Question: Help...Fuel pressure drops after several mins from 5psi to 0psi and shutdowns? - Page 2 - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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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 01-18-2015, 12:26 AM   #11 (permalink)
Freddyack
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1/8th tank....I think you might be having fuel feed issues from the tank. Get the tank 1/2 full and see if it runs better. Conventional wisdom is dont go below a 1/4 tank of fuel.

Try powering the LP as Glagulator says using the red wire with the spade connector. See if you maintain fuel pressure and the engine runs better.

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Old 01-18-2015, 12:53 AM   #12 (permalink)
Glagulator
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The LP test lead is only to power the LP when the key is off. With the key on the PCM activates the relay and the test lead is disconnected.
Need to know if the ECM-B fuse has 12v. when the engine dies.
Need to know if the LP relay is activated when the engine dies. see post 9.
These engines do not die because the fuel pressure drops, even to slightly negative, IF the fuel system is sealed..

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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 01-18-2015, 12:13 PM   #13 (permalink)
Southron Jr
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The fuel system on my Burban was full of all sorts of trash and rust when I bought it. Had similar issues with pressure dropping, eventually replaced the WHOLE fuel system from tank to IP. Might note that I was going crazy trying to fix it and found that the brand new AC delco LP from napa would run for about 30 sec then just dribble fuel. Took it back and got another one and have had no issues since. Tested it by disconnecting the fuel lines and dropping the intake side in at tub of fuel and watching it run and that was when I found the issue.
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80's ish Belarus tractor that just wont die no matter how hard people try.
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Old 01-18-2015, 02:29 PM   #14 (permalink)
DieselPower5
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Quote:
Originally Posted by Glagulator View Post
Put a 12v. test light on the lift pump relay as in the diagram. Easiest way is to wrap a piece of bare wire around the relay terminal, bend it up and wrap it with tape, then plug it back in.
See if the light goes out when the pressure drops.
This will tell you if the PCM is shutting down.
FYI there is a short red wire with a spade connector on the main harness between the under hood fuse relay center and the firewall. That is a test lead for the lift pump. Apply 12v. to that lead to run the LP when the key is off.

Diagram here: Attachment 286721
Excellent Diag info, and i have 2 questions
1. I looked for the red wire and spade connector last eve, and am going to look right now again. Do you happen to have a picture of this or where it is hiding? Once i find it, sure i can turn on the lift pump, but how long should i run it without the truck running, or is it ok to run endlessly to test it, maybe 5 to 10 mins to see if it fails? Now I have my fuel gauge hooked to the "T" fitting, so should i pump fuel into a oil pan, or just let it run and hold pressure to see if it fails after 2 mins like i keep seeing?

2. on the relay, which pin would i hook a wire took?

(be back in maybe 15 mins, as i try to find the red wire and get a few jumper wires connected to and run it for a few mins under pressure...)
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* Tell me your MPG (mine stinks at 14.5 )?
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2-tone Blue & Silver!
* Skinny Tires LT235/85R16 (E) Nexen Roadian ATII
* Rebuilt Injectors 2009 @ 155miles (Now Jan2015 195miles)
* HeathDiesel.com remote mount PMD & Heavy Duty LP
* HeathDiesel.com Turbo Master Arm & Max-E chip. Timing -1.94
-> The Power came alive & woke this sleeping beauty up (Was a dog before, love it now)
* HP now, would it be 50 or 75HP more so far?300HP & 600Ft lbs some day, but how?
* Maybe future 4" stainless exhaust to manifolds?
* Maybe go from 4:10 to 3:73 gears I suppose ? rarely tow enclosed 4k trailer.
* AutoMeter Gauges: Boost, EGT & Trans Temp.
* Maybe future HeathDiesel BiPass cooling system.
* Baja alloy RIMS, but really want Chrome that is easy to clean(but where cheap?).
-> Bought Dec 2005 @ 122k from original owner.
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Old 01-18-2015, 03:12 PM   #15 (permalink)
DieselPower5
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ok, i found the spade connector, the little sucker was hidden below the bundle of wire :-)
will now hook up to 12v, brb.....
__________________
* Tell me your MPG (mine stinks at 14.5 )?
97 Suburban Diesel!
2-tone Blue & Silver!
* Skinny Tires LT235/85R16 (E) Nexen Roadian ATII
* Rebuilt Injectors 2009 @ 155miles (Now Jan2015 195miles)
* HeathDiesel.com remote mount PMD & Heavy Duty LP
* HeathDiesel.com Turbo Master Arm & Max-E chip. Timing -1.94
-> The Power came alive & woke this sleeping beauty up (Was a dog before, love it now)
* HP now, would it be 50 or 75HP more so far?300HP & 600Ft lbs some day, but how?
* Maybe future 4" stainless exhaust to manifolds?
* Maybe go from 4:10 to 3:73 gears I suppose ? rarely tow enclosed 4k trailer.
* AutoMeter Gauges: Boost, EGT & Trans Temp.
* Maybe future HeathDiesel BiPass cooling system.
* Baja alloy RIMS, but really want Chrome that is easy to clean(but where cheap?).
-> Bought Dec 2005 @ 122k from original owner.
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Old 01-18-2015, 03:32 PM   #16 (permalink)
Glagulator
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Lift Pump Prime Lead

For future reference.

1996 and up lift pump prime connector.

LPprimeLEAD.JPG
__________________
There are 10 kinds of people in this world; Those who understand binary and those who don't.

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

Last edited by Glagulator; 01-18-2015 at 03:48 PM.
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Old 01-18-2015, 07:18 PM   #17 (permalink)
Diesel-T
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Quote:
Originally Posted by Glagulator View Post
For future reference.

1996 and up lift pump prime connector.

Attachment 286865
Fwiw I had some difficulty getting a good connection thru this connector .I kind of ended up blaming the lift pump ground . And could have been my cobbled up 12 volt lead .Just saying so as to be aware that a good connection needed to get the lift pump to run . Just saying because I was blaming the liftpump & it turned out to be just fine.
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Old 01-18-2015, 07:30 PM   #18 (permalink)
DieselPower5
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Quote:
Originally Posted by Glagulator View Post
Put a 12v. test light on the lift pump relay as in the diagram. Easiest way is to wrap a piece of bare wire around the relay terminal, bend it up and wrap it with tape, then plug it back in.
See if the light goes out when the pressure drops.
This will tell you if the PCM is shutting down.
FYI there is a short red wire with a spade connector on the main harness between the under hood fuse relay center and the firewall. That is a test lead for the lift pump. Apply 12v. to that lead to run the LP when the key is off.

Diagram here: Attachment 286721
Thanks Glagulator & other Gents!!!

OK, i now have the wires running under hood and then wrapping around thru the windows in a temporary testing setup.

1. NOTE: The fuel heater is still unhooked. (I will hook it up after i finish this post and test the truck again)

2. of course now that i have all this hooked up, the truck will NOT stahl when it reaches 0psi (gee whiz, the sucker idled for 10 mins & idled PERFECTLY, so i pulled it back into the garage to hook up the fuel heater. Soo i can surmise this, now that i have the proper diesel sock installed, i guess the Injection Pump is pulling enough fuel to keep itself idling, would you agree??? (i didn't want to drive anywhere on 0psi)

3. I have a 12+ volt reading on the selenoid leg while it is running and idling, and yes even at 0psi (of coarse I have 12+v as soon as the key is turned on & i never loose the 12+v). So this seems like good news.
(I have voltmeter hooked up to the selenoid and sitting on my dash temporarily)

->>YES the 12+ volts never dropped or went to zero, even though i had 0psi. So it seems the LP is not blowing the breaker in the ECM, which you think it would, so this is strange to me??? I assume the lift pump stops and maybe freezes up and is still drawing some amperage, which should kick out the ECM breaker (hmmm, let me go measure that now)


4. Also I hooked up temporary switch & sitting on my dash for turning on the Lift pump when the key is off, and that worked fine. (hooked up to that LP tap by the firewall)

5. ***Get this*** once the lift pump quit working, it has NOW refused to come back on even after 10+ mins so far.... really??? urggg
i even climbed underneath and tap it with a mini hammer to see if it would jar loose, sort of like a starter in the old days where you would smack it to get it to catch a good armature contact and spin so you could get on your way (i know, showing my age, i did this many times in the early 80s when i was 18 )

6. **Amperage that this lift pump is pulling, now that it seems stuck or frozen, or basically junk, but none the less, it is pulling 1.80amps (thru my digital amp meter via the 10 amp connections (DC 10amp connection) )

7. Get this, now that i pulled it into the garage and shut the truck off, it dawned on me a few mins later to jump back in and turn on the key, and sure enough, i get the 12+volts, and NO lift pump sound, but guess what, i hear a small metal type sound below my drivers seat and the 12v disappears....
hmmmmm So i can only assume, that the lift pump after shutting off the truck is now maybe kicking off the ECM breaker just by simply turning on the key and after maybe 5 seconds or more, something happens and the voltage drops to zero...(and yes the "WAIT" light is flashing as normal for start, even after the 12v drops to 0volts???) So that is weird, because

and YES, i can turn off and immdeiately turn the key back and do it again and the voltage goes right back to 12+v, and then i hear a tiny sound and the voltage drops to 0v. So i did this at least 3 times. So i assume the ECM can not trip and immediately allow me to turn the key off and back on and get the 12v??? or can it? (not sure if the ECM is running a breaker like a protable generator that kicks out, or does the ECM run an amp meter and sees high amps and then kicks off a selenoid and that is why i can immediately turn the key off and on and get 12volts again???) (yes, i am an electronics guy )

8. oh get this, while i was typing this, giving it maybe 10 to 15mins to cool down, the stupid lift pump is now working again when i flip my firewall tap LP switch, wow... So do i assume the ECM is NOT doing this, but the LP cooling down and now working again??

## Sooooo, i am putting on my other "SPARE" older/used lift pump. I will test it and be in 15 mins or so....
__________________
* Tell me your MPG (mine stinks at 14.5 )?
97 Suburban Diesel!
2-tone Blue & Silver!
* Skinny Tires LT235/85R16 (E) Nexen Roadian ATII
* Rebuilt Injectors 2009 @ 155miles (Now Jan2015 195miles)
* HeathDiesel.com remote mount PMD & Heavy Duty LP
* HeathDiesel.com Turbo Master Arm & Max-E chip. Timing -1.94
-> The Power came alive & woke this sleeping beauty up (Was a dog before, love it now)
* HP now, would it be 50 or 75HP more so far?300HP & 600Ft lbs some day, but how?
* Maybe future 4" stainless exhaust to manifolds?
* Maybe go from 4:10 to 3:73 gears I suppose ? rarely tow enclosed 4k trailer.
* AutoMeter Gauges: Boost, EGT & Trans Temp.
* Maybe future HeathDiesel BiPass cooling system.
* Baja alloy RIMS, but really want Chrome that is easy to clean(but where cheap?).
-> Bought Dec 2005 @ 122k from original owner.
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Old 01-18-2015, 07:34 PM   #19 (permalink)
DieselPower5
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Quote:
Originally Posted by Diesel-T View Post
Fwiw I had some difficulty getting a good connection thru this connector .I kind of ended up blaming the lift pump ground . And could have been my cobbled up 12 volt lead .Just saying so as to be aware that a good connection needed to get the lift pump to run . Just saying because I was blaming the liftpump & it turned out to be just fine.
Hmm, you have me curious

Did you clean up your ground connection like i did underneath your rear bumper on the drivers side?
was it as simple as that and your LP and whole situation was fixed?

(so far for me, i did clean that ground and the other grounds up on the intake manifold, but still had my same bad situation the past 2 weeks of bucking and kicking and not drivable from stahling)
__________________
* Tell me your MPG (mine stinks at 14.5 )?
97 Suburban Diesel!
2-tone Blue & Silver!
* Skinny Tires LT235/85R16 (E) Nexen Roadian ATII
* Rebuilt Injectors 2009 @ 155miles (Now Jan2015 195miles)
* HeathDiesel.com remote mount PMD & Heavy Duty LP
* HeathDiesel.com Turbo Master Arm & Max-E chip. Timing -1.94
-> The Power came alive & woke this sleeping beauty up (Was a dog before, love it now)
* HP now, would it be 50 or 75HP more so far?300HP & 600Ft lbs some day, but how?
* Maybe future 4" stainless exhaust to manifolds?
* Maybe go from 4:10 to 3:73 gears I suppose ? rarely tow enclosed 4k trailer.
* AutoMeter Gauges: Boost, EGT & Trans Temp.
* Maybe future HeathDiesel BiPass cooling system.
* Baja alloy RIMS, but really want Chrome that is easy to clean(but where cheap?).
-> Bought Dec 2005 @ 122k from original owner.
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Old 01-18-2015, 07:53 PM   #20 (permalink)
Glagulator
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By "12+ volt reading on the selenoid leg" you mean the Lift Pump Relay?

Another test, When the 12v. drops to 0 after the metal type sound, need to know what the voltage is at the ECM-B fuse.

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There are 10 kinds of people in this world; Those who understand binary and those who don't.

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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