1991 50 notchback

[Ronn]

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]

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]

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]

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