I have a 1991 camaro rs with a 305 TBI. I have aftermarket heads, exhaust, and a performance chip in it. On the highway, the motor is near running around 5000 rpm at around 75 mph. If anyone would have any suggestion that would be great.

 

Sounds like it either has a numerically higher gear set, transmission that either is slipping or not shifting into OD, or the tach is not correct. Does the engine sound like its turning really fast? Do the RPMs go up a lot when you give it some gas?

 

Factory tach? If so, it is a common problem for that year that it is not reading correctly. Does the engine actually sound like it is running that high?

 

I do have a different rear end in it. I am not sure what the gearing is off hand, but when I give it some gas it doesn't seem like the RPMs are increasing that much. Yes it is a factory tach. I had my tranny looked at, they said they saw nothing wrong with it.

 

Do you have a gps cell phone? That should give you mph.
If you have a stock trans & a 3.08 rear end, at 55 mph the tach should read about 1600.

 

I have ran a gps to see my speed, it off by 1 mph about but rpms are high at 55 mph they read the tach says its at 4200 rpm. I am guessing the tach is wrong. Does anyone know if this is a easy fix?

 

I have the same issue. I set my idle with my timing light which also displays engine RPM. Then looked at the factory tach and it read 2,000 RPM. So I've just been keeping that in mind when driving around. I haven't come up with a permanent solution yet as this car is going to be a project and the factory gauges will be coming out anyway. I know this doesn't help you, but I'm interested to see if someone has come up with an easy solution to this problem as well.

 

Sure....

Ignore it.

It's not an "instrument" anyway; it's just a trim package, designed to "enhance" the "sporty" "image" of the car. It's just supposed to move around and mesmerize the buyer. After all, it's just a 305 TBI; it's not like there's any actual danger of ever running teh engine beyond its mechanical capability anyway, because the induction system won't support it. Honestly. I suspect you could have the car sitting still out of gear, and FLOOR IT AND LEAVE IT THERE, and it would just sit there and run like that until it ran out of gas. More than once if you put more gas in it.

Seriously, search this site for something like "tach circuit board repair", and you'll find what's wrong and what to do.

 

Also just as a curious question if you give it easy gas how many times does your tach drop when accelerating under a light to mid load? 2 or 3 times? should be 3 times if you are hitting overdrive and a slight very slight 4th one maybe if the lockup clutch kicks in.

 

The tach will drop 3 and a very slight fourth one near around 70 mph.

 

ok so at least all gears are working then so as others said tach is just F'd or you have some nice gears in there :-)

 

theres a member name is traviz , he has repair chips for 100 . you have a better chance of being hit by lightning than to have a working tach in a 1990-1992 car his chips are moded so they will not break again . easy fix for $100 look him up I'm getting one when I have an extra buck well worth it .

 

Thanks for the help, and Il check out the repair chips.

 

To things, the cheapest and quickest way to find out if its the tach. is use a timing gun with a RPM feature the way krazeefewl did. The fix for the tach. is replacing a bad resister on the back of it with another.Thats the primary fix that you will find with a search.
As sofakingdom and others mentioned above they are absolutely right about these tach.s Mine was bouncing around so much I just unhooked it. I run 3.42's and with over drive a constant 75mph is no problem using the ear dino.and
I would pull the differential cover if for no other reason than to know exactly what gear ratio I have.