Hey All.. Apologies up front for the long post. I've pretty much finished swapping a 5.3/4L60E into a 1993 GMC 2wd that originally was a 4.3L. I used the Fitech Ultimate LS stand alone kit for the swap and the truck itself is running and driving well, but I wanted to keep the factory dash/gauges in the truck. I figured I would leave the original wiring harness with all connections for the original senders in the truck and let that run the oil/volt/temp gauges. So far, I have oil pressure, volt meter and gas gauge working but no temp gauge. I'm also looking for info on where the "speedo" and "tach" wires from the Fitech loom would attach so that the speedometer and tach in the dash would function. There is one wire each for the "speedo" and the "tach" coming out of the Fitech loom.

I have been scouring the internet for information, and this is what I've come up with so far so please correct me if I'm wrong on any of these. Believe me, I would appreciate the feedback. I'm pretty much clueless when it comes to electronics in newer vehicles.. I'm more of an old school guy, and this is my first project that required a computer to make it run! LOL

Speedo: From what I've gathered regarding the speedo, in the original configuration the VSS feeds info into the PCM which then runs to a DRAC module to convert the signal and send it to the speedo in the dash. The DRAC module is a buffer that converts the VSS signal and basically adjusts for different gearing and wheel diameters, etc. so the output to the speedo would be correct for that gearing/tire since they used many different combos in the various models. The Fitech allows for programming of the gearing and tire size, so my thinking is that DRAC module is no longer needed. Which brings me to my next question.. The dash cluster in the truck is electronic, with one connector for everything at the back. I've managed to find what I believe is the pinout diagram for that connector. There shows to be a VSS High and a VSS Low input coming in to the cluster. If I needed to bypass the DRAC module completely, would I then hook direct into one of these? And if so, which one would it be. From what I've been reading, I'm thinking is the VSS High (purple/white) wire, but I don't want to go hacking into wires until I'm fairly confident that I need to.

Tach: This one seems (to me anyway) to be pretty straight forward. There is a tach input showing the gauge cluster pinout, and I'm thinking that the tach wire would from the Fitech would need to be attached here. The Fitech allows for programming of the tach signal so I think I could adjust it from there to make it read correctly.

Temp Gauge: This one has me a little stumped. Originally I put the 5.3L temp sending unit in the truck to run the gauge. The connector was the same on the original wiring harness and matched up to the 5.3L sending unit (two pin), so I figured it would run the gauge. Once the truck was up and running, I found that it didn't work so I began to think that maybe the 5.3L sending units "specs" didn't jive with the gauge and they weren't compatible. So, I bought the adapter to go in the block and used the sending unit from the 4.3L motor.. but still does not work. I was doing some research online and I read something about where the temp signal in the original configuration went through another sensor (MAP maybe??) to feed it information. Well, when I was cleaning up the harness of things I didn't think I would need I'm thinking that I may have taken something out of the signal chain and caused a break where the sending unit signal isn't making to the gauge. The confusing part to me, is that when I turn the key.. they temp gauge will peg out for a split second and then go to zero. So it would seem to me that it's getting some kind of signal and/or power.

Anyway, thanks for taking a look and any and all help and input would be appreciated. I know that posts on the internet are pretty much useless without pics, so here are a few of the truck. Thanks again!!

 

Nice ride! What size are those wheels and tires? Thanks
Jarhead

 

Thanks! Wheels are Riddler 20x8.5 in front, and 20x10 in the back. Tires are 295/40/20 and 255/45/20.

 

VSS High goes to speedometer input. VSS low from the speedometer can go to ground. Your speed is probably looking for a 4000PPM pulse, as this is very common.

If the Fitech has a tach output, then you can just feed that to the factory tach.

Not sure what is going on with your temp gauge, other than maybe the "gauge" is not a gauge at all, but simply a fancy idiot light. Meaning, it just shows "normal" and when things go wrong, it pegs it to the high side.

Andrew

 

Hey Andrew,

Thanks for the information! Really appreciated. With regard to the temp gauge, it worked in the truck prior to the swap and the gauge face is numbered in degrees (100, 210, etc) and would slowly climb as engine temp increased. I may see if I can pick up a harness side connector and try to run it direct and see if I can get it work that way. I'm not ruling out the possibility that I may have gotten a bad sending unit as well. If not, as a last resort the Fitech handheld unit will give me engine temp. I would just really like to have all the factory gauges working. Once again, thanks for the information and help.

 

Glad to help. I would wire the factory sensor directly to the gauge, just to isolate any other wiring issues.

Andrew

 

Will do, thanks again!

 

Hey Andrew.. I think I may have my temp gauge issue sorted. I was going thru a bunch of old pics I had taken during the build process today and putting them into a folder on the computer, and I came across the picture below. I think this may be the culprit as to why my temp gauge isn't working. The pic below shows a single wire connector coming out of what appears to be a coolant sensor that was on the driver's side of the motor. I had taken these pics prior to yanking out the 4.3L for reference. I just checked my original harness in the truck, and thankfully I didn't remove that connector. I ran a jumper wire from the connector to ground and it pegged the temp gauge in the truck when the key is on. So, now I'm thinking that maybe what I'm thinking was the coolant sensor I put in the truck isn't the coolant sensor for the gauge (probably sent the signal to the aforementioned MAP sensor) and this is the connector that needs to be hooked up instead of the other one. I looked on Rock Auto and also found the below temp sensor that says "w/ Oval Connector; With Gauge" for the 1993 with 4.3L and it matches the connector in the truck. I'm going to get that ordered and installed, and extend the wire over to the passenger side head to try it out. Fingers crossed, this'll work.