Conversions & Hybrids - Fuel sender is supposed to be 0-90ohms, right?

Is anyone else using an autometer GM fuel gauge with an FBody sending unit? My gauge is reading 1/2 full when bone dry. It goes way past F when full.

I had the purple fuel sender wire getting split between the PCM pin and the fuel gauge. Thought that might be screwing it up, so I disconnected the PCM - now the wire just goes to the gauge. Still same reading though.

I definitely got the GM gauge. Just double checked my packing slip from Jegs.

You may want to verify with the service manual.

I have the SAME problem!

Chances are you have a 99+ fuel level sending unit in tank and a gauge for the old 98- style.

I have a 97 dash cluster in my car right now with the fuel level gauge hooked directly up to the 99+ fuel level sending unit, and I run out of gas at the half way point on my gauge. The first few times I almost was stranded!!!

I am hoping an intricate series of resistors, electrical tape, and crimps will solve the problem.

I have a 99 sending unit which the factory service manual says is 0-90ohms and an autometer aftermarket fuel gague that is supposed to work with GM 0-90ohm sender.

BUT, you may be on to something. The salvage yard told me that they sold me a 99 tank (with sending unit). But maybe they jooked me.

I'll have to look up the specs for the 98.

98 tank is metal and has a bolt in fuel assembly, where as 99+ plastic tanks have the twist on fuel assemblies.

Well, mine is definitely a 99 then (plastic and twist on).

Maybe I just got a bad gauge...?

I bet your gauge is just calibrated for the older GM level senders.

Maybe this weekend I'll take an ohm meter to both level senders and see how they differ.

*bump*

I didn't ohm them yet but just shoot this back to the top. :)

Did you ever get this figured out?

I just ohm'd my spare 99+ fuel level sending unit... its 40ohm empty 250ohm full.

Well crap. The FactoryServiceManual lies then. I sure coulda bought a gauge that worked in that range. Now I have to jury rig something. Damn.

I have some wheel bearing issues - cars been up on jacks again, waiting for parts for the past 2 weeks. Bearing blew out and scrogged the hub.

I was thinking of putting a 50ohm resistor inline.... but then your full point will be near the 2/3 mark in reality.

So you might just have a more accurate 0/3 to 2/3 gauge?

I ohm checked my 97 fuel level sender and found it to be 5ohm to 105ohm.. approx..

So, to get an accurate signal... truley accurate you need to divide the ohms in half, then subtract 20.. hmm.. is that possible?

I know you can just throw a 50 ohm resistor inline and that will put your E semi-close.. and you can try different resistors to get it how you want, but your full mark is really going to mean you have about 2/3 fuel left.

Just did some math...

If you wire a 166ohm resistor in parallell with the fuel level sender circuit, ...

When the fuel level sender shows 250ohms, you will see 100 (FULL)
When the fuel level sender shows 40 ohm, you will see 32 (1/3)

If you wire a 144ohm resistor in parallell with the fuel level sender circuit, ...

When the fuel level sender shows 240ohms, you will see 90 (FULL)
When the fuel level sender shows 40 ohm, you will see 31.30 (1/3)

So... where's that leave us?? *sigh*.. we'll never really see true E

We need a 40ohm "encourager".

I'm still pissed that my manual steared me so wrong. And of course I threw out the box for my gauge. Arrgh....

Well.. I believe 98 LS1's have the 0-90 ohm sender beacuse they have the metal tanks... and 99+ get the different ones. So your manual may not be that wrong.

What I'm going to try this evening is fabbing my old fuel level sending unit to my 99+ assembly.. and then I'll have a true 0-90 ohm gauge. Perhaps you could look into that?

Ok.. I just refitted my old 0-90 sender to the 99+ fuel assmebly.. took a little bit of work and stuff but now I have at least what I think is an accurate fuel gauge.. time will tell.

I can get an Autometer fuel gauge that reads 240 ohm empty/ 33 ohm Full. So, that is really close, except in the wrong direction. Seems plausible to just reverse the wires though, eh? Put the sender signal to ground and the ground to the sender pole?

If that works, I'd still need a resistor to bump it down past E (or else risk thinking I have a little bit of gas when it's actually dry).

I don't think you can reverse it... resistance is resistance. It's not like +/- voltage.

What you COULD do is this.. what I did.. Call up junk yards and get a ~95-98 fuel pump assembly and just take off the fuel level sender which is 0-90 and kind of rig it up for your tank. That's what I did for mine and it works very well.

Yeah, that does sound really stupid now that you mention it.

So, you swapped the winding part, or the whole level assembly? As I recall, it was sort of a big one piece dealio. Urgh. Sounds like glue may be involved, eh?

Local yards won't sell me the sending unit... gotta buy the whole freakin tank. Ironic that way back when I got the tank, they gave me a 98 (or 97?) metal tank. I made them go get me the "correct" 99 unit. I needed to match up the FPR with the 99 PCM though.

I swapped the whole level sending unit.. Basically, 2 spliced wires to the floating end. Can't just swap the "winding" part, or the part where the metal contacts metal to change resistance, They are very different pieces.

No glue, just a dremel and 2 big tie straps. I cut a nice little housign for it in my 99 fuel pump assembly so it fit snug, then just added the straps so it wouldn't pop out. It was a bitch to squeeze the whole unit into the tank though.

Give www.tacreationsusa.com (http://www.tacreationsusa.com) and see if they have your part.. If THEY don't have it you could try www.speedautomotive.com (http://www.speedautomotive.com) but use them as a last resort.

Or you could look up a part and perhaps order it from GM.

Magnus, you have been very helpful on this issue - much appreciated.

Do you recall, on the 98 sender, how similar the whole unit is to the 99? I just discovered why my fuel gauge was freaking out. When I bought this 99 tank, the sender inside was broken. By the time I discovered it, it was too late to take it back to the yard (30 policy, bastards). Plus, they told me up front (probably knew it was broken) that the sender, etc. was not guaranteed. Anyway, the lower basket part was broken off the upper part - one of the round leg/rod acceptor parts of the upper thing was actually broken off. I jb welded it back together and then re-assembled it. Well, obvsiously that didn't work. Now I have a broken unit, AND there are bits of plastic and jb wled in the tank :( .

So, I am hoping that I can just use the whole 98 unit, just swap my FPR on there. I do not want to have to buy a 99 AND a 98 sender. That would just suck.

At any rate, I think I am going to buy a 98 unit and try and cobble something together.

Anyway, thanks.

Hey man I'm glad I can help. I've SOO been there many times and others have done the same for me.. It makes a world of difference.

The unit is not very similar.. well.. they do the same thing, change resistance, but the physical differences are there. They are not directly interchangeable.

The entire 98 assembly is different than the 99 assembly. Neither complete assembly will work in the other tank. If you have a 99+ tank you NEED the 99+ assembly, but you can indeed use the level sender from a 98 arm with some modification... nothign too difficult though.

Can't seem to get my hands on a 98 or any type of 0-90ohm sender :( .

Hunted around the pick and pull and examined about 10 different tanks. None of the other yards either sell senders or have a 98.

This is sucking.

www.tacreationsusa.com (http://www.tacreationsusa.com)
www.speedautomotive.com (http://www.speedautomotive.com)
www.hpsalvage.com (http://www.hpsalvage.com)
www.billygrahamsfirebird.com (http://www.billygrahamsfirebird.com)

all f-body salvage yards.

Here's my proposed solution to this annoying dilemma:
http://240z.jeromio.com/motorswap/fuelsendermod.jpg

Interesting idea!!! :) Make sure the contact shoes still touch the wire after all the monkeying with it. I had this problem and when the sender wobbles a little the shoes will come up off of it giving you weird readings.

Excellent, excellent thread folks.