gas gauge problems

[rjpohl]

I install my new tank, new sending unit and put 5 gallons in 20 gallon tank.  My gauge still reads Empty.  I checked sending unit with ohms meter before installing it and it rwad like 9 to 68 empty to full.  The old sending unit reads 6 to 48.

I got the gauge to jump to full one time with old sending unit once.  Does tank need to be grounded?  I put thin rubber pads between top of tank and trunk floor.

I tried putting a jumper across the 2 terminals on the plug at tank but gauge stayed on empty.

How should I go about trouble shooting this?

thanks

Bob

 

[OzCoupe72]

Sometimes you need to calibrate the sending unit by bending the rod until you get an acceptable reading.

In your case since you have gas in the tank you could jack up the drivers side of the vehicle so the gas doesn't come out of the tank then remove the sender unit and bend the rod downwards a little, reinstall the sender unit, let the jack down until level then check your gauge reading and if close to 1/4 full then done otherwise repeat the procedure.

Also you say new unit 9 - 68 ohms, are you able to get a reading with 1/4 tank maybe 20 - 30 ohms? If still 9 ohms then calibrate your sender, if 20-30 could be earthing or voltage regulator on the instrument cluster.

Perhaps someone will chime in with other ideas but this is what I would do first.

 

[rjpohl]

I tried unplugging the plug from the tank (new sending unit is in tank).  I plugged it up to the old sending unit and put the float in full position, gas gauge still stays on E.

How do I test the gas gauge itself to be sure it's good.

If I jump connections on plug to sending unit should the gauge read?

thanks

Bob

 

[mudbilly]

Did it work before you put in the new tank and float ?

 

[rjpohl]

Did it work before you put in the new tank and float ?

I don't know if it worked or not.  

Bob

 

[kcmash]

I had a problem once with mine where it would read high.  ie It would run out of gas and show 3/4 of a tank.  I found that I had failed to bolt the resistor on the speedo cluster flex cable to the back of the speedo housing.  It had a ground pad that needed to connect.  Once I installed it correctly the problem went away.

kcmash

 

[midlife]

A couple of things here are unusual. Your first sending unit has an anomalous range of readings, so is your gauge factory stock? If not, all bets are off. The gauge has to match the sending unit. Secondly, the lower value of resistance is when the gauge pegs higher, not lower. 5 gallons of gas in a 20 gallon tank may have a reading of 48 ohms or thereabouts. Thirdly, the tank should be grounded, although the 7123 sending units have a separate line for ground (it is a 2 pin connector).

Thus, one should suspect the ground first. Pull the connector off of the tank and measure resistance from the chassis to each pin: one should be about 1 ohm; the other may be about 14 ohms.

If the ground is good, briefly ground the other pin on the sending unit connector with the key in ACC and see if you gauge pegs high. If it doesn't, it means that there's an issue with wiring or the gauge upstream of the tank.

Once you know the results of this, we can further trouble-shoot your problem and get it fixed.

 

[Stanglover]

The tank itself will be grounded by the straps, so the rubber pads will not make a difference. The wires from the sender may be the problem but I'm no electrical guy, so just a guess, but is there continuity between them. May have to run a wire from the gauge plug  back to the sender end and check. I could be out to lunch on that but I think you know what I'm trying to get across. I'm damn sure some of the other guys will chime in and clear that up.

If you can get a reading, any reading, I can guide you through adjusting the arm, but for now I have to leave till tomorrow am, Friday.

Geoff.

**What did I tell you. the best guy on here just beat me to the post.**

 

[midlife]

We may have stumbled upon the problem as I had a Private Message that said the high beam indicator light is always on. I hard-wired his dash cluster, and the OP was responsible for wiring up the pigtail. The line for the power to the CVR is black/green, and the line for the high beam is green/black, and it is fairly easy to reverse these two wires. Without power to the CVR, the gauge won't work, and the high beam will always be on...

QED. I think that is what happened.

 

[Stanglover]

So, let's assume the gauge now works, but is off a bit. 5 gallons should read 1/4 tank with the car on a level surface. Let's say the gauge reads only 1/8 tank or whatever, the process is you will need to remove the sender without spilling gas all over. For this, you need to jack up the left side of the car as high as possible. I'd recommend using 2 jacks, 1 at the front 1 at the back to lift the car evenly and avoid twisting it or lifting one right side wheel off the ground. then you need to support it with jack stands. I have 6 ton , so nice and high. Once the car is up safely, you can remove the sender, but be careful, gas can still spill out. If the gauge reads lower than 1/4 tank (and if I remember right) bend the arm downward slightly. This will allow the mechanism in the pick-up to read higher. Not sure what that thing is really called, but you get the idea. If you lower the car and it's still off, do it again. It could be a pain in the as*, but if you're like me, you want it correct. After all it's nice to know you can make it to the next gas station!!

Geoff.

 

[rjpohl]

We may have stumbled upon the problem as I had a Private Message that said the high beam indicator light is always on.  I hard-wired his dash cluster, and the OP was responsible for wiring up the pigtail.  The line for the power to the CVR is black/green, and the line for the high beam is green/black, and it is fairly easy to reverse these two wires.  Without power to the CVR, the gauge won't work, and the high beam will always be on...

QED.  I think that is what happened.

I'll check wiring on dash harness in the next few days and report back.  Hopefully I didn't burn up the gas gauge itself.

Bob

 

[rjpohl]

We may have stumbled upon the problem as I had a Private Message that said the high beam indicator light is always on.  I hard-wired his dash cluster, and the OP was responsible for wiring up the pigtail.  The line for the power to the CVR is black/green, and the line for the high beam is green/black, and it is fairly easy to reverse these two wires.  Without power to the CVR, the gauge won't work, and the high beam will always be on...

QED.  I think that is what happened.

I'll check wiring on dash harness in the next few days and report back.  Hopefully I didn't burn up the gas gauge itself.

Bob

I pulled my dash cluster out this morning and checked the wiring.  I feel pretty certain that I have wire it in correctly.  The B17 terminal on the original dash cluster was green with black stripe, I have it connected to the 15 pin on the new harness (from Midlife).  The B5 terminal on the original dash harness had 2 wires that I connected to the #3 terminal on the Midlife harness.

I've attached a couple pics that I hope show the 2 connections in question.

 

[midlife]

Yup, my screw-up; I can't believe I did this, considering I proof out each harness. I guess I went by wire color rather than pin-out (I'll always go by pin-outs from now on). To fix this, RJPohl can either swap the pins on the dash cluster or cut his 2 splices and swap them there. My bad My bad My bad.

Ugh...

 

[Don C]

It's good you got it sorted out, Randy, but it looks like he's going to need the practice pulling his cluster, anyway. It is just a matter of time before that black tape unwinds completely and the connection falls apart or shorts out.

Maybe you should include a wiring 101 when you expect the owner to have to make any connections. Here is one example:

http://www.crankshaftcoalition.com/wiki/Automotive_wiring_101

Rule #1, no household wire nuts

Rule #2, no twisted wire connections (soldered or crimped connectors only)

Rule #3, no wrapping connections with cheap electrical tape (self fusing tape or heat shrink tubing (waterproof preferred) only)

Sorry for being so critical rjpohl, but I've seen too many wiring harnesses fried and/or cars burned up due to bad wiring.

 

[Stanglover]

I can only comment from my own experience, but I gave up on crimp connectors as well. I have had too many over the years that at the time seemed good, tight and strong only to have them fail later, I guess not as good as I thought. Ok for a quick fix until a more permanent joint can be made.

Last summer when I installed the aftermarket center gauges, I took the time to go over the rats nest of wires a PO had left me under the dash. If only he'd at least left the unwanted plugs on and spliced into the wires instead of just cutting them off!! I solder all joints now and cover with shrink wrap of the appropriate color where possible. Sure it takes a lot of time and some frustration, but I know the joints are good and safe.

 

[Don C]

I've never had a crimp connection come apart. I have good quality crimping tools and don't use harbor freight connectors (although I do have several HF tools). I get terminals from manufacturers like 3M, AMP, or Molex. I used to buy a lot from MCM, but they were bought by Newark, and I haven't tried them, even though they have a huge selection of products. I don't do as much as I used, but my supplies are dwindling.

When I want extra assurance I use bare crimp connectors and solder them and insulate them with waterproof heat shrink tubing. For T connections I solder them and then use self fusing tape.

 

[rjpohl]

With Randy’s hell I was able to get gas gauge working. Problem is with 5 gallons in tank the gauge just barely moves above empty. In the morning I will remove sending unit and bend arm down. Any one have this problem before? If so suggestions on how much to bend. I’d like to be able to do this in one try.

 

[Stanglover]

With Randy’s hell I was able to get gas gauge working.  Problem is with 5 gallons in tank the gauge just barely moves above empty.  In the morning I will remove sending unit and bend arm down.  Any one have this problem before?  If so suggestions on how much to bend.  I’d like to be able to do this in one try.

 You didn't read the last post on P1. I can further explain if not clear.

 

[Stanglover]

I've never had a crimp connection come apart. I have good quality crimping tools and don't use harbor freight connectors (although I do have several HF tools). I get terminals from manufacturers like 3M, AMP, or Molex. I used to buy a lot from MCM, but they were bought by Newark, and I haven't tried them, even though they have a huge selection of products. I don't do as much as I used, but my supplies are dwindling.

When I want extra assurance I use bare crimp connectors and solder them and insulate them with waterproof heat shrink tubing. For T connections I solder them and then use self fusing tape.

 I would agree Don, that the better quality ones would do a better job and more reliable. However and me included, most people will just buy whatever the store is selling. I guess that is more what I was referring to.

I did fail to mention in my post that I used Bullet connectors with the plastic covers removed and these were soldered on and covered with heat shrink. That way they can be taken apart if needed.