All, I've done plenty of searching and brainstorming and am trying to troubleshoot a possible electrical issue at my fuel pump. i can't seem to find the specific information I'm hoping for.

I've for a long time had the common stumbling/stuttering issue under low RPMs that plague many blazer owners. To this date, I've changed plugs/wires/cap and rotor, fuel spider assembly, fuel filter and even changed the fuel pump about 2000 miles ago. (Admittedly with a cheap aftermarket unit). The stumbling symptoms still persist and I planned to look at the cam and crankshaft sensors and check the distributor gear soon (I'm in the process of moving and currently in a rental house without most of my tools or garage)

Anyway, to the current more major problem:

Last weekend the vehicle died as I was slowly driving through a parking lot. It would not restart and I listened and didn't think I could hear the fuel pump running. I confirmed that there was no fuel pressure at the fuel rail so I called a tow to get me home. After 30-45 mins of waiting for the truck I tried to start the blazer again and it fired right up and I was able to drive the 10 miles back home. Its been fine for small trips over the last week.

Yesterday it dies again and won't restart. My gf and I were meeting for a walk-through at our new house so she picks me up and we leave the blazer parked for the afternoon hoping it'll fire later and I can get it home. This time it doesn't work and I have it towed home.

I've dropped the tank far enough to disconnect electrical and am trying to check the voltage at the fuel pump harness. I'm not sure of the pinout of the 3 pin oval plug and what voltages I should be seeing here. I have a gray, green and black wire.

green to gray and black to gray both give me 5V with the ignition on. Both of these configurations stay at 5V for 2 or 3 seconds after the key is turned off and return then to 0.

What voltages should I be seeing across these wires? I expected and hoped to find 12V somewhere for the pump but I'm not seeing it. I've swapped relays under the hood and everything on that end seems fine. What should I check next?

This is a 1998 2 door, 2wd blazer with the metal fuel tank.

Brandon

 

Different gen not sure if it applies but on my '94 I had a break in one of the wires inside the tank causing similar problems took forever to track down the problem (I know some 2nd gens the fuel pump/sending unit are all one piece not sure which years and if yours is new this may not be your problem just tossing out an idea from my experience)

 

Yeah it very well could be something like that. If the voltage checks out at the pump then I know I'm going to have to pull the pump assembly and investigate or just replace it. I'm just suspicious only seeing 5V here. Does anybody know if it should be 12 and I have a problem somewhere between the relay and the pump connector?

Edit: OK, I'm an idiot. I finally used the right search terms to find a very useful thread on here which told me I'm looking at the wrong connector! So the voltages seem to check out on the 4 pin pump and sending unit connector. At the turn of the key the pump motor pin gets 12V for a few seconds to prime then drops to zero. Once the ignition is turned to start it bumps up around 10.7V while cranking. I assume under normal conditions the pump should receive full 12V again while the vehicle is running.

So, looks like my wiring checks out and the pump is shot.

Does the original intermittent pattern sound right for a pump that is just dying of natural causes? As far as I can tell, everything with the wiring is making sense now.