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Is this Fuel starvation?

Question: 
2K views 22 replies 9 participants last post by  mrgauge 
#1 ·
I need the 6.5 gurus again...

I have a 94 6.5 1/2 ton (Yep, one of those rare ones.) I was on the highway and noticed stuttering when passing at around 60-65 and puffs of black. After parking and restarting the truck, It felt like it was "missing" while idling and ran rough when I pressed the accelerator. I parked, shut it off and waited. After starting again, I heard 2 "knocks" similar to a rocker knocking and then the engine idled fine. I ran around all day, then the following day, when I was coming home, I had little or no throttle response and a rough ilde.I've got the pmd relocated under the front bumper, and a year old OPS. The LP is about 4 years old. Any help would be appreciated.
 
#3 ·
x2 on above. Looks EGR related to me
 
#4 ·
Here's what we have so far:

EGRs are hard to find on hand around these parts, so I replaced the lp and ops. I swapped the fuel filter as well and dropped a little sea foam in the reservoir and tank. I'm getting reduced or no throttle response when in gear, then the truck dies. It will stay back up with a rough idle. I've uploaded a video:
Https://vid.me/Fp5C
 
#5 ·
Any idea the last time injectors were done?
 
#7 · (Edited)
OBD System Check, Glow Plug System Check, and other diagnostic aids

Note: diagnostic aids are specific to '95 models however all is applicable to '94 models with one notable exception. The '94 model DLC's Fuel Pump Test Terminal is "G"...

IMO.. Easily could be fuel starvation... Be sure to perform the Fuel Pump Relay Circuit Diagnostics and all the Fuel Supply System Checks.
 
#9 ·
It might be the tank sock is shot and needs changing. The injectors are always a good idea to update, but it sounds like you are having other issues to me. Is the ops an ac delco one? Are you sure the lift pump is pumping. I would check the screen filter located in the fuel filter manager as well, they can get pretty clogged. The other option is that you are sucking air in somewhere - could be the old rubber fuel lines at the tank or fuel filter manager.
 
#13 · (Edited)
Only takes one tank of bad fuel to plug it up.
FYI. Anytime the LP is replaced, your supposed to drop, clean and inspet the tank and fuel sender. Also supposed to R&R the fuel senders strainer and o-ring seals for both the LP and fuel sender.


FWIW

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).



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).
 
#11 ·
Start out confirming the simple easy stuff

1st) Perform lift pump test open the fuel filter drain with the truck idling

1a) If the flow is weak try it again with the fuel cap off

2nd) If LP passes with flying colors than install clear line from the IP return line and verify no air is getting into the fuel supply.
 
#17 · (Edited)
If you are asking about clear line to check for air in the fuel, see this Click Here

I would do the Ops Relay Mod to ensure a constant and reliable power supply to that lift pump...
OPS Relay Mod: Click Here. This mod is pretty much mandatory on a 1994. The mod routes power to the Lift Pump through the relay instead of the OPS. The relay is triggered by the OPS, preserving the safety feature of having the OPS in the LP power circuit.

Get these parts:

Relay: NAPA - AR143
Relay Connector: NAPA - ECH EC23 or Relay Connector (with mounting bracket): NAPA - ECH EC38

Get 12v for the relay from the power block on the passenger firewall instead of tapping the Orange wire.

I recommend replacing the OPS with an AC Delco D1808A.
 
#14 ·
Being a 94' have you done the Ops Relay Mod??
 
#16 ·
I would do the Ops Relay Mod to ensure a constant and reliable power supply to that lift pump...
 
#19 ·
Update. I checked the fuel and vacuum lines, and all is well. I replaced my pmd with a new one from pensicola since it looked suspect: http:// tinypic.com/r/xck8i8/ 8

It ran fine for 500 feet, and then back to the same old same old. Rough idle, death, easy start, but no throttle response. I opened the hood, loosened the breather on the fuel filter and heard air release. "PSSSSS". Any ideas?

*This weekend I'm going to drop the tank, and check the sock, and do the ops relay mod.
 
#22 · (Edited)
Pssst, Like hey I have a secret? Or Tssss, Like it sucked air in? Sounds like vacuum or you truck is trying to tell you something..... Or maybe both...
 
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