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Serging/hesitation

5K views 38 replies 9 participants last post by  Brock 7654 
#1 ·
I have a 94 gmc k2500 6.5 TD series f and when it idles it serves/bucks and then if I accelerate it hesitates like it's not getting enough fuel I have replaced the apps sensor and the pmd an relocated it to the front bumper and have put a new fuel an air filter on it and still does it but it I accelerate at a slow rate it doesn't do it what else could be wrong with it one of the local shops said it acted like it had a plunger stuck on the injector pump so he said to put a lil 2 stoke oil in the fuel and see what happens any ideas
 
#3 ·
I had the same problem with my 95 when I first bought it. I had two issues I found. First the lift pump wasn't working. Previous owner wired in a relay for the oil pressure sending unit and wired it in wrong. Check and make sure ur lift pump is working. Second was the o-ring for the fuel heater on the filter housing was bad, leaking fuel and causing it to suck air. I put 2 stroke oil in my tank every time I fill up.
 
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#4 ·
First off check All Grounds using this thread for reference:http://www.dieselplace.com/forum/63...-grounds-grounds-importance-good-grounds.html

Lift Pump Test & OPS Diagnostics check this thread here:Reference Material: Lift Pump/OPS - Diesel Place : Chevrolet and GMC Diesel Truck Forums

Pictures showing how to jump the Lift Pump on a 1992-94 6.5L http://www.dieselplace.com/forum/63...3330-fuel-pressure-oddity-10.html#post6784033

Inspect and clean the FFM screen manager using this thread:http://www.dieselplace.com/forum/63...gine-shutting-off-randomly-3.html#post7520401
 
#5 ·
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#22 · (Edited)
No check engine light no servies throttle light now water in fuel light nothing no codes the lift pump works the grounds are all good clean and attached well the ffm is clean it's making me mad because I'm a diesel mechanic and checked everything and nothing seems to be wrong lol
The air filter is new and I haven't checked the vacuum system yet and how do u check the lift pump for volume and what is it suppose to be at
I find it incredible that a "diesel mechanic" would ask that. Its obviously clear you half assed checked the lift pump too. You likely found sufficient fuel pressure and ASSUMED that meant sufficient flow too..
THATS THE BULLSHIT IM TALKIN' ABOUT! Look in the mirror.. You been schooled so you knowz everything and try as we might, your not hearing us..

Seriously, wondering if I am wasting my time here.. Do you want to learn this **** or just have someone tell you its the IP and be done with it?
Ive read Heath is capable of accurately diagnosis vehicles and IPs over the phone, although admittently he too must rely on the person on the phone is thorough in all those most "Important Preliminary Checks" that routinely are given a quick look see, maybe a passing sniff test and assumed good... Butt Eye digress..

Did you conduct the air leak test EXACTLY AS INSTRUCTED, Step 1, 2, 3, 4, and so on or did you read "Go to step 6" and assumed you could check both sides at once?
If so, you assumed WRONG just like so many Pro's and DIYrs still do!!

Do you have the proper service manual(s) for this vehicle? PLEASE dont tell us your using Haynes, Chilton and all the other unauthorized service manuals. If so, you MUST forget all that worthless bullshit too. If you arent following the FSM, might as well be wearing a blindfold with one hand tied behind your back.

The return line HALF of the air leak test is intended to check the IP itself for possible INTERNAL air leaks and never intended to check for airleaks upstream.
If jumping to step 6 was an accurate CONCLUSIVE test to check for airleaks of the entire system, it would be step #1 to save techs diagnostic time....
That most poopular short cut only APPLIES to the antiquated DB model pump, the DS model pumps predecessor. Unfortunitely few if any GM techs received the "proper training" and instruction or should I stress the total RE-EDUCATION necessary to properly and competently troubleshooting an EFI 6.5TD in order to arrive at an accurate diagnosis. To this day, many still approach the DS pump diagnostics as if its a DB model.. Censored idiots..

GMCorp spent more time instructing there d-techs how to plug in and read the NEW TECH1 scan tools than they spent actually instructing them on the new REVOLUTIONARY ELECTRONIC FUEL INJECTION SYSTEM. So of course they are extemely proficient at reading DTCs and swapping perfectly good parts. Apparently, the industry is still emphasizing how to use them damned scan tools.
Probably dont want to hear this but you most likely misdiagnosed the APP module too.. Butt Eye digress..

Lets get back to the diesel spa (hint).. If theres enough bubbles entering the IP to be seen exiting the DS model pump, Id be surprised if the engine even tries to start much less runs extremely rough at that..
Expect a rough idle, hard start, smokey cold start, etc etc etc if even the most miniscule amounts of air or fuel vapors enter the IP, although hard start and smokey cold starts (white smoke) is most indicative of air leaking into the fuel system overnight...
Sounds as if you may some creeps hanging out at the hidden air port(s).

When was the last time the fuel tank was dropped and cleaned, fuel sender inspected and tested, fuel strainer replaced? If you cant answer that, its likely long overdue.. Another schelduled maint item that only gets thought of when all else fails. Another thing thats always assumed good, no good mechanic worth his weight in salt ever wants to be seen doin' latrine duty, its beneath them and much like thorough troubleshooting, its not nearly as profittable as swapping out good parts for bad diagnosis..
Following proper procedure, anytime the lift pump is replaced, the tank is supposed to be dropped and serviced while replacing the strainer.
SKIPPING all those most laborious time consuming steps and just R&R the lift pump is HALF ASSING the job, and VOIDS the new lift pumps implied warranty... Unfortunitely, because our lift pump aren't located INSIDE the fuel tank, they all ASSUME they dont need to bother with all that other dumb s'it.. IMHO, its this oversight that spawns PMD Goblins.

Did you test the LPR ciruit for proper voltage? Finding 12volts at the LP i far from conclusive.. Slight voltage fluctuations, faulty grounds, poor connecting "SWITCHES" aka OPS may test good until the circuit is LOAD TESTED. Did they teach you that or do you need a tutorial?

How to Test for Fuel Pump Voltage Drop

Have you removed the FFM, cleaned, inspected and TESTED it for possible air leaks? Do not assume because its not dripping fuel it isnt leaking, specially overnight while parked for extended periods.. Most airleaks dont exhibit wet spots and HELL YES an air leak can exist in the PRESSURIZED side of the fuel supply and NOT LEAK fuel to offer up a clue..

If it were only that easy, I wouldnt need to explain all this s'it to you and the rest of the diesel mechanics who routinely get there ass's handed to 'em, although its usually at the customers expense.

If while doing the test things suddenly improved, you may have inadvertantly tightened a loose hose clamp, and/or resealed a fuel hose, or re-established a ground and/or electrical connections. Thats why you must be painstakingly thorough and FOLLOW PROPER PROCEDRES TO INCLUDE THE INSTRUCTIONS TO THE LETTER. Otherwise, your wasting both yours and my time here..
 
#8 · (Edited)
May be getting air in the fuel system. Go to the FAQ sticky at the top of the forum scroll down page till you come to the air in fuel section. You also should read Newbies sticky. lots of needed info in both threads.
Welcome to the forum.
Is your check engine light on? have you checked for Trouble Codes?
 
#9 ·
No check engine light no servies throttle light now water in fuel light nothing no codes the lift pump works the grounds are all good clean and attached well the ffm is clean it's making me mad because I'm a diesel mechanic and checked everything and nothing seems to be wrong lol
 
#10 ·
what's the air filter like? still sounds like air in the fuel or restricted fuel. no fuel leaks? have you checked the inlet screen on the IP to see is it is clogged? you lift pump works but is it putting out enough volume?

also double check your vacuum system for leaks.
 
#11 ·
welcome by the way
 
#13 ·
http://www.dieselplace.com/forum/63...e/39350-reference-material-lift-pump-ops.html

Lift Pump - Small electrical fuel pump that is located on the frame rail under the drivers seat. Noticeable "purring" noise when engine is off. Known trouble spot. This can cause lack of power, hard starting, stalling, etc.

Lift Pump Facts (from GM Service Manual):

  1. The 1988-1993 Model Year lift pump should deliver fuel with a minimum volume of 0.24 liter (1/2 pint) in 15 seconds at a pressure of 40 to 60 kPa (5.8 to 8.7 psi).
  2. The 1994+ Model Year lift pump should deliver fuel with a minimum volume of at least 0.24 liter (1/2 pint) in 15 seconds and pressure of 3 psi minimum with the engine cranking, the ESO disconnected, and the fuel line open after the filter to an approved canister
  3. When the pump is at rest, a spring pushes the hollow plunger in the direction of the outlet. Both the inlet and outlet valves are closed, keeping fuel in the supply line from draining back to the fuel tank.
Lift Pump Trouble Shooting


  • Lift Pump Test & OPS Diagnostics Click Here. See Electricity for troubleshooting practices
  • To view a video on how to jump the Lift Pump on a 92-94 6.5L Click here.
  • Pictures showing how to jump the Lift Pump on a 1992-94 6.5L Here
  • Pictures showing how to jump the Lift Pump on a 1995 6.5L Here and Here
  • How to jump the lift pump on a 1996-1999 6.5L (Pending)
  • 1996+ Lift Pump Prime Connector - Apply 12v to this connector to run the lift pump: Here
  • Reference for operating the lift pump with auto tranny in D and key in crank position Here
got that info from
http://www.dieselplace.com/forum/63...faqs-master-list-information-6-5-answers.html

there is a lot of info in the newbie and FAQ sticky on the 6.5L forum home page
 
#14 ·
OBD System Check
Scroll down for Important Preliminary Checks, Intermittents, and Surges and/or Chuggles.
Notice any consistant CHECKS in nearly all of the "Fuel System" sections?
Not trying to beat you up Butt Eye spect your problem is looking back at you in the mirror.. Drawing from prior diesel experiences is the fast path to misdiagnosis, and needless parts swapping, and it seems youve been busy.
PLEASE STOP!! Needless parts swapping can often complicate matters.
Purge your mind of everything you think you know about the EFI 6.5TD and just hear me out...
You cant "freestyle" with the 6.5TD. Everything must be done A B C D and done thoroughly. Half assing, a quick look see, and passing sniff test simply isnt good enough...
Air leaks and fuel leaks are not synonomous, fact many air leaks wont even exhibit a wet spot to clue you in..
The EFI 6.5TD is a rocket ship, but it can be one tempermental moody ***** when forced to injest air, starve for fuel, or drink stank from the tank while sufficating from a snotty sock.. Lil pun intended.
While reading the following passage, substitute gasoline with diesel..
Fuel Delivery Testing and Diagnostics______________________
"The Powertrain Control Module (PCM) calculates injector pulse-width based on engine speed and load. Pulse-width is further modified to compensate for changes from multiple inputs, including engine temperature, throttle angle, fuel trim and battery voltage. The PCM relies on the fuel delivery system to provide enough gasoline for all possible engine operating conditions. Fuel pressure and volume are considered “known good” values from the perspective of the PCM and are not directly monitored. Typically, fuel delivery problems will not directly set Diagnostic Trouble Codes (DTCs). However, low-pressure or low-volume conditions can cause changes in the operation and performance of the powertrain that may set codes as a symptom of improper fuel delivery. Low fuel pump pressure or volume can cause a lean mixture and fuel starvation at high speeds that may induce lean-related DTCs. Excessive pressure can result in poor fuel economy, rich mixtures and can cause rich-related DTCs to be stored in memory."
______________________________________
Simply put. Dont expect to find DTCs. Your going to have to do some troubleshooting to find this festering thorn in the PCMs eye (hint).
Best move on on and pick up the pace, you got lots to do..
Fuel Pump Relay Circuit Diagnostics
NOTE: '94 model "Fuel Pump Test Terminal" is "G", not "F" as it is on '95 model..


All that check out so far? If so, dont worry. You gots lots more troubleshooting to do if you want to avoid any more dates with misdiagnosis..

Fuel Contamination Inspection and Cleaning
Note: This procedure checks for the presence of water and gasoline in diesel fuel that may cause injection pump and nozzle damage.
1. Remove the fuel filter element and inspect it:
• If water, gasoline or fungi/bacteria are not present, end the inspection.
• If water or fungi/bacteria are present, go to step 2.
• If gasoline is present, go to step 3.
2. Clean water from the fuel system in these steps:
A. Disconnect the batteries.
B. Drain the fuel tank.
C. Remove the fuel tank.
D. Remove the fuel pick-up/sending unit.
E. Inspect the fuel tank and fuel pick-up/sending unit for rust, fungi or bacteria:
• If no rust is present, clean the inside of the fuel tank and fuel pick-up/sending unit with hot water, then dry them with compressed air.
• If rust is present, replace the parts.
F. Disconnect the ends of the following lines:
• Lift pump suction
• Lift pump pressure
• Fuel filter outlet
• Fuel filter drain
• Fuel return
G. Inspect each of the lines and replace any rusted pipes.
H. Dry the inside of each line with low-pressure air.
I. Clean the inside of the fuel filter housing and dry it with compressed air.
J. Disconnect the electrical connector for the fuel shut-off solenoid in the injection pump.
K. Install a new fuel filter element.

L. Install the fuel pick-up/sending unit and fuel tank (add clean diesel fuel to 1/4 full).
M. Connect the following lines:
• Lift pump suction (both ends)
• Lift pump pressure (both ends)
• Fuel filter drain
• Fuel return (at injection pump)
N. Connect the fuel filter outlet and the fuel return line at the pick-up/sending unit to hoses that flow to metal containers.
O. Connect the batteries and crank the engine until clean fuel flows from the fuel filter outlet into a metal container (see Figure 7-59):
• Allow a maximum of 15 seconds cranking time, followed by 1 minute of cranking motor cooling time.
P. Connect the hose from the fuel filter outlet to the injection pump inlet.
Q. Open each injection line at its nozzle end and crank the engine until clean fuel flows from it:
• Use two wrenches when loosening the injection line fittings.
• Allow a maximum of 15 seconds cranking time, followed by 1 minute of cranking motor cooling time.
R. Tighten each injection line fitting at its nozzle:
• Use two wrenches when tightening the injection line fittings.
S. Remove the electrical connector for the fast idle/cold advance temperature switch and jumper its wiring harness terminals with an insulated wire.
T. Connect the electrical connector for the fuel shut-off solenoid in the injection pump.
U. Start and run the engine for 15 minutes while fuel flows from the fuel return line into a metal container (see Figure 7-60).
V. Stop the engine.
W. Connect the fuel return hose to the fuel pick-up/sending unit.
X. Remove the jumper wire and install the electrical connector for the fast idle/cold advance temperature
switch.
Y. Clean the engine of fuel spillage.
Z. Fill the fuel tank and add a biocide, if needed.
3. Clean gasoline from the fuel system in these steps:
A. Determine a procedure:
• If the engine runs, follow steps B, C, J and K.
• If the engine does not run, begin at step C.
B. Drain the fuel tank.
C. Fill the fuel tank.
D. Disconnect the electrical connector for the fuel shut-off solenoid in the injection pump.
E. Remove the fuel filter outlet and connect it to a hose that flows to a metal container.
F. Crank the engine until clean fuel flows from the fuel filter outlet into a metal container:
• Allow a maximum of 15 seconds cranking time, followed by 1 minute of cranking motor cooling time
G. Connect the hose from the fuel filter outlet to the injection pump inlet.
H. Remove the electrical connector for the fast idle/cold advance temperature switch and jumper its terminals with an insulated wire.
I. Connect the electrical connector for the fuel shut-off solenoid in the injection pump.
J. Start and run the engine for 15 minutes.
K. Stop the engine.
L. Remove the jumper wire and install the electrical connector for the fast idle/cold advance temperature switch.

M. Clean the engine of fuel spillage.

Fuel-Specific Gravity Check
Note: The hydrometer fuel quality tester provides a general indication of fuel quality and should not be considered scientifically accurate.
1. Drain the fuel filter housing by doing these things:
• Stop the engine.
• Place a container under the drain valve exit hose at the left front side of the engine.
• Open the drain valve.
• Start the engine and operate it at operating speed until clear fuel appears at the drain valve exit hose.
• Fill a 1 -liter (0.946-quart) container with a sample of clean fuel.
• Close the drain valve and stop the engine.
• Bring the fuel sample to 60° F (16° C).

2. Obtain a fuel quality hydrometer (special tool J 34352).
3. Fill the hydrometer with the fuel sample by doing these things:
• Squeeze the hydrometer bulb.
• Submerse the hydrometer tip into the sample.
• Release the bulb, allowing fuel to enter the glass tube until it floats the glass bulb inside the tube.
• Gently spin the hydrometer to relieve the surface tension of the fuel sample.
4. Read the scale on the glass bulb at the point where the top of the fuel sample contacts it (see Figure 7-61):
• If the top of the fuel sample is in the yellow part of the glass bulb scale (above the green part), suspect the presence of gasoline in the fuel.
• If the top of the fuel sample is in the green part of the glass bulb scale, the fuel has high quality (approximate cetane rating of 46 to 50).
• If the top of the fuel sample is in the yellow part of the glass bulb scale (below the green part), the fuel has moderate quality (approximate cetane rating of 41 to 45).
• If the top of the fuel sample is in the red part of the glass bulb scale, the fuel has low quality (approximate cetane rating of 38 to 40).



Now its time to do some......
FUEL SUPPLY SYSTEM CHECKS
If the fuel supply system is not delivering enough fuel, or air is being drawn into the fuel injection system, driveability could be greatly effected or a "Cranks But Will Not Run" symptom could exist. If other diagnostics indicates, or if the fuel supply system is suspected of not delivering enough fuel or drawing air, it should be tested as follows:

!!Important!!!!
-- Air leaks or restrictions on the suction side of the fuel pump will seriously affect pump output.
-- Make sure there is sufficient fuel in the tank.
-- Check for leaks at ALL fuel connections from the fuel tank to the injection pump.
-- Tighten any loose connections.
-- With engine running, check all hoses and lines for flattening or kinks that would restrict fuel flow.

Lift Pump Flow Check
1. Disconnect the electrical connector for the engine shutoff solenoid at the injection pump.
2. Disconnect the pipe at the lift pump outlet fitting.
3. Install a hose at the lift pump outlet fitting and place a 1 liter/quart container at the hose to collect fuel.
4. Crank the engine and measure the amount of fuel :
-- If more than .24 ltrs (1/2 pint) in 15 seconds, refer to "Lift Pump Pressure Check" in this section.
-- If less than .24 ltrs (1/2 pint) in 15 seconds, refer to "Lift Pump Suction Line Check" in this section.

Lift Pump Suction Line Check
1. Remove the fuel tank cap and repeat the "Lift Pump Flow Check."
-- If more than .24 ltrs (1/2 pint) in 15 seconds, replace the defective fuel cap and refer to the "Lift Pump Pressure Check."
-- If less than .24 ltrs (1/2 pint) in 15 seconds, go to the next step.
2. Separate the lift pump suction line from the fuel sender.
3. Connect the suction line to a source of clean fuel, using an additional hose.
4. Repeat "Lift Pump Flow Check."
-- If flow is more than .24 ltrs (1/2 pint) in 15 seconds, remove the fuel sender and check it for restrictions.
-- If flow is less than .24 ltrs (1/2 pint) in 15 seconds, go to step 5.
5. Check lift pump suction line for restriction:
-- If restriction exist, repair it and recheck the lift pump flow.
-- If no restriction exist, replace the lift pump and recheck lift pump flow.
6. Attach the lift pump suction line to the fuel sender.

Lift Pump Pressure Test
1. Install a tee adaptor at the injection pump fuel inlet connection.
2. Connect a pressure gauge with a dial indication of 0 to 103kPa (0 to 15 psi) to the tee adaptor.
3. Run engine and measure fuel pressure.
-- If pressure is at least 3 psi or 27 kPa go to step 4.
-- If pressure is less than 3 psi or 27kPa, refer to Chart A-5 in SECTION 3 (Fuel Pump Relay Circuit Diagnosis) before replacing lift pump.
4. Remove pressure gauge and tee adaptor.
5. Connect outlet pipe at the lift pump outlet fitting.
6. Clean any fuel spillage.
7. Run the engine to check for fuel leakage.

Fuel System Air Leak Test
1. Install a transparent hose between the fuel manager/filter outlet and injection pump fuel inlet.
2. Start and idle the engine, observing the fuel for air bubbles.
-- If air bubbles are not present, stop the engine and go to step 6.
-- If air bubbles are present, stop the engine and go to step 3.
3. Check the lift pump suction line for air leakage:
-- Disconnect fuel pipe from the fuel sender and plug it.
-- Disconnect the fuel pipe from the lift pump, and install a hand held vacuum pump with gauge.
-- Apply vacuum to the fuel pipe and observe the gauge reading:
--- If vacuum does not drop, connect fuel pipe and go to step 4.
--- If vacuum drops, repair the air leak in the suction line and install the suction line pipe and hose.
4. Check the fuel sender for air leakage:
-- Remove the fuel tank.
Remove the fuel sender from the fuel tank, remove strainer and plug the bottom of the pickup tube.
-- Apply a vacuum to the upper end of the pickup tube, and observe the gauge reading.
--- If vacuum does not drop, install the fuel sender and fuel tank.
--- If vacuum drops, replace the fuel sender, install the fuel tank, connect the fuel pipe and go to step 5.
5. Start and run the engine, observing the fuel for air bubbles:
-- If air bubbles are present, stop engine and recheck steps 3 and 4.
-- If air bubbles are not present, stop the engine and go to step 6.
6. Remove the transparent hose and connect the hose of the fuel manager/filter outlet to the injection pump inlet fitting.
7. Disconnect the return hose from the injection pump.
8. Install a transparent hose between the injection pump and the hose of the return line.
9. Start and run the engine, observing the fuel for air bubbles:
NOTICE: It is OK to see a small stream of air bubbles on snap acceleration
-- If air bubbles are not present, go to step 10.
-- If air bubbles are present, replace the injection pump.
10. Stop the engine.
11. Remove the transparent hose and attach the fuel return hose at the injection pump.
12. Clean any fuel spillage.
13. Run engine and check for fuel leaks.

Following any "Fuel Supply System Check(s)" outlined aboved or otherwise, or any routine maint procedure(s) eg fuel filter change, or any repair(s) eg lift pump replacement and normal engine operation has been restored.. The last step of the process is to check for, make note of, and CLEAR DTC(s).


Then when your done with all that, read this entire thread
Chugging Problems.
Find the link to DTC 78 Wastegate Solenoid Fault and other Diagnostic aids..
Report back.
 
#15 ·
there are no air bubbles in the fuel system and everything tested out fine and it seems to be working its self out since I put in that two stroke in the fuel I drove it all day today and had no hesitation from it and when its in drive and stopped at a stop it doesn't try and buck the only thing its doing now is its idles rough when in park but not in drive and today it had a hard start with a puff of white smoke I don't know if since it set for 6 to 8 months before I bought it that one of the plungers was a lil sticky and is now starting to free up if not does anyone have any other ideas of what it could be?
 
#17 ·
there are no air bubbles in the fuel system
Lets do this one step at a time. Exactly how did you test for air bubbles?
Would your short answer be "Installed a clear hose on the IP oil return circuit and observed for bubbles. Saw nothing."

BTW, what was wrong with the APP? Not trying to beat you up, just it may be helpful clue to your on-going issues..

You might want to read this thread and follow the links and read those threads...
6.5 light serging, hesitation and smoke


Every symptom you have screams fuel starvation, air leak, and/or fuel contamination.
 
#16 ·
to restate its got a new apps, pmd and relocated to the front bumper, new air and fuel filter. the lift pump runs and puts out about 1/2 of a pint in about 15 secs new fuel and has 2 stroke oil in the fuel. it was bucking when truck was at a stop but came out of that and was hesitating going down the road but has come out of that the only thing that's going on is a rough idle and 1 hard start this morning with a puff of white smoke any ideas
 
#18 ·
yes and the app sent dtcs saying that one side was short and the other one was to high and every time you stepped on the throttle it would turn the check engine light on and every time you let off the throttle it would turn it back off and then I couldn't keep a constant speed and it would go from 2000 rpms straight to 3000 in a blink of an eye and its all good i'm new to the 6.5 and I just graduated a year and a half ago so i'm still a "new" mechanic so I appreciate all the helpful hints I can get
 
#19 ·
You skipped the first half of the test.


Fuel System Air Leak Test
1. Install a transparent hose between the fuel manager/filter outlet and injection pump fuel inlet.
2. Start and idle the engine, observing the fuel for air bubbles.
-- If air bubbles are not present, stop the engine and go to step 6.
-- If air bubbles are present, stop the engine and go to step 3.
3. Check the lift pump suction line for air leakage:
-- Disconnect fuel pipe from the fuel sender and plug it.
-- Disconnect the fuel pipe from the lift pump, and install a hand held vacuum pump with gauge.
-- Apply vacuum to the fuel pipe and observe the gauge reading:
--- If vacuum does not drop, connect fuel pipe and go to step 4.
--- If vacuum drops, repair the air leak in the suction line and install the suction line pipe and hose.
4. Check the fuel sender for air leakage:
-- Remove the fuel tank.
Remove the fuel sender from the fuel tank, remove strainer and plug the bottom of the pickup tube.
-- Apply a vacuum to the upper end of the pickup tube, and observe the gauge reading.
--- If vacuum does not drop, install the fuel sender and fuel tank.
--- If vacuum drops, replace the fuel sender, install the fuel tank, connect the fuel pipe and go to step 5.
5. Start and run the engine, observing the fuel for air bubbles:
-- If air bubbles are present, stop engine and recheck steps 3 and 4.
-- If air bubbles are not present, stop the engine and go to step 6.
6. Remove the transparent hose and connect the hose of the fuel manager/filter outlet to the injection pump inlet fitting.
7. Disconnect the return hose from the injection pump.
8. Install a transparent hose between the injection pump and the hose of the return line.
9. Start and run the engine, observing the fuel for air bubbles:
NOTICE: It is OK to see a small stream of air bubbles on snap acceleration
-- If air bubbles are not present, go to step 10.
-- If air bubbles are present, replace the injection pump.
10. Stop the engine.
11. Remove the transparent hose and attach the fuel return hose at the injection pump.
12. Clean any fuel spillage.
13. Run engine and check for fuel leaks.




Lets try again, from the beginning this time..
Do tell us 'bout it tommorrow. Old man needs his sleep.

private question- I suspect APP was likely replaced needlessly. Anyone else think so too?
 
#20 ·
It says if there are no air bubbles from the outlet of the filter to the inlet of the pump skip to step 6 which is to hook everything back up and do the return side of the pump to the return line and check for air bubbles both ways there is no air bubbles that's what I did lol I followed the steps idk if with me doing all the test that I changed something because I can now stomp on it and it doesn't hesitate the only thing it does is have a slight rough idle now lol
 
#23 ·
**** you dude I did FOLLOW THE PRECISE INSTRUCTIONS go and read it again it's says step 1 hook a clear hose from the outlet of the filter to the inlet of the pump and if there is no bubbles then to skip to step 6 which is to hook the lines back up and put the clear hose from the outlet of the pump to the return line and check for bubbles if there is no bubble it says to hook everything back up an check for dtcs THERE IS NO BUBBLES and I did do the lift pump test right thank you very much I maybe a new machanic but I grow up with an old style machanic who never bought anything new and always rebuilt everything so don't give me that **** of I'm just wanting someone to tell me what's wrong with it I was askin for help in solving it because I have done all the other test and nothing failed so don't give me that bullshit If ur going to sit here and talk **** about my machanic abilities then u can go **** off because I'm a DAMN GOOD MACHANIC
 
#24 ·
It still sounds like air to me. I know I recently had a problem with my 6.5, of hard start and running like a bag of smashed hammers, ended up being the return lines on the injectors, I replaced the injectors some time ago and the aftermarket hose is a push-lock rubber hose with braiding around it. The rubber was cracked, not enough to leak any fuel out but enough to let air in causing hard starts as it would leak down over night. the original return lines are rubber with small Odiker (pinch) clamps on them. It was a ***** to find!!!

You might not have air going back to the tank or coming from the tank but if you have air being introduced to the system around the injector return line it could just loop around to the injectors on idle and the higher RPM = higher fuel PSI allowing it to overcome that air. Air being introduced over night could also lead to hard starts and you bumping things in there could lead to it sealing up a bit and the problem somewhat disappearing. That's what happened to me, one day it was there the next gone.

just a thought
 
#25 ·
I've checked all the lines none of them look bad and I started it this morning no problem nothing it's ran all morning no issues not at idle not at speed I had one vacuum line that was split that was under the intake pipe and went back around the back of the motor and to a sensor I replaced that line this morning an not a single issue yet lol
 
#26 ·
good to hear lets see what it does, keep us informed
 
#27 ·
Will do I'm taking it that the vacuum line along with a sticky plunger in the pump from sitting for 6 to 8 months made it tempermental lol it's like I said it's been sitting here for 20 mins and hasn't bucked ran rough nothing
I want to thank everyone for there helpful hints
 
#28 ·
Idling requires least amount of fuel flow.. You need to go out somewhere and put your foot in that ass several times. Conduct some hard pull test..
IF theres an underlying problem, chances are its going to resurface during high fuel demands...


Reference materials
TSB Suction / Vacuum Side Diesel Fuel Filters

Diesel Fuel, Air Vapors And Your Engine

About the Air in Fuel


If it starts bucking during increased fuel demands.
Look for Stanky Tank. IIRC, it did sit for nearly a year..

My appologies. Just never encountered a good mechanic thats as thorough as you having such a difficult time troubleshooting and diagnosing a 6.5 before. Butt Eye will never doubt you again..

Good Luck



 
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