Basic Troubleshooting for CJ gauges
Contents
1. Basic Troubleshooting for CJ gauges Basic Troubleshooting for CJ gauges By John Strenk ae Click on Speedometer for a quick troubleshooting guide The Speedometer gauges Were to start Read me first You need some tools Go out and buy yourself a 12 volt test light for testing circuits A DVM Digital Volt Meter would also be helpful It s really kind of hard to check anything without these instruments These instruments will go a long way in keeping your jeep running in the future In this part of the test the clip lead from the test light 1s connected to the side of the battery or a good known ground How ca you tell if ites a good ground point Attach the clip lead of the test light to the side of the battery and touch the tip of the probe to were ever you want to use as a ground point If it lights up then the ground is good Now connect the test clip to this point Check the fuse Ites labeled eIGN LPSe and is either a 3 amp or 15 amp fuse depending if you have an EEC Electronic Engine Control computer or not It might be blown Use your test light and touch both ends of the fuse If there is power on both ends of the fuse then it is OK Make sure the ignition is in the sON s position http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 1 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges Now pull the red wire off the eI terminal on the Fuel Gauge2. J gauges 12 15 Volts E R1 F A Fuel Temp RA Gauge Gauge R gt R3 Temp En Fuel Lexel PA Sensor alia sane Let s see what happens when you loose a ground for your gauges You may have been driving your jeep for a few years now and you have had intermittent problems with the lights not working and stuff but you don t eally think about what can be happening with your gauges Normally if you loose a ground with a radio or a light it just stops working but this is not so with the gauges The fuel and temperature gauges are run off a current limiter located inside the fuel gauge When you loose your ground to the dash or speedometer housing there is no longer any current regulation in the circuit Now the gauges can pull as much current as it can until it burns up This will over heat the windings on the bimetallic strips on the gauges and windings in the fuel level sensor Here are some pictures of the damage I found from over heating The first picture is of the windings on the gauge You can see were the protective varnish over the wire is urning and flaking off The other two pictures is of the fuel level sensors and they had burnt the wire mount apart One has the windings completely missing and the last has the mount burnt away but still connected So if you have a poor ground on your dash and a full tank the sensor will get hot enough to burn away the sensor How long will it take I found out about 2 secon
3. Liquid Electrical Tapes that you can spray over the area to protect the ground connection after you are done eSome fasteners like a star washer take advantage of the nickel plating The sharp points will break through the oxide layer as the fastener tightened Using a flat washer might not break thru the oxide layer I like to use Kep nutse that have the star washer permanently attached to the nut This makes it easy to install all the right fasteners at one time Iell use these nuts to attach the speedometer housing and any terminal connections All the gauges I have tested have a 10 32 thread e e DON T INSTALL ANY NEW PARTS UNTIL YOU ARE VERY SURE YOU HAVE A GOOD GROUND FOR THE SPEEDOMETER Testing the Gauges OK you have tested all the grounds Every thing now looks good It s time to test the gauges to see if they are urned out You are going to have to put down your Test Light and break out the DVM for these tests If your a contortionist you might be able to still test the gauges in the dash but it is a lot easier to pull the speedometer out now The first thing we are going to do is test the windings of the wires inside the fuel gauge and the ground connection of the gauge to the speedometer housing Label all the wires on the gauges so you will know were to put them back again First we will check From the A terminal to the I terminal The reading should be less than O ohms If this is reading over range or around 50 ohms th
4. and touch inside the plug with the test light and see if you are getting power to the connector If you have power then replace the connector on the I terminal Now If you don t want to take the speedometer out yet your going have to lay on your back to do the following test Connect your Test light to a good ground Then touch the probe of the test light to the I terminal on the back of the Fuel gauge If the light come on steady then your OK so far If the light doesn t come on steady then I would squeeze the plug together a little It may not be tight enough on the stud Then Touch the probe to the A terminal of the fuel gauge It should flash at full brightness about 1 a second If it stays bright continuously then you have a problem with the current regulator It could be as simple as a pad ground or a stuck contact point on the regulator If it doesn t light at all then you probably have a problem with the points on the current regulator or a broken connection ea TO os http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 2 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges Finally touch the probe to the S terminal If the Fuel level sending unit is connected and grounded properly the light will flash but be considerably dimmer The more full the tank is then the dimmer the light If the test light is fully bright as in testing the A terminal then there is somethi
5. are no over range meaning open connection then the sensor is probably OK My temperature meter heated up faster than the CJ s temperature sensor so there is a kind of lag in the readings About a 100 1 difference in mass The actual resistance vs Gauge display is as follows oy gt NOT N Cy 0 Temp gauge calibration C cold 130 degrees 73 ohms beginning of band 171 degrees 36 ohms Top of band 242 degrees 13 ohms H DOU ncecosenatsccconcesscoueee 270 degrees 9 ohms Fuel Level Sensor Yep you can still use your test light again Same test as with the temp sensor Finding a good ground back here may be a little tricky so you may want to run a wire from the post of the battery to the test light clip Pull the wire off the fuel level sensor and touch the probe of the test light inside the plug The light should flash orightly as with the temp sensor If it doesn t then you have a problem with your wiring harness Connect the olug back on the fuel level sensor contact Now touch the test light probe to the contact post The light should continue to flash but depending upon how much gas you have in the tank it could be very dim The more gas in the tank the dimmer the flashing light If the light is still flashing as brightly as you got when just touching inside the probe then you have a problem with the sensor or a ground or just be almost out of gas Touch the test light probe to the top of the
6. ds Let us not forget this is inside your fuel tank You don t see his effect so much on the temperature side as the resistance 1s still plenty high at normal operating temperature If you donet have a good ground on the speedometer housing then check the dash for a good ground If the dash doesnet have a good ground then check the tub If you find a bad ground fix the problem first Be sure to scrape away any paint and rust before you correct the bad ground Donet depend upon the thread of the fastener to provide a good ground Use a file or a grinding wheel to get a good contact After you have secured the http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 5 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges ground paint over it to protect the metal from corrosion A lot of electrical parts in the jeep have a nickel plating This protects the metal from corrosion by developing a thin oxide layer over the surface This oxide layer is easily broken with minimal pressure allowing a good electrical connection such as when you slip a lug over a terminal Trouble is a deep scratch can break through the coating allowing the metal to rust and it will spread out under the coating If you have to clean a surface of a nickel plated device like the speedometer housing try cleaning the area with a brass brush first so you donet scrape away the plating A place like Radio Shack sells a product called e
7. eel drive Hardware for assistance and equipment to allow me to create this article and to my many friends at Jeeps Unlimited CJ Forum who ran to their Jeeps and Factory Service Manuals to help me get information on CJes http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 10 of 10 1 2 2009 5 27 51 PM
8. en you have a contact problem The Contact points on the regulator may be pitted and not making good contact You will then have to fix this problem or buy a new gauge This will call for some open gauge surgery Next we will check from A to S We are measuring the resistance of the heater coil for the gauge itself It should read between 19 21 ohms In some after market gauges I have seen these values a little lower If it 1s O ohms of over range then again you have a problem Now we will check from S to I Again this is checking the resistance of the heater coil for the gauge It should be in the range of 19 21 ohms In some after market gauges I have seen these values a little lower If it is 0 ohms of over range then again you have a problem This test we start looking at the ground connection from the gauge too the speedometer housing We are going to measure from the A terminal to the speedometer housing The resistance should read around 49 to 51 http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 6 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges ohms We are reading the resistance of the heater wire on the regulator this time If it reads over range then we have a broken wire and the regulator is not working If it reads O ohms then you have a short but you would have blown a fuse if this was the case If you show no resistance then your regulator wasn t workin
9. end of the clip lead to one side of the resistor Connect another clip lead to the other side of the resistor and connect that lead to ground Turn the ignition ON and watch and see were the needle comes to a rest It may take 30 seconds to settle down The various resistors the Factory Service Manual recommends are as follows Temp gauge calibration C Cold erener 130 degrees 73 ohms Beginning of band 171 degrees 36 ohms Top of band 242 degrees 13 ohms FCO E 270 degrees 9 ohms http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 7 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges Fuel gauge calibration Empty 73 ohms Half 23 ohms Full 10 ohms If you have any problem with the Fuel or Temperature gauges go to my Speedometer repair article Testing the Sending Units Temperature Sensor OK grab your test light again Connect your clip lead to a good ground Turn your ignition switch to ON Might be a good idea to remove the plug from the ignition coil so you don t burn something up Make sure you have all the wires connected to the gauges correctly Pull the wire off the temp sensor and touch the tip of the test light to the inside of the plug The light should flash brightly just like it was doing before If the light is not flashing or ON then you have a problem with your wiring Check the fire wall connector plug to see if the contact
10. fuel level sensor and see if it flashes If it does flash then you have a bad ground Usually these are very rusty so to double check the ground connect the probe to the side of the battery and touch the probe to the top of the fuel level sensor It it lights then you have a good ground If you have the plug on the sensor and it flashes very bright and you have a good ground then you have a problem with the fuel level sensor Now you will need to pull the sensor out and inspect it and test the resistance at various positions Connect a DVM to the sensor and using the Ohmes scale measure the resistance Empty 73 ohms 1 2 Tank 23 ohms Full tank 10 ohms Its going to be hard to accurately duplicate these position and values so if your close and there are no over range or OR meaning open connection then the sensor is OK http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 9 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges A little WARNING How long does it take to burn up a fuel level sender with a bad regulator or a bad ground eeeeee About 2 seconds L Now this sensor only reads about 20 ohms at full so it will only register a little over 1 2 a tank L Check your Grounds First I hope this article has been of some help to you If you have any comments or suggestions please contact me at Johns76cj5 hotmail com Many thanks to Jason a k a CJSEXER at 4 Wh
11. g and you have been supplying full current to your sensors Plan on inspecting the fuel level sensor later Lastly we are looking at the ground connection from the gauge too the speedometer housing We are going to measure from the I terminal to the speedometer housing The resistance should read around 49 to 51 ohms We are reading the resistance of the heater wire on the regulator this time If it reads over range then we have a broken wire and the regulator is not working If it reads O ohms then you have a short but you would have lown a fuse if this was the case If you show no resistance then your regulator wasn t working and you have een supplying full current to your sensors Plan on inspecting the fuel level sensor later Some of the after market fuel gauges read as low as 36 ohms for this test and still work properly In summery S to ground 68 to 72 S toIl 19 21 Sto A 19 21 ItoA 0 As long as we are under there you can check the Temp gauge Only one test From A to S on the Temp meter It should read 12 21 ohms Same as the Fuel meter from S to A Checking Gauges with resistor load The factory service manual recommends checking the gauges with various resistors to insure the accuracy of the meter movements I would recommend getting a couple of test leads with clips to attach the resistors Pull the plug Off the S terminal of whatever gauge you are testing and connect on clip lead to this point Connect the other
12. ng wrong with the Fuel Level sensor and or wiring ground Still not working Then letes continue Good Grief Grounds The major complaint that our gauges don t work is no surprise in a 20 year or so vehicle If you haven t gone through a major overhaul lately you probably have a grounding problem Maybe your gauges are working OK for now but maybe you ought to inspect your jeep anyway The first thing you should check if you are having electrical problems in a CJ is the ground connection There are 3 major ground parts in a CJ The tub or body the engine and the frame These should all be grounded together in some fashion Usually the post on the battery grounds to the block and the block 1s grounded to the frame with a jumper wire between the frame and the block on the driver side engine mount The tub can be conveniently grounded if you have a auxiliary wire running off the battery terminal Just connect it to the body nearby http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 3 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges Fuel Teme m i Temp sensor Fueltank This is our simple schematic of the basic wiring for our gauges The Fuel and Temperature gauges are inside the speedometer housing and has it s ground The volt meter and the oil pressure gauge have there own ground The fuel level sensor is grounded at the frame with a wire The oil pressu
13. re sensor and temperature sensor ground to the engine block You might want to keep the numbers of Teflon thread sealer to a minimum to make sure the sensors are grounded to the block properly If you have had a leak in your window for a little while you could of started to rust your speedometer Rust is a good way to ruin a good ground It will grow right under what is normally a good ground connection and separate the two surfaces Rust as it turns out is a poor conductor It s bad enough for low current situations like with the gauges but even worse with high current applications like a starter or winch Well lets get to testing the grounds before we begin anything else Take your test lights and connect the clip lead to the side on your battery Touch the probe to the side of the battery to be sure the light is working in the test light Don t laugh I ve had this problem before Now go have fun and touch the probe to such things as the engine block and frame and tub light housings You may have to scrape away some paint or rust to get a good connection If the light doesn t light then you have a bad ground For the gauges I would check the dash to see if it s grounded and then the housing of the speedometer If this is not grounded then you are going to have problems with your gauges http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 4 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for C
14. s are corroded or loose Now put the plug back on and touch the probe to the contact were the plug connects The light should still flash put a little dimmer now depending upon the temperature of the engine The colder the engine the brighter the test light If it flashes as brightly when it was not connected then you have a problem with the temp sensor or the ground on the engine Touch the probe to the side of the temp sensor to be sure it is grounded If it lights up and flashes then it is not grounded Some times people put Teflon tape to seal the threads to much can insulate the temp sender from the block If you have the plug on the sensor and it flashes very bright and you have a good ground then you have a problem with the temperature sensor Now you will need to pull the sensor out and inspect it and test the resistance at various temperatures Connect a DVM to the sensor and using the Ohms scale measure the resistance I put mine in a pot of water and heated it There was a temperature meter to check the temperature of the water This is very crude but here is a sample of what I read with mine Temp F Oa Nw eo o o o 2 o a j 40s http home roadrunner com john strenk Gauge 20web 20page basic_troubleshooting_for_cj_gau htm 8 of 10 1 2 2009 5 27 51 PM Basic Troubleshooting for CJ gauges IN 170 65 8 200 Its going to be hard to accurately duplicate these temperatures and values so if you close and there
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