LTX and LSX Putting LT1s, LS1s, and their variants into Third Gens is becoming more popular. This board is for those who are doing and have done the swaps so they can discuss all of their technical aspects including repairs, swap info, and performance upgrades.

ls1 swap, 2k gas tank, fuel gauge

Old 12-06-2018, 03:59 PM
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ls1 swap, 2k gas tank, fuel gauge

Ok so I'm currently running the 97 Grand Prix sending unit ACDelco SK1083 in the tank from a 2k Firebird. This feeds the right ohms to my gauge and all is happy however I've got to pull the tank again because the pump check valve isn't holding pressure after shutdown. I'm thinking about changing the setup in the process.

So looking through the schematics 98 Firebirds had a wire running from the red c1 connector pin 36 to the cluster for the fuel gauge. I'm thinking this is a ohm based output but can't find any additional info on that. The 99-02 diagrams use a serial data line to the cluster with the fuel gauge and other values.

Looking in HP tuners there are fuel gauge maps.

If its possible to map a 0-90 ohm output onto pin 38 of c2 this would make for a much more sane set up.

I know most people would say not worth the effort--

My other thought was to use an Arduino as a proxy between the 4th gen sender write a few lines of code to map small ranges of the 4th gen sender to single ohm values.

98 pin out http://mrk-motorsports.com/pdf/97-98...%20Pinouts.pdf
99 pin out http://www.mrk-motorsports.com/pdf/9...%20Pinouts.pdf

Last edited by Aviator857; 12-06-2018 at 04:08 PM.
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Old 12-10-2018, 11:11 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

In case you are curious here are the screens in HP Tuners:

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Old 12-10-2018, 12:19 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

I am guessing the output was still serial based or PWM on the 97-98 cars too, just connected directly to the dash instead of through the buss like the 99 and up cars.

When you say Grand Prix sender, you just mean the resistor board, or the whole fuel module?
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Old 12-10-2018, 12:23 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

I put the entire sender assembly on the pump assembly. It wasn't a perfect fit but fit sell enough that I wasn't worried it would fall off. Also there are alot of cheap aftermarket ones for the grandprix though I used the acdelco one.

I used the 4th gen float, pump, and pump assembly.
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Old 12-10-2018, 12:33 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

It's PWM, but was thinking it might drive the gauge since on the firebird it's a voltage splitter. That is the right pulse frequency gives you a different electical protetial and depending on the circuit it may work. Though I'm guessing there, i need to experiment some.
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Old 12-10-2018, 12:34 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

OK, that's sort of what I did. I put the GP resistor board in my 4th gen bucket, the GP plastic bracket didn't fit right, and I didn't feel comfortable trying to get it in. It was easy enough to slide the GP board into the 4th gen plastic bracket. Curios to see what you come up with. I think I may get another 4th gen revised module and see if I can't get the GP board into that instead of the resistors in the dash, since it isn't working in the other thread.
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Old 12-11-2018, 11:37 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

Originally Posted by Aviator857 View Post
It's PWM, but was thinking it might drive the gauge since on the firebird it's a voltage splitter. That is the right pulse frequency gives you a different electical protetial and depending on the circuit it may work.
The gage is not influenced by changes of voltage at the B+ terminal. It reads the same regardless of what voltage you give it.

The fuel level reading is based on current through the coils, not voltage. And not just current, but the ratio of current through the Empty and Full coils -- hence input voltage doesn't matter. The fuel sender basically bleeds off current from the "Full coil" and the more it bleeds off (lower resistance of the sender) the more the needle moves toward Empty. Zero current through the "Full coil" causes the gage to peg on Empty.

Last edited by QwkTrip; 12-12-2018 at 12:29 AM.
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Old 12-12-2018, 12:46 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

I was afraid of that... Well converter box seems like best option.

Here is the new Delphi pump and the grand Prix sender, beyond drilling mounting holes I don't see a way to do this with the redesign. Also just noticed the wire on the new bump is a heavier gauge.

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Old 12-12-2018, 01:43 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

So looking around I see random examples of how to convert PWM to resistance https://electronics.stackexchange.co...ble-resistance

I have the arduino and the digital pot sitting on my desk now if I can get some time to experiment I know I can build one using this method, the only issue is it will need to sweep the POT at every power up. But since the firebird at least is super slow one shouldn't see much of a sweep in one compute cycle, at most the needle may twitch...
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Old 12-12-2018, 02:52 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

Originally Posted by Aviator857 View Post
So looking around I see random examples of how to convert PWM to resistance https://electronics.stackexchange.co...ble-resistance

I have the arduino and the digital pot sitting on my desk now if I can get some time to experiment I know I can build one using this method, the only issue is it will need to sweep the POT at every power up. But since the firebird at least is super slow one shouldn't see much of a sweep in one compute cycle, at most the needle may twitch...
I would be interested in your solution, depending on what you come up with. I am tired of my gauge reading full all the time, lol. If not, I'll probbaly just go with that other $120 recalibration box.
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Old 12-13-2018, 10:02 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

I will build the arduino thing and test it and do a write up, but I've ordered this https://www.ebay.com/itm/372485808354 as I really want to wrap up my car by EOY (AC, Cruise control, reverse lights, clutch safety switch is all that I have left, well and replacing the pump which leads to the reason for the original post.

I emailed the company and they confirmed its a full linear extrapolation, so you set full, half, empty but it will sweep the gauge linearly from E to F with your fuel gauge, the way their website is listed I was afraid it only output for the 3 points on the gauge.
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Old 12-13-2018, 10:21 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

One thing I do like about the Classic Instruments converter is that it has outputs for a warning light. That would be a nice thing to add to the car, easy enough to do with an LED in the cluster. Would be a nice thing for the temp and Oil pressure too. Think you could add those in your arduino?
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Old 12-13-2018, 10:32 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

Any thing is possible. I believe the pcm has an output for oil light.

The one issue is if the sensor is ohm based you can't run multiple devices off the gauge. So you have to read the value with the Arduino and then memic the out to the gauge. If it's wrong for fuel at most you are out a few dollars for a gas can, if it's wrong on oil... Or temp... Then the cost goes up.

Having the Arduino light an LED based on a number is easy though.
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Old 12-13-2018, 10:58 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

I only paid $250 (mins money I got harness and what I'll get for the cats), so $100? for the LR4 The old corvettes got a low fuel light that worked in conjunction with the gauge, analog based, I could probably replicate that for both gauges

https://www.ebay.com/sch/i.html?_fro...rning&_sacat=0
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Old 12-13-2018, 11:12 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

Does anyone have a graphic of all the lights (idiot lights) in a firebird cluster?

I know security, check engine, brake, what are the other unused cells... surprising I couldn't find a graphic and I don't have the owners manual.
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Old 12-13-2018, 11:17 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

That is a pretty good deal I bought the donor for 2500, 96k miles and used so much of the car I had a hard time getting a scrap metal guy to take the rest LOL-- I think after I bought other and sold parts my swap comes in just over 3k. Though I have more money into things like clips, screws, bolts, lower air dam and decided to replace the AC with all new parts... I haven't tallied the total cost of the project... not sure I want to
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Old 12-13-2018, 11:27 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

On a 98 PCM red pin 41 is the oil pressure lamp, however its not used on 99+ not sure if the PCM has the code in it for the 99+ to use the pin or if HP tuner can enable it. You could always flash the PCM with a different OS but that gets a little sketchy sometimes.

Not sure the LR4 though... if it has a oil output lead then you could simply wire a bulb in...
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Old 12-13-2018, 11:33 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

I mean I have thousands more into the conversion, but as long as the engine doesn't explode and take out parts it won't cost a lot to put a different 4.8 back in the car
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Old 12-13-2018, 11:40 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

Just occurred to me could make a adapter plate that snaps into the new pump design and receives the grand prix sender..... if you really wanted to keep that set up. My thought though is pumps die and get replaced do I want to deal with re mounting that sender every flipping time... probably not. Also could cut a hole in the tank and put in a after market sender but I'm afraid since I'm running full emissions I couldn't seal it well enough to avoid evap errors.
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Old 12-13-2018, 12:17 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

Something to hold the GP sender would be a good idea, I thought about that too, but I didn't want to mess with it, I din't have time. I was using a friends lift to change my pump out, I couldn't mess around
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Old 12-13-2018, 06:27 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

Originally Posted by Aviator857 View Post
Does anyone have a graphic of all the lights (idiot lights) in a firebird cluster?
This is for my 89. Post #651, https://www.thirdgen.org/forums/ltx-...ml#post6111293

Very well could be different depending on year. Just shine a flashlight through the hole in the back if you want to see what the screen is. It is a piece of cake tracing the circuits on the green screen back to the connector pins.

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Old 12-14-2018, 09:02 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

Thanks QwkTrip

scooter A thought on the oil pressure light. If you are running a late version thirdgen oil sender it has the circuit to power the fuel pump if there is oil pressure. This switch is off if no oil pressure and on if it has oil pressure (not sure the cut off pressure). You could use a mosfet to build a NOR gate and wire it so that when power is supplied to the gate then the LED is off, if no power is supplied to the gate then the LED is on.

https://www.allaboutcircuits.com/tex...ate-circuitry/

Or you could simply use the oil switch to kill the fuel pump if no oil pressure but you would have to have a while cranking bypass on that.
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Old 12-14-2018, 09:27 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

Scooter or better yet wire one lead to ground, one to your oil pressure light, and the sensor lead to the gauge. Then you don't need the nor gate ... sorry over complicated it since in the LS wiring only uses the sensor out on the sensor.
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Old 12-14-2018, 10:44 AM
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Re: ls1 swap, 2k gas tank, fuel gauge

That's way more complicated than I can comprehend, lol.
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Old 07-12-2019, 04:37 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

http://www.mycockpit.org/forums/showthread.php?t=12209 this explains in great detail how the fuel gauge works in these cars.


I've also started working on an arduino based buffer for the tach and speedometer. Its two fold I can now use this to calibrate the gauge by building a calibration table in code. But a side (and fun benifite) is I can now drive the gauges from computer games, that is in some racing games I can use the fire-bird speedometer and tach, I can also map the needle sweep to custom ranges.

I think though for the fuel gauge I'm going to use the coil out of a after market gauge inside the factory cluster (with the factory gauge) vs using a buffer box for the fuel.

Here is a video of the tach being driven from my laptop through the arduino and the high side switching circuit I bult (gets me the 12vdc (blue) vs 5vdc (yellow) wave form)





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Old 07-13-2019, 09:49 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

So I bought one of the fuel gauge converter boxes. It works ok, but is slower to react. But it makes a high pitch sound, I'm sure in the car I would never hear it but still.

I'm also Playing with rebuilding the entire cluster with modern stepper motors, using the factory housing and faces, waiting on a few electronic parts to build the stepper driver.

But then I started playing with the simple solution. Thoughts on my cardboard mock up adapter to use the grand Prix sender on the new style Delph pump housing?



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Old 07-13-2019, 10:03 PM
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Re: ls1 swap, 2k gas tank, fuel gauge

Though probably can't get that in the tank, may have to mount it vertical like the old style and use the old style float arm
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