Hello -

I'm in Charlotte, NC, and have a 2002 Chevy Silverado 3500 tilt bed, VIN
1GBJC34U22F129260 and a 6.0L gas engine. It has a temperamental fuel gauge. For the most part, it seems to work more or less ok during the warmer months. But when it gets cold, uh oh - quits working.

Note: This truck has two fuel tanks - front and rear. We have not used the rear tank in maybe 5-6 years due to the fuel gauge problem. Last time we did fill the rear tank for an out of town trip, didn't even make it out of town before someone flagged us over and said fuel was running out of the
front tank - and it was. Had to get containers and siphon the remaining fuel out of the rear tank.

The symptoms as of today are as follows (a fairly warm day today):
Note: The front tank is almost full and the rear thank is empty.

1. Sometimes when I get in the truck, the fuel gauge is reading right about 1/2 tank (varies a bit). But sometimes it is not. IF it isn't, sometimes I can just bang the top of the dashboard once and it will jump up to 1/2 tank. But sometimes it won't. Nice.

2. As soon as the ign key is inserted into the keylock (not turned on yet), the needle immediately drops to empty (if it was reading 1/2 tank).

3. When the key is turned one click for the first time, the fuel gauge needle will then jump up toward 1/2 tank or a bit more but immediately drops back to empty - and stay there. Starting the motor makes no difference - still shows empty.

4. If I cut the motor off (if started), remove the key and wait 10-15 seconds, then re-insert the key and turn one click, the needle jumps up again but usually not quite as far as it did the first time. Then immediately goes back to empty and stays there.

5. If I then remove the key for maybe 40-50 seconds (gauge still showing empty), the needle will then jump back to the 1/2 tank level and stay there as long as the ign key is removed (sometimes - but not today).

A. Another odd symptom: Last summer I filled the front tank one day. Can't remember now if the gauge was working before filling the tank or not. But, upon starting the truck, I saw the needle swing all the way around past full to about the 5 o'clock position! Wow! As I drove off, it stayed there. But then a few minutes later I looked at the gauge, and it was reading 1/2 tank and behaved normally for the next period of time. Only saw it do this one time.

This weekend a GM Tech and I checked on this problem. We pulled the front pump and checked the sensor operation. Appeared to be fine - when the float was down (empty) we read right at 40 ohms. When float was raised, read right at 250 ohms. Both readings match the specs on my GM Service disc for this truck.

This pump (Carter 25338939-03 GM#?) does have the older square connector but I replaced the harness end earlier.

Then we looked at the aux pump. The Tech immediately said the fuel line connections didn't look right. We traced the lines and saw that the Return line was connected to the middle tube, which he said was supposed to be the vent tube (like the front pump). This is a Carter pump also (P/N 25317845-xx - from my earlier records, but the Tech thought it looked like 25312945-xx). The label is badly faded now.

Well, given that the vent tube has a check ball in the inside portion of the vent part, that may well explain why we had gas running out of the filler neck years ago. The check ball would have blocked the returning fuel so it had nowhere else to go but out the filler neck.

We pulled the rear pump out, and found that the upper sensor wiping finger (for the variable resistor strip) was broken off half way over - not making contact. Bottom finger appeared ok but the whole sensor metal parts had corrosion/film from being exposed to air for years. Not nice.

Both these pumps have a 'F" and "R' printed on the top of the outer tubes so it makes sense that 'F' is for fuel output and 'R' is for the return line. Seems reasonable anyway.

We took the sensor out so I could check it. Got the same resistance readings as on the front pump (with a bit of extra cleanup effort). We did put 12vdc to the motor and it ran (doesn't mean it will pump gas, tho). Reinstalled the pump.

A few minutes ago I grabbed a potentiometer that read from 0 to 250 ohms; set it for 41 ohms. I then jumpered it to the rear connector across the dark blue and orange/blk connector pins. Cut the ign switch on - didn't make a bit of difference. The fuel gauge needle jumped to 1/2 level and right back to empty. So much for that step.

So, my questions are:
1. When the truck is parked with no key in the ign, is it supposed to show 1/2 tank or any level other than empty?

2. When a stepper motor in the instrument cluster goes bad, does it just totally fail to move or does it do erratic things?

3. Does this sound like a fuel level sensor problem or not.

4. Is the PCM a separate PCBA from the ECM? Where is it on this truck? The Tech said the ECM was in a box next to the battery, but he suggested I not unplug it due to losing the settings. Does the same warning apply to the PCM?

This sucker has kicked my fanny long enough - needs to get fixed! I would really appreciate any ideas on this.

Thx

Fred English
Charlotte, NC
704/568-6895

 

Yo, two more questions ...

5. With fuel in the rear tank, at what point (how often) does the PCM/ECM power up the rear pump to replenish the fuel in the front tank?

6. Given that the rear pump sensor has failed (now seeing 0 ohms), what effect will this have on the PCM/ECM's function as far as indicating the fuel level?

Fred

 

Hi, Tanin Auto Electronix here! We are vendors on the site and want to offer some assistance. You asked:

2. When a stepper motor in the instrument cluster goes bad, does it just totally fail to move or does it do erratic things?

The answer is yes, it'll be intermittent at first and then they'll eventually just stop working all together.

We have the 2002 Silverado Stepper Motors that you are looking for here:

1995-2002 Stepper Motor Air Core Chevy Buick Tahoe Sierra Silverado

Check out the link and let us know if you have any questions at all!

Thanks,