How to get gauge working??

[Bluebell]

There is a fifth connector on top of the pcm.

 

[Bluebell]

I wonder why the buffer is ground on the pcm and why buffer pin D also went pcm.
There's also a green wire from in tank pressure sensor, dk green that was cut at the 4 pin connector on firewall but its showing it goes to vcm 25 evap..

So 3couple wires probably causing this issue.
Vcm 25 evap wire
Buffer pin D purple/white that used go pcm as fuel level
Then buffer pin m that went pcm as ground.
then theres voltage on the purple/white wire

I read somewhere that the earlier fuel gauge had a ground and power and the 3rd was a varying voltage to counter balance the power wire. Which moved the needle.
But I dunno. I was expecting just varying ground resistance.

 

[Bluebell]

It's strange .

So today I learned some things the hard way, after removing the truck bed.
I test fuel pressure other day and it was a little off spec, so I put a dw200 in the factory module.
Had planned use an ac delco sender for a 5.7 but as it turns out. It will not fit 4.3 tank.
Why gm made different tanks/openings who knows.
What I did do is test the 4.3 sender and it appears it's a 40-240 ohm sender. Actually works well.
So how was I getting something different before and thinking it was 0-90, let's just call it my ignorance and one click too far on the old multimeter.
So after all this run around, I been looking at all this wrong.
Need search some more.

 

[AK49BWL]

Oh wow, that changes things. Now the buffer module has meaning to me because the gauge requires a 0-90 ohm signal. 98+ also uses a different resistance, maybe also 40-240, but it's routed through the PCM which converts the signal to PWM 0-90 for the gauge. How weird they'd use a different sized assembly tho... Is it a one-piece thing where you have to replace the entire unit or is it one you can still replace the pump motor individually from the sender body? Because the all-in-one have to replace everything units is more 98+ techy, not 97... Maybe the 4.3 trucks were getting a little ahead in certain aspects lol, hence their having a pressure sensor when the V8 trucks didn't until 98.

 

[Bluebell]

Oh wow,

First off. I appreciate your help through this, as otherwise I would have never figured this out. Those diagrams are priceless.

The sender units are totally different. The opening for the lock ring is way smaller on the v8 unit. The v8 is all metal sender. 4.3 was plastic, 4.3 uses quick connects, v8 uses screw fittings. I was able pull the 4.3 pump out and put the dw200 in its place. I had cut an opening for the dw200 sock filter to stick out but it went in easily enough.

The whole 0-90 and 40-240, pcm control. No pcm control, was confusing, especially with the 97 year being the odd ball.

I found out the 97 4.3 pcm only uses the second fuel signal. Pin d. for accessories, it doesn't convert anything.

After testing the gauge with ground vs 12v and seeing the gauge oppose its reading. I grabbed couple AA batteries and - to ground and positive to gauge. The needle moved to 1/4 tank. So that gave merit to the thinking it needs a bolt signal not resistance to ground.

I then tried a bunch different configurations of the buffer wires. No luck.
I blew every cluster fuse there was in doing so. Lol

But the 5v signal was random and not always 5v. That stuck in my mind.
So after all this. I focused on that, and on the LS pcm I knew the oil sender wasn't being used. As I'm using the obs oil sender and wiring.
So I ran a wire from 5.3 blue pin 7 oil sender 5v reference to the buffer module.
She works!!!

I tested the buffer output wire to gauge and it doesn't change the ohm it sends out a 5.XX signal to the gauge. Which seems even more odd. Guessing the engineer for 97 was fired. Lol

Thanks again

 

[AK49BWL]

Very interesting! And not at all how I expected things to turn out lol. But the fuel gauge works like it's supposed to now?

 

[Bluebell]

Very interesting!

I edited my post when you replied. May be info there you would find interesting and missed. About sender and the buffer output.
Yeah. Far as I can tell it's fine
It sweeped when I turn key on and went back to 3/4 full which should be about right.

 

[AK49BWL]

Good deal, good deal. And here I thought only 95 was the really screwed up year for mixed and in-between parts lol. Guess we can add 4.3-bearing 97s to that list!

 

[Bluebell]

Now I need figure out why that wire wasn't consistent 5v and where it came from. Lol.