shut cause around 70 mph it was bogging out , right now when key on I don't hear the lift pump prep , extremely hard to start it takes me about 10 15 minutes to start the truck, and when it does start a check engine like it on and rpm pulse and the motor sounds very very different , everyonce in a while during driving periods it will suddenly shut off for a spit second , it will run dead =" like I Jammed the breaks "run dead dead runnnn dead runnn dead dead dead , the more I hit the gas to try to get it to go and stop from dying it bogs out more to the point where it's gonna shut off and I have to pull over shut it off and restart it but still acts up , ops reads roughly just under 40 psi and I everyone in a while I have to tighten the batt cables on the batts because they come loose idk how. And also notice when it's acting up the volts gauge reads lower then normal but that's with all light on , both heaters on , and it doesn't over heat it runs about 180 / 190 ,,also I forgot to mention , when the truck is off and in gear besides neutral and park if I turn the key to start I hear the lift pump , but don't hear it when it's running, and when I open the waste valve the truck stays running and getting a decent amount of fuel coming out .. Dealerships can't find the problem and has several codes coming up all pertaining to the ip circuits , iv checked all wire plugs and did ground and lead and load tests on all the wires in the harness for shorts such.. Also idk if this is normal but when cranking it the speed gauge comes up to 10 mph and rpm come to about 3 / 500 please help me someone
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Old 02-21-2015, 02:41 PM
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I have a 95 6.5 td k2500 suburban , now I have been having a ton of problems with this thing lately. I had replaced " with new " the injectors , the filter , injector pump " three times " , pmd , fuel pump relay, fly by wire throttle sensor, fuel tank , parts of the fuel lines that were rusted , crank shaft position sensor , .. Here are some things still clearly wrong with it.. The vacuum pump stopped working so I temporarily wired the waste gate shut cause around 70 mph it was bogging out , right now when key on I don't hear the lift pump prep , extremely hard to start it takes me about 10 15 minutes to start the truck, and when it does start a check engine like it on and rpm pulse and the motor sounds very very different , everyonce in a while during driving periods it will suddenly shut off for a spit second , it will run dead =" like I Jammed the breaks "run dead dead runnnn dead runnn dead dead dead , the more I hit the gas to try to get it to go and stop from dying it bogs out more to the point where it's gonna shut off and I have to pull over shut it off and restart it but still acts up , ops reads roughly just under 40 psi and I everyone in a while I have to tighten the batt cables on the batts because they come loose idk how. And also notice when it's acting up the volts gauge reads lower then normal but that's with all light on , both heaters on , and it doesn't over heat it runs about 180 / 190 ,,also I forgot to mention , when the truck is off and in gear besides neutral and park if I turn the key to start I hear the lift pump , but don't hear it when it's running, and when I open the waste valve the truck stays running and getting a decent amount of fuel coming out .. Dealerships can't find the problem and has several codes coming up all pertaining to the ip circuits , iv checked all wire plugs and did ground and lead and load tests on all the wires in the harness for shorts such.. Also idk if this is normal but when cranking it the speed gauge comes up to 10 mph and rpm come to about 3 / 500 please help me someone

It would help to have all the codes you are getting first of all because without them it is a shot in the dark. And then you did say you wired the waste gate closed and that may be an over boost problem but with out the codes we won't know that so get the codes and we can go from there.
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Old 02-21-2015, 03:57 PM
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It would help to have all the codes you are getting first of all because without them it is a shot in the dark. And then you did say you wired the waste gate closed and that may be an over boost problem but with out the codes we won't know that so get the codes and we can go from there.
Ok yea I'll get the codes, how do I contact you with the codes or will you keep an eye out for my message ? How does that work?
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Old 02-21-2015, 04:48 PM
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Ok yea I'll get the codes, how do I contact you with the codes or will you keep an eye out for my message ? How does that work?
Keep an eye on your email inbox.
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Old 02-21-2015, 04:54 PM
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Ok thank you and codes are 17 , 18 , 35 , 36 , 54 , 73
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Old 02-22-2015, 05:42 AM
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Got all that money for new IP's, PMD kits, lift pumps, fuel tanks, fuel lines, etc, but wired the wastegate shut to "temporarily" fix busted vacuum pump? Surprised DTC 78 wasnt there also.. Was that problem ever properly repaired?
Of course the engine will bog (lack power) at 70mph when the turbo isnt working properly, and the PCM will default to "Backup Fuel" ie cuts BOOST (or so it thinks) and reduces/fix's FUEL when excessive boost is detected, only youve wired the WGV shut so your likely not seeing the "signs" excessive black smoke as you would under "normal" operating conditions when exposed to increased engine loads.. Rather, your more likely feeling the lack of power due to reduced/fixed fuel rates. Fix and/or restore the stock vacuum pump/ boost system asap..

As to the "Fishbiting, and the more you press the accelerator, the worse it gets..." paraphrasing of course.


Undiagnosed air leak most likely, possibly resulting from fuel restriction..



17, 18, 19, 35, 36, and other spooky DTCs can and are often result from air infiltration. In fact, those are the most COMMONLY found DTCs following a routine fuel filter element replacement and other fuel supply system repairs, anything that opens the sealed fuel system requiring "Bleeding Air From Fuel Supply System" (see attached). Note the last step of the procedure thats rarely ever done by pro's or DIYrs alike.

DTC 56 PCM Fuel Circuit Error diagnostic aid states and I quote "Check to see if DTC 17 is also stored, if there is refer to that chart first, if not, replace PCM."
Note DTC 17's Diagnostic Aids (attached)......



Can we assume the fuel sender was also replaced with the new fuel tank?
Was the fuel strainer replaced and if so, was it replaced with the correct one?
Nearly all new aftermarket replacement 6.5L diesel fuel senders come pre-assembled with the WRONG (gasoline) fuel strainers that in cold weather operations, severely restrict fuel flow, which can quicly overheat (prematurely and permanitely damage) lift pumps and/or OPS.
If it doesnt look exactly like the fuel strainer w/ visable by-pass (see attached), one on the left being new replacement, guess what.... Probably going to have to PAY them to check and likely redo the common fork up..
If its all new, almost gauranteed its the WRONG strainer and is most likely RESTRICTING FUEL SUPPLY and prematurely damaging the lift pumps and/or OPS..


And before others tells you to delete the fuel strainer in lue of an in-line fuel flter. Just know that doing so may actually exacerbate the fuel restriction (starvation) problem, specially during cold weather operation.. A fuel heater was incorporated into the FFM housing for a reason, speaking of, does it even work?
Its also possible to have aerated fuel aka air leak although there isnt an external air leak present. I'll skip the science lesson and point you to this TSB 94-6R2- Suction / Vacuum Side Diesel Fuel Filters

Clogged pre lift pump fuel filter, restricted fuel strainer, same thing. Exposes the fuel to high vacuum releasing fumes, vapors (not liquid fuel) might as well be a knife being repeatedly jabbed in the Optical Sensors eye, PCM often freaks and may take a time out. OBD1 models are the worst, most sensitive to air, cloudy fuel, contaminated fuel, read anything that disrupts the OS most important PCM INPUTS, is a problem..



Theres a little known SAFETY FEATURE programmed into the PCM that got lost in the programming notes editing room floor. Optical Sensor provides the PCM with the most important signals. When OS signals are missed, the PCM is for all intensive purposes, "flying blind" on auto pilot aka "Backup Fuel". Depending on the frequency and/or severity of the condition, the PCM may take a short break to re-evalute the s'ituation...

Can I get a PMD anyone..

Fuel is the only form of lubrication of these most expensive injection pumps, as such GM took steps to protect these IPs, if even from ourselves.. Cant have inattentive operators trashing IPs everytime the run out of fuel or attempting to run on fumes... If that makes any sence, need more coffeee..


Excessive Cranking, Hard Start, No Start, are also driveability symptoms of AIR INFILTRATION. See attached "Intermittents," notice a reoccurring theme?




Needlessly throwing new parts at it presents another problem. 3rd recent replacement IP for example. We must assume it was properly installed and TDCO procedure was properly/successfully done, much like the rest of the work thats NOW IN QUESTION AGAIN... Surprised the stealership hasn't misdiagnosing a faulty PCM yet, if the tech(s) claim "PCM not communicating" grab your s'it and RUN FOREST RUN....
Hate to say it but you must start over again, assuming nothing. New yesterday, dont matter.. Good Luck..
Attached Thumbnails
Help please ? 6.5 td lift pump problems-bleeding-air-fuel-supply-system.jpg   Help please ? 6.5 td lift pump problems-chart-3a-engine-cranks-but-will-not-run.jpg   Help please ? 6.5 td lift pump problems-chart-3b-engine-cranks-but-will-not-run.jpg   Help please ? 6.5 td lift pump problems-fuel-strainer-diesel-pass.jpg   Help please ? 6.5 td lift pump problems-dtc-17a.jpg  

Help please ? 6.5 td lift pump problems-dtc-17b.jpg  
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Old 02-22-2015, 10:31 PM
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Originally Posted by HeavyChevy95 View Post
Got all that money for new IP's, PMD kits, lift pumps, fuel tanks, fuel lines, etc, but wired the wastegate shut to "temporarily" fix busted vacuum pump? Surprised DTC 78 wasnt there also.. Was that problem ever properly repaired?
Of course the engine will bog (lack power) at 70mph when the turbo isnt working properly, and the PCM will default to "Backup Fuel" ie cuts BOOST (or so it thinks) and reduces/fix's FUEL when excessive boost is detected, only youve wired the WGV shut so your likely not seeing the "signs" excessive black smoke as you would under "normal" operating conditions when exposed to increased engine loads.. Rather, your more likely feeling the lack of power due to reduced/fixed fuel rates. Fix and/or restore the stock vacuum pump/ boost system asap..

As to the "Fishbiting, and the more you press the accelerator, the worse it gets..." paraphrasing of course.


Undiagnosed air leak most likely, possibly resulting from fuel restriction..



17, 18, 19, 35, 36, and other spooky DTCs can and are often result from air infiltration. In fact, those are the most COMMONLY found DTCs following a routine fuel filter element replacement and other fuel supply system repairs, anything that opens the sealed fuel system requiring "Bleeding Air From Fuel Supply System" (see attached). Note the last step of the procedure thats rarely ever done by pro's or DIYrs alike.

DTC 56 PCM Fuel Circuit Error diagnostic aid states and I quote "Check to see if DTC 17 is also stored, if there is refer to that chart first, if not, replace PCM."
Note DTC 17's Diagnostic Aids (attached)......



Can we assume the fuel sender was also replaced with the new fuel tank?
Was the fuel strainer replaced and if so, was it replaced with the correct one?
Nearly all new aftermarket replacement 6.5L diesel fuel senders come pre-assembled with the WRONG (gasoline) fuel strainers that in cold weather operations, severely restrict fuel flow, which can quicly overheat (prematurely and permanitely damage) lift pumps and/or OPS.
If it doesnt look exactly like the fuel strainer w/ visable by-pass (see attached), one on the left being new replacement, guess what.... Probably going to have to PAY them to check and likely redo the common fork up..
If its all new, almost gauranteed its the WRONG strainer and is most likely RESTRICTING FUEL SUPPLY and prematurely damaging the lift pumps and/or OPS..


And before others tells you to delete the fuel strainer in lue of an in-line fuel flter. Just know that doing so may actually exacerbate the fuel restriction (starvation) problem, specially during cold weather operation.. A fuel heater was incorporated into the FFM housing for a reason, speaking of, does it even work?
Its also possible to have aerated fuel aka air leak although there isnt an external air leak present. I'll skip the science lesson and point you to this TSB 94-6R2- Suction / Vacuum Side Diesel Fuel Filters

Clogged pre lift pump fuel filter, restricted fuel strainer, same thing. Exposes the fuel to high vacuum releasing fumes, vapors (not liquid fuel) might as well be a knife being repeatedly jabbed in the Optical Sensors eye, PCM often freaks and may take a time out. OBD1 models are the worst, most sensitive to air, cloudy fuel, contaminated fuel, read anything that disrupts the OS most important PCM INPUTS, is a problem..



Theres a little known SAFETY FEATURE programmed into the PCM that got lost in the programming notes editing room floor. Optical Sensor provides the PCM with the most important signals. When OS signals are missed, the PCM is for all intensive purposes, "flying blind" on auto pilot aka "Backup Fuel". Depending on the frequency and/or severity of the condition, the PCM may take a short break to re-evalute the s'ituation...

Can I get a PMD anyone..

Fuel is the only form of lubrication of these most expensive injection pumps, as such GM took steps to protect these IPs, if even from ourselves.. Cant have inattentive operators trashing IPs everytime the run out of fuel or attempting to run on fumes... If that makes any sence, need more coffeee..


Excessive Cranking, Hard Start, No Start, are also driveability symptoms of AIR INFILTRATION. See attached "Intermittents," notice a reoccurring theme?




Needlessly throwing new parts at it presents another problem. 3rd recent replacement IP for example. We must assume it was properly installed and TDCO procedure was properly/successfully done, much like the rest of the work thats NOW IN QUESTION AGAIN... Surprised the stealership hasn't misdiagnosing a faulty PCM yet, if the tech(s) claim "PCM not communicating" grab your s'it and RUN FOREST RUN....
Hate to say it but you must start over again, assuming nothing. New yesterday, dont matter.. Good Luck..
I have not fixed the waste gate but will promptly, and the fuel filter heat is working, and iv had each ip taken to a specialist shop with equipment designed to bench test the ip's each of the two came back bad, as far as install was all done by two different dealerships. At one point before I bought the truck I saw the ecm was replaced " not the original " the truck was also fine up until I had to replace part of the fuel line on the frame rail , the rubber section going from the frame rail to filter " between the lift pump and filter " ever since then iv had problems with it not running right and stalling. And while replacement of that part the filter was flushed and changed. The truck then sat for about ten years and recently have been trying to get it fixed for my sons graduation gift cause has loves the truck and they are very hard , almost impossible for me to find. And I do once in a while see air in the clear line I put in on the return from the ip. But I don't see any leaks beside a oil leak by the oil filter , but I have cleaned and changed the filter and not sure where it's coming from, I don't know if that has anything to do with my problems though. And it's the original strainer I believe , but have notice the fuel gauge floats , I heard there is a plate that comes loose in the tank and bends the pick up shut , and that's why it floats. I'm not sure how true that is. And you have given me very useful information thank you.. A lot ton. But back to the truck as far as noticing a reoccurring theme , none that I or can induce. Tho I do know the battery cables kept coming loose till I replaced the bolts. Some times it starts in less then a second after glow and runs flawlessly , sometimes more then half it takes seer minutes of key on key off and quick blurps of the starter
I can get it to start fine, other wise it takes 5 or so straight minutes of cranking and it's guaranteed to run shitty with a light on surging and stalling, there are times where it will start and run fine but stall restart shitty or it will start shitty run it a bit shut it down restart and run flawlessly for several miles fine or times it will be that process and stall.
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Old 02-22-2015, 10:40 PM
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Yes coffee is very neededdded. I'm chasing this ghost and it's driving my crazy and running my wallet dry
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Old 02-22-2015, 11:42 PM
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I forgot the "Intermittent" Diagnostic Aids, here they are...
The trend I was referring to is nearly all have "CHECK: For air in the fuel supply to IP."


to be continued.
Attached Thumbnails
Help please ? 6.5 td lift pump problems-driveability-symptoms.jpg   Help please ? 6.5 td lift pump problems-excessive-smoke-1.jpg   Help please ? 6.5 td lift pump problems-excessive-smoke-2.jpg   Help please ? 6.5 td lift pump problems-fuel-knock-combustion-noise.jpg   Help please ? 6.5 td lift pump problems-hard-start-1.jpg  

Help please ? 6.5 td lift pump problems-hard-start-2.jpg  
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Old 02-22-2015, 11:44 PM
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some more..
Attached Thumbnails
Help please ? 6.5 td lift pump problems-important-preliminary-checks.jpg   Help please ? 6.5 td lift pump problems-intermittents-1.jpg   Help please ? 6.5 td lift pump problems-intermittents-2.jpg   Help please ? 6.5 td lift pump problems-lack-power-sluggish-spongy-1.jpg   Help please ? 6.5 td lift pump problems-lack-power-sluggish-spongy-2.jpg  

Help please ? 6.5 td lift pump problems-poor-fuel-economy.jpg   Help please ? 6.5 td lift pump problems-surges-chuggles.jpg  
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