Replaced the fuel pump once several years ago. Just funny I could hear fuel pump priming until I changed the ignition switch. I do want to test the wiring and I've been trying to figure out how to get to the fuel pump connector without dropping tank. I did solder in the newer style connector when it was replaced last time but I can't remember details. Hoping if I remove spare tire I'll be able to reach up there to unhook the connector for testing. The topper is that the gas tank is full 🤣. I filled it up back when the Russia invasion started because I figured the price would get crazy. So I have a full tank of cheap gas that I need to transfer to the Toyota. Lol.

 

Since your concerned about the effect of replacing the ignition switch on the power to the fuel pump that's why I suggested testing at the priming tab at key on because you are testing the entire circuit except the last wire run to the pump including the ignition switch. I changed my pump 15 years ago so I cant remember if you can get to the connector with the tank in place. If you have power to the priming tab and no fuel pressure then you can try tapping the tank which sometimes jars a frozen pump loose temporarily and then you could pump the tank out through the schrader.


George

 

Yes I think I read something about testing that prime terminal. So turn key to run. Test the prime terminal for 12 volts. If that's a go, leave key in run position and go thump on fuel tank? Thanks for your patience!

 

The first thing would be to test if 12 V shows up on the priming tab for the few seconds after Key on. That tells you if you have power making it all the way through the circuit except for that last wire run to the fuel pump. With regards to trying to get the pump to turn on to empty the tank you would hook a drain hose up to the Schrader into a gas can, apply fused 12 V to the priming tab them climb under the truck and bang the tank with a rubber mallet a couple of times to see if you can get the pump to turn on. You would either have to use an air conditioning gauge set hose that has the depressor in the center to open the Schrader valve or remove the Schrader core with the appropriate tool

 

Have your LIM gaskets been replaced? They are like wisdom teeth and almost always need to come out. This thread made me think of your situation:

https://blazerforum.com/forum/2nd-ge...blazer-104509/


George

 

The intake gaskets have been replaced twice. I've had the Jimmy since 2006. The kit that was used last time in 2016 was 98002T. I believe that's full upper and lower?

 

Test light at prime terminal came on for 2-3 seconds after turning key to run. Put the 12v straight to terminal and thumped on tank using flat side of 2x4 (can't find my rubber mallet) making sure I didn't hit the tank with end of board. After several thumps I could hear sort of a fizzling noise, thought I'd cracked the tank 😳 but as a 53 yo woman I'm sure I wasn't hitting it as hard as a man would, lol. The noise stopped after I took 12v off prime. Pump never ran, just made that strange noise. I think there is space I can reach in and unplug the fuel pump connector. Can you tell me which terminals I should test for 12v and ground? It is the newer flat plug that came with my last new pump.

 

When you are testing the quality of the power that arrives at the load (fuel pump) its important to test both the power feed as well as the quality of the ground AND with the load applied. Now I realize that this may be difficult with that insane fuel pump set up but if you can manage it the correct approach would be back probing the connector while its still attached at the gray and black wires from the harness. Now there is a blk ground for the pump and a black ground for the sender so you would have to try both grounds and do the test twice. Fused 12v at the priming tab and test. If that wont work due to access then disconnect the harness and if you can get to it we can put a dummy load on gray and blk and test.


George

 

Before crawling under the truck today, I tried again to start it. First the fuel pump has decided to run today (banging my head) 2 seconds at key on and 2 at key off. Also runs when I put 12 volts to prime terminal. But it still won't start. Just for "fun" I sprayed a little carb cleaner in the throttle body and it will start and run for just a second or 2. So does that sound like the pump isn't delivering enough fuel to keep it running? With the pump not running the other day and deciding to run today, is it likely the pump is on it's way out, or should I still check wiring at pump? I could see where a bad connection or ground could vary with the weather. And could low voltage/ground issues cause the pump to not put out enough pressure? As far as checking fuel pressure, I'd have to borrow a gauge and it would have to be a day the pump wants to run. 😂

On a side note, with the price of gas I'd sure like to get that full tank into my other car. I've read to pull the vent or fill hose off the tank and siphon from there. Sound like a good plan considering my pump may or may not run at the time?

 

You really should confirm with a pressure gauge. Yes you should always check the wiring, many a good fuel pump has been replaced (sometimes more than once) with an inferior after market brand and when they come here we start testing the wiring.


George