MENU Subscribe to a Magazine
  • Sign in
  • Join

Subscribe to Print or Digital! Save up to 83%

Magazine Muscle Mustangs & Fast Fords
Magazine Mustang Monthly
Magazine 5.0 Mustang & Super Fords
Magazine Modified Mustangs & Fords
  • Print Subscriptions
  • Digital Subscriptions
  • Gift Subscriptions
  • Subscriber Services
  • Back Issues
  • Personalized Cover
  • Subscribe to a Magazine
Item Posts    Sort Order

Erratic gauges

 
bigdiehl
New User
Posts: 26
Joined: 03/12
Posted: 12/06/13 11:50 AM

I have a 1988, 4 cylinder Mustang.  My ammeter gauge works fine, my temp gauge doesn't work at all (stuck on cold), my oil pressure gauge reads full pressure at first then drifts down to low, and my fuel gauge sometimes reads right and other times reads full when I know its not.

My winter project is to make these things all read right.  Is this a typical problem with these cars and is it even possible?  There is no voltage regulator on this model, so are the gauges bad?

I have had this car since new and the fuel and oil gauges have always been erratic, but the temp gauge problem came about much later.  

Post Reply
wayne712222
User
Posts: 103
Joined: 10/13
Posted: 12/06/13 02:25 PM

there is an article in one of the mustang mags here.. on fox body gauge cluster issues..

i think this is at least one of them.. thanks mustang man.. who wrote the article.

http://www.mustangmonthly.com/techarticles/mump_1303_how_to_diagnose_gauge_problems/

a few cars might be column shift..   sometimes the column has to be dropped..

on these cars that have a PRND2L down the middle of the cluster.. please find the cable that attaches the indicator cable to the column.. if you don't remove the screws and free that cable and clamps.. you will break your indicator and will not display in the proper gear..


do run a voltage drop test first..

engine running.. headlights on.. digital volt meter to 20 volts DC..

1. Negative battery post to the positive battery post.. 14.1 to 14.8 volts DC.

2. Negative battery post to the engine.. 0.04 volts DC MAX.

3. Negative battery post to the body.. 0.02 volts DC MAX..

4. Engine block to the Body.  0.02 volts DC MAX..

if you get more than the 4/100ths or 2/100ths of a volt.. you have a bad connection on the ground circuit on that side..

why am i having you check the grounds up front..

the oil pressure sender has only one wire..

the temp sender has only one wire..

the gas gauge only has one wire..

if you have a bad ground up front.. you won't have a good ground to the gauge cluster.. and you won't have enough electrons to operate the circuit as designed.

this test i can perform in a minute to verify the grounds under the hood..  

Post Reply
22fast.ak
User
Posts: 107
Joined: 05/09
Posted: 12/07/13 01:52 AM

Wayne I want to thank you for all the time and information you provide on the forum. BUT several times I have seen you refer to a column shift on a Mustang.  I have looked and looked and there never was such an animal.  Found this quoted on one of the other Mustang boards:

No Mustang ever made has come with a column shifter. They have all been floor shift, from Job 1 in 1964 to today. I have no idea what you've got going on there, but you are either confusing the column lock mechanism (70-up) with a column shift, or you've got a non-Mustang column in there. Also, the neutral safety switch is on the transmission or was in the original shifter, depends on the original transmission...........
__________________


I guess we can put this in the same category as 4-door Mustangs and station wagon Mustangs!  

Mel  

Post Reply
wayne712222
User
Posts: 103
Joined: 10/13
Posted: 12/07/13 08:33 AM

guilty..  but there are other fox body cars that do have column shift..  i never rule anything out..


Mustang 4Door Zps6c393d01  

Post Reply
wayne712222
User
Posts: 103
Joined: 10/13
Posted: 12/07/13 08:43 AM

want to build one of those.. reskin a falcon sedan. and you can have the only other 4 door mustang..

now.. i wonder. did falcons come in wagon shape..

i grew up here in hollywood..  a guy who lived down the street from me.. worked for petersen.  he drove home all kinds of cars..  he brought home the trans am wagon one night..  i was in awe... he complained that the radiator leaked..   he would do parking brake turns in front of my house just to annoy my mom..  i never knew his name.. but i always looked into his parking spot as i went by where he lived..

Transamktype002c  

Post Reply
22fast.ak
User
Posts: 107
Joined: 05/09
Posted: 12/07/13 02:39 PM

Yes there are some REALLY cool customs!  I have seen a Mustang station wagon!  TOTAL custom.  Also a Mustang Pick-up.  There was a 65-66 mustang convertible mounted on an old bronco frame to make it a 4X4 (looked like a monster truck).  I guess Henry Ford was right . . . you can have any way you want (as long as you have the *** and time}!  

Can you imagine a guy sitting in the dealership in '65 trying to build something like these?  Mustangs had lots of options and people could pick and choose so there are some real weird combinations.  Not like today where you have to select a "package" and get all the crap THEY think you need.  AHHHHH,the good ol'e days!  Mel  Grin  Grin  Grin  

Post Reply
bigdiehl
New User
Posts: 26
Joined: 03/12
Posted: 12/11/13 10:00 AM

Thanks Wayne.  Assuming the grounds are good, the article states to ground a sending unit wire to the engine to test the gauge to see if it moves.  Other sources say to do this with a resistor between the sending unit wire and engine.  How do I connect a resistor to the sending unit wire?  where do I get these resistors, at Radio Shack?  

Post Reply
wayne712222
User
Posts: 103
Joined: 10/13
Posted: 12/11/13 11:09 AM

i take it that we are talking about either the temp gauge or the oil pressure gauge..


the sending unit wire is the wire that plugs onto the sending unit..


i normally test gauges in this fashion..

key on.. wire hooked to sending unit.. no reading???

disconnect wire at sending unit.. does the gauge move??

touch wire to engine block.. does the gauge move..

if the gauge moves.. full scale in either direction.  then the wiring and the gauge are working properly.. and there is probably an issue with the sending unit..


there are 2 types of sending units. for both oil and water temp

there are switches that operate the LIGHT..

oil pressure switch is closed at ZERO pressure..  opens the circuit at 3 PSI..
this allows the oil light to turn on when the oil pressure drops to ZERO or almost ZERO..

the oil pressure sending unit is a variable resistance unit.. it will change the resistance when the oil pressure changes.

similar features on the temp sender..

coolant temp switch is OPEN circuit below about 235 or 245F closes at that temp to turn on the HOT light...

coolant temp sender is a variable resistance to change the gauge..

on either types of sender.. if you have gauges.. no reading.. pull the wire.. key on.. the gauge may move or not.. ground the wire and the gauge should go the full range the other way... again this proves the gauge and wiring is hooked up and working..


do you have an ohm meter.. .

set it to 2K OHMs scale..

oil pressure switch
engine off..  do you have close to 0 ohms of resistance to the engine block..
if you start the engine.. it should go to OPEN or OL.. on the display.
if you have variable resistance.. then its a sending unit for a gauge..

engine temp switch..

engine cold.. should be an OL or OPEN measurement at 200 or 2K ohms.
you should not try to over heat the engine to test the other range.
you can remote the sender and carefully boil some straight coolant on the stove.. to get it close to 250F.. water will never reach this temp .. boils at 212..

now.. if you get variable resistance.. you have a temp sender..

the reason i wanted you to do the voltage drop.. is the ground side is half the circuit.. if the engine is not grounded to the firewall.. and the gauges not grounded to the firewall.. you may only have half a circuit and that won't operate the gauge or the voltage regulator to supply pulsed power to the gauge..  

Post Reply
wayne712222
User
Posts: 103
Joined: 10/13
Posted: 12/11/13 11:20 AM

88 mustang 5.0 temp sender for the gauge.

set your ohm meter to 200 OHMs.

76 OHMS AT 100^F (38.8^C)
24 OHMS AT 220^F (104.4^C)

measured between the terminal on the end of the sensor and the engine block..

 

Post Reply
bigdiehl
New User
Posts: 26
Joined: 03/12
Posted: 12/11/13 11:40 AM

So you don't think grounding the sending unit wire directly to the engine is a problem?  The manual says to connect a resistor between them first to avoid possible damage to the gauge.  That's why I was asking how one connects one of those little resistor things you see at Radio Shack to the sending wire.  They don't explain that part.  

Post Reply
wayne712222
User
Posts: 103
Joined: 10/13
Posted: 12/11/13 06:51 PM

bigdiehl
New User | Posts: 22 | Joined: 03/12
Posted: Today 09:00 AM

Thanks Wayne.  Assuming the grounds are good, the article states to ground a sending unit wire to the engine to test the gauge to see if it moves.  Other sources say to do this with a resistor between the sending unit wire and engine.  How do I connect a resistor to the sending unit wire?  where do I get these resistors, at Radio Shack?  




but did you spend the 2 minutes and run the voltage drop test below???



voltage drop test

engine running.. headlights on.. digital volt meter to 20 volts DC..

1. Negative battery post to the positive battery post.. 14.1 to 14.8 volts DC.

2. Negative battery post to the engine.. 0.04 volts DC MAX.

3. Negative battery post to the body.. 0.02 volts DC MAX..

4. Engine block to the Body.  0.02 volts DC MAX..

if you get more than the 4/100ths or 2/100ths of a volt.. you have a bad connection on the ground circuit on that side..


post results..


1...____________

2...____________

3...____________

4...____________

you would not believe how many fox body cars and hundreds of others that i have  found ground issues on over the past 30 years..

i found one chevy truck.. that has 8.5 volts between the engine and the body.. on test 4..  those gauges were all over the place..

don't stand and wonder why the circle saw does not work..  when the cord is either extension is cut in half..  or its dangling out of the outlet..  or that the wires have fallen off the poles out in the back yard. i am not mad.. or yelling.. run the test.. it takes only a few minutes.. try it on a different car also..


as for shorting the sensor wire to the engine.. thats only for a few seconds..  not long enough to hurt the engine.. if you are alone..  do it key off.. short it.. turn the key on and see what happens.. does it move.. give it 5 seconds.. turn the key off..  

Post Reply