After engine rebuild engine won't start. Zero fuel pressure.
Fuse to fuel pump is good and get 12 volts when key is on.
I'm also getting 12 volts to the tank between purple and black, even when key is off but goes to zero when key is removed.

I don't have a schematic of what's supposed to happen but the grey wire is 12 volts to the pump according to picture. I'm expecting 12 volts between black and grey for at least 2 seconds when ignition is turned on. I'm not getting anything at all.

I've read other blogs that say their is a fuel relay under the passenger dash but my dash appears to be a solid piece but I can't get a good look as I have it up on a lift and can't get doors open very far.

Does power to the fuel pump depend on the fuel relay energizing? If so, where is that relay located on a 96?

Does anyone have a schematic? I've looked in the shop manual and haven't found it and it's a 2 volume GM manual (new style).

 

I just read my service manual other day the location for the fuel pump relay in my 1996 is on the passenger side, and I think there may me other relays located with the fuel pump relay. When the ignition is turned on, the relay will have the fuel pump function to pressurize the fuel system. The oil pressure will permit more action to make the fuel pump work. With your engine rebuild a lot of stuff was taken apart, disconnected, perhaps you have something disconnected.

 

I still have problems but resolved the fuel pump/ fuel relay. I did not have the engine grounds connected. (Two wires just below windshield motor). So now the fuel pump is engaging however, I'm still not getting fuel pressure. So either the pressure gauge is bad, I have an obstruction in the line, or the fuel pump is actually bad. I do get a trickle of gas when I depress the Schrader valve, just no pressure at the gauge during the initial 2 seconds or when I have oil pressure.

I'm not sure how to proceed. I'm thinking replace the filter and while line is disconnected make sure I can blow air through it.

Are there any other suggestions?

 

I got mixed signals as to where this relay is on a 96. I contacted Chevy and the looked up in their online tech manual and said it was in the engine compartment next to blower. WRONG! Other posts in this forum said it was in passenger side console and showed picture of glove box with relay access but my Vette doesn't have a glove box. I called a a Corvette center in Virginia and they said remove passenger side kick panel and side panel and it was on a little shelf where you have to get on your back and stand on your head.

I'm glad I found the problem elsewhere.

 

Something else to try. Have some sit in your car and show them how to turn the ignition switch to only the on position. You can remove the gas cap lid and put your ear to the filler neck and tell the person to turn the switch on and listen for the operation of the fuel pump. If you hear it for 1 1/2 to 2 seconds run you know it is functional. Then continue to listen and let the person with your Vette in park or having the clutch pushed in with a manual transmission try to start the car and listen for the fuel pump. I do not know if the engine turning over will give enough oil pressure for the fuel pump operation.

 

70ZZ3 96LT4, I responded earlier that I got fuel pump working. Engine ground wasn't connected.

I still don't know the pressure. The test gauges I've tried may not push the Schrader down far enough. I can hear the pump and disconnected the quick connect and pumped some in a container. So I know the fuel rail is getting gas but just don't know how strong the stream is.

In any event I'm not getting fuel to the cylinder and replacing the fuel filter didn't change anything.

 

OK - On all the LT1/LT4's the fuel pump is powered when the PCM energizes the fuel pump relay OR when you have about 15 psi of oil pressure. If you look at the oil pressure switch at the back of the motor (yes, it's a bit of a PITA to get to on an LT1 C4's - but I think it's a lot easier getting to the oil pressure switch connector than getting to the fuel pump relay = and doing a relay bypass while standing on your head). Anyway - that switch is what normally keeps the fuel pump running - AND what can be used to run the fuel pump for diagnostics. If you pull the connector on the oil pressure switch and put 12V on Terminal "D" - (I believe it's a red wire) you should be powering the fuel pump.

I've had the same problem with a fuel pressure test gage not sufficiently pressing on the Schrader valve on the manifold log - but there is a real simple solution to that - get a tire valve core tool, and remove the little Schrader valve - then hook up the pressure tester (just remember to put the valve core back when you're done). You should see about 45 psi or more very quickly when the pump switches on - any kind of significant delay means that you have a restriction in the lines. You can also do a flow test without the Schrader valve in there - just clamp a piece of fuel hose to the od of the pressure test port - you should see more than a gallon in 2 minutes (also known as a two liter soda bottle in a minute).

If you find a restriction - I'd suggest either changing the fuel filter or hooking up the pressure tester to the fuel filter input and trying again as a first step.

GOOD LUCK !

 

You can put a jumper from the red wire to the orange wire in the oil pressure switch connector and turn on the fuel pump.