DMac94
Newbie
Hey guys, first time poster. I have gotten a lot of great information off of the site over the years as I've had my truck for about 17 years now, so I figured I would come here with questions.
A little backstory: I have a 1994 C1500 with about 130k miles with a 350 and auto trans. The truck is pretty much bone stock, the wiring hasn't been molested, and the truck has no rust as it has never seen salt (I mention this since it may be relevant to diagnosis since I have read that some folks have fuel pump issues related to corrosion).
On to the issue: OCCASIONALLY when I hit the throttle from a stop, the truck will cough or hesitate for a second and then recover. It doesn't die, but it sputters long enough for me to be weary of pulling out onto a busy road where I need to accelerate quickly. It only does this if the truck is under load and is even more likely to do so if I am starting off on a steep uphill. I performed a fuel pressure test and see a very steady 11-13 psi (TBI truck) at idle and when revving the truck up in my driveway.
I then went for a ride holding the pressure gauge out the window (I teed in by the fuel filter and my gauge hose was just long enough to reach to the driver window). The fuel pressure is still very steady at 11-13 psi under normal driving and hard acceleration.
HOWEVER, when I can get the truck to cough/sputter when taking off from stop, the fuel pressure drops erratically, sometimes even going to 0 psi. I am baffled by the situation since the truck runs great otherwise.
Of note, I did replace the fuel pump about 8 months ago with a Delphi when the truck lost fuel pressure (by some miracle, this happened after a two hour trip right as I pulled into my yard). When I removed the fuel pump, it turned out that the old rubber hose between the pump and sending unit in the tank had split, but I replaced the pump and sock screen anyways since they were 30 years old. *I also replaced the fuel filter* The tank was very clean inside. The truck ran fine for maybe 6 months, and this intermittent hesitation/sputter issue started about 2 months ago.
Any ideas?
The fuel pump doesn't know how much load the truck is seeing and should be running consistently, so I wonder if somehow the truck is cutting power to the pump under only this very specific circumstance for some reason. I know the fuel pump primes for only a couple of seconds after turning the key on without starting the truck, but does the fuel pump keep running if the truck stalls out or thinks it is dying?
Something else I speculated was that maybe, somehow, the fuel pressure regulation in the TBI assembly is allowing a ton of fuel to bypass to the tank return, but only under this specific circumstance, but this seems less likely since the truck runs great at all other times.
I feel like my next course of action is to go to the local junkyard, and grab the two connectors where the sending unit plugs into the truck harness, and rig up a little harness I can plug up inline to check pump feed voltage while I'm driving. Maybe even set up a battery in the bed running to the pump so that I know the pump is 100% getting a steady power supply and see if the problem persists.
Anyways, any insight or suggestions are welcome, thanks.
A little backstory: I have a 1994 C1500 with about 130k miles with a 350 and auto trans. The truck is pretty much bone stock, the wiring hasn't been molested, and the truck has no rust as it has never seen salt (I mention this since it may be relevant to diagnosis since I have read that some folks have fuel pump issues related to corrosion).
On to the issue: OCCASIONALLY when I hit the throttle from a stop, the truck will cough or hesitate for a second and then recover. It doesn't die, but it sputters long enough for me to be weary of pulling out onto a busy road where I need to accelerate quickly. It only does this if the truck is under load and is even more likely to do so if I am starting off on a steep uphill. I performed a fuel pressure test and see a very steady 11-13 psi (TBI truck) at idle and when revving the truck up in my driveway.
I then went for a ride holding the pressure gauge out the window (I teed in by the fuel filter and my gauge hose was just long enough to reach to the driver window). The fuel pressure is still very steady at 11-13 psi under normal driving and hard acceleration.
HOWEVER, when I can get the truck to cough/sputter when taking off from stop, the fuel pressure drops erratically, sometimes even going to 0 psi. I am baffled by the situation since the truck runs great otherwise.
Of note, I did replace the fuel pump about 8 months ago with a Delphi when the truck lost fuel pressure (by some miracle, this happened after a two hour trip right as I pulled into my yard). When I removed the fuel pump, it turned out that the old rubber hose between the pump and sending unit in the tank had split, but I replaced the pump and sock screen anyways since they were 30 years old. *I also replaced the fuel filter* The tank was very clean inside. The truck ran fine for maybe 6 months, and this intermittent hesitation/sputter issue started about 2 months ago.
Any ideas?
The fuel pump doesn't know how much load the truck is seeing and should be running consistently, so I wonder if somehow the truck is cutting power to the pump under only this very specific circumstance for some reason. I know the fuel pump primes for only a couple of seconds after turning the key on without starting the truck, but does the fuel pump keep running if the truck stalls out or thinks it is dying?
Something else I speculated was that maybe, somehow, the fuel pressure regulation in the TBI assembly is allowing a ton of fuel to bypass to the tank return, but only under this specific circumstance, but this seems less likely since the truck runs great at all other times.
I feel like my next course of action is to go to the local junkyard, and grab the two connectors where the sending unit plugs into the truck harness, and rig up a little harness I can plug up inline to check pump feed voltage while I'm driving. Maybe even set up a battery in the bed running to the pump so that I know the pump is 100% getting a steady power supply and see if the problem persists.
Anyways, any insight or suggestions are welcome, thanks.