lift pump

[davidstereo]

I replaced the lift pump about four months ago and ran fine for a while now I am having the same hiccup problem shifting from second through third. When it does it I can floor it and usually get it to stop but as soon as I slow down and speed back up it does it again. This only happens about every other time I drive the truck, its my daily driver. Is there something that would cause this lift pump to go bad or should I just expect to replace the pump every four months? Pump came from ssdielelsupply. Also replaced ops and relay at same time lift pump was replaced. Dave

[simon]

What makes you think it is the liftpump?

Hook up a 20 psi gauge to the water drain cock located on the coolant crossover and read the pressure at idle and 2000 rpm. if you got around 5 psi at idle and 2 psi at 2000 rpm then it aint the liftpump.

If you stomp on it and the problem goes away then there is plenty of fuel.

I could be wrong about the exact values, but not by far.
Others will pipe in no doubt.

[davidstereo]

The reason I think it is the lift pump is this is exactly what I relpaced the last time it was doing this exact same thing and the problem stopped. If it isn't the lift pump then what could it be. Thanks, David

[rameye]

gage the fuel pressure....could be the OPS switch.

gaging is the right move.

[tommac95]

Poor fuel delivery (as clogged filter, occassionally clogged fuel-pickup 'sock/strainer' in tank, or a pinhole in the fuel pickup {corrosion}, and once in a while a 'stuck' OPEN bypass valve in the pickup line above the sock/strainer; and , again rarely , clogged low-pressure fuel lines , on input OR return to/from tank/FIP) has same symptom [sometimes!] as a failing FSD/PMD.

Note that fuel starvation can result from bad OPS, or LP , or bad connection in those lines ... and also from a bad ignition switch contact . The sole function, by design, of the OPS , is safety in event of incident when LP ON , and a leak on its' output {maybe in accident}.
Thus a pressure/delivery test proves many things are OK (or not). In some cases a check of voltage to LP can be helpful. My used vehicle 'arrived' with an aftermarket LP connected with wires cut/twisted together, and well-corroded within loose electrical tape-covering ; it exhibited "clogged-filter/FSD symptoms", in the form of "hot start , stall". Or , for smooth running , ensure smooth/adequate electric , and fuel {simple , ehh?}.
Similarly , a relay can save the OPS. As John C. offered , a diode may protect the OPS.

I believe John Kennedy has a complete accessory kit to energize the LP using solid state means. This should help extend the life (MTBF) of the LP. That is , Kennedy's kit is an improvement/upgrade to/over the OEM circuitry, insofar as the OPS [OEM configuration] will deliver voltage spikes to the LP , which can predispose the LP to untimely demise....

[BamaChief600]

Question about the lift pump. When the ignition key is turned on is the pump supposed to come on? or does it come on when starting?

[tommac95]

>or does it come on when starting?
Generally not when ignition only (unless when engine running with oil pressure).
When cranking the LP should be ON.

[bcbigfoot]

I replaced the lift pump about four months ago and ran fine for a while now I am having the same hiccup problem shifting from second through third. When it does it I can floor it and usually get it to stop but as soon as I slow down and speed back up it does it again. This only happens about every other time I drive the truck, its my daily driver. Is there something that would cause this lift pump to go bad or should I just expect to replace the pump every four months? Pump came from ssdielelsupply. Also replaced ops and relay at same time lift pump was replaced. Dave


What brand of lift pump? I recently had a problem with a a Carter lift pump. I figured it was time to change the original pump, 14 years old and 180000 miles. I put on the Carter pump and it was putting out 7psi at idle. After only 500 miles the truck would run rough at idle almost a light surging or partial miss and was worse after the truck had run for a hour or so. I changed injectors but that didn't help. Finally I rechecked fuel pressure and it had dropped to 5psi when cold and hot was at 4psi. I changed back to the original lift pump and the truck ran good again. I didn't think a few psi would make a difference but apperently it does on the mechanical pumps. I would certainly check your fuel pressure. Buy a 20$ test gauge and duct tape it to the windshield and drive around for a few days see what it does.

[davidstereo]

I will do the pressure test and get back to you guys. I have also been experiencing harder starts lately. Do you think this might have somethin gto do with the hiccups?

[bcbigfoot]

I will do the pressure test and get back to you guys. I have also been experiencing harder starts lately. Do you think this might have somethin gto do with the hiccups?


Hot starts or cold starts?

[davidstereo]

I have recently found that the truck will drive fine until it warms up. After about fifteen minutes or so of driving the truck will start the hiccups. Also the hard starting is only when hot. Do the 93's need the PMD? Or is that only for 94's and up?

[bcbigfoot]

No PMD's on the 93's. What I found with my bad lift pump was, the engine would idle OK when cold but start idleing rougher when it ran for a while 1hour +. I believe the fuel would heat up in tank and thin out a little and pump it self would heat up and drop 1 to 2 psi causing the rough surgy idle.

[davidstereo]

I checked the pressure and I am ordering a new lift pump today.
Thanks, dave

[Kennedy]

I have recently found that the truck will drive fine until it warms up. After about fifteen minutes or so of driving the truck will start the hiccups. Also the hard starting is only when hot. Do the 93's need the PMD? Or is that only for 94's and up?


The hard hot starts are indicative of the injection pump getting worn. MP described a method of test that involved using 10% clean motor oil to fuel ratio to improve the viscosity. What happens is the head/rotor assy gets worn and as the fuel warms/thins it cannot build proper pressure.


As we discussed on the phone, install my lift pump hrness (already in your posession) and then we are sure that the pump is getting power. Then check filter, lift pump supply etc. You'll then hear the lift pump come on momentarily at key up to verify operation.

[davidstereo]

I don't have the harness But I will be ordering tomorrow as soon I get a reply email. By the way kennedy has some of the best customer service i have ever seen thank you for your help. Dave

[Kennedy]

I don't have the harness But I will be ordering tomorrow as soon I get a reply email. By the way kennedy has some of the best customer service i have ever seen thank you for your help. Dave

In your signature you list new IP. Was this new or reman?

[davidstereo]

The Ip was a reman from the dealer in 01 before I bought the truck. I was lied to by the dealer that I bought the truck from. I recently recieved the receipts from the previous owner and they told the true story. All that stuff in my signature is true but it all happened in 2000 or 2001 instead of last year.

[davidstereo]

I have recently had two hot days in a row and both days the truck has next to impossible to start. It finally starts after two or three minutes of cranking I feel that it may be the ip but I am going to install the harness and see what happens.

[BamaChief600]

Well I replaced lift pump switch and after having some battery issues I used my rig to go camping. Now I seem to have fuel leaking from the fuel filter area. Is there a check valve or switch to shut off lift pump if filter is too full? At initial start up it doesnt seem to leak but as I get going and I stop I notice it coming off the back of the engine.

[tommac95]

Forrest-
The OEM filter assy is pressurized by the LiftPump. The hose connections leak , as do the oring sealing the bottom cover (which doubles as fuel heater). So , may want to examine the filter housing, etc. Pretty much anything in the valley of the Vee(8) drains thru a hole in the rear of the intake man(?) or block(?) which goes to the ground via bell housing.

[BamaChief600]

Forrest-
The OEM filter assy is pressurized by the LiftPump. The hose connections leak , as do the oring sealing the bottom cover (which doubles as fuel heater). So , may want to examine the filter housing, etc. Pretty much anything in the valley of the Vee(8) drains thru a hole in the rear of the intake man(?) or block(?) which goes to the ground via bell housing.

Well I took the assembly apart and found the lower ring was loose. So while I had it off I cleaned it up a bit and good as gold.