I've got a couple questions about testing the fuel pump and relay. I'm sure you guys can do a better job of answering them than the POS service manual.

-'86, L98. I removed the fuel line that connects to the rail and have no fuel output when cranking. Can't hear the pump prime, either.
-Applied 12V to terminal G on ALDL connector - no fuel flow. Does that bypass the fuel pump relay or just send power to the relay?
-The fuel pump relay is next to the brake booster, correct? Service manual says it's near the blower motor.
-I jumped terminals D & E of the relay next to the booster while the relay was plugged in. Still no fuel flow but I hear a click near the MAF relays.

Barring any other suggestions I was going to pull the pump out and test it before I order a new one. TIA.

 

Grounding the G terminal by connecting a piece of wire between A and G might give a better result...

Removing the fuel line and then trying to get the pump running is asking for trouble... in my eyes at least.

If you don´t have a fuel pressure gauge, OK, but you only have to push in the small pin in the schrader valve on the rear right of the fuel line to see if fuel squirts out (have a shop towel ready to wipe off if it comes out).

Here´s one; http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf

And another one; http://www.corvettebuyers.com/c4vettes/l98.htm

Have you pulled a fault code from the ECM?

Or is there another reason for testing the fuel system?

Does the engine turn when trying to start?

Fuel pump relay is nr. 3; http://members.shaw.ca/corvette86/Co...0View%2086.pdf

 

Check the fuse?
Terminal G bypass the relay but still goes through the fuse

 

Terminal G is a feed to pump bypassing the relay allowing you to supply 12 V directly to confirm pump operation
Putting it to ground (A) will do zilch

 

Oops, sorry, my bad.

Does the 86 have a loose connection coming out of the harness near the brake booster so you can connect that one to 12 volt to make the pump work?

Possibly the same as G?

Edit last one; guess not according to your scheme.

 

Vette, I checked for fuel at the schrader valve by pressing the pin - no fuel. That's why I removed the fuel line. Yes, I have a stored code for a lean condition, I forget the code #. The reason I'm checking the fuel system? Educated guess, my car won't start!

Rod, I did check the fuse first and it's fine. I just want to make sure the relay itself isn't bad before I order a pump. Looking at the schematic, it looks like 12v to G on the ALDL still goes through the relay, and is switched through A on the relay, maybe I'm reading it wrong. The Haynes manual suggests jumping D to E on the relay, which I did, but still no fuel.

 

You may have blown the fusible link, it supplys the relay and the oil pressure switch.

http://members.shaw.ca/agent86/Fuel%...elivery-8A.pdf

 

Tested for continuity or 12 volts. Apply 12 v to "G" again, and see if it makes it to fuse.

 

You're reading it right. This is another myth like the Oil Pressure Switch cuts fuel on loss of oil pressure that just won't die. ALDL pin G does not bypass the Fuel Pump Relay. The Fuel Pump Relay could be bad to the point of not allowing 12v to the pump through the fuse either from the battery or ALDL pin G. Pin A is the common to NC (Normally Closed) contact pin D and when energized by the ECM, to NO (Normally Open) pin E. I've seen the common pin fail open and it wouldn't make with either pin D to ALDL pin G or to BATT when energized through pin E. Keep in mind though that even in this failed state, cranking to the point of building oil pressure, would still power the pump, all else being good.

 

Thanks Ray & Agent. I pulled the pump earlier and applied 12V and ground - it doesn't make a sound so I ordered a pump.

I'm going to recheck some wiring in a minute.

 

1990 base model coup if the run circuit for the fuel pump is not controlled by a oil pressure switch what is the control that would disable the run circui for the fuel pump. Replaced fuse, relay,fuel pump, and oil pressure single wire switch. Under that switch I have another sending unit which is about a inch longer that has 3 wires in the plug. I would suspect that would be the one that would be the interrupter circuit that is being mentioned in other posts. If this is true then I would like to know if there is anyone that knows what wires to jump to by pass the switch. I have the 2 second initial circuit to the pump when key is turned on, checked with meter and heard. Ii am working without the help of the wiring diagram which aboviously a handicap. Any helpful advice would be emencly appreciated.. Thanks Raypdq

 

1990 C4 Base model, driving fine, starting fine, and I backed the car into my driveway and installed a front and rear camera a few days ago, March 2024. I finished my project and was going to get a sandwich. The car started, then it died. It would not start again. Nothing else was changed. I sprayed some starting fluid into the intake, and the vehicle started, and then of course, died again.

I noticed that I did not hear the fuel pump prime. So, I came here to see what posts are on-line. I did the following tests and came up with the conclusion based on my research.

I checked the 10 amp fuse and it was not blown. The fuel relay, located on the passenger side and under the black plastic cover with the interior light in it, was not tested or replaced. I removed the rubber boot on top of the gas tank and checked the wiring that goes into the tank. No damage was observed,

I tested the connector terminals with a test light and turned the ignition on to see if the purple, green, or beige wires lit the test light up, simulating the few seconds the ECM activated the fuel pump to prime. No prime. I have a black, purple, and beige wire on the fuel tank side of the connector. I wanted to apply 12 volts to either of the beige or purple wire, but I have not learned which one activates the fuel pump. (I learned that it is the beige wire that sends 12V to the fuel pump)

Will someone tell me if it is the purple or beige wire that activates the fuel pump when 12 volts are applied? (Beige wire, 12 volts applied, activates the fuel pump)

The car will start but quit as though it is starving for gas.

Will someone please give me the fuel pump relay testing procedure? If someone knows what my problem is, please share. Thanks

 

altownsend, you're resurrecting a 14 year old thread... Pretty much every forum on the internet will prefer you start a fresh topic, where you're more likely to get a reply that pertains to your problem.

I've attached a PDF with some testing info and wiring diagram, I don't remember the exact testing procedure off hand. You need to see if the pump itself is getting power and is capable of pushing fuel to the engine, first. There's a fuel pressure regulator/diaphragm under the plenum, too, IIRC, that can prevent you from getting enough fuel if the reg. is bad.

 

Thank you sir, C4boy,

Another member informed me that I had posted on this old post. I did not know that this post was in the wrong spot. I solved my fuel prime issue. It was the ground on the mounting plate not connecting to the metal tank. I fixed that grounding problem, and I am back to driving daily, again.