Hi, I have a 98 chevy p/u w/5.7 automatic. The engine starts momentarily then quits. If I try it again it does it over & over, with no effect. The fuel pump runs momentarily then shuts off. I used a test light on the pump wires & the power comes on then off & stays off untill you cycle the key again. It is not showing any codes.Does anyone have any ideas???
THANX
WLRDLR49

I would check fuel pressure first. If you don't have a gauge see if you can keep it running by having someone spraying starter fluid into the breather.

It will run w/starting fluid.The fuel pump runs for a second then shuts off. The power to it shuts off too.

Then follow the wire back. Check the oil pressure switch also.

It's an electronic problem for sure. My guess is some sort of conflict with the anti-theft system.

Good thoughts. Your not using the spare key by chance are you?

Check or replace the fuel pump relay first.And it could also be a bad fuel pump,but more likely the pump isn't receiving a constant power supply.There are two ways to determine if the pump is getting a constant uninterrupted power supply.One is a voltmeter on the power wire to the pump...at the pump.And the other is to introduce a NEW power supply and bypass the old.I have personally seen and repaired automatic transmission codes and non functioning transmissions because the power supply for the transmission ran THROUGH the ignition switch,and the ignition switch was BAD.I mean the truck would start and run..but the trans would not work..stuck in 3rd gear.Could be a similar problem.And BTW..the truck with a bad igniton switch was a 97 Chev 1500.The diagnostic procedure for diagnosing the ignition switch was to run a NEW temporary wire from the battery..with a FUSE spliced inline to the fuse box.You want to locate the FUEL pump fuse and unplug it.Turn the ignition key to ON and backprobe the fuel pump fuse contacts.One will have power,the other will not.Run your temporary fused wire from the battery to the fuel pump fuse blade in the fuse box that does NOT have power on it(a test light is handy here) and see if that cures the problem.What you are doing with this procedure is BYPASSING the ignition switch with a direct power source to verify yes or no the ignition switch is problematic,or if you have a power SUPPLY problem.Nothing to it.lol

Could I run a new keyed wire to the fuel pump?

Possibly.You would need an empty port in your fusebox that powers up with the key on,and would need to be positive that the circuit has a wire diameter able to handle the circuit voltage and ampere loads of the fuel pump.The other issue too,which i'm not sure of is this:When and if the ignition switch goes "bad"...does it go bad because that one particular circuit has a problem,or is the ignition switch itself simply incapable of conducting the amount of power needed by all the circuits powered up by it?The method i described in my last post is to determine IF the power supply is indeed the problem.

a good way to test it is to just run a rather large wire straight from the batt to the pump. See if this will keep the vehicle running???

Alright..back up and REREAD my original post.Locate the fuel pump FUSE in the fusebox,pull it out..One blade will have power on it when the key is on,the other blade will be DEAD.Run a wire from the battery with an INLINE fuse in the temporary wire to the fuse block.This wire doesnt need to be any larger than a 14 or 16 gauge as it's a TEMPORARY wire.You don't want an UNFUSED power wire.This is a test...testing,testing.(diagnostic procedure).Hook your temporary battery wire to the DEAD blade in the fuesblock (fuel pump).Now the pump should be running..Fire the engine..If the engine fires and DOESN'T die..you know you have a power SUPPLY problem to the fuel pump,most likely a bad ignition switch.The power supply for the fuel pump runs through the ignition switch.This diagnostic test is to determine if the ignition switch is bad or not,by cutting it out of the loop.It sounds like ALOT of work,but if you have it straight in your mind and know what you're doing,it really takes less than 1/2 hour to do,including fabricating the temporary wire with an inline fuse,one end blade connector and one eyelet connector.

I have worked on early 90s pickups where the oil pressure sender was malfunctioning, causing the fuel pump to be shut down after the initial startup. If you have tested the pump and know that it is working try to unplug the oil pressure sending unit and run a jumper wire between the leads. The plugs that I have seen have three wires, I believe that one is power, one is output to the gauge and one completes the fuel pump circuit. If you connect the right wires you should hear the pump activate whether the truck has the ignition on or not. If you connect the wrong wires either your gauge will peg out, or nothing will happen. Try different combinations until you hear the pump or run out of combinations. Hope this helps.