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Fuel Tank Pump-Gauge Mystery Solved!!!
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Author:  Turbo Tim [ Mon Jun 09, 2008 12:04 am ]
Post subject:  Fuel Tank Pump-Gauge Mystery Solved!!!
Ok I dropped my tank today and did some comparisons. I took the new pump unit and the old CRD sending unit and placed them side-by-side and compared them. They are both the same electrically. They have the same output for every angle from empty to full. Then I noticed that the original CRD float arm is about ½ inch shorter than the pump module arm. If you look at them from the pivot point center to the first bend down by the bottom of the module unit (at empty tank), you will see that the CRD is shorter.

Swapped the arms and now it measures like it used to. Now I am tweaking it so that ¼ tank is really reading ¼ tank.

Let me know what you guys find out…
Author:  geordi [ Mon Jun 09, 2008 9:13 am ]
Post subject: 
So when the tank is reading "Empty" on the stock arm, how much is actually left in there? Can the pickup still get to the fuel, even below where the arm is?
Author:  dgeist [ Mon Jun 09, 2008 9:24 am ]
Post subject:  Nice find.
I'm glad everyone's working out all the kinks of the cummins pump install before I run this tank down low enough to do the work. Tim, did you happen to snap any photos of what you're talking about and what kind of length difference are we talking about?

Dan
Author:  dritchie [ Mon Jun 09, 2008 10:02 am ]
Post subject: 
I thought all you had to do was cut away the right half of the indexing tab on the Cummins pump. Is this not true?

Dave
Author:  Turbo Tim [ Mon Jun 09, 2008 10:42 am ]
Post subject: 
I would post pic’s but I don’t have any way to put them up on the net.

I am still working on how I want the gauge to read as this morning I am dropping the tank again to tweak the gauge. (Thought I had it right the first time).
My tank has a seam in the middle, and being a 20 gal tank, this would be the 10 gal mark. It is right at 7 inches off the bottom. With an empty tank, I poured in 5 gal of fuel and it measured 3 ½ inches off of the bottom. To me that should read ¼ tank on the gauge. Right now it is reading just under ½ tank or just over 1/3 full. I am going to fix that.
I am trying to make my ¼ tank mark the calibrated spot on the gauge. Then everyone that drives it knows that is really ¼ tank or 5 gal left and time to do something about it.

I am using a pair of wires with pins on the end so I can tweak the arm, and turn the key on and check the gauge before I stuff it back up in the hole. When I get done I’ll take a pic of the “Tweaked” arm for my calibration to show. Maybe I’ll just have to email those who want pic’s or I’ll do something.

The tank has a molded spot on the bottom for the sump of the pump to fit into so it can suck the tank clean of fuel. Maybe a quart left over from totally empty.

Also note that there is a “Roll Over” valve on the fill snoot. I had to take some wire and make a few bends in it to make it hold the valve open so I could pour all the fuel out to measure it. This valve will not allow anything (like a hose) to go through it so no need to worry about buying a locking fuel cap.

I’ll keep ya’ll posted…
Author:  dritchie [ Mon Jun 09, 2008 1:25 pm ]
Post subject: 
Turbo Tim wrote:
I would post pic’s but I don’t have any way to put them up on the net.


You could put them on: http://www.fotopic.net/
It's free for the basic service, then just link them back to here.

Dave
Author:  Joe Romas [ Mon Jun 09, 2008 1:44 pm ]
Post subject:  Re: Fuel Tank Pump-Gauge Mystery Solved!!!
Turbo Tim wrote:
I noticed that the original CRD float arm is about ½ inch shorter than the pump module arm. If you look at them from the pivot point center to the first bend down by the bottom of the module unit (at empty tank), you will see that the CRD is shorter.


So does the longer arm hit something and not go all the way down? Seems to me if the longer arm is not restricted then it would react slower going from full to empty and maybe stay in the middle range longer if my thinking is correct :( How was your new sending unit reading? When I swapped mine both old and new read the same one mark over E with the same amount of fuel in the tank. Right now I'm just below half a tank so I guess I'll get a gallon in a can and see if I run out before it reaches E :wink: As a recap I cut the tab to get identical positioning.
Author:  Turbo Tim [ Mon Jun 09, 2008 4:04 pm ]
Post subject: 
It doesn’t have anything to do with the tab indexing. There is plenty of room in the tank if the float is in a different spot. It has to do with the length of the arm from the pivot point. The CRD arm is ½ inch shorter and that will change the calibration.

I have a pic so somebody PM me and I’ll email it to them so they can put it up for all to see..
Author:  dritchie [ Mon Jun 09, 2008 7:16 pm ]
Post subject: 
Here is a picture of the pivot arm that Turbo Tim sent to me to post for him:

Image
Author:  dgeist [ Mon Jun 09, 2008 7:50 pm ]
Post subject: 
Turbo Tim wrote:
It doesn’t have anything to do with the tab indexing. There is plenty of room in the tank if the float is in a different spot. It has to do with the length of the arm from the pivot point. The CRD arm is ½ inch shorter and that will change the calibration.


I just checked my (currently uninstalled) Cummins unit in the garage and the float is EXACTLY parallel and flush with the base of the sump and at the bottom of its swing if you place it on a flat surface. Taking into consideration the small sump depression mentioned previously, the skew of float location makes perfect sense. Tim, do you have any pictures that show the base of the tank (the molded shape) that can confirm that regardless of slight "yaw" variation with different indexing, simply swapping the float arms should take care of any inaccuracies (and yes, you can email me and I'll post it).

Dan
Author:  Turbo Tim [ Mon Jun 09, 2008 8:04 pm ]
Post subject: 
Sorry but I didn’t take a picture of that. I threw the old CRD unit away but kept the sending unit for “Just In Case.” Glad I did.
Both units are (or were) parallel to the bottom. The arm is shorter on the CRD.
I do remember that I tweaked the arm up just a tad so that the center line or bottom of the float was just about ¼ inch above the bottom of the plastic unit housing.
This followed the original CRD calibration on the gauge that exactly 5 gallons of fuel in the tank (3 ½ inches) that the gauge shows just under ¼ tank. I figured that was Ok to keep it “Wife Proof.”
Author:  litton [ Tue Jun 10, 2008 12:38 pm ]
Post subject: 
My stock gage is almost exactly 2 gallons off (reads high) and that sounds like the case with all the senders. I'm wondering what the float is made of? Can it be drilled and a srcew/washers added for weighting the arm a bit help with callibration. Conversly, attaching a weight to the arm near the float.

It almost sounds like the same float is used in gassers and the higher spefic gravity of diesel would cause the float to "float" higher, hence an errror.
Author:  MTB_TDI [ Tue Jun 10, 2008 2:28 pm ]
Post subject: 
Tim,
do we still need to index the new cummins pump if we switch the arms out?
Author:  dgeist [ Tue Jun 10, 2008 2:29 pm ]
Post subject: 
litton wrote:
My stock gage is almost exactly 2 gallons off (reads high) and that sounds like the case with all the senders. I'm wondering what the float is made of? Can it be drilled and a srcew/washers added for weighting the arm a bit help with callibration. Conversly, attaching a weight to the arm near the float.

It almost sounds like the same float is used in gassers and the higher spefic gravity of diesel would cause the float to "float" higher, hence an errror.


ummm, if this were the case, you'd have a material that is able to consistently "float" just below the surface. I highly doubt that's the case. Pretty much no matter what reasonable liquid is in the tank, that float's going to be on the top of it. The slide potentiometer is not weighted at all.

If you want to add a trim feature, then the trim dial under the seat seems like the most effective way to do it. Start messing with your float and you'll put a hole in it and permanently register empty.

Dan
Author:  Turbo Tim [ Tue Jun 10, 2008 4:02 pm ]
Post subject: 
This is really simple.
First, DON”T put any holes in the float. It is supposed to float! The CRD and the truck floats are the same. Just the length of the arm is different. It takes all of 20 minutes to drop the tank (when almost empty) and put back in if you have already done this mod.

No you don’t have to mess with the indexing of the tab, but I would anyways just so that the float axis is in the original orientation (left to right in the tank). Just cut about ½ of it off and the unit will be in the original axis.

Switch arms with the new unit, cut part of the tab off, and you’re good to go. If you really want to mess with something, bend the arm up about a ¼ of an inch at the float end and you too can have 5 gallons left in the tank when it is just below the ¼ tank mark on the gauge.
(You can always do what I did before I put the tank back in. While it is still on the ground, pour in 5 gallons of fuel, set the sender on top of the tank and partially lock the ring, hook the two middle wires up on the connector to the other two middle wires on the CRD side connector, turn the key on and see what the gauge says. You could do this before you bend it and after you tweak the bend. Just make sure you turn the key off each time so you get an instant reading on the gauge when you turn the key on).
Author:  bugnout [ Tue Jun 10, 2008 9:48 pm ]
Post subject: 
Turbo Tim wrote:

No you don’t have to mess with the indexing of the tab, but I would anyways just so that the float axis is in the original orientation (left to right in the tank). Just cut about ½ of it off and the unit will be in the original axis.

Switch arms with the new unit, cut part of the tab off, and you’re good to go. If you really want to mess with something, bend the arm up about a ¼ of an inch at the float end and you too can have 5 gallons left in the tank when it is just below the ¼ tank mark on the gauge.
(You can always do what I did before I put the tank back in. While it is still on the ground, pour in 5 gallons of fuel, set the sender on top of the tank and partially lock the ring, hook the two middle wires up on the connector to the other two middle wires on the CRD side connector, turn the key on and see what the gauge says. You could do this before you bend it and after you tweak the bend. Just make sure you turn the key off each time so you get an instant reading on the gauge when you turn the key on).


Nice find, I knew it had to be something simple. Another user suggested taking the resistance measurement between pin 2 and 3 before you take the original sender out, then adjust(bend) the arm until you get the same resistance with the unit installed. Should ensure a one for one swap.

I wish it only took 20 minutes to drop the tank. I have to drop the rock lizard rear bumper, the tank skid then the tank. Thats whats keeping me from changing out the arm :D
Author:  05crd [ Fri Jun 13, 2008 1:46 pm ]
Post subject: 
Changed out the arm last night and centered the unit but didn't really need to as all the locations are flat but figured as long as it was out :roll: Checked that empty was empty and filled it with 5 gallons and it is at the quarter mark so I guess that solves it, thanks much!
Author:  dgeist [ Fri Jun 13, 2008 1:51 pm ]
Post subject: 
I'm down to below 1/4 tank today and I have a reprieve from the wife for baby-duty for fathers' day. I think I'll gift myself a new lift pump installed with the advice above :) I'll be sure to take a few pics of the critical stuff while I'm working.

Dan
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