Problem just as title says. I have been up for two hours already late for work trying to figure out why I am not getting fuel. Thought maybe a clogged fuel filter so I popped off the forward line drained it put it back on as I have had a fuel filter problem before. This time I turn the ignition on while I am outside to listen to the fuel pump. Turn on the key -cricket chirps-. Been trying to find the wire schematic for the circuit as the relay is not the problem(THANK GOD). I am a ***** when it comes to making sure I go to ignition hear my fuel pump kick on wait a sec then crank it up.

I have been hitting up the search button for the past 45 minutes with the normal key words.

Testing methods I have performed:
My multi meter has no way of checking current across the relay. I can only do voltage and ohms. Relay is good. ECM I and ECM B both have the correct voltage.
PIN 30 on relay is energized.

Problem found now I just have to back track from fuel pump harness to the power source! 0.136VDC - F/PUMP supply

 

Is there a possibility that the fuel pump is bad? I just replaced my last weekend. The pump turned on but it creating 56lbs of pressure to fuel injectors. Turn the key off for 10 seconds.....turn the key back on (do not attempt to start yet) for 5 seconds than try to start the truck. If it trys to start even for a split second that pump is working, just not strong enough to make pressure to run. my .02$

 

Can not read fuel pressure if the fuel pump does not turn on.

Hoping PCM is not tied ANYWHERE in here as well. As I have two other problems with the truck where PCM is also listed as the source of problem.

EDIT: Got a snap shot of the chassis side of the F/Pump connector. Took some measurements, but as I JUST found my Chilton's Repair Manual I had no clue which was which. Now I am going to go back out with my repair manual and retake measurements and see whats reading what. But I will post my measurements to the adjacent pin.


1- 5.10VDC - Sending unit signal
2- 0.136VDC - F/PUMP supply
3- 1Ω - F/PUMP ground
4- 88Ω - Sending unit ground

I have identified the problem. Now to fine tune where the problem originates.

Edit- I still can not get the F/PUMP supply to read battery voltage. Even completely bypassing the relay. -dumb founded-

 

The grey wire at the fuel pump module is the feed for the pump. When the ignition is initially turned to the RUN position, the PCM activates the fuel pump relay for ~2 seconds. If the PCM does not receive a signal from the crankshaft position sensor, it deactivates the fuel pump relay. You need to test for battery voltage on the grey wire at the fuel pump module during the 2 second "pump prime".

Your connector to the fuel pump module appears to be ok BUT, it has known "issues" of overheating causing high resistance, (open circuit) to the fuel pump. The connector should be replaced when you replace the module. Most replacement fuel pump modules come with the new style connector in the box:





Also, the 88 ohm reading for the fuel level sender ground is too high, needs to be less than 5 ohms to ground.

 

I have a floating gauge. That is why my sending level numbers are wacky. I have the tank out now. Got pissed and yanked it out. Only need to replace the middle QD. One side got stuck and snapped like a twig. Also I am a electrician so you can use electrical terms.

Also I am getting .096 VDC during that 2 sec.

 

There are 3 quick disconnect fittings on the module:

3/8" is fuel pressure to injectors, (up to 108psi)
5/16" is fuel return (pressure varies)
1/4" is fuel vapor (less than 3psi)

The ONLY one that MIGHT be able to be repaired is the vapor line. If the pressure or return line fitting snapped, replace the module assembly.

 

The lines their self broke the middle one; the plastic lock ring. The hardlines didn't break. It was that hard plastic crap going from pump to the T-fittings on the chassis. I am replacing the F/PUMP anyways. After the crap it put me through today.

It did feel good though taking my electrical knowledge and learning some more electrical of the truck. I am thinking since the tank is out about replacing the entire F/PUMP power supply line as it is not hard getting into the junction box and everything is visible.

 

Be sure to use a DELPHI or AC DELCO pump.

 

I read people had problems with certain brand pumps. Pricing a OEM one first then those. Got a buddy who works for GM.

 

Well the last Delphi I bought was $275 from CarQuest about a month & half ago. If your buddy works for GM then he of anyone should know how picky these Blazers are about OEM parts. The last Airtex I ever bought after 6 month & less than 10,000 miles cost me buying another pump. I put in a Delphi & two years later & 45,000 miles it is still running strong & this was in a Honda Civic. I'm told Delphi makes OEM Pumps for several manufactures.