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LS swap in my 87 k5

tennbowtie said:
On the fuel gauge I've got 4v on it when the switch is on. I've switched to 4cyl mode on the tach and no difference, I'll try adding a resistor later.
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Pretty sure you should be going by ohms not volts on the fuel gauge. There will be a 12v switched power and ground. Then the fuel gauge sending wire you should test for ohms. I forget what the gm gauge reads at for full, half, and empty. If you can google Those numbers that will tell you a lot.

The ground wire from the fuel tank should read very low ohms to another ground point. If it reads high; clean your ground and make sure it is tightened down all the way.

Are you 100% certain you have the engine speed wire? I believe the engine speed and vehicle speed wires are both white.
 
tennbowtie said:
I checked both volts and ohms, with the switch on it's open switch off it's 4ohms
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Unfortunately I dont have any more advice for you.

Your positive the gauge worked before all the swap stuff?

Hopefully someone more knowledgeable will chime in. I would ASSume that it would read the same key on or key off if the sender was working properly.
 
For the tach, the PCM outputs a 4 cylinder ground pulse signal. Your Tach is probably looking for a 12V square wave.

As mentioned above you do fix it with a resistor. The value of it doesn't matter much, somewhere around 1.5k ohms is fine. Hook one side of the resistor up to a 12V ignition source and the other side of the resistor up to the white engine speed wire coming from the PCM. Hook your tach up to the leg between the resistor and the PCM.

When the ground from the PCM is on the tach will see roughly 0V. When the ground from the PCM is off it'll see 12V through the resistor. The resistor is simply restricting current flow through the PCM's ground pulse driver and saving it from burning out.

If your fuel gauge is reading over scale full then it is seeing infinite resistance, aka it isn't connected to the sending unit. If you accidentally hooked the fuel pump and sending unit wires up backwards you may have burnt the sending unit out (I've done this more than once, doh!). Make sure the tank is properly grounded as well.

You can test the wiring up to the tank by disconnecting the sending unit wire at the tank and grounding it. The gauge should go below empty when shorted to ground.
 
Russell thanks for the advice, I disconnected the pump and sender grounded the sender back to the gauge and read E, so the gauge works? Ohmed it back to the tank and read 111.7, I also double checked at the firewall to make sure I didn't swap the two up and I didn't. I'm hopping the sender wire fell off when I put the tank back in. Everything but the gauges works awesome, a little shutter at WOT I think that's the o2 sensors they will be here Thursday. I'm very pleased with it.
 
Added resistor and tach works, thanks again for the help. If work allows I'll get to the fuel gauge and speedo Friday.
 
I noticed this morning my clicker didn't work for my headlights, luckily there are stuck on bright. I think I took power from it when I put the new gauges in but not sure, anyone else ran into this yet?
 
I can't think of any reason why that would happen? Maybe your high beam switch rod fell out of place?

Speedo is the same thing as the tach. Outputs a ground pulse. Need the pull up resistor to get the speedometer the 12V square wave it needs.
 
I haven't had much time to work on the truck, but what time I did I messed with the speedo. I still can't get it to work, is there a way to see if I'm getting signal from the ECM and if so what am I looking for?
 
I messed with the truck a little today, I got the speedo and tach working now, no go on the fuel gauge yet. I've been driving it a lot and it seems like it doesn't have any low end power. It might be the 3:42 gears and 35" tires but It will not even turn the tires over. I thought about buying a 212/218 cam, anyone running it or no of anything better?
 
tennbowtie said:
I messed with the truck a little today, I got the speedo and tach working now, no go on the fuel gauge yet. I've been driving it a lot and it seems like it doesn't have any low end power. It might be the 3:42 gears and 35" tires but It will not even turn the tires over. I thought about buying a 212/218 cam, anyone running it or no of anything better?
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Seriously depressing I have 3:73's 700r4 and 28" tall tires and I cant break them free leaving a stop light. I almost wondered if I had a wrong stall on my TC.
 
Do you guys have your torque management and traction control deleted? My 03 Tahoe with a 5.3L will shred the tires from a full stop just by mashing the pedal after deleting that stuff. Before it would chirp the tires or slide going around a corner but would not roast them.

The 5.3L is a very peppy engine, it should make your truck jump into action.
 
Russell said:
Do you guys have your torque management and traction control deleted? My 03 Tahoe with a 5.3L will shred the tires from a full stop just by mashing the pedal after deleting that stuff. Before it would chirp the tires or slide going around a corner but would not roast them.

The 5.3L is a very peppy engine, it should make your truck jump into action.
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I know torque management is gone on mine. I would assume traction control would be gone too... all emissions is gone and I have a premium fuel "performance tune" granted my trans still doesnt downshift right; there is no down low power. I can ring it out in first and second gear though.
 
My suburban with 3.73s and 33s with the 5.3 will not spin the tires ever. Only when going around a corner.
 
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