Fuel Gauge and Oil Pressure Gauge - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Full Size Jeep Forum > Fuel Gauge and Oil Pressure Gauge

Stainless Steel Door Hinge PinsPoly Door Hinge BushingsFS: 2007-2013 Jeep Wrangler "HALO" Angel Eye Kit

Reply
Unread 03-19-2013, 09:34 AM   #1
GuyPatterson
Registered User
 
Join Date: Jun 2012
Location: Austin, TX
Posts: 33
Fuel Gauge and Oil Pressure Gauge

Background: I bought my 1990 GW about 9 months ago, and I've slowly been getting her fixed up. The gas gauge has always read empty with the warning light on. My oil gauge has always worked okay, except it would bounce up and down with accelerating/decelerating.

I installed a new sending unit last weekend - install went perfect, but no change. I took out the instrument panel to check the connections and everything looked fine - after reinstalling, my oil gauge is always reads max pressure. Also, the sending unit is correctly grounded.


Any thoughts? Could the wire from the sending unit to the instrument panel be damaged somewhere? Should I try installing a new fuel gauge?

GuyPatterson is offline   Reply With Quote
Unread 03-19-2013, 09:50 AM   #2
timgr
Registered User
1975 CJ6 
 
Join Date: Dec 2012
Location: Medford, MA
Posts: 463
What does the TSM say?
__________________
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D
timgr is offline   Reply With Quote
Unread 03-19-2013, 11:32 AM   #3
RockRollin
"Positive.....I think"
 
RockRollin's Avatar
1990 FSJ Wagoneer 
 
Join Date: Apr 2012
Location: Grand Haven Mi, USA
Posts: 1,073
1st. You can access the fuel sending unit by removing a round inspection plate under the rear seat, drivers side, under carpet. Could be a saturated float.
2nd. Sounds like reverse polarity, not sure. Is it reading high with ignition on, without engine running?
__________________
"I like fun" Edd
Clawed: 90GW, TFI, Streetfire, 3"lift all spring, 31"BFG ATs, working RKE, Edel2131, Holly 1850, mild cam,
05 Renegade OME 927, 947, top plate, JBA 4.5s
RockRollin is offline   Reply With Quote
Unread 03-19-2013, 11:48 AM   #4
timgr
Registered User
1975 CJ6 
 
Join Date: Dec 2012
Location: Medford, MA
Posts: 463
Previous reply was not flip.

Don't know about the '90 TSM, but the other manuals have a procedure for testing the gauge and sender in place. Likely any late-80s Jeep TSM would be suitable.
__________________
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D
timgr is offline   Reply With Quote
Unread 03-19-2013, 12:11 PM   #5
RockRollin
"Positive.....I think"
 
RockRollin's Avatar
1990 FSJ Wagoneer 
 
Join Date: Apr 2012
Location: Grand Haven Mi, USA
Posts: 1,073
I've seen many pages from TSM online, and your right, if you can find the procedure. That's a lot like stopping and asking directions though isn't it
__________________
"I like fun" Edd
Clawed: 90GW, TFI, Streetfire, 3"lift all spring, 31"BFG ATs, working RKE, Edel2131, Holly 1850, mild cam,
05 Renegade OME 927, 947, top plate, JBA 4.5s
RockRollin is offline   Reply With Quote
Unread 03-19-2013, 12:48 PM   #6
timgr
Registered User
1975 CJ6 
 
Join Date: Dec 2012
Location: Medford, MA
Posts: 463
As I recall, a disconnected oil pressure gauge (ie sender open) on these later cars will peg the gauge to the max. So you could have left the wire off or interrupted the connection somehow. I would suspect something physical related to removing the instrument panel, for the oil gauge.

You really need the TSM to test the fuel gauge, in order to know the resistance range of the fuel sender. The sender is very easy to test. Did you test the sender with your multimeter for ohms at min and max before replacing? I suspect not. If the old sender tests ok (ie gives the correct ohms readings at min and max), you can use it as a tester for your gauge. At the gas tank, connect the sender wire to the old sender and ground the base, and move it over its whole range. If the gauge does not move, that indicates the gauge is not functioning.

It's possible that you have a bad connection between the sender and the dash. Remove and reseat any connectors between the sender and the instrument panel. Hook up your old gauge at the tank, and measure the resistance from the gauge wires (disconnected from the gauge) to the sender. You should get the same readings through the sender wire and ground that you got by testing the sender directly.

If the wiring checks out, and the sender tests right, then that leaves the power source or the gauge. Did you test power to the gauge? I don't know whether it should be 12V or some regulated voltege - the TSM will tell you that. But if the wires are ok, you have power to the gauge, and the sender works, the gauge has to be kaput.
__________________
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D
timgr is offline   Reply With Quote
Unread 03-19-2013, 01:25 PM   #7
RockRollin
"Positive.....I think"
 
RockRollin's Avatar
1990 FSJ Wagoneer 
 
Join Date: Apr 2012
Location: Grand Haven Mi, USA
Posts: 1,073
I read this as having replaced the oil sending unit. If the fuel sending unit is tripping the low income light, that tells me it "sending".
Timgr did AMC use a reverse polarity compared to Chrysler. If the oil sending unit is for an earlier "AMC" it would register max with reverse polarity.
__________________
"I like fun" Edd
Clawed: 90GW, TFI, Streetfire, 3"lift all spring, 31"BFG ATs, working RKE, Edel2131, Holly 1850, mild cam,
05 Renegade OME 927, 947, top plate, JBA 4.5s
RockRollin is offline   Reply With Quote
Unread 03-19-2013, 01:54 PM   #8
timgr
Registered User
1975 CJ6 
 
Join Date: Dec 2012
Location: Medford, MA
Posts: 463
Quote:
Originally Posted by RockRollin View Post
I read this as having replaced the oil sending unit. If the fuel sending unit is tripping the low income light, that tells me it "sending".
Timgr did AMC use a reverse polarity compared to Chrysler. If the oil sending unit is for an earlier "AMC" it would register max with reverse polarity.
Reversed from Chrysler? Don't know about that. Somewhere in the '80s the polarity reversed. I think that the polarity prior to that was the same as Stewart-Warner and Ford? With infinite ohms (open) zero and shorted to ground pegged at full.

If you search the archives at IFSJA I'm sure you will find a thread that discusses both the polarity and the values in ohms.

Looking at an older TSM, they have a very nice flow chart for diagnosis of gauge problems. There's no shame in reading the fine manual.
__________________
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D
timgr is offline   Reply With Quote
Unread 03-19-2013, 02:10 PM   #9
RockRollin
"Positive.....I think"
 
RockRollin's Avatar
1990 FSJ Wagoneer 
 
Join Date: Apr 2012
Location: Grand Haven Mi, USA
Posts: 1,073
Quote:
Originally Posted by timgr View Post

Looking at an older TSM, they have a very nice flow chart for diagnosis of gauge problems. There's no shame in reading the fine manual.
No, no shame at all. I tend to look after I'm in deep. Gives me a chance to sit and rest a minute.
__________________
"I like fun" Edd
Clawed: 90GW, TFI, Streetfire, 3"lift all spring, 31"BFG ATs, working RKE, Edel2131, Holly 1850, mild cam,
05 Renegade OME 927, 947, top plate, JBA 4.5s
RockRollin is offline   Reply With Quote
Unread 03-20-2013, 07:19 AM   #10
BJ's Off-Road
Registered User
1979 FSJ Cherokee 
 
Join Date: Oct 2004
Location: Gig Harbor, WA
Posts: 1,379
Fuel sender ohms:

1963-1985 FSJ's use 73 empty and 10 full

1986-1991 were 100 full (maybe 110 -- doing this from memory) and 0 empty
BJ's Off-Road is offline   Reply With Quote
Unread 03-25-2013, 09:40 PM   #11
GuyPatterson
Registered User
 
Join Date: Jun 2012
Location: Austin, TX
Posts: 33
Thanks tigmr and everyone else. Oil pressure gauge is fixed. Also, I tested the new fuel sending unit and it is working correctly and sending a good, correct signal all the way to the fuel gauge (thanks to BJ's Offroad for the new sending unit). I actually tested my old sending unit as well, and it also sends a correct signal all the way to the fuel gauge.

However - the gauge still reads empty and the low fuel light remains on.

I'm convinced it has to be the fuel gauge. I took the fuel gauge out and the needle stays put no matter where you move the it to (unlike the other gauges that slowly move to empty when the power is off).

Anyone know where to get a replacement? I could not find one on BJ's or teamgrandwagoneer. As a refresher - my GW is a 1990.
GuyPatterson is offline   Reply With Quote
Unread 03-26-2013, 09:21 AM   #12
timgr
Registered User
1975 CJ6 
 
Join Date: Dec 2012
Location: Medford, MA
Posts: 463
The fuel "sender" is just a variable resistance. If you replace the sender with a fixed resistor of the proper value, the gauge should read the amount of fuel that corresponds with that resistance.

If you have voltage to the gauge, and the resistance between the sender and ground measures what it should, it's hard to find fault with anything but the gauge. If you are not convinced, remove the gauge and test it on the bench using a battery and your old sender.

Your local Chrysler dealership may be able to get a replacement gauge for you. Otherwise start looking for a used replacement.
__________________
1) '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps. 2) '82 J20 360/T18/NP208/3.73, KOs, 7600 GVWR 3) '75 CJ-6, 304/T15, PS, BFG KM2s, soft top 4) '95 VW Golf Sport 2000cc 2D
timgr is offline   Reply With Quote
Unread 03-27-2013, 11:07 AM   #13
GuyPatterson
Registered User
 
Join Date: Jun 2012
Location: Austin, TX
Posts: 33
Quote:
Originally Posted by timgr View Post
The fuel "sender" is just a variable resistance. If you replace the sender with a fixed resistor of the proper value, the gauge should read the amount of fuel that corresponds with that resistance.

If you have voltage to the gauge, and the resistance between the sender and ground measures what it should, it's hard to find fault with anything but the gauge. If you are not convinced, remove the gauge and test it on the bench using a battery and your old sender.

Your local Chrysler dealership may be able to get a replacement gauge for you. Otherwise start looking for a used replacement.
Thanks. As you can probably tell, I'm new to working on cars. I used my multimeter to test the sender and it read the correct OHMS (or very close to it) and the signal travels all the way to gauge itself.

I tested the gauge like you suggested, and it doesn't work at all. I found a new gauge on Ebay. I'll let you know if it solves the issue.
GuyPatterson is offline   Reply With Quote
Unread 03-28-2013, 08:04 PM   #14
GuyPatterson
Registered User
 
Join Date: Jun 2012
Location: Austin, TX
Posts: 33
Got new gauge! Installed and working great!
GuyPatterson is offline   Reply With Quote
Unread 03-28-2013, 08:22 PM   #15
RockRollin
"Positive.....I think"
 
RockRollin's Avatar
1990 FSJ Wagoneer 
 
Join Date: Apr 2012
Location: Grand Haven Mi, USA
Posts: 1,073
Got to like some closure.
When I got my guage working agian I (with great confidence) let it get to 1/8 tank. Upon leaving the house for the five mile drive to the gas station, became aware that I had a 2-1/2mile driving distance at 1/8tank. Might want to find the true empty mark.
Even at fill up I only put in 16 gallons, so with mine, I don't belive the new pickup is reaching bottom
__________________
"I like fun" Edd
Clawed: 90GW, TFI, Streetfire, 3"lift all spring, 31"BFG ATs, working RKE, Edel2131, Holly 1850, mild cam,
05 Renegade OME 927, 947, top plate, JBA 4.5s
RockRollin is offline   Reply With Quote




Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.