Everyone enjoys a story about someone else’s minor misfortune, right?

[mdrogersmdr2]

Something to amuse y’all during this trying time, and a question:


1983 733i, 130k miles, purchased from original owner. Going through the baseline process, minor issues but idle was around 1,000. Did all the usual stuff: plugs, rotor and cap, valves adjusted, new vacuum hoses, fixed leaking pods and replaced hvac tees, cleaned, lubed and tested ICV, checked TPS, adjusted sweep on AFM, checked cold start valve for leaks, replaced temp sensor, checked temp sensor resistor, verified voltages/resistance at ICM, replaced ICM with Programma rebuilt, replaced ECM from one from parts car, and verified no other vacuum leaks. Idle was still 950-1,000, albeit much smoother.


Here’s the dumb-ass part: I always noted high rpms at freeway speeds (3,400@80), figured the previous owner put in a 3.91 diff since there was no tag and it calculated to that number. I finally get around to counting revolutions, son of a gun if it isn’t a 3.25! So I buy a $20 laser tach and as you guessed, idle is 750-770 and 2,500 indicated is about 2,100. Ha ha on me, at least I did a thorough baseline.


So, can the tach be owner calibrated or does it need to be sent to a shop?

[ross1]

What is your tach's resting position? Could be just a matter of repositioning the needle

[mdrogersmdr2]

Unfortunately zero.

[Hit Man X]

Do you have a three speed auto or five speed manual? A 3.91:1 would do around 4000rpm @ 70mph in 1:1. I do about 2600rpm in OD on the ZF with it on the 10/84 at 70mph. Anyway, I never really thought these stock instruments worked that well. Speedos tend to be off 3-5mph.

Have a link to your digital tach? The pickup on my timing light died and now I cannot check it either.



I am sure some shops do it, who is the issue!

[mdrogersmdr2]

Manual, g260/5. https://www.summitracing.com/parts/wmr-w89719

[Hit Man X]

Ahhh... makes sense on the RPM. 0.81:1 is that OD ratio versus 0.72:1 on autos.

Speedo in 10/84 reads 4mph high per GPS. I just keep that in mind.

[Kenneth1948]

So, the easiest way to achieve a little lower ratio with a 5 - speed is to install the differential from an automatic?

let me see, is this a dumb question? it won't be the first or the last, I'll go ahead and post it anyway!