HELP 1991 gt problems

[1991stanggt]

First of all I'm 18 and I have a 91 gt with a full exhaust, intake, and underdrive pullies and 74 k miles(one of a few kids with a real american muscle car). So far I've been having the follow problems: my voltage indicator goes up and down with the rpms of the engine...a few months ago i bought a new battery thinking the old one was dead but that didnt help...it still does the same thing...even if you push both window buttons at the same time you can see it go down. I'm assuming its an alternator problem but any suggestions/help would be appreciated. Also, my horn and cigarette lighter don't work and everytime I try to replace the fuse it blows...any ideas??? One more problem is my check engine light started coming on so I bought a code scanner...It came up with Throttle Position Sensor which seems right because sometimes if I give it gas and let off it still gives it a little more gas and revs a little on its own...ANY help on any of these would be appreciated greatly.

Thanks a ton


Matt

 

[sleeper89]

do you have a big stereo system? if yes you likely need to upgrade to a 130amp alt from the sn95 stangs. this is really a good solution even if you do not have a big stereo because the stock alternator is pretty weak at its job when running just the factory accessories such as lights/defrost/stereo, especially after 13-16yrs of service. start the engine and test the voltage across the battery posts. if the alt is still good it should read ~14.4v.

for the fuse you will need to do a little searching to find where the circuit has shorted out (ie power running directly to ground bypassing the "load").

put a voltage tester on your tps with the engine off. it should increase smoothly from about .999volts up to (don't remember....).

hope that helps, if you have more questions you can pm me and i'll try my best to lead you in the right direction.

-steve

 

[lqqknloh]

my horn cigarette fuse kept blowing. there was a penney down on the bottom where you put the lighter in.could hardly notice it. who knows could be the problem wouldnt hurt to check.

 

[bradranger]

replace it

I would replace the tps, I had it go bad and its not a fun day with it acting up. If you voltage is up and down like a lot of mustangs with a stock alternator, you will be ok but if you put a sound system in you will probaly need to upgrade. I need to myself.

 

[rowdie- stang]

I just took the stereo out of my car.... I have a pa performance 200 amp alternator if anyone is interested. Make me an offer!

 

[1BAD89GT]

"First of all I'm 18 and I have a 91 gt with a full exhaust, intake, and underdrive pullies and 74 k miles"

Is the alternator under driven also?If so thats why your voltage drops at idle and picks back up with higher rpms.

 

[speed1972]

put a voltage tester on your tps with the engine off. it should increase smoothly from about .999volts up to (don't remember....).

It should max out at 5 volts with the throttle wide open.

As far as replacing this piece, I wouldn't do it yet. I think you may be getting a code because of the alternator. Replace the stock (weak) one with a 3G alternator like a 130amp off a 94-95 model. You'll have to modify a couple parts but it is a simple process...just search on here and you'll find a wealth of knowledge. Your voltage problem will go away and very possibly your tps issue....
Larry