[ROVERNET - UK] RE: Final Drive Issues

Eric Russell p6rovers at yahoo.com
Wed Feb 20 23:48:47 GMT 2008

Replying in support (please note, Glen :-),
I would say that I use an automotive RPM meter which I
attach as Glen suggests.  This compares exactly with
my car tachometer so I use the auxillary tach for
under-the-hood tuning instead of having to keep
referring back to the dash tach.


--- Glen Wilson <rovercar at comcast.net> wrote:

> Adrian McDonald wrote:
> > I should have said that I "inter"calibrated by
> tacho with a multimeter. I set the engine rpm at
> 1000, 2000, and 3000rpm on the tacho and read what
> the digital multimeter displayed
> Are you saying you used a DMM that counted pulses or
> frequency? Or are 
> you referring to an automotive DMM reading
> independently from the 
> ignition system? I may be missing a detail or two
> from the discussion, 
> but it might be a good idea to take a step back if
> you are approaching 
> this problem from an electrical engineer's
> perspective. Check the engine 
> rpm with some sort of simple automotive rpm counter
> based on readings 
> from the engine coil and see what that reads. It's
> entirely possible 
> that a counting DMM may give you inaccurate readings
> at the dash 
> tachometer, especially if the dash tach functions
> more on the basis of 
> current pulses than on voltage pulses.
> Remember, a $20 automotive tune-up meter from Pep
> Boys is probably much 
> more of a precision instrument than the tach in your
> car with all the 
> hysteresis and needle bounce. Verify the actual
> engine rpm measured 
> independently at the engine and then revisit the
> differential question. 
> You can also just go out on the interstate and check
> the 
> odometer/speedometer by watching the green mile
> markers by the side of 
> the highway and running ten miles. You can even time
> it to check your 
> speed. This will tell you if your
> tiresize/rearendratio/speedometer are 
> giving reasonably accurate readings.
> Glen
> >  at the same time. The rpms on the tacho matched
> the rpms on the multimeter, hence I deduced that my
> rpms were right. That left me knowing with 99%
> certainty I was doing 3000rpm in 4th gear while
> driving along, and being 98% sure I was only doing
> 40 something mph instead of 58.5mph.
> >
> > Also, I am not sure how to reply to messages on
> this thing. Not only a new P6 fiddler, but a new
> forum-er too!
> >
> > Adrian
> >
> > _______
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