What's the crap that cakes up the FUEL SENDER in the tank? and how to clean it all.
08-06-2003, 04:55 AM
#1
Three Wheelin'
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What's the crap that cakes up the FUEL SENDER in the tank? and how to clean it all.
After downloading all the values for the fuel tank sender from Paragon http://www.tech-session.com/kb/index...x_v2&id=72&c=4 and Clark's garage, we finally figured out that the problem with the 944 NA fuel gauge was the sending unit.
Made sure the tank was pretty empty of gas, grounded myself constantly (no sparks please!) and went at it.
Removed the cargo mat and then the 10" square of foil backed fiberglass matt (really good stickum on that sucker, and no residue either!) exposing a 4" plastic cap with 17 y.o. black goo. Pried that off (goop was still pretty pliable and re-useable!) to expose the top of the sender unit and connector. No resistance value registered, so I followed the instructions on other Rennlist posts to remove the 2 feed lines and used a heavy drift (nice old tie rod end!) and a hammer to slowly knock several of the plastic tabs on the screw off top that holds the sender in place. MAKE SURE YOU REFERENCE MARK THE EARED LOCKING CAP TO THE GAS TANK FOR REPLACEMENT!
Once that was off, it was pretty evident what the problem was. That sender unit was CAKED in hard brown crusty CRAP - so bad that I could not figure out that it was a 8mm nut on the bottom of the unit until I picked it - chiseled it off with screwdriver! When I got that cap off and then the base and alum tube surround off to expose the fine wire and float mechanism, I couldn't believe the CRAP on the central guide rod! The float was "stuck" about 1/3 way up - couldn't even budge it because of the brown crap on the rod!
The sensor wires seemed fine and the float look OK, so a shot of WD 40 and then brake cleaner followed by chipping away / scraping the rod with a utility knife followed by 400 grit sandpaper finally succeeded in freeing that float! The movement of the float itself cleaned both wires pretty well, and running a fingernail up and down the length of both wires got rid of anything left. I reassembled the sender and proceeded with testing the resistance values.
My digital VOM showed all the right values at full and empty, so back into the tank it went! Sealing it all back up, using the drift to reseat the tank locking cap to the original position. It took another full turn of the cap to "lock it" back into the original position. You have to be careful, as the gas tank is plastic, and over tightening it can apparently lead to cracking the tank threads, or the tank itself!
Once completed, a quick continuity check, hooking up all the lines, and firing up the engine showed that it was all worth it. The sender unit correctly displayed a "reserve" light!
A quick trip to the gas station and 3 gallons of 92 octane to make sure it worked in case I had to pull it out again. Tank shows just under a 1/4 tank, so it looks like it worked!
Simple enough process, just be careful to do it outdoors, and GROUND yourself from time to time to eliminate static sparks! You don't need the special Porsche tool to remove the sender locking ring, but a good heavy drift to knock the tabs and shock the thing into loosening works well. Get a digital VOM to check resistance too.
Then patience and a delicate touch to clean off all that hard baked crap! Looks like real old hardened molasses! Bet it doesn't taste too good though!
Made sure the tank was pretty empty of gas, grounded myself constantly (no sparks please!) and went at it.
Removed the cargo mat and then the 10" square of foil backed fiberglass matt (really good stickum on that sucker, and no residue either!) exposing a 4" plastic cap with 17 y.o. black goo. Pried that off (goop was still pretty pliable and re-useable!) to expose the top of the sender unit and connector. No resistance value registered, so I followed the instructions on other Rennlist posts to remove the 2 feed lines and used a heavy drift (nice old tie rod end!) and a hammer to slowly knock several of the plastic tabs on the screw off top that holds the sender in place. MAKE SURE YOU REFERENCE MARK THE EARED LOCKING CAP TO THE GAS TANK FOR REPLACEMENT!
Once that was off, it was pretty evident what the problem was. That sender unit was CAKED in hard brown crusty CRAP - so bad that I could not figure out that it was a 8mm nut on the bottom of the unit until I picked it - chiseled it off with screwdriver! When I got that cap off and then the base and alum tube surround off to expose the fine wire and float mechanism, I couldn't believe the CRAP on the central guide rod! The float was "stuck" about 1/3 way up - couldn't even budge it because of the brown crap on the rod!
The sensor wires seemed fine and the float look OK, so a shot of WD 40 and then brake cleaner followed by chipping away / scraping the rod with a utility knife followed by 400 grit sandpaper finally succeeded in freeing that float! The movement of the float itself cleaned both wires pretty well, and running a fingernail up and down the length of both wires got rid of anything left. I reassembled the sender and proceeded with testing the resistance values.
My digital VOM showed all the right values at full and empty, so back into the tank it went! Sealing it all back up, using the drift to reseat the tank locking cap to the original position. It took another full turn of the cap to "lock it" back into the original position. You have to be careful, as the gas tank is plastic, and over tightening it can apparently lead to cracking the tank threads, or the tank itself!
Once completed, a quick continuity check, hooking up all the lines, and firing up the engine showed that it was all worth it. The sender unit correctly displayed a "reserve" light!
A quick trip to the gas station and 3 gallons of 92 octane to make sure it worked in case I had to pull it out again. Tank shows just under a 1/4 tank, so it looks like it worked!
Simple enough process, just be careful to do it outdoors, and GROUND yourself from time to time to eliminate static sparks! You don't need the special Porsche tool to remove the sender locking ring, but a good heavy drift to knock the tabs and shock the thing into loosening works well. Get a digital VOM to check resistance too.
Then patience and a delicate touch to clean off all that hard baked crap! Looks like real old hardened molasses! Bet it doesn't taste too good though!
08-06-2003, 10:48 AM
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It may be the same problem that plagued old Z cars. The steel tanks were lined with a "polymer" of some sort that would come free over the years. I had a problem with dropping fuel pressure when the stuff would get all over the pick up. It appears like fine sheets of brown mica. I had the tank flushed, cleaned and re-lined with a "modern" goo. If the problem re-occurs, you may want to remove the tank and have it resealed at a radiator shop. (They like it to be filled with water whenever they work on it!!)
I hope this helps.
I hope this helps.
05-22-2010, 09:36 PM
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Just took my fuel sender out today and found the same stuff caked on mine, but I couldn't figure out how to get it apart far enough to clean it properly. I took the small nut off the bottom and there's sort of a cup that comes off, then another nut and the bottom cover came off, but there must be a way to remove the float from that tube, and I couldn't figure out how. Maybe I was just too chicken that I was going to break something.
Anyone got tips on the next step to dismantle and clean this thing?
Anyone got tips on the next step to dismantle and clean this thing?
05-22-2010, 10:03 PM
#5
Nordschleife Master
Gasoline left sitting too long will turn to varnish, and deposit itself on EVERYTHING..
IF your sender is that bad, also suspect would be everything between the pickup (a screen that is probably close to clogged), and the motor (all the lines, the pump, the rail, the fuel pressure regulator, the damper, AND the injectors...
Whitchhunter can clean / flow / report on the injector health ( http://www.witchhunter.com/ )
everything else should at least be cleaned.... or replaced.
more info available here: http://sos-power-sales.com/Service/FuelVarnish.aspx
IF your sender is that bad, also suspect would be everything between the pickup (a screen that is probably close to clogged), and the motor (all the lines, the pump, the rail, the fuel pressure regulator, the damper, AND the injectors...
Whitchhunter can clean / flow / report on the injector health ( http://www.witchhunter.com/ )
everything else should at least be cleaned.... or replaced.
more info available here: http://sos-power-sales.com/Service/FuelVarnish.aspx
