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Discussion Starter #1 (Edited by Moderator)
This Chump is Stumped. Interested in opinions.


1997 Suburban K1500 310K miles original engine and transmission.
New fuel injection pump.
Recent injectors.
PMD replaced.
Recent fuel filter.
Fuel fresh and from good source.



After sitting for a day or two truck will start up just fine runs as it should. While still warming up, back out of driveway and start accelerating out of neighborhood up a hill. Truck cuts out intermittently otherwise runs fine. By time I get to the next traffic light no symptoms at all. Can drive down interstate, next several hours, start stop nothing. Purrs like a kitten. Only misses after a start and setting for a day of inactivity.


I hear the lift pump click as you would expect when turning ignition on. Perhaps clicking does not necessarily indicate fuel is being pumped?


Thanks in advance for help.
 

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A few things I have had issues with on fuel supply...
-check valve on lift pump discharge built into (LP) not holding---might cause air intrusion
-fuel line that feeds the LP suction from the tank has leak---cause air intrusion
-fuel filter canister has slight leak that hides in the engine valley--more likely to cause fuel leak
-fuel flow is restricted during heavy engine loading (inner fuel tank sock restriction)---more likely to cause sputter hiccup under heavy throttle
 

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Discussion Starter #4 (Edited by Moderator)
Thank-you

Great feedback thank-you! Do you know if the sock in tank can be accessed without dropping the tank? Truck is 22 years old and as diesel goes in a tank there might be alot of snot in the bottom potentially clogging the pick up. Not sure how long this truck will continue to go but I care for it and it certainly has served the family. Thanks again. I will post when I come to a resolution.
 

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Great feedback thank-you! Do you know if the sock in tank can be accessed without dropping the tank? Truck is 22 years old and as diesel goes in a tank there might be alot of snot in the bottom potentially clogging the pick up. Not sure how long this truck will continue to go but I care for it and it certainly has served the family. Thanks again. I will post when I come to a resolution.
The only other way to access the tank in a Suburban is to cut an access panel into the floor of the body.
Otherwise, you are stuck dropping the tank.
One way to test the sock is to disconnect the fuel line at the lift pump and blow compressed air through the line towards the tank.
The air should dislodge any contaminants off the sock and allow fuel to flow for a test run.
After reassembly, take it for a drive and see if it improves
 

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This is also something I have done with limited success...use existing or buy another Lift Pump (LP). You will need about 6 foot of rubber fuel line.

Disconnect the normal LP suction line (S1), use caution fuel may escape, be ready to plug off line just like if you were preparing to change out the LP.

Run temporary fuel line down the filler neck of the fuel tank, hook up LP suction to the temporary line and hook up LP discharge to S1 normal LP suction line tank side of the OEM lift pump suction.

Supply 12V to the temporary LP and viola fuel will now flow backwards into the tank and back-flush the snot off the tank sock. More effective than blowing air IME.

HTH's
 

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Discussion Starter #7
So here it is January and I finally was able to do more troubleshooting.



When I jump the relay for the lift pump and open the vent on the top of the fuel filter I get plenty of flow (mess in a real hurry). Thinking that perhaps the issue was with the relay and/or oil pressure switch I replaced both. New Omron relay and new oil pressure switch after shelling out about $65 for the Snap-on crow foot tool to reach it.


Still have the issue. Perhaps the o-ring on the filter cap?



You can start the engine cold and it runs great. Back out of driveway and go about a 1/4 mile up a hill to a light and it misses. After that maybe once or twice then nothing. Can drive it long distance on Interstate with no issue. Miss does not return until engine cold again and has been sitting.
 

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So here it is January and I finally was able to do more troubleshooting.



When I jump the relay for the lift pump and open the vent on the top of the fuel filter I get plenty of flow (mess in a real hurry). Thinking that perhaps the issue was with the relay and/or oil pressure switch I replaced both. New Omron relay and new oil pressure switch after shelling out about $65 for the Snap-on crow foot tool to reach it.


Still have the issue. Perhaps the o-ring on the filter cap?



You can start the engine cold and it runs great. Back out of driveway and go about a 1/4 mile up a hill to a light and it misses. After that maybe once or twice then nothing. Can drive it long distance on Interstate with no issue. Miss does not return until engine cold again and has been sitting.
The bleeder screw on top of the filter is for bleeding air, not for checking fuel flow.
Start the engine and then open the t valve for 30 seconds and let fuel drain into a container.
You should see 1/2 pint of fuel in the container in 15 seconds.
If you see no fuel flowing from the drain line and/or your engine dies during that 30 seconds your lift pump is too weak to support the engine and needs to be replaced.

Did you replace the OPS with an AC/Delco brand?
If not, aftermarket parts will bring gremlins to a 6.5L, change it.

Install a piece of clear fuel line as I mentioned in post #2
 

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Discussion Starter #9
Saw a post this morning that said there should be no vacuum in fuel tank. Truck has been sitting all night. Opened the fuel cap and whoosh... vacuum. Could this be it? As far as I remember always has done this.
 

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Saw a post this morning that said there should be no vacuum in fuel tank. Truck has been sitting all night. Opened the fuel cap and whoosh... vacuum. Could this be it? As far as I remember always has done this.
A slight vacuum is normal. If you open the cap and hear a large "Whoosh" then you would have a restriction in the fuel system and would need to modify your fuel cap for better venting.
 

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The best test is to measure the pressure of the fuel.

You CANNOT start throwing parts at it with a chance to introduce "new bad parts" (I know it is a moron statement) into the system.

All sensors and electrical parts need to be ACDelco, otherwise you ran a chance of introduce another issue.

Is there any DTC? I have something similar to this when CPS was weak, it shows DTC, though.
 
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Thanks OKDually! As soon as the weather improves here I will try that test.

Uggg....OPS Autozone lifetime warranty
Return the Autozone OPS.
The reason that they have lifetime warranty is for you to be their Quality Controller.

Order ACDelco D1808A from Amazon or RockAuto.
 

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Discussion Starter #14
So I started the truck, opened the t-valve on top of engine and she filled a mason jar 16 oz or more in about 15 seconds and did not stall with valve open.
The Omron relay is GM exact replacement.
I guess I can try to clear line and see if air is detected after sitting several days.
Ran errands this weekend and over 100 miles on Interstate no issue. Only Saturday morning when heading up the hill. Weird.
 

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So I started the truck, opened the t-valve on top of engine and she filled a mason jar 16 oz or more in about 15 seconds and did not stall with valve open.
The Omron relay is GM exact replacement.
I guess I can try to clear line and see if air is detected after sitting several days.
Ran errands this weekend and over 100 miles on Interstate no issue. Only Saturday morning when heading up the hill. Weird.
The clear fuel line will help locate any air in fuel.
 

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So I started the truck, opened the t-valve on top of engine and she filled a mason jar 16 oz or more in about 15 seconds and did not stall with valve open.
The Omron relay is GM exact replacement.
I guess I can try to clear line and see if air is detected after sitting several days.
Ran errands this weekend and over 100 miles on Interstate no issue. Only Saturday morning when heading up the hill. Weird.
It is not the relay, it is the OPS that is picky.

There is a thread here that actually measure the amount of amp passed on by aftermarket OPS to the LP compare to the ACDelco.
Here it is:
https://www.dieselplace.com/forum/63-gm-diesel-engines/21-6-5l-diesel-engine/249105-failed-ops-report-manufacturere.html
 

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Where did you mount the new PMD, and did you use factory harness?
And drill a tiny hole in the fuel cap to remove the vacuum in the fuel tank until you can buy a new fuel cap.
 

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Discussion Starter #18
okay for some reason I do not see my last post but see the post and response in email from JMJNet


my thoughts... relay carries the load of the fuel pump... ignition and then OPS have to carry current of relay coil...


I could not find a schematic illustrating the relay internals but wonder if it has a fly-back diode across the coil. A fly-back diode normally blocks current when the relay is energized (in parallel with coil) but when relay is de-energized the collapsing magnetic field induces a voltage of opposite polarity and the fly-back diode then conducts protecting the OPS from excessive voltage. If the fly-back diode fails open then the voltage spike from the relay will ultimately paste the OPS. This is why I replaced the relay. OPS is relatively cheap so will replace with OEM GM part...
 

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Discussion Starter #19
New PMD is mounted on heat sink off of intake. Yes I know not optimum. Going to look for pictures of where others have mounted on bumper as I have a whole new kit. Might install both... one fails going down the road just move the cable.
 

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New PMD is mounted on heat sink off of intake. Yes I know not optimum. Going to look for pictures of where others have mounted on bumper as I have a whole new kit. Might install both... one fails going down the road just move the cable.
The recommended spot to mount the PMD is right behind the Front License Plate Bracket, inside of the front bumper
 
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