1996 Caravan Fuel Pump/Sender Unit Question

I have just replaced the fuel pump assembly in the warped tank of my 96/3.0 carvan with one from another 96. They look identical. Fuel guage reading is now incorrect - reads too low, which I believe means resistance from sender is too high vs the old one. Does anyone know if different spec senders were used on these units? Is there anyway to change the calibration on the guage? I assume there is some voltage regulation in the circuit somewhere, and I wonder if there is any adjustment possible.

Reply to
Mike C1
Loading thread data ...

Is this a trick question? You did say that the tank is warped, right?

Possibly the float rod on the "new" assembly got bent during the changeover, or perhaps the old one had been "tweaked" to compensate for the mishapen tank (and if you're the orginal owner, you may say that you know that not to be the case).

Ignoring that issue, you might consider trying (throught trial and error with, say, a near-empty tank) to bend the float rod to make it read correctly - but you may have to choose between a reasonably accurate reading with the tank "full" or with the tank near "empty" (near empty would be the logical choice).

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

..

CC replaced thousands under warranty. Our 96 was changed out in 98 IIRC

Reply to
Tom Ruta

The way you worded your original post ("I have just replaced the fuel pump assembly in the warped tank of my 96/3.0 carvan with one from another 96..."), I took it to mean you had and still have a warped tank and that you changed out just the sending unit/fuel pump assy.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

This is correct. I still have the warped tank in the van. I purchased the van used in 1999, and the original owner failed to have the tank replaced under warranty. It will hold about 12-13 gallons. I replaced the fuel pump assembly with another one which I got from a wrecking yard, and was told that it was from a 1996.

The pump works fine, but the guage reads between E (when half full of gas) and about 1/3, when full of gas. The float assembly moves ok on the replacement unit. It just seems to me that the resistance range of the sending unit is different than the old one I removed.

For what it's worth, I don't think the warping affects the reading. While the inward warping of the tank does push the pump assembly vertically (vs the mounting plate), it is on a spring which allows this this movement.

I just wondered if there was an option to flash the PCM when the tank is full, indicating that the voltage the computer is seeing from the sender means 'Full'.

Thanks for the replies.

Mike C

Reply to
Mike C1

LOL!

ca...

Reply to
Hank

Oops - Tom - I confused you with the OP.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

OK - here's what I think's going on: The fuel level sender is at its lowest resistance when the tank is full - I don't know the specs. on your van, but typically it would be on the order of 60 ohms (float full up position). It goes to something on the order of 1000 ohms when the tank is empty (float all the way down).

I think the wiper is slightly corroded (adding resistance into the reading). This makes sense because: (1) It has been sitting unused for a while (no wiping action to clean it off) possibly in fuel, possibly in air, possibly in mixture of air and moisture or fuel and water, and (2) Higher resistance pushes the reading to towards empty (higher resistance => lower gage reading). This would also have the effect of compressing the gage scale downward (towards 'E'), which you are also seeing.

Take it out, and carefully remove any covers from around the resitance element and wiper. Very carefully clean both. Be careful - those wires on the resistance element are very fine and delicate (meaning "easy to break", in which case you throw it away). Try using some TV tuner cleaner (Radio Shack).

To monitor your progress, read the resistance across the sensor (via the two connector pins) at float full-up and full-down positions before you start, and then as you clean it. I'm betting you will see the resistance come down to the levels given above, and it will start reading right.

Another type of problem that you see on sending units is broken resistance element wires (they can completely wear thru from a lifetime of cycling), but the behavior you are describing is not consistent with that. I have no doubt that the wiper and/or resistance element wire wiping surfaces are corroded - it fits the history of sitting in a junk yards for an unknown period of time and the symptoms you have described.

I can't emphasize enough how delicate those wires are. You might try just moving the float up and down a bunch of times (to wear thru the corrosion) after squirting TV tuner cleaner (or electrical contact cleaner) onto the resistance element and wiper without otherwise directly contacting the element or wiper with your hands or any tools. The other thing to watch out for when fooling with the wiper is springing the wiper back a little so it doesn't make good contact with the proper amount of pressure against the resistance wires - another reason to avoid directly messing with it.

Let me know how it goes.

Sorry for the confusion earlier on in the thread - I confused Tom Ruta with you when he posted. Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

...

No worries Bill.

Reply to
Tom Ruta

Brilliant. Thank you Bill. I will bet you are correct, and I had not thought of corrosion on the sender. This would explain the symptoms, as I see essentially higher resistance through the range. The range you mention is correct - on my old sender it is 80 to 1000 ohms. I did check that the part number on the senders were the same before I installed it - but I never checked the actual resistance. Aghhhh.

I am going to take the lazy approach initially - pour in some fuel additive and go through a few tanks of gas to see of the movement of the wiper will clean the contacts itself. If not, out comes the tank again.

Thanks again - your post was extremely helpful.

Mike C

Reply to
Mike C1

You're welcome. Sorry you have to drop the tank to get to it.

Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")

Reply to
Bill Putney

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.