So I've been out of the country for about a month. I took my 3.1 out for a drive the other day and noticed thr RPMs seem to be running rather high compared to what I remember.

At 50mph im at about 3100RPMs in 5th gear, and pretty sure it used to be around 3100 at 70 mph instead its now around 4000.
Any ideas to what the problem could be?
Idle seems to be fine and normal. Higher than normal rpms only while driving. No problems shifting or with the trans jumping out of gear.

3.1 v6, 5 speed. Transmission, clutch and pressure plate were all replaced about a year and a half ago.

Thanks!
Josiah

 

Since you have no torque converter to have failed , and nothing done to the car recently , my guess is that it's your tachometer that has failed (super common problem on our cars) and that the engine IS actually turning the same revs/per MPH as it was before . Now , had you changed tires , the differential ("Rear end") or transmission , well then yea , the gearing could be different . In other words , there is nothing on that car that could fail and change your gearing ratio on it's own . In the OLD days , when some standard transmission's overdrive was engaged by a solenoid , well yea , but there ain't nothing like that on our stick shift third gens .

My guess = Replace your tach ............

 

Check the tach against a meter. Also, does it sound louder or quieter than the rpms suggest? Any clutch slip?

 

Thanks for the replys
The tach seems to be fine.. Unfortunately. I plugged in my other guage clusters and im gettimg the same readings too.
And when it says im running at 3000, it sure sounds like it.
No clutch slips at all.
Getting pretty bad gas mileage driving on the highway now.

I did actually just change from 15 inch rims to 17 inch g35 rims and lower profile tires, but didnt think that would have much effect on it.

I had a guy come a start my cars every week for me while I was gone.
I dont think he went joy riding.

Thanks!

 

Well they're ya go , You DID change something that most certainly WILL have an affect to your gearing !

Just because the rims are 17 rather than 15 , matters not . BUT ! , , If the new rim and tire combo is of a lesser diameter than the original , you have "geared down" your ratio by the use of the less diameter tires !

No way to fix this except to put the original sized tires back on it ......

 

To explain it better , if your original setup was 15 inch rims with say 5 inches of rubber , you had 20 inches of diameter . If you went to 17 inch rims with only 2 inches of rubber , your effective diameter dropped to 19 inches .

And YES , that one lousy inch can and does change your effective gear ratio , in your case by a rather noticeable amount ...

PS , the calibration of your speedometer is now not correct , either .....

 

Hmm, I tried to go with tires that were close to the olds tires diameter..and they slightly smaller. It makes my speedo off by maybe 1mph.
I also put on 1.25 inch adapters for those infiniti wheels. But idk if that would make a difference.
It just seems like a huge leap in rpms and gas mileage, does it really make that big of a change? 80s got me in the yellow.

 

The adapters don't make a difference but tire diameter does. Go to 1010tires.com for example and calculate the diff. They have a tire size calculator.

 

Um, assuming a stock rearend on a 3.1, which would either be a 3.23 or 3.42 (should be a 3.42 with manual), your tach has been off as long as you can remember. With a 3.42 at 72, you should be at about 2500. Less with the 3.23. Assuming the tires are within minimal differences (about 1/2" or so diameter change), and if the tach isn't that far off (as you've said it sounds close), the rearend may have been changed.

:edit: And the original tire diameter is about 26.5"...

 

Thanks to everyone for the help and input so far!

I put on my old rims and tires today and im still running at about the same RPMs.
How would I go about checking if the rear end is original?

And if it is original, is there a problem that could have been there all along as nd just gotten worst over time? I mean, this car was sitting in a field for about 7 years before it jumped into my arms.

Thanks again
Josiah