a few months back i noticed to things to indicate my tachometer was not reading accurately. first was my friend had a different gear ratio then me and claimed his rpms to be about the same at given speeds. then when i went to get inspected, and they hooked my car up for the emission test i noticed over the guy's shoulder the computer read the RPMS out and it was like 200 higher then what the gauge in the car read. i know inaccurate gauges are hardly a rare problem with our cars but is there a way to fix it?

and admitadly i have an A4 and arguably no need for a tach, but its just for piece of mind to move my car close to perfect, its slightly annoying to confess such minor problems with the car to people. plus if this tranny goes im hoping for an M6 swap, and the tach will be more important then. and no im not putting a aftermarket tach haning off the pillar until for whatever reason i build my engine to rev over 7 grand

 

The factory tachs are commonly noted for being about 200 rpms off, but maybe not in all parts of the rpm range. Not a lot you can do about it.

 

i beg to differ sir.

I fixed my tach on my 97 T/A. I had the scanner connected and it was showing the actual rpm and I noticed my tach was off 200. So i pulled the glass off the cluster, pulled out the needle while engine running and threw the needle back in where I wanted it. perfect reading now.

 

Ditto on that one. I hooked up one of those digital RPM tachs to my MSD box...when I swapped out the gauges I put the tach in sinq with the Digi RPM meter. I was curious if the Digi meter was off or if the Factory tach was off. When I had the car diagnoised and they hooked her up to the tech 2. You could see the Live RPM readings. The Digi tac was right on the money so the Stock RPM meter was off. If you know someone with an Autoxray "or" something that can allow you to read the actual engine RPM's than you can adjust your needle the same way.

 

I don't call that recalibrating. The tachs are apt to read perfect at some rpms and not at others like I previously mentioned, though not all tachs are going to be the same. You would need to observe the tach through all rpm ranges and compare to a scan tool. If it is off the same everywhere, then moving the needle could be a solution.

 

if its anything like GM speedos that are off, its not off by a set amount, more like variable based on RPM. At 1000RPM it may be dead on, at 3000RPM it may be 100RPM off, and at 6000RPM it may be 200RPM off. I submit as support for this theory that most people I know that talk about their factory tach being off never seem to mention it telling them they idle at 1100RPM.

That being the case, simply moving the needle back is going to really throw off the rest of the RPM range

 

yeah i thought about that range thing too so i left the scanner hooked up so i can compare pcm RPM and tach RPM and had someone drive the car in different rpm ranges. perfect readings every 1000 RPM.