Datto70

Hi, To check if your speedo is working properly go find a 5km odometer check and record how far your odo shows over the 5k's (do the test at the posted speed limit as speed has no relevance with this test) - if the odo shows around 4.2 k's or even under 4.5k's then the problem is unlikely to be the speedo - if the odo shows between 4.9 & 5.1ks then the speedo is likely to be the problem. If the speedo checks out, then you are looking for a component in the gearing so the speedo cable is not spinning at the correct number of revs/km eg speedo drive, the diff changed to a lower ratio and the speedo drive not changed to suit, or wheels/tyres are not standard but i doubt that as the wheel/tyre combination would have to be a lot smaller than standard to make that much difference - most of us put wider & higher tyres on which reduces the revs per km and this causes the speedo to read slightly slower relevant to actual speed ie more accurately - which is why most speedos have a 5% fast read built in ex-factory. If you need help with correct speedo drive ratio i would need to know your diff ratio & tyre size. Cheers, Tel

The RB30E engine is very prone to this problem. In most cases it is the AFM (ECU throws a code 12). The 1st thing i usually do is check that the resistence across Pins 1 to 6 on the AFM is 382 +-2 Ohms. If all is good there then squirt some WD40 or similar on the connections and then reinstall the plug & the dust boot - it's amazing how much crap still gets under the dust boot. It may or may not run properly for a day or 2 as the ECU has to relearn the signals from the AFM. If the easy way doesn't work then if you can get access to a Gregory's #242 manual Pg 83 for the detailed method to test the AFM. I can scan the pages & send to you if required.