3 replies to this topic

[mpihornet]

I put an mpi engine in my hornet, there is no tach.

im assuming i can use just about any tach from any car that has a coil pack, or any rover that uses a brain. because the mpi instrument cluster can be so expensive, im looking into using one from some same year range rover/mg.

Any suggestions?

[mpihornet]

Ok seeing as its been viewed 69 times, (and not all me) someone else must be intereseted in this subject.

over at the MG-rover forum my good friend tehcnozen had an answer for me.

"All of the MEMS systems have a tachometer drive which provides 2 pulses per engine revolution, it's the same for distributor or coilpack ignition. I would expect that a "standard" tachometer (one designed to be connected across old style points) would not operate at all.

The difference is that the MG-R tachometers operate on the frequency of the signal whereas the "standard" units measure the AC voltage of the signal.

The MEMS signal has no AC voltage present.
Here is what the tech details say....

This signal output, derived from the CKP sensor, has two pulses per engine revolution, at a frequency range of between 0 and 267Hz (0 to 8000 rev/min) and a duty ratio of 50% ± 5%.

So a suitable tachometer would have to be matched to this frequency range otherwise it will not read correctly."

he then pointed me to these at a fiver plus shipping...
http://www.ebay.co.u...bc#ht_632wt_816

which i had already bought, and am waiting to get in my grubby little fingers. I can then either put it in a beans can, my spare bullet mirror casing, or swap the movement into a vintage smiths tach, assuming the sweep is the same.

there are white ones too but they were an extra tenner (gulp)

So there you have it: the problem, the solution.

Technozen is the dude who will program new fobs to your 5as just for joining the mgrover forum, it cost me £12, was worth every penny. he does not need the ecu unless its not married to the 5as. I sent him my unmarried ecu, 5as and 4 random fobs, and pow, got it all back working perf. I was going to send him my 2 spare sets of ecu's, 5as, and fobs, but have not got around to it yet... he is a star.... hence the font 48 quotes..... I cant take credit for his hard work and vast knowledge...

[Sprocket]

The MPi tacho is connected direct to the Low tension voltage of one of the coils in the coil pack. This is different to all the other Rover/ MG tachos that are connected to the ECU.

Thos poses you another problem if you wish to use a tacho from another car, since the MPi uses a wasted spark type ignition, therefore, only being connected to one of the coils, only senses half the ignition events. The MPi tacho is one of a kind, although some say you can tweak the normal Mini tacho to read correcton an MPi coil, and vica versa. How accurate this is, is subject to speculation.

Basically if you fit an SPi tacho on an MPi engine, it will read half the actual RPM. On the other hand, if you fit an MPi tacho in an SPi car, it will read twice the actual RPM.

[mpihornet]

IF thats the case, then any wasted spark motorcycle (not mechanical) tach should work, like the old gpz1100 for example....

I got one of the fiver tachs and Ill let you know if it works. if it doesn't, ill try a bije tach. If its off by a factor of 2 i May just make my own face for it or fill them in with white out and marker pen.

yeah! Rat rodz!


thanks for the info.