dano, I'd look into the fuel level sender, I think you'll find the problem there.

pettyfog, These old eyes didn't notice the dotted line, you're right, same connector Not sure why they put the "C4" on the schematic. I pulled out my GM schematic and found the circuit and pin numbers all match with the schematic you posted. The (Alldata???) schematic shows only the pertinent circuits which makes it far less confusing to understand. The GM schematic shows the entire vehicle on 61 pages in a pdf. Looking further I found that both the fuel level sender ground and the fuel pump ground both go to a ground splice pack on the left side of the dash, (figure that one out). From the splice pack the fuel pump ground runs all the way back to the left rear crossmember and grounds there, (WTF???). The level sensor ground runs from the ground splice pack out to another splice near the alternator where it joins other sensor grounds and eventually terminates at pin 19 at the PCM.

To eliminate several feet of cheesy 18ga wire, (which also adds resistance), whenever I replace a fuel pump on one of these things, I always solder on a 14ga wire at the fuel pump module connector and go directly to the rear crossmember with both the level sender and fuel pump grounds. It greatly reduces possible problem areas AND gives the pump a path with far less resistance to ground. I firmly believe this helps with maximum pump output pressure and longevity of the pump.

 

i was thinking about adding additional ground wires too the sending unit and fuel pump but didn't know if it would effect the calibration of the unit.

 

The only way it would affect calibration is if the ground circuit has high resistance, in which case you're improving it! The new style "flat 4" module connector


uses 14ga wire. Solder both grounds together, (black wire & orange wire) and run one 14ga wire to a good clean chassis ground. If you really want to make a difference in pump performance, run a 14ga wire from the grey wire up to the fuel pump relay. Less resistance, higher voltage to the pump, easier path for amperage to flow, all equal better pump performance. Some years, (not your 1999) use an additional feed circuit for the fuel pump that runs through the oil pressure sending unit. The problem with that is it doesn't use the additional path during cranking, only when oil pressure is above ~7 psi.

 

I remember 3 years ago changing the pump and having to change the connector to the new style but I don't remember if it was a Airtex pump or Delphi pump
I just hope that the sending unit I got (AC Delco)will fit it and fix it.

 

3 years is a long time for an Airtex. Rare to get that much out of them unless you park it for a couple years When you get the module out, take a picture down inside the module toward the top of the pump. Post the picture, very easy to identify a knock off pump from an AC Delco.

 

well I hope to have it on the lift tomorrow and have the tank out. we don't drive a whole lot of miles a year about 7000 miles so it been in the tank about 21,000 miles. we have had it 8 years and only put 58,000 miles on it. and that's with my wife driving it, I am night blind so I drive at night, and I only drive about 3200 to 4000 mile a year. when we got it it only had 74,000 miles on it, so at 110,000 miles on it when the first pump pump went out. it's now got a 132,000 miles on it now it's had a charmed life.

 

Thanks for the info on the cracked nipple....I had no idea it could be fixed - that is good to know! Maybe one day I'll actually write up the fuel pump R&R procedure....

Dano440 - good luck! Let us know how you make out!

Jonboy

 

blazer is off the lift now and now the results.

1. it is Airtex fuel pump
2. removed old sending unit, the fingers were wore off and not making contact with the rheostat part for the gauge.
3. AC Delco sending unit would slide on but would not lock on.
4. solution press brass pivot out of old sending unit and the new one and swapped the new parts over on old sending unit.
5. next problem connectors didn't match up inside.
6. un-soldered the wires off old unit and re-soldered to new unit.
7. plugged everything back in installed the float.
8. put it back in the tank
9. re-installed the fuel tank back in the blazer
10. I now have a working fuel gauge. YEAH!!!!!!!!!!!!

this was the first time I see 1/8th of tank fuel (3.3 gallons) run down to the closest gas station and add 5.4 gallons and had a 1/2 tank, drove back to town and filled it the rest of the way up to full and we will how it does this week.

 

Nice job on reporting! That's another thing about Airtex, their **** is not exact replacement, gotta fool with everything to make it work. Good job figuring it all out! Next week when the pump quits, put in an AC Delco module assembly

 

lesson learned on cheap parts