Speedo under reading...

[Swanny_UK]

Hello there,

Ive got a \'95 FD with a little bit of a speedo issue.  It under reads by quite a bit.  When I say quite a bit I mean at an indicated 20mph its showing 30mph... and at an indicated 50mph Im doing 70.

Now I understand the car has a speedo converter fitted, and the ApexiPFC Commander is able to display the real speed.  Im a little lost as to where to start looking though.  I found the thread here discussing an intermittant speedo failure, but I gather thats when its working or not, not reading way off.  Can anyone point me in the direction of a good place to start?:xconfused

[grinder]

having odd size wheels and tyres can do this

the better halfs scenic is about 10 mph out

what wheels and tyres have you got on the car

are you sure that its still not showing in KMS

70 KMH= 43.75 mph

so you are showing 6.25 mph under - your wheels could throw it out this much

why dont you drive at 60mph for 1 min and see if you do 1 mile ??

you can cross check this thru a sat nav unit aswell

[Swanny_UK]

what wheels and tyres have you got on the car

are you sure that its still not showing in KMS

you can cross check this thru a sat nav unit aswell

Ah good point! forgot to mention.  Its a TypeR on standard 17" BBS rims, 235/40/R17 tyres on the front and 255/45/R17 tyres on the rear.  

I had thought about that - but the speedo should be over reading surely, as 60mph would be 100km/h?

Ive got a road angel, and this gives a very accurate GPS derived speed, and the Apexi speed reading is quite accurate at the moment.

[grinder]

i didnt think that any RX7 came standard with 17 BBS rims - so you might have aftermarket wheels

you need to work out now what rolling distance you have and what you should have , this could cause the over reading

im sure that only the 99 cars came with 17\'s are standard

im sure a FD wheel should be 205/55/16 and i have no idea what to do with that info !! LOL

Stu

[grinder]

OPPS my mistake - a stock FD tyres is 225 - its the FC thats 205

have a look at this

http://www.torquecars.com/tuning/alloy-wheels.php

[RemarkLima]

I thought the RZ or something came with 17" BBS rims? I\'ve got some 17" BBS rims with FD stamped on them

Also on the tyre pressure info sticker in the door there\'s a section for the standard 16" and another for the 17" wheels.

But if the PFC is reading the correct speed (in kmph) and the speedo is converted it\'s probably the speed converter, can you bypass it and see if it reads right in kmph if you see what I mean?

[Swanny_UK]

... this could cause the over reading

Ah - i was under the impression they were standard on the model.  I see what you mean, but its over reading though

I thought the RZ or something came with 17" BBS rims? I\'ve got some 17" BBS rims with FD stamped on them

Also on the tyre pressure info sticker in the door there\'s a section for the standard 16" and another for the 17" wheels.

But if the PFC is reading the correct speed (in kmph) and the speedo is converted it\'s probably the speed converter, can you bypass it and see if it reads right in kmph if you see what I mean?

Yup - same stickers on my door section.  Ah good point - eliminate the speedo converter see what it says!

[grinder]

sorry about the wheel thing - im a FC owner and i dont know much about the new fangled FD

[RemarkLima]

Heh heh, I htink that was the case, but it may just have been a factory option?

[johnf]

I\'ve had the same issue for over 4 years, solved it by buying a road angel.

Not only know my speed but get the bonus of speed camera warning.

[Swanny_UK]

I\'ve had the same issue for over 4 years, solved it by buying a road angel.

Lol - thats encouraging!  Ive got a Road Angel Classic - I tend to drive based on that, my last car under read a little, just so I can squeeze the most out of the speed limits

Now... if I can just fix the cigarette lighter!!

[grinder]

the cig lighter should be a 10 min fix - remove - put in a new one

[nikp]

The dials can get sticky with age. Happened to mine. I had to replace it. Once replaced it observed the correct speed fine.

[danrx7]

I had the same problem and removed the converter that was wired in behind the clocks - problem solved. Im can only assume that there is another one attached elsewhere? Reads in mph and no 112mph limit .
 
Might be worth checking if you have the dash apart.

[Swanny_UK]

I had the same problem and removed the converter that was wired in behind the clocks - problem solved. Im can only assume that there is another one attached elsewhere? Reads in mph and no 112mph limit .
 
Might be worth checking if you have the dash apart.

...lol thats another good point!  It had crossed my mind but I thought... naaah... cant be, surely!  Well I\'ll have a lil look when I get my new stereo head unit.  Cant... take... much... more... Radio2 :Hammer