I have a 94 k3500 6.5 that I just acquired. My first 6.5. It has 201k miles on it and I don't know the history on it. The truck starts right up and idles but it won't take fuel when I push on throttle. Once the truck warms up well it starts taking fuel and runs great. It usually takes 10-30 minutes to take off. The lift pump looks new and I've overlooked it some but I'm not familiar with it. The truck it kinda rough and I don't want to sink a fortune in it. Please help and thanks

 

I don't understand description "won't take fuel" if it is running/starting it is taking fuel, anytime fuel delivery is suspect ALWAYS CHANGE the on engine fuel filter in the center rear of the engine as one never knows when you get a bad load of fuel partially or completely compromising fuel flow.

Yours being a 94 is OBD-I electronics so you don't have the redundant power to the lift pump and all coming from the OPS (oil pressure switch) that has a dual role powers lift pump upon sensing oil pressure, and also providing internally a second circuit for dash display of oil pressure, you can have oil press showing on dash but still have a bad OPS feed to the lift pump.


Since you are # ??? owner of this it might be prudent to change this "just because" as an elimination and refresh as they do wear out over time, they aren't that expensive anyway.

If you have a "old school" vac/press test gauge get about 8' of vacuum hose connect one end of it to the outlet/90 deg angle fitting to hose running down behind the water-pump FFM drain valve (brass valve chrome Tee handle center front of the engine) . then snake that hose into the cab taking care to not create a "pinch point" in the hose dead-heading the pressure feed to the gauge, either tape gauge to the windshield for viewing from inside or run hose into cab with gauge .

Start truck and open T handle on valve, this will give you the pressure from the lift pump being supplied to "dirty side " of the filter, if filter is new/clean it will basically also be what fuel is being supplied to the IP.

You should have 7-10 psi at idle with a factory style lift pump if healthy.

If you don't then lift is bad, power to lift is missing, "sock strainer" in tank is plugged, or you have a rotten line/hose and you are sucking in air.

Assuming you idle pressure is correct, take truck for a "road/load test" with gauge connected do some basic driving 3-7 psi is "normal" higher is better, then do some acceleration tests floor it and observe pressure if it drops to 1 psi and recovers quickly then ok but healthy lift should not drop below about 1.5 psi for any amount of time, if it gets to 0 or less than 1 and struggles to recover/supply fuel then fuel delivery is compromised. Most probable offender then would be the lift pump, if going with a OEM pump stay with the AC Delcos, a lot of "JUNK" pumps out there at different part houses Airtex one of the most commonly found one.

Aftermarket pumps need to be Diesel fuel rated with ability to "flow on fail" impulse /plunger pump the IP can pull it's own fuel if lines don't have air leaks and filter is clean, performance will be compromised but you shouldn't be stranded.

Vane lift pumps like the Cummins use may starve you of fuel if the pump stops and one of the vanes blocks either the suction or discharge port of the pumps casing.

One last thought to lack or intermittent lift power, the gnd for the lift pump is on the top of the frame rail more/less below where the fuel filler neck crosses over the frame rail, single 18 Ga black wire with ring lug that needs to be spotless.

Take a piece of emery cloth polish lug to bright clean, then also on frame for clean contact point, then also bolt contact face, after cleaning liberally coat them all with di-electric grease to keep moisture from corroding again, or if you can find it a spray of "Corrosion Block" spray is awesome usually found at boating stores.

Tighten all that up and then use you DVM and check for resistance to gnd 1 probe on the newly cleaned bolt, and other on a good spot on frame or my best confirmation to one of the 2 negative terminals of you batteries, should be less than 1 ohm resistance or whatever your meters lowest resistance capability is when just reading through your leads touching each other.

 

What I mean by "it won't take fuel" is when I press the accelerator pedal nothing happens, it starts great and idles great it just won't rev until it gets hot. Someone else told me to check the lift pump operation also but I thought If the lift pump was not operating properly then it would be hard to start, but again I'm not familiar with this engine. Thanks for the reply

 

As long as the line between the IP and tank is fully primed, the IP has ability to pull its own fuel, you may be having a APP issue but lets look into the fuel delivery troubleshooting 1st.

 

Ok guys have some more info for you to calculate. The coolant temperature sensor didn't fix the problem. I have power on the lift pump after you crank it a few seconds. When it's running the water drain has a good steady stream coming out of it when opened. No service engine light or codes. It is a little stubborn to start when it's cold. It starts and dies a couple times before it will stay running and then it white smokes for a minute or so. I looked it over and checked the wiring today and it all looks good. When it starts it may rev after 1 minute or it may take 20. I stomped the pedal several times with no change. When it starts revving then it runs perfect. Please help me with next step!

 

A good, steady stream is highly subjective. If it is leaking out vs pouring is a big difference. I checked mine and it was coming out, but turns out it wasn't enough and my fuel sock was clogged. As I had no idea how much fuel should come out, it resulted in a misdiagnosis and more greenbacks out of my pocket. It should fill up a red solo cup under 20 seconds or so.

Mine turned out to be a clogged sock, which fell off in the tank when I removed the fuel sender. I just left it off, but you have to be careful when getting low on fuel.

A new metal top fuel filter is mandatory at this point, and an oil change. Probably wouldn't hurt to have the tranny fluid swapped and a new filter put in. Just make sure they use the good rubber gasket for the tranny, not the cheap cork gasket. Otherwise you will have a friggin tranny leak nightmare.

If possible, straight wire the lift pump just for diagnosis purposes as well. If you splice into the hot wire from one of the power ports on the fuse box, and add a switch, it will help by bypassing the OPS.

 

Ok great info, I'll check it out tomorrow thanks a lot

 

Getting closer every day. Took the fuel filter housing off today and cleaned, it was very nasty. Got that all cleaned out and sealed up and checked the hoses for leaks. It has good fuel delivery ti the filter because it was completely empty and I cracked the air bleed valve on top and fired it up, it only took a couple seconds to push fuel out of the top. Truck starts on first try and takes fuel way quicker than before but still not perfect. I did notice something unusual though. When I start the truck it idles at 500. I can press the pedal and it will climb to 1000 then stop. I can play with it a few seconds and it will start revving like a champ, then after it starts working properly it idles at 1000. Seems like the idle may have something to do with my problem? I checked power to the glow plugs also. They have power on them until the light goes off on dash. I read somewhere that they should have power on them for a few seconds after it starts but no sure. I will check it again tomorrow after it sets all night. I really appreciate your guys help I've almost got it road ready thanks to you all.

 

Make sure all the glow plugs are connected and working properly.

Still think you might have a fuel delivery restriction.

 

Did you do the lift pump diagnostics I defined above ??? if you don't have a vac/press test gauge......get one......they are like $20 most auto part stores, it is an invaluable test tool.