97 C2500 5.7 No start without priming

[opposed4]

My Chilton manual not much help. Looking for diagnostic steps for CSFI injection problems. The engine (over 100,00 miles) will start and runs fine, after pouring in some gas through the throttle. Once warmed up, it will start right up, as long as the engine is warm. After sitting overnight it loses gas pressure and won't start. I think the fuel pump is ok, (filter is new), as it will accelerate hard on the highway. The fuel pump relay is working ok. Would the pressure regulator cause this problem? Where is the vacuum line on the outside of the intake manifold, that goes to the pressure regulator? Since the pump only runs for 3 sec after you turn on the key, how high should the fuel pressure be at startup? What keeps line pressure up when engine is off? This has been a progressive starting problem from an occasional no start when hot to no start at all when cold, unless primed. Thanks for any reply remedies.

[amac209]

pressure must be at least 60psi or the injectors won't work. will it start if you cycle the key on and off about 4 times, waiting for the pump to stop each time?? i assume you already have a pressure gage. most likely is the check valves in the pump are shot and losing pressure after it's shut off. try pinching the return line with some visegrips while the gage is attached with the engine off, does it still loose pressure?? if not the regulators your problem. follow the fuel lines to the regulator there should be a vacuum line attached pull it off and look for any fuel leaking into it. just so you know chevy fuel pumps die all the time. the easiest way to replact the pump is to remove the bed assuming you don't have a canopy or big tool box back there. if you change the pump always replace the fuel filter. good luck

[opposed4]

Originally Posted by amac209

pressure must be at least 60psi or the injectors won't work. will it start if you cycle the key on and off about 4 times, waiting for the pump to stop each time?? i assume you already have a pressure gage. most likely is the check valves in the pump are shot and losing pressure after it's shut off. try pinching the return line with some visegrips while the gage is attached with the engine off, does it still loose pressure?? if not the regulators your problem. follow the fuel lines to the regulator there should be a vacuum line attached pull it off and look for any fuel leaking into it. just so you know chevy fuel pumps die all the time. the easiest way to replact the pump is to remove the bed assuming you don't have a canopy or big tool box back there. if you change the pump always replace the fuel filter. good luck

Thanks amac209 for the tips. Just got a new pressure gauge but am waiting for the windy weather to leave (carport). The incoming-return lines are all steel from the manifold on back towards the tank. Rechecked the upper composite intake, and the only vacuum lines are for the brake booster and the pcv valve. Have cycled the key on and off to run the pump 6 times but it won't start. First I need to see what the fuel pressure is, then find a way to block the return line. Since the regulator is under the upper manifold, plugging the return line will be the key to finding why the line pressure drops. I did have a problem with the fuel filter being plugged up when I first bought the truck. Maybe there's junk in the tank and I'll have to remove it to replace the pump anyway, but have had the truck for several years with no problems.

[sofunkingcool]

Had the same prob with my 96. Ended being the fuel pump not enough pressure to start it but when running it was fine. ONce you put the gauge on it will tell the story .That's what happen to mine

[opposed4]

Hooked up pressure gage and turned key on-off several times to run pump and pressure came up to 60 psi. Cranked it over and pressure dropped to 50 psi. No start. I primed through throttle with gas and it started on first crank. Pressure stays at 55 psi while warming up. Engine runs smooth and when revved up the pressure drops a couple psi.
You would expect the engine would be gas starved at this lower pressure but it still accelerates hard- up past 70 mph with no miss. Checked pressure after running for 30 min and it was still 55 psi. After sitting for 2 hours, the pressure has dropped to 25 psi and goes back up to 60 psi when pump is turned on. Will figure out a way to plug the return line tomorrow so I'll know if it's the pump. No smell of gas leak under the hood. Plan on using a plugged piece of fuel hose and clamp it on the metal return line where it has a splice by the back of the intake. Can't find any info on how the pressure regulator works in the system. Anyone know of a web site that explains in detail how the CSFI injection system works? I've got a Chiltons GM Trucks 88-98 manual but it's lacking in detailed description of how CSFI operates, and says nothing about the actual psi. Would have bought a Haynes if one was available.

[amac209]

try this sitehttp://www.lindertech.com/injinfo1.pdf
it doesn't describe everything but should give you a general idea

[Jeremy-WI]

You can find a section of rubber hose between the fuel filter location and the engine, you will have to get under the vehicle to see it

[djlacavera]

Hi, I am having the exact same problem you have described.
Did you figure it out? If so can you share the info. with me, before I go nuts!!!
Thanks much, Nick

Originally Posted by opposed4

Hooked up pressure gage and turned key on-off several times to run pump and pressure came up to 60 psi. Cranked it over and pressure dropped to 50 psi. No start. I primed through throttle with gas and it started on first crank. Pressure stays at 55 psi while warming up. Engine runs smooth and when revved up the pressure drops a couple psi.
You would expect the engine would be gas starved at this lower pressure but it still accelerates hard- up past 70 mph with no miss. Checked pressure after running for 30 min and it was still 55 psi. After sitting for 2 hours, the pressure has dropped to 25 psi and goes back up to 60 psi when pump is turned on. Will figure out a way to plug the return line tomorrow so I'll know if it's the pump. No smell of gas leak under the hood. Plan on using a plugged piece of fuel hose and clamp it on the metal return line where it has a splice by the back of the intake. Can't find any info on how the pressure regulator works in the system. Anyone know of a web site that explains in detail how the CSFI injection system works? I've got a Chiltons GM Trucks 88-98 manual but it's lacking in detailed description of how CSFI operates, and says nothing about the actual psi. Would have bought a Haynes if one was available.