stonehands Posted October 21, 2019 Share Posted October 21, 2019 Hello all, Installed a new used gauge cluster. 1986 Comanche 2.5 5 speed manual. put the one with larger numbers and fat needles in. replaces water temp and oil pressure switches with new sending unites. removed fuel pump and checked the sending unit in it. 0-90 ohms. All gauges move but do not read correctly. Oil shows 75 psi running cold. Fuel shows empty with low fuel light on with 7 gallons in tank. Tack reads about 400 rpm at idle (i think it should be 7-800 ish) Never ran car long enough to check temp. If i but all sending unit wires at sending unit to ground all gauges go to zero with key on. unplug all sending units with key on gauges go to 100. (using 0 to 100 for ref.) I get 12v to cluster via white with black line. Only seeing about 6-7 volts at sending units. Is this the bad ground under dash issue or something else? Thanks for reading my dribble. Link to comment Share on other sites More sharing options...
Warren Mohler Posted October 21, 2019 Share Posted October 21, 2019 13 minutes ago, stonehands said: Hello all, Installed a new used gauge cluster. 1986 Comanche 2.5 5 speed manual. put the one with larger numbers and fat needles in. replaces water temp and oil pressure switches with new sending unites. removed fuel pump and checked the sending unit in it. 0-90 ohms. All gauges move but do not read correctly. Oil shows 75 psi running cold. Fuel shows empty with low fuel light on with 7 gallons in tank. Tack reads about 400 rpm at idle (i think it should be 7-800 ish) Never ran car long enough to check temp. If i but all sending unit wires at sending unit to ground all gauges go to zero with key on. unplug all sending units with key on gauges go to 100. (using 0 to 100 for ref.) I get 12v to cluster via white with black line. Only seeing about 6-7 volts at sending units. Is this the bad ground under dash issue or something else? Thanks for reading my dribble. sounds like ground problem since all gauges are affected, I had a XJ with same condition, ground strap from cyl. head bolt to firewall was not there made one up all ok Link to comment Share on other sites More sharing options...
Pete M Posted October 21, 2019 Share Posted October 21, 2019 was your cluster out of another 4cly Jeep? are you able to adjust the tach? Link to comment Share on other sites More sharing options...
stonehands Posted October 21, 2019 Author Share Posted October 21, 2019 it was out of an XJ 4.0 not tach adjustment. Link to comment Share on other sites More sharing options...
eaglescout526 Posted October 21, 2019 Share Posted October 21, 2019 You will need to adjust the tach to read the 2.5L properly. As for the other gauges you will need to keep at it and see why their readings are off. Link to comment Share on other sites More sharing options...
Eagle Posted October 21, 2019 Share Posted October 21, 2019 20 minutes ago, stonehands said: it was out of an XJ 4.0 not tach adjustment. Well, that explains why the tach is wrong. The tach counts firing impulses. A 4-cylinder has 2 impulses per revolution, a 6-cylinder has 3 impulses per revolution. Say your 4-cylinder is idling at 900 RPM -- that's 1800 impulses. Now divide by 3 -- a 6-cylinder tach will show 600 RPM. Link to comment Share on other sites More sharing options...
stonehands Posted October 21, 2019 Author Share Posted October 21, 2019 I read another article that said the gauges output 5v. Is that correct? Link to comment Share on other sites More sharing options...
Ωhm Posted October 21, 2019 Share Posted October 21, 2019 5 hours ago, stonehands said: I read another article that said the gauges output 5v. Is that correct? No. Power for gauges is B+ (12vdc). Link to comment Share on other sites More sharing options...
stonehands Posted October 21, 2019 Author Share Posted October 21, 2019 So i unplug wire from oil pressure sensor. I then put a meter on it to ground with key on. It reads 6v. Is that correct? I get 12v at the Gauge Cluster plug that feeds the cluster. Link to comment Share on other sites More sharing options...
Ωhm Posted October 21, 2019 Share Posted October 21, 2019 Good question. Don't know, but that could be a valid reading. Oil gauge has three (3) legs. B+ in (feed) Through gauge, through sending unit, to ground (This wire is where your reading 6vdc) Through gauge to ground Link to comment Share on other sites More sharing options...
stonehands Posted October 21, 2019 Author Share Posted October 21, 2019 yes reading 6v to sending unit. Can a bad ground to dash for the gauge cluster cause this? Link to comment Share on other sites More sharing options...
Ωhm Posted October 21, 2019 Share Posted October 21, 2019 21 hours ago, Warren Mohler said: sounds like ground problem since all gauges are affected, I had a XJ with same condition, ground strap from cyl. head bolt to firewall was not there made one up all ok Check this and do Cruisers tip. http://cruiser54.com/?p=110 Link to comment Share on other sites More sharing options...
Eagle Posted October 21, 2019 Share Posted October 21, 2019 Do you have an ohmmeter? With the gauge lead disconnected, check the resistance of the oil pressure sender with the engine off. Then start the engine and check the resistance again. Report results. Link to comment Share on other sites More sharing options...
Eagle Posted October 21, 2019 Share Posted October 21, 2019 8 hours ago, stonehands said: it was out of an XJ 4.0 not tach adjustment. What year XJ? If it's a Type 2 cluster, the tachometer is adjustable. Link to comment Share on other sites More sharing options...
cruiser54 Posted October 22, 2019 Share Posted October 22, 2019 Do the ground upgrade as suggested. Also unplug and plug back in the 2 connectors on the cluster. Contact cleaner at the same time. If it gets to this point, here's some references. Link to comment Share on other sites More sharing options...
stonehands Posted October 22, 2019 Author Share Posted October 22, 2019 I believe it was out of an 89 - 90. I adjusted the tack and it works now. There is a wheel on the back and top of the tach (top left looking at the back). I drilled a hole in the top of the cluster back. Centered about 1/2" in from back edge an just clearing the closest bulb socket on the back just to the left of the gauge. I can get a pick in an turn it. turned all the way clock wise. I will do the following: (report back when complete) -Additional ground to dash -Pick up a oil pressure tester and check with it. -Test oil pressure sending unit and compare to above still not sure why i only get 6V to oil pressure sending unit. Getting 12v to fuel level sending unit. no breaks or shorts in blue wire from sending unit to C101. C101 to cluster connector is where i get the drop. Cruiser54 do you have calibration info for fuel sending unit. I found my windings in the slide had a break so i took one off an old fuel pump/sending unit and replaced it. I get readings as i move the float but with 8 gallons in tank it is on E with low fuel light. Float may not be adjust correctly. That thin copper prong that slides up and down the windings got bent. I straightened it but may not be where it is suppose to be. Link to comment Share on other sites More sharing options...
Eagle Posted October 22, 2019 Share Posted October 22, 2019 For your year, I believe the fuel gauge is also 0-88 ohms, same as the oil pressure sender. Zero ohms would be empty, 88 ohms would be full. Link to comment Share on other sites More sharing options...
Ωhm Posted October 22, 2019 Share Posted October 22, 2019 3 hours ago, stonehands said: Getting 12v to fuel level sending unit. Was this voltage measurement taken on C139_B? 3 hours ago, stonehands said: no breaks or shorts in blue wire from sending unit to C101. C101 to cluster connector is where i get the drop. C101??? Do you mean C100_C6? Link to comment Share on other sites More sharing options...
stonehands Posted October 23, 2019 Author Share Posted October 23, 2019 For fuel gauge: Voltage read on pin B (tan wire) at plug to ground (blaok wire) Took out fuel pump-sending unit. It works but, doesn't move needle off empty until about halfway up. Once all the way up gauge reads full. Half of the float travel does nothing for the gauge. Continuity check with meter verifies reading of gauge. 0 to 90 ohms for full travel but, very little at bottom 1/4 of movement then starts to go up faster after that. must be in the winding on the slide is off. For oil gauge: Didn't get to mess with it last night. Wire checking was from sending unit to firewall engine side (12v). Then from firewall to cluster connector (6v).must be something under the dash. Link to comment Share on other sites More sharing options...
Ωhm Posted October 23, 2019 Share Posted October 23, 2019 48 minutes ago, stonehands said: For oil gauge: I don't get the increase in voltage between firewall and cluster (6v) to between firewall and sending unit (12v). Should be the same wire. Need four (4) measurement on the same connector. Disconnect C105, on the Engine Harness side, measure voltage at C105_B with both the KEY OFF and the KEY ON. On the Alternator Harness side, measure voltage at C105_B with both the KEY OFF and the KEY ON. Link to comment Share on other sites More sharing options...
stonehands Posted October 23, 2019 Author Share Posted October 23, 2019 i put battery power to one end and meter to ground the other. The fire wall connection was pulled apart. So power to pin at fire wall engine side connection then meter to ground at sending unit wire connector. 12v Then power to pin at fire wall cab side and meter to ground at cluster connector. 6v Does that help. just checking wires for breaks or shorts. When i checked the whole circuit i got 6v. This prompted me to check each side of the firewall connections to find the side $#!& went south. Cab side. Link to comment Share on other sites More sharing options...
Ωhm Posted October 23, 2019 Share Posted October 23, 2019 1 hour ago, stonehands said: So power to pin at fire wall engine side connection I'll take that to mean the plus side of the voltmeter. 1 hour ago, stonehands said: then meter to ground at sending unit wire connector. I'll take that to mean the negative side of the voltmeter was ground near the sending unit and not the sending unit wire. 1 hour ago, stonehands said: So power to pin at fire wall engine side connection then meter to ground at sending unit wire connector. 12v If this circuit with firewall connector (C100) disconnected, should not have 12v on it. If so, does it have 12v with both the KEY OFF and the KEY ON? Link to comment Share on other sites More sharing options...
stonehands Posted October 23, 2019 Author Share Posted October 23, 2019 There is no power in the circuit until i put it there. I disconnect and put 12v from battery at one end and meter to ground at other end. I am only going from end of wire to end of wire. not connected to sending units. I am not a literary master so pardon my poor explanation. Link to comment Share on other sites More sharing options...
Ωhm Posted October 23, 2019 Share Posted October 23, 2019 43 minutes ago, stonehands said: I am not a literary master so pardon my poor explanation. CC Forum is a great place for solving problems, just remember sometimes your questions are answered with more questions. 43 minutes ago, stonehands said: There is no power in the circuit until i put it there. I disconnect and put 12v from battery at one end and meter to ground at other end. I am only going from end of wire to end of wire. not connected to sending units. This style of testing is more of a continuity check from one end of a wire to the other end. You showed this wire is good from end to other end. With everything connected, except the wire at the sending unit, your reading of 6v maybe a good reading. You need to know if your cluster is grounded properly. Need a ohmmeter. Link to comment Share on other sites More sharing options...
Ωhm Posted October 23, 2019 Share Posted October 23, 2019 Download the 88 Electrical Manual to your hard drive. Your 1986 will have 99% of the 1988. Helps explain Connector numbers and Cavities callouts. Allows everyone to be on the same page. https://comancheclub.com/topic/12083-electrical-manual/ Also, when checking connectors, check where the wire meets the terminal. Can be a problem area. Link to comment Share on other sites More sharing options...
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