I just don't get it. My lift pump has been doing fine until today. I decided to check the how much voltage was present at the plug on the lift pump. I had 14.25 volts while running. Hey great! Not so fast... I plugged it back in and nothing happened. Not a sound from it; no vibration indicating it was running. I shut off my motor and it doesn't run for the few seconds as usual. So you think, "Hey easy. Bad lift pump." Not so fast. I hotwired it using the fuse on the firewall to the power block right by it and it purred away with good flow from the T-valve.

So I have 14.25 volts at the plug while running, but no action from the pump. While shut off and hotwired, the pump runs. What in the world?

sounds like the oil pressure switch has gone bad...it controls the lift pump

I thought this, too, but why would I be getting 14.25 volts at the plug down on the lift pump if the OPS was bad? And why would it suddenly quit just because I unplugged and plugged in the plug?

Yesterday, (other thread) I replaced a fuel filter and was waiting for delivery of a lift pump at the local "Advance/Discount auto" because it was acting "funny", **read - intermittent**. When I picked up the new pump, the old one wouldn't work. I turned the key and heard -nothing-. After 10 minutes of head scratching, I tried it and it worked! Went home and put a new one in! 10 minutes later, no more problems. My OPS worked great but that doesn't mean the output to the pump was "hot" when it was supposed to be, or that there was a good ground. I checked all of them. No smoking gun, just a dead pump.

I guess it wouldn't hurt to try a different lift pump. I consider myself lucky to be over 202,000 miles and have never replaced the lift pump. Lots of OPS though. Might even solve my drain-back problem. What does a lift pump cost?

"Could" be that the contacts of the OPS are so worn that they can't handle the current required by the lift pump, but still measure the correct voltage.

It's like trying to get 5,000 gallons per minute out of a garden hose. It just ain't gonna happen no matter how much pressure (voltage, in electrical lingo) is in the system.

I guess it wouldn't hurt to try a different lift pump. .......snip........... What does a lift pump cost?

Mine was $67 plus tax.

I just changed my LP yesterday after about 1 month struggling with hard start and surging and died. The LP test did not give me fuel out of the fuel drain line and there was 14.x V down there. It looks like the LP was still running (purring) but it was not giving a steady flow of fuel. I put in my spare LP and I also have the Kennedy Lift Pump controller so I installed that also. Now it is nice, you can hear them pumping as soon as the ignition is on. This morning I tried it again and it still starts without surging anymore.

You guys have brought up some excellent points here and I'm sure the answer is here somewhere. The OPS is only about a month old, but I'll probably replace that first since I have to get in there to put the relay in anyway.

The lift pump pumps well when I short it and force it to run, but it may be time to replace it, too.

Thanks for all the help! Feel free to chime in if anyone else has a thought.

Shane

You guys are not going to believe this and will think I'm crazy. Here's the story: I replaced the OPS and no change. I pull the plug on the LP to check voltage at the plug and the plug is full of DIESEL, with no voltage. I check all around the plug, the wires, the pump, and there is no diesel anywhere else. Just in the plug. And it continues to drip slowly. I check for voltage and there is none. I do some more checking and the 20A fuse on the firewall is blown, so I replace it and the LP works like it is supposed to.

But what about the diesel in the plug?! Anyone else see this before? All I can figure out is that diesel is running past a seal in from the pump into the electric motor and then running, through capillary action, through the wires to the plug. This may be making the LP draw a lot more current, which may have messed up my near new OPS and blown the fuse. Any guesses?

I know this sounds crazy, but it is exactly what's happening.

Sounds aboot right. I have seen that happen a lot.

You're kidding. A lot? So, sounds like a new lift pump? This one certainly doesn't owe me anything considering is has 202,000 miles and is original.