Under load it sputters. Ran great for 6mos. after we emptied fuel tank, top seal was allowing water in the tank. Emptied it, new fuel filters every week for 3 weeks to make sure we were good. Ran great for long time. Before the water in tank issue we changed the ip, new grounds, pdm, already moved, starts right up, runs great until a hill or get on it heavy. What could it be? Lift pump only gets the the truck started then ip takes over, correct? Thanx in advance.
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1994 GMC 3500 hd 6.5 turbo diesel
- Thread starter Boblaw66
- Start date
No, lift pump should be running...
Would the lift pump cause this since it only happens under load and starts right up and running s great wxcept under load? I don't have the bleeder for the fuel or the bracket, been looking. Thanx for your help and knowledge. I'm a contractor and only some of this stuff from my buddy working on it. Unfortunately he just had surgery, stage 3 or 4 bladder cancer, so I guess I can't get him to help. Lol. I'm like 20mins west of Philly but still hard to find people really knowledgeable about these motors. Everyone days, change this, change that, oh, change that too. We've about changed everything but the lift pump. No injectors, cracked a couple open and seemed fine. It ran fine For 6 mos. Like I said. Long message, Sorry!
dbrannon79
I'm getting there!
Welcome @Boblaw66
when under load are you getting any smoke from the tail pipe? could be not getting enough air from the turbo or clogged air filter.
lift pump should be providing 8-14 psi continuously to the IP. the factory GM lift pumps are garbage for keeping up with the demand of these engines. they fail within usually a couple of years and it's good to have a spare in the cab to keep with you.
check to see if your starting to roll coal (black smoke) under load and check your fuel pressure at the IP inlet idling and under load. these two things will help us diagnose your power loss.
when under load are you getting any smoke from the tail pipe? could be not getting enough air from the turbo or clogged air filter.
lift pump should be providing 8-14 psi continuously to the IP. the factory GM lift pumps are garbage for keeping up with the demand of these engines. they fail within usually a couple of years and it's good to have a spare in the cab to keep with you.
check to see if your starting to roll coal (black smoke) under load and check your fuel pressure at the IP inlet idling and under load. these two things will help us diagnose your power loss.
MrMarty51
Well-Known Member
Yes, pressure at the inlet port of the injection pump is the best location.
To mee it seems the fuel system is starving for fuel.
A possibility that the IP has worn enough that it now is failing to pull enough fuel to provide the injectors with the fuel required to allow the system to pull under load.
I have been warned that when these injection pumps are not provided with the proper amount of fuel, and pressure, that it will kill the injection pump.
If it were My truck, and if I could not afford a raptor or an AirDog lift pump system, get on Leroy.com website and order in His lift pump and harness system, along with the fuel pressure tap that fits the top of the FFM filter, then a sending unit can be screwed into that fitting, along with the pressure snubber, snubber is an absolute must item between the pressure tap and the sending unit. Without that snubber in between any port and the fuel pressure sending unit You will get a lot of false readings.
Then mount the gauge in the cab. Keep a watchful eye on that pressure gauge, if ever it starts falling off towards zero then get another lift pump installed.
@Will L. advises to run two sending units.
One SU at the lift pump and the other at the inlet port of the injection pump.
A toggle switch in a handy location allows a person to observe pressure at either location at the flip of a switch.
I finally dumped the big bucks and got the AirDog system.
@ak diesel driver He installed the Raptor system on His truck.
I think now I would most likely have also gone with the Raptor system but I wanted the best, and, like You will also hear in here, buy once, cry once.
Expand the pic to see a better view of the gauge needle on the right side gauge of the pod.
Pre FFM, or, right at the Air Dog pressure port.
And Post FFM, at the injection pump port, via a length of 5/16ths” SAE 30R9 fuel hose in order to get out where there is room for the snubber and the sending unit.
My advice, do not run that engine another second longer until You verify the lift pump fuel pressure.
To mee it seems the fuel system is starving for fuel.
A possibility that the IP has worn enough that it now is failing to pull enough fuel to provide the injectors with the fuel required to allow the system to pull under load.
I have been warned that when these injection pumps are not provided with the proper amount of fuel, and pressure, that it will kill the injection pump.
If it were My truck, and if I could not afford a raptor or an AirDog lift pump system, get on Leroy.com website and order in His lift pump and harness system, along with the fuel pressure tap that fits the top of the FFM filter, then a sending unit can be screwed into that fitting, along with the pressure snubber, snubber is an absolute must item between the pressure tap and the sending unit. Without that snubber in between any port and the fuel pressure sending unit You will get a lot of false readings.
Then mount the gauge in the cab. Keep a watchful eye on that pressure gauge, if ever it starts falling off towards zero then get another lift pump installed.
@Will L. advises to run two sending units.
One SU at the lift pump and the other at the inlet port of the injection pump.
A toggle switch in a handy location allows a person to observe pressure at either location at the flip of a switch.
I finally dumped the big bucks and got the AirDog system.
@ak diesel driver He installed the Raptor system on His truck.
I think now I would most likely have also gone with the Raptor system but I wanted the best, and, like You will also hear in here, buy once, cry once.
Expand the pic to see a better view of the gauge needle on the right side gauge of the pod.
Pre FFM, or, right at the Air Dog pressure port.
And Post FFM, at the injection pump port, via a length of 5/16ths” SAE 30R9 fuel hose in order to get out where there is room for the snubber and the sending unit.
My advice, do not run that engine another second longer until You verify the lift pump fuel pressure.
Will L.
Well-Known Member
Welcome.
No, lack of a proper lift pump will ruin the ds4 or db2 much sooner.
Some permanent changes are suggested to solve the issue now & for future.
You have a ds4 ip (injection pump).
Out the front of the ip is a 1/4” fuel line in an upside down U shape. Replace it with clear line. You need about 6” and 2 new screw style hose clamps for it.
fuel-line.com
Thats best type. Otherwise from a hardware store you can get the pvc kind but it needs replacing every few years. Install it and leave it for quick inspection. Air Bubbles are a key to a problem, as is any visible contamination. Seems simple & not helpful but is GM’s #1 task in diagnostics. #2 is the fuel pressure gauge.
Installing a metal T fitting between the ip and the inlet hose fitting is suggested so that there is no rubber after the t fitting. At that T fitting put in the sensor for a fuel pressure gauge and permanently mount a gauge on the dash to see while driving. A quality one will set you back a couple hundred dollars but can make the difference of an ip lasting 10,000 miles or 250,000 miles.
8-14 psi is where it should be.
Adding a gauge permanently isn’t required but definitely pays for itself. The 2 sensor thing Marty shared is simply helps with knowing when to change the fuel filter rather than guessing. Can always be added later if you choose.
Factory LP (Lift Pump) can not put out what is required. This leads to the quest for a good one. This is where $$ starts getting silly. Best? FASS with their filters. If you are in an area requiring a fuel heater then they sell one for their pump.
Then you can eliminate the factory FFM(fuel filter manager). The filter itself is adequate at 5 microns, but the water separation capacity is a tablespoon (maybe 2, I can’t remember). Then the rest goes through and can damage the ip and injectors. The fuel heater is adequate but tends to need replacing about once every 125,000 miles. The fuel we have now has tons more water in it than original diesel did because of the alcohols mixed in.
There is something called FTB- Feed The Beast. The inlet at the ip is 5/16 from FFM & is best altered to 3/8 like the rest of the system.
Imo doing all of it is best, but it doesn’t hurt me to spend other’s money. Haha
Seriously, start with clear hose & pressure gauge.
No, lack of a proper lift pump will ruin the ds4 or db2 much sooner.
Some permanent changes are suggested to solve the issue now & for future.
You have a ds4 ip (injection pump).
Out the front of the ip is a 1/4” fuel line in an upside down U shape. Replace it with clear line. You need about 6” and 2 new screw style hose clamps for it.
1/4
The original Fast Flow Fuel Line. Suitable for jet-skis, snowmobiles, go-karts, ATVs, motorcycles, and other motor sports applications that require a 1/4" low pressure fuel line. Available in Clear, Neon Green, Neon Yellow, Neon Orange, Blue, Red, Smoke, Pink, and Purple. All colors are...
fuel-line.com
Installing a metal T fitting between the ip and the inlet hose fitting is suggested so that there is no rubber after the t fitting. At that T fitting put in the sensor for a fuel pressure gauge and permanently mount a gauge on the dash to see while driving. A quality one will set you back a couple hundred dollars but can make the difference of an ip lasting 10,000 miles or 250,000 miles.
8-14 psi is where it should be.
Adding a gauge permanently isn’t required but definitely pays for itself. The 2 sensor thing Marty shared is simply helps with knowing when to change the fuel filter rather than guessing. Can always be added later if you choose.
Factory LP (Lift Pump) can not put out what is required. This leads to the quest for a good one. This is where $$ starts getting silly. Best? FASS with their filters. If you are in an area requiring a fuel heater then they sell one for their pump.
Then you can eliminate the factory FFM(fuel filter manager). The filter itself is adequate at 5 microns, but the water separation capacity is a tablespoon (maybe 2, I can’t remember). Then the rest goes through and can damage the ip and injectors. The fuel heater is adequate but tends to need replacing about once every 125,000 miles. The fuel we have now has tons more water in it than original diesel did because of the alcohols mixed in.
There is something called FTB- Feed The Beast. The inlet at the ip is 5/16 from FFM & is best altered to 3/8 like the rest of the system.
Imo doing all of it is best, but it doesn’t hurt me to spend other’s money. Haha
Seriously, start with clear hose & pressure gauge.
jrsavoie
Recruit
A permanent fuel pressure gauge is very helpful.
1995 and older needs the lift pump relay upgrade
MrMarty51
Well-Known Member
I really like that relay harness that Leroy makes and sells. The one with the little push button switch that turns on the lift pump and makes a real nice aid in bleeding the air from new filters.
Thanx Marty, I'll check for smoke tomorrow. When this truck was screwed up last year I was looking up stuff and one guy put on marine lift pump In his truck. Not saying I would do it, just saying.
I'll check tomorrow when it's light out. Dbrannon. Thank you
Speaking of t-valves. Do u know anywhere I could get an original one that goes on the bracket on the thermostat? I've tried but can't find one. I noticed someone before I got it just put like a screw or something in the hose, I'm guessing he didn't have one either. I didn't notice, I'm not a mechanic, I'm a contractor. I love learning this shit for future too. I can't find that bleeder or the bracket. Thanx in advance.Welcome.
No, lack of a proper lift pump will ruin the ds4 or db2 much sooner.
Some permanent changes are suggested to solve the issue now & for future.
You have a ds4 ip (injection pump).
Out the front of the ip is a 1/4” fuel line in an upside down U shape. Replace it with clear line. You need about 6” and 2 new screw style hose clamps for it.
Thats best type. Otherwise from a hardware store you can get the pvc kind but it needs replacing every few years. Install it and leave it for quick inspection. Air Bubbles are a key to a problem, as is any visible contamination. Seems simple & not helpful but is GM’s #1 task in diagnostics. #2 is the fuel pressure gauge.1/4
The original Fast Flow Fuel Line. Suitable for jet-skis, snowmobiles, go-karts, ATVs, motorcycles, and other motor sports applications that require a 1/4" low pressure fuel line. Available in Clear, Neon Green, Neon Yellow, Neon Orange, Blue, Red, Smoke, Pink, and Purple. All colors are...
Installing a metal T fitting between the ip and the inlet hose fitting is suggested so that there is no rubber after the t fitting. At that T fitting put in the sensor for a fuel pressure gauge and permanently mount a gauge on the dash to see while driving. A quality one will set you back a couple hundred dollars but can make the difference of an ip lasting 10,000 miles or 250,000 miles.
8-14 psi is where it should be.
Adding a gauge permanently isn’t required but definitely pays for itself. The 2 sensor thing Marty shared is simply helps with knowing when to change the fuel filter rather than guessing. Can always be added later if you choose.
Factory LP (Lift Pump) can not put out what is required. This leads to the quest for a good one. This is where $$ starts getting silly. Best? FASS with their filters. If you are in an area requiring a fuel heater then they sell one for their pump.
Then you can eliminate the factory FFM(fuel filter manager). The filter itself is adequate at 5 microns, but the water separation capacity is a tablespoon (maybe 2, I can’t remember). Then the rest goes through and can damage the ip and injectors. The fuel heater is adequate but tends to need replacing about once every 125,000 miles. The fuel we have now has tons more water in it than original diesel did because of the alcohols mixed in.
There is something called FTB- Feed The Beast. The inlet at the ip is 5/16 from FFM & is best altered to 3/8 like the rest of the system.
Imo doing all of it is best, but it doesn’t hurt me to spend other’s money. Haha
Seriously, start with clear hose & pressure gauge.
dbrannon79
I'm getting there!
I'm not sure they are available anymore, others can verify that. if the hose is there and just plugged off, iirc that T valve is just a brass drain valve with one end having 1/4" hose barb for the hose coming from the FFM (fuel filter manager). the other end is open, the original had another barb to connect a hose you could put into a cup or bottle to catch fuel when you drained the FFM or primed the air out.
someone correct me if I am wrong.
Yes the drain valve is still available........................
https://real4wd.com/product/cock-drain-fuel-water-separator/
jrsavoie
Recruit
I prefer a toggle switch.
I passed on Leroy's harnesses a few times because there were things I want. A toggle switch for on/off. Prime feature. Mountable relay socket instead of a mountable relay.
Now I would just order his and change what I want. It would still save considerable time, as opposed to starting from scratch.
MrMarty51
Well-Known Member
Got one on the way.
MrMarty51
Well-Known Member
I took that nice little press button switch from the Leroy Harness I have and wired it into the Air Dog Harness.
I questioned the AD co if they had such a harness but they did not.
I do now.
jrsavoie
Recruit
Yeah, the line is there, I'll just do that and then hopefully find a bracket or have one made. Thanx
jrsavoie
Recruit
Better to mount ine permanently.
To test, I've heard the Harbor Freight gauges work just fine