Repairing fuel level sender in minivan

Hi All,

Just a short post for anyone who has this problem.

Tonight I repaired the fuel level sender in my 94 T&C AWD. It was not
working at all and showed the tank
always empty. I pulled the tank and pulled out the fuel pump. On the AWD
the sender is on the side. It
is a Carter electric fuel pump used in these and the sender's part# is
Carter -73 0337 if that helps anyone.
What I found is that on mine the sender had worn slightly. As a result when
it was in use the wiper arm on
the sender that wipes against the rheostat was pulling away from the
rheostat. I took two safety pins and using
the sides of their pointed ends I carefully bent the wiper near it's hub so
that it pressed closer to the rheostat
plate so that it would make contact all of the time. Then I reassembled
everything. So far it's working, knock on
wood.

This job is a rather nasty one. The fuel tank collects dirt and dust and
when you get under it to disturb it
all that showers down on you. And getting the quick disconnect fuel
fittings apart on an AWD is a bitch due
to limited clearance. I found that using a cheater bar on a flare wrench
with a block of wood as a fulcrum
I was able to lever the wrench sideways so that it was pushing on the quick
disconnect with enough force
to make it come apart. I was actually having it push on a plastic grommet
that is sold for the purpose of
pushing apart the quick connect fittings.

Also it's almost impossible to drain the tank once again due to clearance.
I simply filled a 5 gallon gas can
half full with gas and then just drove the van normally during the day until
the van ran out of gas, then put in
a gallon or so of gas then drove the van home. I didn't trust the draining
procedure in the manual so I did
this in preparation of working on it.

Ted

 

Ted, was this the van that you did the transmission rebuild on? If so,
how did it go putting it back together?

-Kirk Matheson

 

Hi...

Thanks very much for sharing this. Mine shows empty if there's less
than 3/4 left, and the dealer wants to change the whole pump/sender
unit... expensive.

I have the luxury of getting at it through the trunk, so guess I'll
have a go at it myself

Thanks again, and take care.

Ken

 

What normally causes this problem is the center of the rheostat wears out
and bending the arm will not help if this occurs.
I don't understand, if you are going to go thru all that trouble to remove
the in tank pump to repair the sending unit why not replace the sending
unit, I thinks its about 80 bucks.

Thats alot of work to put back together to find out it didn't fix it.

Glenn Beasley
Chrysler Tech

 

Ken, depending on the mileage of your vehicle the dealer may have suggested
replacing the intire pump because the next thing to go will be the pump.
If I get a problem like that in the shop with a vehicle with 100k or more on
it. I will give the cust 2 options, the sending unit and the pump, same
labor. If they plan on keeping the vehicle I would advise the pump and most
owners that plan on keeping the vehilce for awhile will take the complete
pump as the repair

Glenn Beasley
Chrysler Tech

 

Yup. On this one, that didn't happen. The center of the rheostat was still
nice
and shiny, plenty of material there. I've seen the fuel level sender on a
non-AWD
vehicle and the rheostat on it is a lot smaller, and in my uneducated view,
looks
a lot flimsier.

Well because exactly what you said about the fuel pump. I priced the parts
before even tearing into the job, and the sender itself is not available
from the
aftermarket, and the cheapest aftermarket fuel pump/sender I could find was
in the
$180 range. I couldn't even imagine what a new fuel pump/sender from the
dealer would cost, I'm sure it's a lot more than $180 if the sender itself
is $80.

My thought when going into it was that if I was going to start buying any
parts I
would buy the complete fuel pump/sender assembly. It seems dumb to buy just
the sender then have the fuel pump kick the bucket 6 months later and then
if
you buy an aftermarket replacement you get the sender again, so your $80 you
spent on the first sender is now wasted. But before buying anything I
wanted to
get a look at it - with this van considering how the prior owner treated it,
the
problem could easily have been elsewhere, and not in the sender at all.

If I had found the center of the rheostat worn out then I would have made
the
decision whether to just replace the entire pump/sender assembly, or to do
nothing, put it back together then just drive it until the fuel pump dies,
without a
level guage. Based on the difficulty getting the tank out I probably would
have
swore a blue streak then just bought the pump/sender assembly.

It was a calculated risk. After the bending procedure I tested it and even
putting a fair about of lateral force on the float arm and moving it, the
wiper
did not pull away from the rheostat. And it tested out good on the
ohmmeter while moving the arm (I used an analog ohmmeter of course)
no dropouts.

Of course, the wiper could simply have lost spring tension and it will
just wander away from the rheostat in a few months and I'll be back
with no guage. But at least now I know proof positive that the dash
wiring to the sender does in fact work.

Ted

 

Yes. I did the R&R, Transmission Exchange http://www.txchange.com did the
rebuild.

I added to the pictorial some of the showstoppers. The biggest one is that
the van's frame
is bent. I knew that it had been involved in a collision before I bought it
but I did not know
how bad it had been bent.

The worst bending is in the front where the front engine/transmission mount
bolts to, right
under the radiator. The frame there is bent up, which is a common problem
with front
end collisions on these vans. Obviously the front trans/engine mount is
thus higher
than it's supposed to be. The result of this is that the engine is rocked
backwards
somewhat more than it's supposed to be.

With a regular non-AWD this would not matter. However with an AWD it does
because
it causes the power transfer unit and rear driveline output shaft to
basically dip down. In
my case it is at least an inch lower than it's supposed to be. Thus when
the engine revs under
load, such as if you power brake it, the engine shifts in the mounts (like
it's supposed to do)
and the rear driveline bangs down on the crossmember, with much loud
scraping and banging.
I'm sure it's not good for the driveline output shaft. Worse, because the
power takeoff from the
transmission is not parallel to the rear carrier, it causes massive
driveline vibration. When
I first test drove it, when I got out on the highway it sounded like I was
driving on a
steel grating bridge.

Obviously the correct way to fix this is to pay someone with a laser frame
alignment
machine $800 to straighten it out. And I may eventually do this. But in
the meantime I
have shimmed the engine mounts. I shimmed the rear trans mount with 4
washers,
(the LH side mount) and the front engine/trans mount with as many washers as
it
could take and still have threads left to hold the nuts on. And I also
passed a bolt through
the holes in the front engine/trans mount rubber to help give that mount
some extra stiffness.

This helps tremendously. The PTU power output shaft is still a few degrees
off parallel
with the rear carrier. But not as badly as before and so it does not
vibrate on the highway
anymore. There's a few oddball resonances in it, for example at 30Mph
there's a
resonant point in the driveline and it will moan, but that stops when I hit
33 or more Mph.
And more importantly I can start off from a stoplight with normal throttle
and not have
the driveline bang against the crossmember.

Ted

 

I'll bite. Why was an analog ohmmeter necessary for testing the
rheostat?

Is there something unusual about the rheostat?

Granted, it's easier with an analog to see a smooth, clean reading
sweep so probably almost having to graph the data.

If the rheostat is a small area, I see your point about the analog
meter.

Generally I reserve the analog for testing capacitors. My analog uses
so much current for its testing that it can actually polarize delicate
electrodes if I'm not careful. But it's a cheap analog meter though.

 

Has nothing to do with that. A DVM, even a graphing one, is not
anywhere near sensitive enough for a changing resistance like testing
a potentiometer (rheostat)

The problem with potentiometers (pots, in the trade) is as Glenn said
areas of the resistance material can wear out. This can be seen by
when you move the wiper arm of the pot (turn the handle, slide
the level, whatever) and you see the needle of the analog VOM move,
if the wiper hits any areas where the resistance material is missing, even
minute, tiny areas, there will be a slight almost unnoticable stumble
or drop of the needle as it is sweeping up the scale of the VOM.
You may not see this unless you wipe the arm back and forth several
times. Of course, it's arguable if for a fuel level guage you need that
kind of
sensitivity, but for an audio pot you certainly do.

A non-graphing DVM will of course be nothing more than a jumble of
numbers, and even a graphing one probably would not show that kind of drop..
And a cheap, small pocket analog VOM without a sensitive needle would
also probably not show it either. An oscilloscope could show it, of
course.

I have several DVMs also, my analog meter is an older Radio Shack model
back when RS actually sold decent analog VOMs, with a large meter in it.
Besides testing pots, it is also useful for testing diodes, as DVM's
generally don't
supply enough power to a diode to get it to work.

Unfortunately, the big problem with analog meters is that they are only as
good as the meter used, and it is expensive to make a large, sensitive
meter. Back in the olden days, even though a good multimeter was
expensive, an oscilloscope was far more expensive, so people were willing
to pay for an expensive multimeter. Today, scopes are cheap and the
few testing tasks that you can't use a DVM for and need an analog
meter for, a scope can do. So, people buy scopes and DVMs and can
do everything that an analog meter can do, so there's no market for
the good ones anymore.

Ted

 

Your good explanation reminded me that I have what used to be a very
expensive HP (got it surplus from a FAA radar station that was still
using wire-wrapped boards in its electronics - I'm thinking, wire
wrapped and this is what tracks airplanes, uh oh...) analog meter that
did millivolts. It weighs what, 10 or 20 pounds and runs on AC. I guess
I could send some current down the rheostat/pot and use that? I guess I
got this because I needed to do microvolt, µV, readings at that time
and was tired of always fussing to get the voltage up enough for an
oscilloscope to read. I really needed a 6? digit DVM but they are still
the same price, about $1000 for a good Fluke.

With the 'scope, would you not need to send current down the pot to see
a trace? Or do scopes now take resistance readings? I have the very
last of the old but fast Tektronix analog scopes - but have not used it
in a long time so can't remember if the scope can generate current - it
has a test current, probably a square wave at 1000 Hz and 1 volt p-p if
I'm too lazy to breadboard the thing properly.

 

Well this is theoretical since we all know that most mechanics and
dealerships
are parts-changers and probably none of them would test a pot. But what I
would do if I was going to use a scope is to run some temp jumpers from the
sender to the connector on the underside of the vehicle that plugs into the
fuel pump, turn the vehicle on and use the vehicle 12v power.

Usually in audio circuits what happens is that the cheap circuits run DC
voltage
through the pots along with the AC signal. That lets them reduce the amount
of circuitry in use. Over time the DC power burns out points in the pot.
You
can hear it if you have ever turned the volume control on a cheap radio that
has a few years on it and you hear a lot of scratching and static when the
volume
knob is turned. So with a scope you would just jack into the circuit itself
right at the pot.

Ted

 

Except you would quite possibly burn out the pot, as it is designed to
work on 5 volts, more or less.

 

Do the cars drop to 5 volts in a typical 12 volt car circuit with
regulators or dividers when there are electronics? I guess they'd have
to.

I have seen 5 volts for chips, that is, logic chips and custom chips
and integrated chips, but not for pots. That pot is usually a physical
thing, hmmm, it was a physical thing. They do have digital resistors
which are controlled by logic. But I thought this was a physical analog
resistor thingee with a wiper so how could it burn out? They make them
that cheaply now? If so, one more thing to worry about.

Would not the 5 volts be for the logic stuff over the analog pots?
Don't mean to second guess you here but I'm just surprised that analog
pots would be so vulnerable to only 12 volts. I can't recall my specs
but usually most stuff I would buy would be much higher in specs, to
24?? volts, but it's been a long time since I had to talk to Digi-Key.

I was suprised to hear Ted's talk of the DC carried with the AC in
cheap audio circuits and burning out the pots. I gather these are
rather small and delicate pots? Must be fine wires to burn up. Or maybe
carbon instead. But the audio circuit would have the DC and AC much
higher than 5 or 12 volts? Or maybe high amperage? Stuff never gets
simpler.

 

Posted too quickly. He could not burn out the pot since he is not doing
anything but scoping an existing circuit. Ted is not introducing
anything and most oscilloscopes are so loaded up, I forget the tech
term but millions of ohms of resistance, they don't add to any
circuits.

All he is doing is looking at the electricity that already exists in
the vehicle as it flows between the sender and fuel pump. If there are
any burps, he knows something is not working correctly.

This is safe. What I once did, 'scoping an extremely high voltage
strobe light was not safe. It burned up the metal of my 'scopes probes.
Vaporized the metal.

I guess your point is if he hooked up 12 volts to a pot that is outside
the vehicle? As I said in my previous post, I did not know pots could
be vulnerable to such a small difference from 5 to 12 volts if there
were simple analog pots, that is, just physical metal or carbon with no
logic to them.

 

They can't. What 'burns up' pots is current, not voltage. You could,
possibly,
put a Van De Graph generator on a vehicle fuel level sensor and using a high
voltage probe, see some voltage difference with 100,000 volts on it or more.
This is the same generator you see in the science museums that make people's
hair stand on end.

If you put a 12 volt battery that can source 100's of amps across the
terminal of
a level sensor you would not have a level sensor any longer.

On the vehicle in question the same plug the fuel pump uses also carries an
additional
pin for the level sender, I assumed this was obvious since I mentioned that
the aftermarket replaces these sensors only as a complete fuel pump
assembly. And
you are correct the idea was to run jumpers from the existing fuel level
sensor pins
in that plug, not from the fuel pump power source pins in that plug.
(actually, the
fuel pump and level sensor share 1 pin in the plug, as a matter of fact)

Ted