HomeHOW TO DO AN ADVANCED SEARCH.
Mon Jul 08, 2013 3:56 pm by Admin
For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.
When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).
After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …
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Ray's 1987 944 LS1 Build & Swap
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Page 14 of 14
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Fuel Gauge Gremlin
Raymond-P Mon Apr 15, 2024 4:04 pm
My original fuel gauge and the replacement cluster fuel gauge has never moved on ignition, even though I know the tank had more than 10 gallons of fuel.
Assuming the gauges were both functional, the next step was to check the tank sending unit and possibly replace it. As you may know, it can easily be accessed through the rear hatch by folding back the carpet and removing the vapor barrier and plastic access cover.
I thought this might be a common problem and worth posting.
When I removed the access cover, I found an abandoned mouse nest… no bones though!!
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Tank Sending Unit Location > < Old Mouse Nest >
After disconnecting the battery, I gently pried off the wiring harness connector and started to remove the fuel lines. The fuel feed line was too short and rigid to flex out of the way, so I removed the hose clamp altogether which did help. The return fuel line was smaller and longer and can be removed easily.
Be careful not to damage these hoses removing them.
Before removing the lines entirely, I realized I should check the gauge function first. So, my next challenge was to learn what resistance values (Ohms) I should be getting on my multimeter, and equally important, which terminals I should be checking.
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Sending Unit Lead ID > < Harness Plug without Retaining Cap >
Note: I removed the harness terminal cap to expose the wires and make sure they matched the sending unit.
I checked on the Clark’s Garage website where there is documentation on the proper ohm resistance values for the fuel gauge markings. I used the values for a “late model” 944. Importantly, I learned that the correct terminals to test for resistance were “G” (GREEN wire) and “T” (BROWN wire). Terminal “W” (WHITE wire) activates the Low Fuel light. Below is a listing of the correct resistance values:
Status Ohms
Empty > 63.2
Reserve 63.2
1/4 Tank 42.2
1/2 Tank 21.2
3/4 Tank 8.6
Full 2.8
With this knowledge in hand, I proceeded to check my sending unit expecting a reading that reflected a substantial level of fuel...something less than 20 Ohms.
Unfortunately, I got a reading of 78+ Ohms which is MUCH TOO HIGH, even for a bone-dry tank. This could only mean problems with the resistance wires inside the sending unit as the resistance increases as the fuel level drops and the float moves down the sending unit.
Not expecting to be able to recondition the sending unit, I checked my Porsche Manual to get the correct part number and ordered a replacement sending unit on Amazon. URO Parts, $115 plus PA tax.
[You must be registered and logged in to see this image.]
< Tank Sending Unit Porsche PN 944 641 037 01 >
In 2 days the new URO sending unit arrived and the float moved freely inside. It seemed I was good to go. I soon found out that I did not have the necessary tool to remove the sending unit lock ring, or as Porsche calls it the “Union Nut.” I did have large Channel Locks (somewhere) but rather than grind up the lock ring, I opted for a unique oil filter wrench available at Harbor Freight that was perfect for the job. At only $10 it was the way to go.
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< New URO Sending Unit > < Harbor Freight Oil Filter Wrench >
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Removing the Lock Ring > < Failed Seal & Corroded Mechanism >
The lock ring does not exactly spin off easily. The fuel lines prevent the entire unit from spinning along with the lock ring, which means you only get about a 1/4 turn with each set of the wrench.
Once the lock ring was off and I removed the unit, it was clear that the sending unit was completely shot! Fortunately, the sending unit rubber gasket at the top was in good shape and I was able to reuse it. As for the fuel level, I was lucky. It was barely low enough to do the job without having a major fuel spill when removing the lock ring.
[You must be registered and logged in to see this image.]
< Fuel Level – Just Low Enough >
Reinstalling the New Sending Unit
This was my 1st effort, so I was just winging it. Below is the procedure I used:
1. Lube the lock ring threads with Sil Glyde (silicone lubricant).
2. Apply a thin layer of Permatex Permashield gasket sealer on the underside
of the sending unit flange. (I smelled fumes when I first exposed the sending unit, so I suspected a leak.)
3. Slide the gasket into place under the sending unit flange and apply another
thin layer of Permashield on the tank side of the gasket.
4. Slip the lock ring over the sending unit fuel line tubes and position it on top of the sending unit flange. (This must be done BEFORE lowering the unit into
the tank.)
5. Lower the sending unit with lock ring in place, down into the tank.
(I had to be extra careful not to create a fuel tank overflow.)
6. Wiggle the sending unit slightly until it’s firmly in position.
(There seems to be some sort of cavity in the tank bottom to secure the
bottom of the sending unit.)
7. Hold the assembly down, push aside the fuel lines, and hand thread the lock ring until JUST SNUG and you can still spin the sending unit.
8. Apply a film of Sil Glyde to the inside of the rubber fuel lines using a Q-Tip.
9. Rotate the sending unit counterclockwise within the lock ring to engage the
fuel feed line. (The feed line is rigid and just long enough for a neat
installation. There is no “bending it” for removal or installation.)
10. Continue rotating the sending unit to fully engage the fuel feed line.
11. Be sure the feed line hose is on up to the collar and install the hose clamp
with the lock screw up and to the left.
12. Tighten the lock ring. (Don’t get crazy, you’ll know when it’s tight.)
13. Install the fuel return line and tighten the hose clamp. Be sure the hose clamp
is installed with the lock screw up and to the right.
14. Reconnect the wiring harness.
Below are some pics of the process:
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Sil-Glyde on the Lock Ring > < Permashield on the Sending Unit Flange >
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Permashield on the Flange Gasket > <Hand Starting the Lock Ring >
[You must be registered and logged in to see this image.]
< Fuel Feed Line Engagement > < Fuel Feed Line in Place >
[You must be registered and logged in to see this image.]
< Tightened Hose Clamps > < Reconnected Harness >
So now I’m flying high thinking I just eliminated my fuel gauge gremlin. I connected the battery and energized the ignition….but I GOT NOTHING!!
[You must be registered and logged in to see this image.]
I pulled my multi-meter out again and checked the resistance across the brown and green terminals of the new sending unit. This time I was expecting a very low number like 5 Ohms, consistent with nearly a full tank of fuel. Instead…the reading was the same as before, 78+ Ohms!!! What is going on?????
I pulled the new sending unit back out of the tank, disassembled it, and below is what I found. It was DEFECTIVE. Note the broken wires that determine the resistance and hence voltage sent to the fuel gauge. GO FIGURE!
[You must be registered and logged in to see this image.]
< New Sending Unit with Broken Resistance Wires >
This one is going back, and I immediately ordered a replacement. When it arrived, the packaging was better, and it had a sticker that the first unit did NOT have regarding a locking pin for the float mechanism. At this point it seemed I was sold a returned defective unit, or possibly it was damaged during shipping.
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Replacement URO Sending Unit > < Float Locking Pin >
I checked the defective unit, and it had no provision for a float locking pin. That explains a lot. Without the float locking pin, I suspect it was an older model.
Before installing this 2nd new unit, I removed the locking pin and checked the resistance between the Green and Brown wire terminals at the “full” and “empty” float positions. I’m happy to report that the numbers were good!
Empty 68 Ohms
Full 4.4 Ohms
Not exactly the Clark’s Garage numbers but that might be because it was a dry test.
Confident that the sending unit was functional, I proceeded to install it as noted before. Once again, I reconnected the battery, engaged the ignition, and VOILA...
I have a working fuel gauge!
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< New Sending Unit Lead ID > < Success!! >
LESSON LEARNED: Check your new parts when you can…BEFORE INSTALLATION!
Next up…. Dyno Day!!!!!!!!!!!!!!!!!!!!! [You must be registered and logged in to see this image.]
Assuming the gauges were both functional, the next step was to check the tank sending unit and possibly replace it. As you may know, it can easily be accessed through the rear hatch by folding back the carpet and removing the vapor barrier and plastic access cover.
I thought this might be a common problem and worth posting.
When I removed the access cover, I found an abandoned mouse nest… no bones though!!
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Tank Sending Unit Location > < Old Mouse Nest >
After disconnecting the battery, I gently pried off the wiring harness connector and started to remove the fuel lines. The fuel feed line was too short and rigid to flex out of the way, so I removed the hose clamp altogether which did help. The return fuel line was smaller and longer and can be removed easily.
Be careful not to damage these hoses removing them.
Before removing the lines entirely, I realized I should check the gauge function first. So, my next challenge was to learn what resistance values (Ohms) I should be getting on my multimeter, and equally important, which terminals I should be checking.
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Sending Unit Lead ID > < Harness Plug without Retaining Cap >
Note: I removed the harness terminal cap to expose the wires and make sure they matched the sending unit.
I checked on the Clark’s Garage website where there is documentation on the proper ohm resistance values for the fuel gauge markings. I used the values for a “late model” 944. Importantly, I learned that the correct terminals to test for resistance were “G” (GREEN wire) and “T” (BROWN wire). Terminal “W” (WHITE wire) activates the Low Fuel light. Below is a listing of the correct resistance values:
Status Ohms
Empty > 63.2
Reserve 63.2
1/4 Tank 42.2
1/2 Tank 21.2
3/4 Tank 8.6
Full 2.8
With this knowledge in hand, I proceeded to check my sending unit expecting a reading that reflected a substantial level of fuel...something less than 20 Ohms.
Unfortunately, I got a reading of 78+ Ohms which is MUCH TOO HIGH, even for a bone-dry tank. This could only mean problems with the resistance wires inside the sending unit as the resistance increases as the fuel level drops and the float moves down the sending unit.
Not expecting to be able to recondition the sending unit, I checked my Porsche Manual to get the correct part number and ordered a replacement sending unit on Amazon. URO Parts, $115 plus PA tax.
[You must be registered and logged in to see this image.]
< Tank Sending Unit Porsche PN 944 641 037 01 >
In 2 days the new URO sending unit arrived and the float moved freely inside. It seemed I was good to go. I soon found out that I did not have the necessary tool to remove the sending unit lock ring, or as Porsche calls it the “Union Nut.” I did have large Channel Locks (somewhere) but rather than grind up the lock ring, I opted for a unique oil filter wrench available at Harbor Freight that was perfect for the job. At only $10 it was the way to go.
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< New URO Sending Unit > < Harbor Freight Oil Filter Wrench >
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Removing the Lock Ring > < Failed Seal & Corroded Mechanism >
The lock ring does not exactly spin off easily. The fuel lines prevent the entire unit from spinning along with the lock ring, which means you only get about a 1/4 turn with each set of the wrench.
Once the lock ring was off and I removed the unit, it was clear that the sending unit was completely shot! Fortunately, the sending unit rubber gasket at the top was in good shape and I was able to reuse it. As for the fuel level, I was lucky. It was barely low enough to do the job without having a major fuel spill when removing the lock ring.
[You must be registered and logged in to see this image.]
< Fuel Level – Just Low Enough >
Reinstalling the New Sending Unit
This was my 1st effort, so I was just winging it. Below is the procedure I used:
1. Lube the lock ring threads with Sil Glyde (silicone lubricant).
2. Apply a thin layer of Permatex Permashield gasket sealer on the underside
of the sending unit flange. (I smelled fumes when I first exposed the sending unit, so I suspected a leak.)
3. Slide the gasket into place under the sending unit flange and apply another
thin layer of Permashield on the tank side of the gasket.
4. Slip the lock ring over the sending unit fuel line tubes and position it on top of the sending unit flange. (This must be done BEFORE lowering the unit into
the tank.)
5. Lower the sending unit with lock ring in place, down into the tank.
(I had to be extra careful not to create a fuel tank overflow.)
6. Wiggle the sending unit slightly until it’s firmly in position.
(There seems to be some sort of cavity in the tank bottom to secure the
bottom of the sending unit.)
7. Hold the assembly down, push aside the fuel lines, and hand thread the lock ring until JUST SNUG and you can still spin the sending unit.
8. Apply a film of Sil Glyde to the inside of the rubber fuel lines using a Q-Tip.
9. Rotate the sending unit counterclockwise within the lock ring to engage the
fuel feed line. (The feed line is rigid and just long enough for a neat
installation. There is no “bending it” for removal or installation.)
10. Continue rotating the sending unit to fully engage the fuel feed line.
11. Be sure the feed line hose is on up to the collar and install the hose clamp
with the lock screw up and to the left.
12. Tighten the lock ring. (Don’t get crazy, you’ll know when it’s tight.)
13. Install the fuel return line and tighten the hose clamp. Be sure the hose clamp
is installed with the lock screw up and to the right.
14. Reconnect the wiring harness.
Below are some pics of the process:
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Sil-Glyde on the Lock Ring > < Permashield on the Sending Unit Flange >
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Permashield on the Flange Gasket > <Hand Starting the Lock Ring >
[You must be registered and logged in to see this image.]
< Fuel Feed Line Engagement > < Fuel Feed Line in Place >
[You must be registered and logged in to see this image.]
< Tightened Hose Clamps > < Reconnected Harness >
So now I’m flying high thinking I just eliminated my fuel gauge gremlin. I connected the battery and energized the ignition….but I GOT NOTHING!!
[You must be registered and logged in to see this image.] I pulled my multi-meter out again and checked the resistance across the brown and green terminals of the new sending unit. This time I was expecting a very low number like 5 Ohms, consistent with nearly a full tank of fuel. Instead…the reading was the same as before, 78+ Ohms!!! What is going on?????
I pulled the new sending unit back out of the tank, disassembled it, and below is what I found. It was DEFECTIVE. Note the broken wires that determine the resistance and hence voltage sent to the fuel gauge. GO FIGURE!
[You must be registered and logged in to see this image.]
< New Sending Unit with Broken Resistance Wires >
This one is going back, and I immediately ordered a replacement. When it arrived, the packaging was better, and it had a sticker that the first unit did NOT have regarding a locking pin for the float mechanism. At this point it seemed I was sold a returned defective unit, or possibly it was damaged during shipping.
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Replacement URO Sending Unit > < Float Locking Pin >
I checked the defective unit, and it had no provision for a float locking pin. That explains a lot. Without the float locking pin, I suspect it was an older model.
Before installing this 2nd new unit, I removed the locking pin and checked the resistance between the Green and Brown wire terminals at the “full” and “empty” float positions. I’m happy to report that the numbers were good!
Empty 68 Ohms
Full 4.4 Ohms
Not exactly the Clark’s Garage numbers but that might be because it was a dry test.
Confident that the sending unit was functional, I proceeded to install it as noted before. Once again, I reconnected the battery, engaged the ignition, and VOILA...
I have a working fuel gauge!
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< New Sending Unit Lead ID > < Success!! >
LESSON LEARNED: Check your new parts when you can…BEFORE INSTALLATION!
Next up…. Dyno Day!!!!!!!!!!!!!!!!!!!!! [You must be registered and logged in to see this image.]
Raymond-P- Posts : 385
Join date : 2013-06-29
Age : 68
Location : Beaver, PA
DYNO DAY !!!
Raymond-P Mon Apr 15, 2024 6:46 pm
Well, my friends, if you have been following my project thread, you know that this day has been a long time in the making. Importantly, I would never have been able to get this far without the guidance and support of many of you!
THANK YOU ALL!
I made an appointment for DYNO DAY at CJ Rombold Engine Builders well over a month ago after the electrical system was sorted out and a base tune was applied. Rombold did my engine machine work, rebuilt the heads, and assembled and balanced the rotating assembly.
Rombold uses a Mustang Chassis Dyno which I was told is “stingy” with the numbers.
Admittedly, I was stressed over the prospect of a decade of effort and expense going up in smoke if somewhere along the way, I made a fatal error. Especially when my nephew convinced me it would be best to trailer the car to Rombold’s….
just in case of a mishap!!
Starting and running the engine was a great milestone,
but this was the Moment of TRUTH!!
[You must be registered and logged in to see this image.]
< Loaded on the Trailer >
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Arrival at the Shop > < Ready To Go w/Blower in Place >
I am ecstatic to report that Dyno Day was a complete SUCCESS!!!
The tune effort included a complete street tune, and 4 WOT pulls to get the timing and fuel mixture just right. Total cost was $650, $250 base plus 4 hrs. of tuning at $100/hr. I can come back anytime I think an adjustment might be needed.
YES, of course I have a VIDEO for you!
It’s 24 seconds long and was the last segment of testing with the 4th WOT pull at the end. TURN UP THE VOLUME.
Ray's DYNO DAY Video
Below is the “tale of the tape.”
To summarize:
All WOT pulls were just a shade over 6000 RPM. The sound in the shop was deafening.
The printout I was provided, listed the following:
379.7 WHP at 6,023 RPM, and
356.2 lb-ft WT @ 4,693 RPM
(Both with the Mustang WCF or Weather Correction Factor, applied.)
I know next to nothing about chassis dynos but from what I have read, the Mustang dyno reports lower output values than a Dynojet, with differences ranging from 5 – 15%. One resource I came across advertised a 1.13 conversion factor.
Not that I care much, but on a Dynojet the car would check in at ~429 WHP!
One other question I got answered was about the BHP. My target build number was 450 BHP. The accepted drivetrain power loss of a manual transmission car is 15%. Working my 379.6 WHP backwards yields 446.6 BHP…very close to my target!
One last thing…the engine was built to exceed 7000 RPM. I wonder what another 1000 RPM does to the numbers?
One day I’ll find out, but until then, I’m a HAPPY CAMPER!
Next up…. Momo Steering Wheel Upgrade!
THANK YOU ALL!
I made an appointment for DYNO DAY at CJ Rombold Engine Builders well over a month ago after the electrical system was sorted out and a base tune was applied. Rombold did my engine machine work, rebuilt the heads, and assembled and balanced the rotating assembly.
Rombold uses a Mustang Chassis Dyno which I was told is “stingy” with the numbers.
Admittedly, I was stressed over the prospect of a decade of effort and expense going up in smoke if somewhere along the way, I made a fatal error. Especially when my nephew convinced me it would be best to trailer the car to Rombold’s….
just in case of a mishap!!
Starting and running the engine was a great milestone,
but this was the Moment of TRUTH!!
[You must be registered and logged in to see this image.]
< Loaded on the Trailer >
[You must be registered and logged in to see this image.] [You must be registered and logged in to see this image.]
< Arrival at the Shop > < Ready To Go w/Blower in Place >
I am ecstatic to report that Dyno Day was a complete SUCCESS!!!
The tune effort included a complete street tune, and 4 WOT pulls to get the timing and fuel mixture just right. Total cost was $650, $250 base plus 4 hrs. of tuning at $100/hr. I can come back anytime I think an adjustment might be needed.
YES, of course I have a VIDEO for you!
It’s 24 seconds long and was the last segment of testing with the 4th WOT pull at the end. TURN UP THE VOLUME.
Ray's DYNO DAY Video
Below is the “tale of the tape.”
To summarize:
All WOT pulls were just a shade over 6000 RPM. The sound in the shop was deafening.
The printout I was provided, listed the following:
379.7 WHP at 6,023 RPM, and
356.2 lb-ft WT @ 4,693 RPM
(Both with the Mustang WCF or Weather Correction Factor, applied.)
I know next to nothing about chassis dynos but from what I have read, the Mustang dyno reports lower output values than a Dynojet, with differences ranging from 5 – 15%. One resource I came across advertised a 1.13 conversion factor.
Not that I care much, but on a Dynojet the car would check in at ~429 WHP!
One other question I got answered was about the BHP. My target build number was 450 BHP. The accepted drivetrain power loss of a manual transmission car is 15%. Working my 379.6 WHP backwards yields 446.6 BHP…very close to my target!
One last thing…the engine was built to exceed 7000 RPM. I wonder what another 1000 RPM does to the numbers?
One day I’ll find out, but until then, I’m a HAPPY CAMPER!
Next up…. Momo Steering Wheel Upgrade!
Raymond-P- Posts : 385
Join date : 2013-06-29
Age : 68
Location : Beaver, PA
Good #'s
JW1970 Mon Apr 15, 2024 6:59 pm
Congrats Raymond!
It's been a long time for you to get to this moment. Those are really good #'s. Mine made 365hp at the wheels and I would be lying if I didn't say the car is scary fast!
It's been a long time for you to get to this moment. Those are really good #'s. Mine made 365hp at the wheels and I would be lying if I didn't say the car is scary fast!
JW1970- Posts : 39
Join date : 2019-02-19
Raymond-P likes this post
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