Guages not working
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New User
Joined: Feb 2005
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Guages not working
I have a 90 ford f-150 with a 302 and i just put a different 302 in it. After the swap the oil pressure guage and temperature gauge quit working. Both of these guages worked in the truck i took the motor out of. I tried replacing the sending units from the original motor and that didnt do anything. Does anybody know why this problem occurred or how to fix the problem. Or should i just put different guages in?
Tuned
Joined: Feb 2003
Posts: 495
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From: Cincinnati, Ohio
Make sure you have the engine properly grounded to the vehicle. Sounds silly but if for some reason the engine block isn't grounded properly, gauges that utilize resistance based sending units won't work if their bases aren't grounded. If you disconnect the wire at the sending unit and ground it against a known good ground the gauge should top out. If it doesn't then there is something wrong with the gauge or the wire from the gauge to the sending unit. If it does then either the sending unit(s) is bad, not likely in two cases, or the sending unit(s) is missining its ground.
John
John
More Turbo
Joined: May 2004
Posts: 544
Likes: 8
From: BC, Canada
Another thing to check is the fuse for the gauges, fuse #18 (in a '90) is for the oil, temp & fuel gauges. Check the gauges like jtmerritt said, ground the wire at the sender and gauge should go full scale. ...Terry '90 F150 302
Junior User
Joined: Apr 2002
Posts: 78
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From: Monroeville, AL
If the sending unit is missing its ground, what should I do. I'm having the smae problem with my Autometer trans temp gauge. I've even run the ground on the back of the gauge to the battery ground and it didn't help. How do I ground the sending unit?
Thanks,
Jim
Thanks,
Jim
Tuned
Joined: Feb 2003
Posts: 495
Likes: 0
From: Cincinnati, Ohio
If you ground the wire to the gauge, the gauge should top out. If the gauge doesn't top out then either your ground isn't good or you don't have the gauge wired correctly or the gauge is bad. Are you sure you have the gauge wired correctly? The autometer trans gauge, if it is like my Autometer Z series, requires a 12v feed to power the gauge and the sending unit feed. The sending unit should ground by the threads into the tranny unless you have too much teflon tape on the sending unit threads.
John
John
Junior User
Joined: Apr 2002
Posts: 78
Likes: 0
From: Monroeville, AL
Yes, mine is an Autometer Z series. I sent the gauge back and Autometer said it tested OK. I get movement up to 100 degrees when I start the truck, but it goes no further. Long story, short... I broke my first sending unit trying to stop a leak (didn't use teflon tape) and had a shop install the second sending unit...hasn't worked since. That's when I sent the gauge back. Autometer sent another sending unit (free!). The gauge will top out when I ground the sending unit wire, just didn't know if I could run a separate wire from the sending unit to a ground to ensure that it was grounded. I'm gun shy about taking the sending unit out after my experience with breaking the first one!! I fear that the sending unit is bad.
Jim
Jim
Tuned
Joined: Feb 2003
Posts: 495
Likes: 0
From: Cincinnati, Ohio
I don't know how much torque you are putting on the sending unit but I wouldn't go much further than just beyond where it won't leak. That probably is about 20 ft lbs. Best way is to take a 3/8 ratchet and socket and hold the wrench with your index finger over the ratchet mechanism. This will keep you from over torquing the sending unit. I would be reluctant to use a sending unit that doesn't match the gauge. Also, I used a thin coat of RTV on my sending unit and it worked fine. I don't like using teflon tape on engines or trannys because of the chance a piece can get loose and float into someplace causing problems.
John
John
