fuel gauge needle hits the oil needle

[D2 Cat]

Dave, what should happen if I shorted the two wires (black & purple) at the connector by the tank?

With no connection the needle is at 5 o'clock----which I guess is way past full.

If the wires are shorted shouldn't the needle go the other direction----towards empty?

 

[Dave Barbieri]

Dave, what should happen if I shorted the two wires (black & purple) at the connector by the tank?

With no connection the needle is at 5 o'clock----which I guess is way past full.

If the wires are shorted shouldn't the needle go the other direction----towards empty?

You're right Len. My bad. I forgot the gauge was horizontal, not vertical - been way too long since I sat in my truck! :nonod: If you connect the two wires, you're completing the circuit and feeding max signal voltage to the gauge. Now the needle should swing to "empty". Just outta curiosity, have you checked for voltage at the connector?

 

[D2 Cat]

bk95td, I recently replaced the inj, gps, return lines. When I was on the passenger side I cleaned one strap and replaced one from chassis to frame and frame to eng.

Cleaning grounds and checking connections seems to be an ongoing process, at least until I get the PO's bugs eliminated.

 

[D2 Cat]

D2, it is on the top of crossmember above the axle. It is somewhat cumbersome to reach.

I replaced my FSU due to rusted lines and hoped it would fix the gauge reading problem. I cleaned that ground to within an inch of its life, too. Guess what? Still f'd up. Instead of 3/4 being full, it was worse- full to cap is shown as 1/2 tank now. I even played with the FSU float while grounded and out of the tank. It did not work on the gauge.

My oil pressure gauge also acts stupid. Goes straight down with key off, and goes up to 0 when driving (typically 40psi).

I have cleaned grounds over, and over, and over, and over. No difference.

GRRRRRRRRRRRRRRRRRRRRRR

I sent a PM to Dave, but then realized he may be on a trip and out for a while....
Steve---where is this ground? Above the axle on a cross member...? I've looked several times, but I haven't seen it.

I did find the connection in the harness going to the tank and separated it. The ground located right there on the top rail was in terrible condition. I cut off the eye and spliced on enough wire to reach over to the clean spot on the cab where the ground from the fill tube goes.

I connected the two wires coming back to the fuel tank (black and purple). With the key on the needle moved from the middle of the zero in 40 on the oil pressure gauge to right between 3/4 and F on the fuel gauge.

So I was going to go to town and fill the tank and observe what happened. Nest time I started the engine the gauge went to a horizontal position. It moved a little when I would brake hard. I was trying to see if the float was moving at all.

I also noticed the volt (battery) gauge would flicker when I used my turn signals which I did not notice before today.

I thing I've got ground problems. I

How about if I run a ground from the cab (where I relocated the ground today) back to the frame rail?

I'll remove the connector and see if it's not a good connection.

How difficult is it to remove the bed? If I need to remove the tank, I'd rather look down on my work and keep the filth from falling on me and know when I'm done It's working.

 

[Steve93mustanglx]

the ground u found is the one in question. Mine was nasty, rusted, and corroded but cleaning it did nothing for me.

As I recall lifting the bed is 4 bolts and a wiring harness for each light, but u may want to check around...

 

[bk95td]

8 bolts and the filler neck to remove the box. If you have the lifting equipment ,it's easier to remove the box than drop the tank.

 

[D2 Cat]

I'm about ready to replace the FSU.

I checked with O'Reilly and they said they had to order one and it was $120. I've got to do some scouting, 'cause I think I can find one for less money. Anyone have any part #'s and rices? Does anyone know if this part # applies, FG01E? I saw one on Ebay.


In the past to remove a bed, I cut a couple of 2x6's to fit under the lip of the bed. Put one in front and one in back. Connect them with a chain and lift with my backhoe. Just pull it up and set 3-5gal. buckets under it.

Looks like some Kroil and an impact wrench should make quick work of it.

 

[bk95td]

Don't forget to unbolt the tailight ground and unplug the tailights You may want to check out Rockauto for the sending unit. Much cheaper than the price you listed.

 

[Matt Bachand]

I'm about ready to replace the FSU.

I checked with O'Reilly and they said they had to order one and it was $120. I've got to do some scouting, 'cause I think I can find one for less money. Anyone have any part #'s and rices? Does anyone know if this part # applies, FG01E? I saw one on Ebay.


In the past to remove a bed, I cut a couple of 2x6's to fit under the lip of the bed. Put one in front and one in back. Connect them with a chain and lift with my backhoe. Just pull it up and set 3-5gal. buckets under it.

Looks like some Kroil and an impact wrench should make quick work of it.

try rockauto. They wre the cheapest for me. I think my rear assembly was 70 bux cheaper than napa! Thats alot of bux!

 

[Dave Barbieri]

Hey, one other thought - Before you pull the bed/tank/FSU, check your harness one last time to be sure it's not a wiring problem. It may seem like a hassle, but I gotta tell ya Len, spending the time/energy/$$$ to replace the FSU only to find out that's NOT the problem is gonna be a serious butt kicker. :mad2: At this point, one more hour spent making sure you're on the right track is a small thing. :thumbsup:

Remove your instrument panel and disconnect the harness at the back of the IP. Since you already have the harness disconnected at the FSU, the gauge wire to the FSU is now electrically isolated. OK, now test the wiring for the FSU:

• Check for continuity from the IP harness pin to the FSU harness pin. You should read continuity, since it's a solid wire connection from the gauge to the sending unit.
• Now, ground one probe, then check for continuity from the IP harness pin to ground. You should see no continuity - wide open. This checks for a ground from the gauge back, and will tell you if the harness is grounded somewhere on the frame or sheet metal.
• Leave one probe grounded, and check for continuity from the FSU harness pin to ground. Again, you should see wide open. This checks for a ground from the sending unit forward. It's sort of a repeat, but it's a good double-check.
• Last, check for continuity from the 'Ground pin' at the FSU harness to ground. Here you should see continuity, since that pin is wired to the chassis ground.

OK, for these four steps, you should have seen continuity from pin to pin and from the FSU 'ground' pin to ground. There should have been NO continuity from either 'gauge' pin to ground. If this checks out, your harness is good. :smile5:

You can also do one final test on the FSU itself, before you pull it. You need to have some kind of idea how much fuel is in the tank. Connect your meter to the two harness pins at the FSU. You should read somewhere between 0 and 90 ohms:

• 0 - 3 ohms if the tank is empty
• 45 ohms at half-full
• 88 - 92 ohms if full
• Reconnect the harness at the FSU, go to the IP harness and repeat the test. Ground one probe and check for resistance at the IP pin. Your reading should match what you saw at the FSU.

I realize this is review; you're just double-checking to save some $$$. If the meter readings don't even come close to matching reality, it's the FSU for sure. If you decide to pull it, you can re-check the FSU on the bench. It'll also be a great time to replace or remove the sock and to also check the inside of the tank for cleanliness/grunge/fungus. A hassle, but time well spent. :thumbsup:

 

[D2 Cat]

Now Dave....I was going to set back and watch the rain today.

I will make the checks before I start dis-assembling. I never did check the resistance at the FSU.

In my simple minded way I though of connecting the gauge in the gasser inst. cluster directly to the FSU to see what happened as a temporary test.

But then, if I extend wires up to the cab I could just clip my digital meter to them and have a custom built gauge, as temporary as it is!

 

[Dave Barbieri]

Now Dave....I was going to set back and watch the rain today.

Oh c'mon Len, don't crap out on me now! ):h ):h

I will make the checks before I start dis-assembling. I never did check the resistance at the FSU.

In my simple minded way I though of connecting the gauge in the gasser inst. cluster directly to the FSU to see what happened as a temporary test.

Yeah, checking at the FSU might save some $$$. It won't necessarily identify a dead spot in the resistor, but it will give you a good hint as to FSU accuracy/condition.

But then, if I extend wires up to the cab I could just clip my digital meter to them and have a custom built gauge, as temporary as it is!

Interesting thought... Don't see why it wouldn't work. Sorta reminds me of this guy:
http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=27549416

 

[Burning oil]

If you have bought FSU then before pulling bed.......I would try my test below first. Simplest way I know, it works or it does'int.

Thats normal if the FSU is bad. I still think its your FSU giving the problem. If you know your parts guy take your truck up and see if he will let you plug in a new FSU.

Just unplug the old one back at the frame then plug a new one in with it out of the tank obviously. I am able to see the gauge cluster from the rear, but you may need someone to watch the gauge as you slowly move the float around. See if it act normal then.
It would take 2-3 minutes to check that way out in the parking lot.

 

[D2 Cat]

I was going to remove the bed to replace the fuel sending unit. Upon seeing the position of the bolts and the lack of room for wrenches I opted for dropping the tank.

FSU reads from o-172 ohms with no consistency and many open spots. The shaft that holds the rotating arm of the float has too much play to keep the resistor in position for a constant connection.

With the new FSU the gauge also continued to drift way past full and even past horizontal.

I replaced it with one from a gasser inst. cluster. It seems to work fine. I will post back if I'm wrong!

Only two screws hold the gauges in place, so it's not difficult to replace them.

I've also got a complete cluster for a diesel I could use, but just wanted to experiment with the single gauge first.

 

[Matt Bachand]

Still reading between 0 and 172 OHMS? I thought all these were 0-90 FSU's.

Please tell me what your new empty and full OHMS are when you can as I'm still fighting my odd readings from my 0-90 aftermarket fuel gauge (glowshift). I am going to buy a 2nd one shortly to monitor rear tank level, then another toggle switch to run the rear pump.

First want to nuke it with a biocide.

 

[Joey D]

I was going to remove the bed to replace the fuel sending unit. Upon seeing the position of the bolts and the lack of room for wrenches I opted for dropping the tank.

FSU reads from o-172 ohms with no consistency and many open spots. The shaft that holds the rotating arm of the float has too much play to keep the resistor in position for a constant connection.

With the new FSU the gauge also continued to drift way past full and even past horizontal.

I replaced it with one from a gasser inst. cluster. It seems to work fine. I will post back if I'm wrong!

Only two screws hold the gauges in place, so it's not difficult to replace them.

I've also got a complete cluster for a diesel I could use, but just wanted to experiment with the single gauge first.

I pulled the bed on my truck to do the sending unit. It was very easy. i changed out the fuel lines as well as they were all shit.

 

[D2 Cat]

Matt, I measured it before installing but it's written down on a tablet out in the shop. I am pretty sure it was 12-92 ohms.