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LTX and LSXPutting 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.
I know this has been discussed before, however, I am looking to upgrade to the LS1 Plastic Tank when I drop my rear end later this summer.
Looking for the easiest method to have it function on the stock gauge properly.
Has there been an easy solution made yet? Such as someone actually selling the gauge with the resistor, or I think I remember reading something about a Grand Prix sending unit?
The resistor swap in the gauge doesn't work. That is LS swap folklore. Somebody is going to post here and say it worked on their car. No it didn't, they just have low standards for success. But it's okay if you're willing to always remember where your tank is empty. Mine is bone dry at 1/4 on the gauge, and I better find a gas station pretty damn fast at half tank.
Changing the sending unit does work, but you kind of have to hack up the wiring inside the tank.
Another possible option is to make a device that re-scales to 0-90 Ohm. Haven't seen anybody do that yet.
I have been researching this for a friends LT5 swap. He also has an LS1 4th gen. tank and wants to retain the stock fuel gauge. What I have found is that you can swap the fuel module (bucket) from a V6 car which has the 0-90 ohm sending unit and that it is a direct drop in. It has also been mentioned that the sending unit from the same V6 cars can be fitted to the LS1 module. I cannot personally verify these because I retained the LS1 sending unit when I performed this swap and I'm using Dakota Digital gauges which allows you to select the type of sender you have installed. Anyone with first hand knowledge please chime in, we have not finished the tank swap and I would like to verify the above information.
I used a fuel pump module for a 02 firebird with 5.7 from rockauto, must use the spectra premium brand fuel pump (part number sp3368m) as some of the others have updated the design and swapping the resistor chip wont work with a different style float arm attachment. I then ordered part number sk1083 also from rockauto, these are the 0-90 ohm resistor for a 97 or 98 grand prix pump. I just unsoldered the 2 wires connecting it and resoldered the correct one onto the spectra fuel pump assembly, not hard to do if careful and gas gauge works flawlessly to this day.
What I have found is that you can swap the fuel module (bucket) from a V6 car which has the 0-90 ohm sending unit and that it is a direct drop in.
I'm astonished I can be here for so long and this is the first time I've ever heard of this! What a beautiful solution that would be! Please keep us posted how it works out and if the V8 pump is direct fit.
I just unsoldered the 2 wires connecting it and resoldered the correct one onto the spectra fuel pump assembly, not hard to do if careful and gas gauge works flawlessly to this day.
That's pretty simple. Better than cutting wires which is what I see other people doing.
I'm not up on my knowledge of wire solder. Is there a special type that should be used inside the fuel tank?
I did the 0-90 ohm sender swap, NO SOLDERING IS NEEDED!
We must be talking about two different methods. The one I did uses a fuel level sender from (I think) a V6 that sits in the tank. You have to unsolder the old sender and re-solder the new one in its place. Its only two joints, but I can't imagine any way of doing it that wouldn't involve resoldering.
Soldering is easy. I cant imagine how someone could swap in a ls without knowing how to solder. Easy to learn if you haven't done it. Solder and heat shrink on all underhood electrical connections is a must anyways if you want no problems down the road.
The Grand Prix sender. I just took the terminals out of the connector and put them in the other connector.
Originally Posted by NCFarmLife
We must be talking about two different methods. The one I did uses a fuel level sender from (I think) a V6 that sits in the tank. You have to unsolder the old sender and re-solder the new one in its place. Its only two joints, but I can't imagine any way of doing it that wouldn't involve resoldering.
If that's the one pictured in the other thread then you could have just moved the terminals out of the one connector and put them in the other connector.
this method does work and is what i used on my LS3 swap back in 2009 (see post 45 for some additional pics, but basically scooter's pic shows it great)
as noted it fits the old bucket design and my one long term worry about it was will it be hard to find in the future since it wasn't on a lot of vehicles
summit still shows it though as a good part, for ~$120
You want the Herko sending unit kit. It's about a 15 min swap if you have the tank out of the car. Switches the 4th gen sender to a 0-90ohm so it works with the third gen gauge.
I'm trying to remember how I did mine, it has been a while and was one of the easier things on the swap, so I didn't have to mess with it much = not too memorable. I think I did the 0-90 ohm sender swap, but it's not super accurate, I get about 100 miles into a tank before the gauge drops below 'full'. Flip side of that is that I have at least 2 gallon reserve when I hit E. I usually will gas up when I've hit about 325 miles. Honestly, I like having a bit of fudge on both sides of the gauge and it may have resistors that aren't in the best shape. Either way, I think you've got some great methods here at your disposal.
Thanks for all the replies, I can definitely make something work here.
I think I will be going with the Grand Prix sender.
Will let everyone know whenever I get this rolling.
An update to my first post, I pulled a sending unit out of a 2001 V6 Firebird and it is 40-260 ohms, so FAIL. Going to go with a Grand Prix unit (thanks Scooter).
Another follow up, here are some part numbers for the fuel sender:
GM 25319676. This sells for over $100? Wow!
Herko GFC31. About $25, free shipping. This is the one I’m going with
Dorman 911-005 These are available at Auto Zone for about $35
Another follow up, here are some part numbers for the fuel sender:
GM 25319676. This sells for over $100? Wow!
Herko GFC31. About $25, free shipping. This is the one I’m going with
Dorman 911-005 These are available at Auto Zone for about $35
The fuel module is reassembled and it turned out well. The Herko GFC31 has the correct 0-90 ohms scale, and the AeroMotive 340 pump fits perfectly. It was incredibly simple upgrade, the pump has a new harness with larger gauge wires and the sender wires are re-pinned to the pump harness. The hardest part was removing the corrugated supply hose from the old pump.
The senders may not be an exact fit on the secondary lock or the connector that they come with. this is no problem as you can remove the sender wires from the connector they come with and repin them into the old connector as they are exactly the same (the fuel pump terminals got larger on newer buckets but the terminals for the sender remained the same and are easy to remove and move if necessary to your old connector as a direct fit. the sender lock itself isn't a big deal if it doesn't match you can just drill a small hole at the top of the sender and bucket and pass a small tie wrap ... the bucket side rails themselves really hold it well anyways
i have used both the GM and Herko, i do not have direct experience with the dorman part number
Another follow up, here are some part numbers for the fuel sender:
GM 25319676. This sells for over $100? Wow!
Herko GFC31. About $25, free shipping. This is the one I’m going with
Dorman 911-005 These are available at Auto Zone for about $35
Where did you get these part numbers from?
Dorman 911-005 is a bad part. Same 40-200 Ohm range as 4th gen F-body. Just went to AutoZone and tested it. That part cross references to Silverado trucks with Gen 3 LS engines.
As i said i have used both the GM and Herko, those are good 0 - 90 ohm sensors. You can order the Herko direct from their website. i just ordered another one last week
I can't get GFC31 to come up in a search at the Herko website. Which website did you use?
But I think that's the one you said isn't quite a direct fit though, right? (needs zip tie)
I just spent the big bucks on an AC Delco with 2 in the pack. I get the sense those parts are no longer manufactured so having a spare in my stock pile seemed wise.
Hey everyone, I apologize if some of you have had issues with the information I posted here. The part numbers that I gave earlier came from an extensive internet search. We ordered the Herko GFC31 on eBay and it was exactly what we needed, it was a simple connector re-pin and clipped onto the 4th gen. bucket and the gauge in his car works great. As far as the Dorman part number, I never verified it, but included it because it was listed as a cross referenced number and available nationwide. The ACDelco twin pack is expensive because it has 2 units in the package to cover the mid model Sierra change over from the 0-90 to the 40-260 sending unit. You discard the sender that you do not use, which I feel is a waste of money. We did the conversion using the entire 4th gen. tank and bucket, so I do not know what it would require to do the conversation with the old style bucket in a plastic tank. Again, I never intended to give bad information. I just wanted to pass on what worked on this build.
Hey everyone, I apologize if some of you have had issues with the information I posted here. The part numbers that I gave earlier came from an extensive internet search. We ordered the Herko GFC31 on eBay and it was exactly what we needed, it was a simple connector re-pin and clipped onto the 4th gen. bucket and the gauge in his car works great. As far as the Dorman part number, I never verified it, but included it because it was listed as a cross referenced number and available nationwide. The ACDelco twin pack is expensive because it has 2 units in the package to cover the mid model Sierra change over from the 0-90 to the 40-260 sending unit. You discard the sender that you do not use, which I feel is a waste of money. We did the conversion using the entire 4th gen. tank and bucket, so I do not know what it would require to do the conversation with the old style bucket in a plastic tank. Again, I never intended to give bad information. I just wanted to pass on what worked on this build.
hey your info was good other than it sounds like the Dorman part number from what qwk found out... for some reason the herko number seems to change around as i have bought it both under the GFC31 and also FC31 so again good helpful thread here i think for a lot of people as i tend to post all my info in my swap threads only versus in more topic specific threads. this thread is easier for people to find in a search so quite helpful
I dont know why you guys make it hard on yourselves? I listed current part numbers for the fuel pump and sender resistor chip from rockauto. Real easy type in numbers and order them. It works like factory and wont give any issues.
I dont know why you guys make it hard on yourselves? I listed current part numbers for the fuel pump and sender resistor chip from rockauto. Real easy type in numbers and order them. It works like factory and wont give any issues.
Not everyone wants to use the spectra part number you listed
The spectra pump housing is the best option because it works with the resistor swap some of the other buckets wont work because they redesigned the float arm attachments. I see it is a delco resistor now as I just checked. They are spendy but they also send you 2 so sell one to a fellow member and its half price then its not so bad a deal.
This has already been said, but I'll just repeat it here anyway because I've actually got the parts in my hands looking at them right now.
I just received GM part number 25319676 (also known as SK1083). This is the kit with two senders for a '97 Grand Prix naturally aspirated engine. The top retainer clip does not insert into the slot on an original 4th gen bucket. (I've kept an old bucket just for purposes like this so I can do mockup work without removing my fuel tank.) Both senders are 1.6 - 90 Ohm. The only difference is the style of pins in one of the connectors, which is inconsequential since those wires and connector can be tossed.
This has already been said, but I'll just repeat it here anyway because I've actually got the parts in my hands looking at them right now.
I just received GM part number 25319676 (also known as SK1083). This is the kit with two senders for a '97 Grand Prix naturally aspirated engine. The top retainer clip does not insert into the slot on an original 4th gen bucket. (I've kept an old bucket just for purposes like this so I can do mockup work without removing my fuel tank.) Both senders are 1.6 - 90 Ohm. The only difference is the style of pins in one of the connectors, which is inconsequential since those wires and connector can be tossed.
You might need the herko gfc31 kit it will come with a new up to day plug that swaps out the factory plug on top of the bucket. Good luck have done this same kit on my car and still have a wacky fuel gauge.
Finally got my hands dirty and did the resistor swap for myself. Makes so much more sense now that I've seen it and done it. Scooter totally nailed it with his technique. Straight up factory fit without cutting, soldering, or zip ties.
Post #1479 shows the resistor card completely removed from the holder. Swap it over to whichever holder that properly fits your bucket assembly and slap it back together.
I'm new here. I own a 03 blazer that the fuel gauge is just inaccurate even after changing senders and everything. So anyways after doing a bunch of research on what to do I recently ordered the herko gfc31 sender and a 0-90 gauge. Just my luck tho somehow I got a 40-250 sending in the package and am now waiting on a replacement
I also Got the herko gfc31 on scamazon and its a 40-240. I'm going to try an FC31 from fleabay and see if its right. If not I did notice that there is a little strip of resistor/carbon on the zero side of the sender that's 40 Ohms. Removing the strip and bridging it with solder gets me 0 ohms at empty with a sender from the junkyard. I'll see if adding a parallel resister to cut the 200 ohms to 100 will get the "full" side working but I have my doubts.
I also Got the herko gfc31 on scamazon and its a 40-240. I'm going to try an FC31 from fleabay and see if its right. If not I did notice that there is a little strip of resistor/carbon on the zero side of the sender that's 40 Ohms. Removing the strip and bridging it with solder gets me 0 ohms at empty with a sender from the junkyard. I'll see if adding a parallel resister to cut the 200 ohms to 100 will get the "full" side working but I have my doubts.
I bought the GFC31 off eBay and measured it. Was fine.
Shoot, wish I had seen that the last time I had the tank out. I really dont want to pull it again. I ended up using a converter box, which worked for awhile... but now I only get from 1/4 (Full) to empty
07-08-2020, 11:49 PM
Got some good ideas showing up here. 
