fuel pump wiring problem I think. (ground)

[bracketshark]

Working on a friends 99 silverado Z-71 with the 5.3 engine, The problem: hard starting but finally does and ran well. We checked the fuel pressure and found ~55 psi, when the power is cut off it fell like a rock to less than 40, so we decided on a new delphi pump from the GM dealer. We installed it along with the new wiring harnes that came with the new pump. Thanks goodness we tried it before reinstalling the bed because the truck wouldn't start,we couldn't even tell if the pump was running. We went back to the connectors that was provided with the new pump and made sure we had good connections/ they were good. After considerable checks to see if we had power to the connector, we felt like the power was there. Next we hooked another ground from the frame to the black wire on the new harness, we could then hear the pump running and the truck fired right up. We then removed our temporary ground while the truck was running and it continued to run but we could tell it wasn't running correctly. One thing I have to mention is now we don't have the fuel pressure gauges so we don't know what the pressure is doing, but we will tommorrow. Has anyone got any Ideas on the grounding problem, where it might be? I found 2 wires coming out of the harness under the drivers side door and clean them up but it made no differance. The temporary ground has a bright blue arc to it when it is connected and disconnected when the pump is running. Is it going to be OK to leave the pump grounded to the frame if we can't find another problem? I'm thinking now the old pump might have had the same voltage problem. Thanks for your suggestions.

[j cAT]

if fuel pressures drop quickly on shut down this means injector problems. if this is the case you cats will get plugged with carbon.not seeing your wiring i can only guess that a bad connection or defective pump.grounds on tank are for static charges not for current flow.

[rjeffery]

Originally Posted by j cAT

if fuel pressures drop quickly on shut down this means injector problems. if this is the case you cats will get plugged with carbon.not seeing your wiring i can only guess that a bad connection or defective pump.grounds on tank are for static charges not for current flow.

Rapid pressure leak-off can also mean that the check valve is bad on the fuel pump. This allows the fuel in the lines to drain back into the tank and starves the engine for fuel on start up. If an injector was bad he would have other problems and definitly an SES light. It would also not run well once started.

I had the same pressure leak-off problem. Replaced my pump and it works great. As far as your grounding problem, I would try a new pump.

[bracketshark]

This IS a new pump (delphi). I'm thinking the low pressure issue was there on the old pump being caused by the ground issue. Unless I can find out differant info my plan is to ground the pump to the frame, where it seem to run correctly, then verify fuel pressure and leak down #'s are good. If this works out my intentions will be to leave it like this. I would like to find out where the black wire in the harness comes from but I don't think I'm willing to tear the harness apart to find out. We still might come up with a schematic later today though. I've got a local GM tech checking on it for me. Thanks and all suggestions are appreciated.

[rjeffery]

I understand that you are having problems with the new pump. What I meant was return the new pump and get a replacement with a new wiring harness. Sometimes you can get bad parts out of the box.

[j cAT]

Originally Posted by j cAT

if fuel pressures drop quickly on shut down this means injector problems. if this is the case your cats will get plugged with carbon.not seeing your wiring i can only guess that a bad connection or defective pump.grounds on tank are for static charges not for current flow.

the fuel pump ground is black wire term., C the power voltage to pump IS GRAY WIRE term. B.the ground wire black is grounded to the left frame rail near body mount. this may have been riped off when removal of componets...........make sure pressure does not drop off quickly on shut down........also when checking for voltage don't forget that open ground wires or rusted loose grounds will occur. whenever possible check directly across device don't just put meter black probe to frame or body ground.

[J-Ri]

The ground on the frame gets very rusty (should be where j cAT said). Just remove the bolt, clean the frame, and probably replace the terminals. Spray some battery terminal protector or undercoating on it to keep it from rusting again.

[bracketshark]

Thanks to j caT and J-Ri for your information on locating the ground location. I just got home from getting the truck running before reading your post but you were right on. In my original post I said the bed was left off just to check everything out, I thought this was smart- not so. It turns out the ground connects to the same bolt that the ground wire off of the tank fill strap hooks to, since it wasn't connected guess what- no ground. I never even saw another wire on the bolt when the strap was removed. Thanks for being willing to help, I was begining to think this might become a PITA to find. Thanks to all.