• Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech

1991 50 notchback

  • Thread starter Thread starter Ronn
  • Start date Start date Jun 26, 2005
R

Ronn

New Member
Jun 26, 2005
1
0
1
Jun 26, 2005
#1
  • Jun 26, 2005
  • #1
Hi,
I have a couple of problems with my 5.0.I purchased the car from the original owner in January 2005.It was always garaged never seen rain or snow and only has 10,000 miles.
The first problem is the car has 3.73 gears in rear,I have changed the tailshaft colored plastic tooth gears 3 times in the T5 and still the speedo is off 10mph.When I first started changing the gears the speedo was 15mph off.I went from a white gear to a black to a red.I do know he put 17"wheels and tires P245-45-17".
What to do next?I would appreciate some input.Thanks!!!Ronn
My other problem is that the factory volt gauge only works only when I go fast but then stops working when I slow down.I checked the belt.I just noticed now the fuel gauge is not working also because I ran out of gas.The needle is pegged full.The fuel gauge did work fine.Are they related to the same problem.Is this a known factory recall at the time?Is it because the car sat for years of non use?Is it the whole gauge cluster?
The oil pressure and cooling gauges are working fine right now.Again if you have any answers I would appreciate the input.Ronn
 

HISSIN50

"How long does it take to get help in here?
15 Year Member
Nov 29, 1999
31,179
34
129
Jun 26, 2005
#2
  • Jun 26, 2005
  • #2
Ronn, Welcome to the boards!

The stock alternator will likely have you sitting at 12 volts or so at warm idle. it can discharge at warm idle with accessories on. A parts store will often check the charging system for free. That is a quick and dirty way to test stuff.

The FP gauge is problematic. I would look for a bad sender, grounded sender wire (which pegs the gauge full) or bad anti-slosh module. Others who have delved into the Fuel gauge stuff will have more info. Good luck.
 

bullitstang1313

Member
Jan 21, 2003
713
0
16
Indianapolis / Columbus, Indiana
Jun 27, 2005
#3
  • Jun 27, 2005
  • #3
I had a problem with my fuel level gage and it turned out to be the fuel level sending unit. You can check this to see if it is the problem but it requires dropping the fuel tank. The resistance from the sending unit should be around 30 ohms empty and 200 ohms full. As for the speedo problem, you probably wont be able to find a plastic gear that will compensate for the 17 wheels and 3.73's. Someone recently posted a topic on this where you can get a custom calibration unit, you might try searching.
 

89CopCoupe

Banned
Feb 17, 2004
606
0
0
Post Count City
Jun 27, 2005
#4
  • Jun 27, 2005
  • #4
A 245/45/17 tire is so close to factory height and is not the speedo problem.

'83-'89 T5's have a 7 tooth "drive" gear ... '90-'95 have an 8 tooth.

Being that your car is a '91 model, I'm sorry to inform you they do not make a "driven" gear for the 8 tooth 3.73 car ... the closest gear you can get is the white 23 toofed gear for 3.55s that will read 5% fast.

Maybe buy a new FRPP T5Z w/ 7 tooth drive and a Red 21 to get it accurate ($1200 later) ... or buy a set of 3.55s ($250) or do what the guy above has said

The speedo thing would drive me crazy too ... especially with a low mile notch
 
You must log in or register to reply here.

Similar threads

Z
Right side of cluster not illuminating 91 LX Hatch
  • Zeke1995
  • Jul 21, 2025
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
1
Views
198
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Jul 21, 2025
General karthief
Fox Xtremely high fuel consumption
  • PonyGTrider
  • Apr 11, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • 9 10 11
Replies
213
Views
6K
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- May 9, 2026
PonyGTrider
Resolved 93 Mustang 5.0 - Cranks but does not start
  • dan50
  • Jul 18, 2026
  • Fox 5.0 Mustang Tech
Replies
6
Views
466
Fox 5.0 Mustang Tech Jul 18, 2026
dan50
O
Progress Thread LTD-ing
  • OX1
  • Mar 15, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
8
Views
512
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Apr 6, 2026
OX1
O
F
Fox 1990 Mustang GT 5.0 A9L – Engine suddenly shuts off but immediately restarts when key turned
  • FishermansFriend
  • Aug 9, 2026
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
Replies
16
Views
669
1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk- Aug 30, 2026
General karthief
Share:
Bluesky Email Share Link
  • Mustang Forums
  • 1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-
  • Fox 5.0 Mustang Tech
Menu
Log in

Register

  • Forums
  • What's new
  • Media
  • Resources
  • Contact
  • Sponsor
X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?

X

Privacy & Transparency

We use cookies and similar technologies for the following purposes:

  • Personalized ads and content
  • Content measurement and audience insights

Do you accept cookies and these technologies?