1998 Suburban fuel gauge always on empty

[Paul S]

Hi all, first post on here. I have recently procured a 98 K2500 Suburban with the big 454. ~230k miles

I am having several common issues with the gauges. The speedometer and tachometer are both reading about 30% high. At idle, OBD reports 700-800RPM, tach says ~1100. Speedo says 100 when OBD and GPS say ~72. I searched all over the internet and did not find any solution for this problem aside from replacing the cluster. It seems that the problem is likely with the circuit board inside the cluster that controls those gauges, as the PCM (via ODB) has the correct speed/RPM, and the odometer is incrementing correctly. I am suspicious of the electrolytic capacitors on the cluster PCB. I have some replacements on order, will solder on and see what happens...

I'll also need to re-oil the fuel and oil pressure gauges. They do the typical 98 GMT400 vibration. Probably should replace the cluster illumination with LED's while I'm in there.

The issue I don't understand is my fuel gauge. It is always stuck on empty. The gauge motor itself works - I can make it move when I take out the cluster and apply external power. Cutting the purple/white wire that goes from the PCM to the fuel pump does not change anything. This wire connects to pin 13 of the gray/white PCM connector. I measured a resistance to ground of about 4800 ohms on this pin, which seems way off. I would expect something around 100-200 ohms based on my research (the tank is somewhere between half and three quarters full). But if the resistance to ground on this pin is so high, I thought the gas gauge should be stuck full?? I am hoping someone here has better insight for what the PCM does with the fuel level on the '98+ GMT400. Most of the info I can find is for the pre-'98 0-90 ohm system.

 

[GoToGuy]

Have you looked in the OE service manual, at all? Maybe try using the factory diagnostics.
If you replace incandescents with LED , you will not have a dimming function.

 

[1998_K1500_Sub]

I'll also need to re-oil the fuel and oil pressure gauges. They do the typical 98 GMT400 vibration.

You can fix the "hummingbird" fuel gauge with a tune of the ECU.

If you plan to be modifying the tune, fix the fuel gauge at the same time.

See https://www.gmt400.com/threads/120-mph-cluster.52101/post-1216167

I am hoping someone here has better insight for what the PCM does with the fuel level on the '98+ GMT400. Most of the info I can find is for the pre-'98 0-90 ohm system.

The factory service manuals are here in .pdf form, grab them for your '98:

88-98 Service Manuals

Over the years I have collected a bunch of GM service literature. Links to PDF Scans of service and STG manuals and a links to the Parts manuals. You'll need the FREE Adobe Acrobat reader to open these files. Get it directly from Adobe here {http://get.adobe.com/reader/} If you're not...

www.gmt400.com

 

[movietvet]

Welcome to your first post at the forum. Could you post some pics of this Suburban?

 

[AK49BWL]

I'm guessing it's probably the same as my 0411 PCM; if there's a problem with the sender, be it a wire short or open, or value out of range, the PCM will command 0 or empty to the gauge.

 

[Pinger]

All but one of my myriad fuelling issues with my 1999 'Burb have been due to the connections between the fuel pump pigtail and the main harness. Find it lying atop the fuel tank, easiest accessed at the tank's front just behind the rear axle (on mine at least).