chestypuller- yeah, it's frustrating. Although, I'm getting pretty good at dropping the tank. Only took me about 20 min lol.

Spittybays - Good idea. I'll give that a shot tonight or tomorrow after work. Probably tomorrow.

 

Did you check for battery voltage on the grey wire at the pump connector when the pump is running? Did you check resistance on the ground wire at the module connector? Should be less than 5 ohms at all times. If either one fails, the pump will not build pressure.

 

I checked for voltage and ground. The ground is good. I didn't check voltage while it was running, just at key on. It gets 12v for two seconds when key is switched on. While I have the pump and tank down, I'll jump the pump and see what voltage it holds at.

Say the pump isn't getting full voltage. Could that cause it to not build adequate pressure? What about the lines from the connector outside the tank, to actual fuel pump inside the tank? If there is too much resistance on those could it cause the problems I'm getting? Just trying to come up with stuff here.

 

has to have good voltage its like a variable drill, not enough power and it goes slow,probably burn up with low voltage too. i had a drill do that with a small gauge ext cord that was to long while using it.

 

Absolutely! Low voltage and high resistance will both cause the pump to be weak... and burn it up prematurely too.

EDIT: Check voltage drop at the pump motor. Voltage Drop Testing

 

Ok. The rain here delayed me a few days. But I took the day off work so I could have three full days to cuss at, I mean, work on the Blazer.

I returned the Autozone pump that failed on me (or, possibly, I broke...) and went to a different store and rented another. The fittings on this one seemed much tighter.

I bench tested the fuel pump (1 week old Delco). Container of gasoline, 12v straight from the battery. I ran it up to 80 psi, and learned there is an "overflow" of sorts built into the pump. There is a port at the top to bleed off pressure.

After ten minutes, it was down to 64 psi. After 20 minutes, it was down to 57 psi. From what I have read, I believe these numbers to be acceptable.

I also jumped the pump under the hood (with gas tank and pump removed) and checked my voltage at the pump connector. 12.8 volts to ground, so I can assume the actual wiring to the pump is good. I'll be putting the gas tank back together later and testing voltage under load.

So at this point, I think it's safe to say the pump is not the culprit. I'll be updating this thread throughout the day as I troubleshoot this piece of sh... I mean, fine automobile!

 

Seeing how everything is built in china or Mexico these days, it's possible that pump could've been wired backwards from the factory. I've been seeing that alot lately - not in fuel pumps, but in other items. Lighting, etc.

 

I think this machine is messing with me. Just got the tank back together. Did a leak down at the test port. Key on engine off, 60 psi. After ten minutes its down to 52 psi. It fires right up, no problem. I'm about to see how it drives.

I know there is not really a running fuel pressure spec, but does 50 sound about right to anyone?




EDIT: It works fine. Starts great, runs like a raped ape, and pulls to 5K through 1st and 2nd. I don't get it. But it seems to be fixed (at least for now).

The only thing I can think of is that the fuel pump connector might have gotten dirty or corroded, and me plugging and unplugging and sticking DVOM leads in there might have cleared it up? Who knows.

Thanks to the Captain, Spittybays, and everyone else who pitched in and offered me advice.

 

80psi at the pump is fine. The pump has a built in bypass that is designed to protect the pump from over-pressurizing, that's what you saw squirting. Obviously your bypass is set at 80psi, which is fine. The 10 minute leakdown to 64psi is fine. Bottom line, the pump is fine.

When you check fuel pressure and leakdown at the service port, you're checking regulated fuel pressure and leakdown based on regulated pressure. Those numbers will always be lower, normal.

Your regulated pressure of 60psi is at the low end of the allowable pressure, (regulated pressure must be 60psi to 66psi). Low regulated pressure will cause leakdown pressure to be lower as well. Replacing the fuel pressure regulator should take care of both.