fuel level sender compatability issue

[Fire67]

Hey guys, I'm hoping someone on here can help me figure this out.

I have a '00 TA fuel level sending unit that absolutely has to be used because of the fuel tank being used... In my buddy's '96 TA. The sender's output to the gauge uses a different Ohm range. Can this be corrected with resistors or something?

[Twisted Z]

Hmm..

Check with the Merv

[Fire67]

the Merv huh... I remember that guy, didn't think he was still around. I'll see what I can do about finding him. Is he already a member on here?

[Alex94TAGT]

Is the needle on the dash buried at Empty or at Full?

The fuel level sensor is just a potentiometer -- a variable resistor -- attached to that float arm. I believe the lower the fuel level gets, the more resistance the fuel level sensor creates, and thus eats up power from the gauge (making the needle drop). I wouldn't rule out the possibility that the float is stuck or that the potentiometer is shot.

There are three wires going into the tank: power (gray), ground (black), and a purple signal wire sent to the dash. I honestly cant remember if the pump and level sensor are wired in series or parallel - maybe you can remember since you've dealt with it recently.

It seems to me that you've got a few possible problems. First off, even though you would theoretically be reusing the stock (+12v) LT1 wiring, the LS1 fuel pump might draw more or less amperage/current, or the LS1's wiring might deliver more or less power to the pump. THEN you have the possibility of the potentiometers of the fuel level sensors being in a different resistance range or having a wider or narrower spread. Maybe the LT1 and LS1 dash gauges have different input levels.

If you still have the old LT1 pump, I suppose you could test it for current (by putting a voltmeter in series with it) and then measure the potentiometer for resistance. Compare to the components in the LS1 setup. With great luck, the resistance ranges might be similar but just too low on the new LS1 setup, and you could theoretically add a resistor in series to shift it up to where it needs to be. (Resistors in series just add up, but resistors in parallel have an inverse relationship.)

voltage (in volts) = current * resistance
resistance (in ohms) = voltage / current
current (in amps) = voltage / resistance

(You can think of current as the 'flow' and voltage as the 'pressure'.)

If all else fails, you could always just fill up using the Odometer. ;) Should be good if you fill up every 200 miles...

[Fire67]

Alex! Long time no see buddy! What's with that thing still not running? Loose interest? Nice to see you around though...

Spoke with the Merv, and he said that on the 99+ LSx cars the fuel level sender sends the signal to the PCM. Then its wired to the BCM, which finally relay's the signal to the gauge. He had no idea whether or not the signal was modified in any way by these components, but did state that he could not get the LS sending unit to work with the LT1 gauge.

I'm going to buy a new multimeter today (my old one broke a few weeks ago), so that I can tell what range the stock sending unit outputs.

The Sender and the pump share the same ground wire, with the power and signal wires being seperate. On the LS cars, the pump and sender have their own seperate grounds.

I do know from experience with my own car that the pump is not a part of the equation. As I completely removed the pump from my stock tank and the fuel level gauge still works. I don't even have the gray wire in the harness anymore. Just the purple and black.

Anyhow, I've determined I've determined that the easiest most gauranteeable route is going to be an aftermarket tube style level sender like the one's sold by Jegs and Summit. Just gotta match up the ohm range and we're good.

[Alex94TAGT]

Hey man -- good to hear from you too.

Sounds like you've got this figured out then. I had no idea that the LS1's ran it through the PCM. Weird.

My car is running fine actually -- I've put about 7000 miles on it. I just don't have the supercharger on yet. I still need to retorque the main caps and get a pulley machined. I just don't have as much time to work on it as I used to, plus I've been riding motorcycles. ;)

[Fire67]

Damn motorcycles ruin good car guys!!!!! Besides that, they tend to kill them. Please be careful on that thing. I just had my uncle and one of my racing buddy's get killed on their motorcycles.

Ahh, forget about re-torquing the main caps! That's no fun, I didn't retorque mine.

Get that pulley machined and put that baby together. At least in time for the shootout, I'd love to see that car in person.

I'll get my car finished up as soon as I get some free time from working on everyone else's toys. Just gotta hook up my new Digital 7 ignition system and finish tuning the new computer. And hope that the HVC2 coil doesnt destroy the gm opti too quickly.

[Alex94TAGT]

Haha, that MSD coil looks like a beast. Might want to have your optispark blessed by a priest before you start out. ;)

I'm just a little scared to run that kind of power without checking the rods/mains. I heard one guy say that his main bolts were loose even after 1000 miles. My head studs had backed out a little bit -- already got those taken care of though. Maybe I should have double-nutted the main studs? haha. Either way, I gotta fix a leaky rear main seal and swap the clutch out.

How are you liking FAST? Worth the money? I was always intending on using the stock PCM for the blower -- using an impedance box for low-z injectors. Already have the tune set up, just don't know how well it'll end up working once I get there.

[Fire67]

Nah, I'm just gonna rivit the metal to the rotor, and locktite & superglue the rotor screws and hope for the best.

I have heard of retorquing the head studs, and mine definitely needed it. The mains i've never heard of anyone going back over. But since you mention it, I will go ahead and check them whenever I decide to replace my leaking oil pan gasket. On the other hand, I cannot see the rod bolts needing to be retorqued due to the fact that they were stretched rather than torqued on my motor. I dont know if you've ever done rod bolts to a stretch gauge, but it takes an ass load of toque to get them to stretch.

As far as computers go... I went with the stock pcm for a little while. I had the Acceleronics Versa-fueler and 75# injectors at first. The injectors werent big enough, but some fuel pressure adjustments fixed that. The main problem I found was that as soon as the motor went into boost, the pcm was blind. So we'd lie to the tables to get what we wanted for an output. This was fine for that day, but the next time we pulled it out the weather would be different and the tune would be off.

It would not be too far off, but it would be off enough to cost power or even damage something. And it got real annoying to have to adjust for it or at least double check it every time.

So I broke down and bought an Accel DFI system for a bargain and started installing it. Then I had a friend of mine get killed right in the middle of building his mustang for him. He owed me some money, so his father gave me the FAST XFI system he had bought for the car.

So far it seems to be going well. I started the car up on the old ignition system, and did some idle and part throttle tuning driving up and down my street. Tuning this ECM is alot more user friendly, and being able to tune in real time helps a ton. Couldnt tell you any more as that's as far as I've been able to get so far.