rmytych

I have just completed a front to back replacement of everything related to the fuel system in my 1991 C4... fuel pump, sending unit, filter and injectors. The gas tank was cleaned, not replaced. I finished putting everything back together today to run a pressure / leak test and got a big nothing. With the ignition on / engine off, I’m getting no power to the sending unit / pump assembly. The fuse checked out okay.

This was working when I parked the car and disconnected the battery about 2 weeks ago..

I only added 2 gallons of fresh fuel to run the pressure / leak test. If there is not enough gas in the tank, is there a pump shut off that turns off the juice to the pump to keep from burning it up? I thought 2 gallons would be plenty.

Any suggestions would be helpful.

65Z01

I think 2gal should show up in the "add fuel" area, if you have such on your '91?

rmytych

Just a notice that says - RESERVE
Probably the same thing.

JimLentz

Check if you have fuel pressure with gauge.

rmytych

I connected that before I even reconnected the battery.

I order everything from the guys at Fuel Injector Connection. The ONLY difference is the pump is a low pulsation one that called for eliminating the pulse dampener... which was perfect going back onto the new sending unit.

I took digital pix of the original unit and the new set up and everything looks right.

Hope to dig an little deeper tonight. Every suggestion helps!

Thanks.

TheBlaster9001

Ignition on, engine off, you will only have power for 3ish seconds after you put the key forwards. No constant power until cranking (with oil pressure) or the engine is running. Could this be your issue? It took me a bit of cranking to bleed the air out of the lines once I had replaced my sending unit.

Can you hear (or see on a multimeter) the pump run for a few seconds one you hit the key forward? I had a brand new pump that was dead out of the box. If you can verify 12 volts at the sending unit after key on, then we know where to look.

I would check the fuel pump relay if you don't have power during those few seconds. You can also ground pin G on the ALDL to force the fuel pump to run.

vader86

Check for hot power at the sending unit and got none? Ground the terminal on the ALDL connector and see if the pump comes on, Terminal G I think. If that causes it to run the FP relay is the likely culprit, going from memory.

If it does not run then the circuit is likely broken somewhere.

rmytych

I know about the oil pressure time out. I disconnected the plug and tried to get a voltage reading with a multimeter on the “car side” and got nothing from the time the key was turned. I’ll walk through all these steps again... I have to admit, I was pretty frustrated that in trying to make things better, I created a new issue.

Grounding the G pin... is that with ignition on / engine off? Please let me know.

Thanks!

vader86

Ignition set to run.

rmytych

Thanks!!

65Z01

On my '88 it takes +12Vdc on ALDL pin G to force the FP to run constantly. This applies power through the FP Relay and the FP Fuse to drive the FP.

Space387

there should be a red single wire that terminates to nothing near the brake booster/ battery. If you jump this to the 12v terminal on your battery it should force the pump on. If by doing this you have pressure replace your relay. Should be located under the passenger side dash, there will be a block of 3 relays closer to the center dash facing the front of the car. In this block the relay closet to the passenger side of the car is your fuel pump relay. Swap with a known good and retest. This is what I had to do about 2-3 weeks ago

PatternDayTrader

Did they really call the pump a "low pulsation" unit ? lol.

rmytych

I took a step back and started over. Double checked everything starting at the fuse and cleaned all connections and re-seated them. And... instead of trying to race the 3 second time out to the multimeter, I rigged a test light for instant 12v confirmation (working alone).

I have power and fuel pressure... good fuel pressure... good enough to make my fuel pressure gauge line leak. - It’s okay to laugh... we’ve all been there.

Cleaned up the mess and had to walk away. Should be dry tonight so I can do a proper leak check with no guessing.

Thanks all for your thoughts!!