Paul S
Newbie
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.
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.