Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Fuel sending unit and guage questions ******(PICS)******

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BlueOx, Jul 26, 2002.

  1. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    I'm now on the fuel system part of the TBI swap and have some questions. I bought a new FI fuel tank and sending unit for a 90 Blazer for my swap and it time for them to go in but, which wire goes to the fuel guage? I have not received the sending unit yet so I had to use a old one. Today I went to the junk yard and picked up the complete hard fuel line and return line from the front to rear. while I was there I grabed the fuel sending unit (well just the top) for reference.

    The TBI wiring harness has a plug on it for the fuel pump. The plug has two wires, one of the wires (blk/wht) is a ground the other looks to be a power wire (gray and comes out of the "E" spot on fuel pump relay). The sending unit I have for reference has wires with the male end that mates to the one on TBI harness and has a black loose wire that looks to be the same as a gound. My question is, I need to find out which wires are which. I also need to know which one is the fuel gauge wire and how do I splice it in to the new wire/s

    I would try to figure it out but I dont want to make any sparks in or near my fuel tank.

    PICS
    Thanks
    Charles
     
  2. reddog64

    reddog64 1/2 ton status

    Joined:
    Nov 9, 2000
    Posts:
    3,325
    Likes Received:
    0
    Location:
    Federal Way, Washington
    if one is brown, then that is the wire that tells you how much fuel you have in the tank
     
  3. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    nope none are brown. 1 gry, 1 blk/wht, and 1 blk (single wire looks to bolt to the frame. The blk/wht and gry wires are the ones in the plug. I know the blk/wht one is a ground wire because it runs to a ring that bolts to the block.


    Charles
     
  4. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
  5. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,975
    Likes Received:
    189
    Location:
    Roy WA
    Put 12v to each and see which one turns the pump on lol.

    IIRC, the wires actually change colors at the plug. PINK is the gauge wire, but like I said, IIRC, it changes color once it goes through the plug.

    Neither of the two wires in the *plug* are grounds. One is 12V for the pump, (from the relay) one is gauge, and the black wire by itself is the ground. Colors are wrong, lower left corner though http://92b4crs.tripod.com/86wiring/dia-pics/22-2.jpg You can see GM changed color at that connector too...not sure why they do that, it just confuses things.

    If you don't have the sender in the tank yet, or don't mind pulling it again, you could check resistance on both wires to ground, and move the flaot while doing so...only one will vary resistance based on the float. (*think* that will work)

    Or, wait part of the day until someone else can look in their manual : (

    Sorry I'm not home, I'd have this definitively answered, as I've got the entire fuel pump harness in my garage...
     
  6. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    Yeager, thanks for the info. I thought the other wire was a ground too because I checked continuity from the plug to a gound wire(same color) in the front of the harness. I was thinking it was pliced in some where. I was also thinking about cutting the wire and splicing in the gauge wire.
    What do you think

    thanks
    charles
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,975
    Likes Received:
    189
    Location:
    Roy WA
    I actually like having theplug there, just because it's going to make it a bit easier to install/remove the tank and not have to worry so much about ripping wires out or whatever.

    Not that its really a huge concern, it realistically makes not much difference, but when you finally run the wires up to the front of the truck, and anchor them to the frame, when you go to pull the tank, you can only let it down so far before having to reach up on top of the tank, all the way to the sending unit, to disconnect those wires.

    I'd much rather have a plug to disconnect right there, to eliminate that hassle. I'd hit the wrecking yard up for a 2 prong GM plug, anything with the same size terminals should be suitable to use as a replacement. I'd bet Camaro's, Vans, etc. that are injected will use a same or similar plug.
     
  8. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    yeager, what I ment to say was that I was going to tap into the plug with the gauge wire. The listed plug is said to be the power wire and the guage wire. If this is so and the gauge wire is in deed grounded in my harness will this have ill efects on the gauge reading? I was thinking about splicing in the gauge wire but if the wire I am splicing it into is a ground won't it peg out the guage?

    thanks'
    Charles
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,975
    Likes Received:
    189
    Location:
    Roy WA
    Hope this answers your question, as I'm kind of confused as to what you just posted, but don't take my confusion personally /forums/images/icons/smile.gif

    The pink/gauge wire, if grounded, should cause the fuel gauge to peg "FULL".

    Its my understanding that the fuel gauge "sees" the resistance from the float assembly in the tank, so (and I believe I'm correct in saying this) there will always be continuity to ground, but it will be in varying "degrees" if you will. If the tank is full of gas, the resistance should be almost nothing. (grounding pink wire=full) As the tank level decreases, resistance should increase.

    If my electrical diagnosis is incorrect, I hope someone corrects me. : ) If no correction, I'm going to play with my sending unit/wires tonight and get you a solid answer, because I want to make sure I understand the operation as well as I *think* I do.
     
  10. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    yeager, sorry to confuse you. Now that I read it for myself it really doesnt make sence. Cut and dry, I just want to know why the gauge wire in the new harness is grounded and what would happen if I just cut the wire and splice in the old gauge wire.
    The thing is I just dont want to explode when I start the truck for the fist time.....LOL /forums/images/icons/grin.gif /forums/images/icons/grin.gif
     
  11. K5 NUTT

    K5 NUTT 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,611
    Likes Received:
    0
    Location:
    Grand Junction Colorado
    Creamed my tank on july 4th...a nic3e big rock made it past my skid plate...go figure. So tonight i put in an aftermarket tank....$130 thru rockauto.com...steel baffle...no worries about the famous gm plastic baffle breaking loose anymore. Sending unit has a 2 wire weather pack connector...gray wire and a purple wire...and of course the black (ground) wire that goes to the frame. Full tank is about 90 ohms....empty is around 3 ohms. Gray is your 12vdc from the pump relay...and purple is the sending unit wire. When i swapped tbi into my 79 i did the same deal....fuel tank and sending unit from a doner 87-91 K5...along with all the hard lines to make it real simple....the only thing i learned was the after market tanks are alot better than the gm tanks as the gm tanks use a plastic baffle that allways comes loose and in some cases knocks the fuel pump off the sending unit. Hope this helps.

    Azblazer
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,975
    Likes Received:
    189
    Location:
    Roy WA
    What AZBlazer said : )

    Just went and checked mine, and its purple on the sender side turns to pink, which is gauge, and gray is 12v to the pump. Black is ground as always.

    So blk/wht for you would be the gauge wire. That wire will have continuity to ground based on the float position (float fully up in the "full" position has no continuity to ground, although from my testing here, it appears the sending unit is pretty darn sensitive and varies wildly on resistance when holding the thing relatively steady)

    Thought I had this figured out myself, but no. Connect pink gauge wire to blk/wht on sending unit and you should be good to go. Might I suggest a non-permanent connection to test first? /forums/images/icons/smile.gif

    Hope AZBlazers and my post at least clears up your dilemma...I think it does. Right?
     
  13. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    Well, I took the harness out if the truck to snap a few pics. These are some of the pics of what I'm talking about. If you look at the plug then look at where the wire is spliced in you will see that it is grounded. When the sending unit comes in I will plug it in, cut the spliced in wire out and test it. Look at the pics and tell me what you think.
    PICS

    Thanks,
    Charles
     
  14. K5 NUTT

    K5 NUTT 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    1,611
    Likes Received:
    0
    Location:
    Grand Junction Colorado
    /forums/images/icons/blush.gif I hope you didn't cut that ground splice out of the harness...i work on this kinda stuff for a living...allthough in freightliners...pete's...volvo's etc. I would have to assume as i haven't started to rework a harness for my chalet yet...but i'm 90 percent sure that ground splice is your sensor common...an ecm generally has two plugs...one is your inputs to the ecm for calculations for the internal logic...and the other is for outputs...ie: fan control...iac motor..etc...usually called the oem plug in diesels...as it has to graft into the truck harness....anyways all the sensors on the engine share a common ground to save wiring nightmares.

    The sending unit looks to be a bit worse from wear and tear...the fuel lines require a 20mm and a 16mm wrench...buy some new orings for them at the dealership...all fuel orings are tan in color for some reason. The sending unit i pulled out of my tank was a bit touchy also...the new sending unit i had thanx to ebay($50)...was clean and steady on my fluke 88...where as the old unit was a bit jumpy...which i will try to repair for the chalet. I used the old pump and sending unit as a means of transfering half a tank of fuel to the new tank and away we went...if you have need for those factory weatherpak connectors i have a bunch of them laying around between work and my home garage...pep boys sells them also...they require a special tool to unlock the terminals from the connector body...i can provide you with PN#s you can take to the gm dealer to buy them if needed.

    Azblazer
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

    Joined:
    Dec 13, 2000
    Posts:
    26,975
    Likes Received:
    189
    Location:
    Roy WA
    Again, I will point you to AZBLAZERS post...I didn't realize you were up near the ECM! I thought we were talking about the backside of the wiring, right at the tank. In just a quick glance of the '88 Camaro wiring diagram, I see that black/white wires are all ground in the ground distribution chart, and the fuel pump relay is one of the ones that is tied into one of the *numerous* ground splices.

    I wouldn't cut that, thats for sure. You really should be looking this stuff up in the wiring manual for the donor vehicle though. I'm telling you, working on the TPI stuff I am now, I'd be *thoroughly* lost without it.
     
  16. BlueOx

    BlueOx 1/2 ton status

    Joined:
    Aug 6, 2000
    Posts:
    239
    Likes Received:
    0
    Location:
    Houston, Tx
    AZBLAZER and dyeager, thanks for all the info about this subject. I really wasn't sure about cutting the wire out of that splice. I have looked in numerous wiring diagram books and none of them show that wire grounded. The books do show a hot fuel-handling module with the same color wires as the plug and a pink wire leaving it for the gauges. What's that all about? I don't have those wires in my harness. OK, here's what I got. The fuel sending unit needs a ground wire (to frame), power wire (fuel pump), and the gauge wire (to complete the ground), right? Now here's what I was thinking of doing. I'm going to take the plug off the wires and add a three-wire weather pack to the fuel sending unit wires (frame ground wire, power in wire, and to the gauge wire). Then I'm going to do the same thing to the wires in the harness, but I will add the existing gauge wire in the pack. The way I see it the sending unit needs a ground and the wire I was going to cut is a ground, so I'll just use that one and not the frame. How does that sound?

    AZBLAZER, I have been looking for those weather packs connector but have had no luck at the parts stores. If you have a bunch that you wouldn't mind getting rid of; I would be interested in purchasing them from you.

    Thanks again,
    Charles
     

Share This Page