NP Speed Posted July 3, 2006 Share Posted July 3, 2006 A few years ago I fitted a Weber Alpha 3D to a carb'd Vauxhall HPC and am ashamed to say that ever since the tacho has been reading at about 50% and now has packed up altogether! Webcon have been taken over in the meantime and don't really want to know. Presumably the tacho is not happy with the output from the ECU - is it possible to have a Caterham tacho recalibrated, and does anybody know who does this type of work? Cheers Nick Link to comment Share on other sites More sharing options...
Peter T Posted July 3, 2006 Share Posted July 3, 2006 You need to get the signal from the ECU changed.Obviuosly they did not check it when you had it fitted. You will also need a pull up resistor for the tacho feed, the Alpha signal is only 3 volts and doews not feed enough current to trigger newer Tachos. Part number 9990300700 WFCP. R500 Mango Madness Link to comment Share on other sites More sharing options...
Chris W Posted July 4, 2006 Share Posted July 4, 2006 Nick If the problem is indeed that the Alpha unit only gives out 3v, it is very easy electronically to design a small interface box which would take 3v input and give out 5v or 12v or whatever your sytem actually needs. I could knock one out for you for about £20; the cost and time is actually in designing, etching, drilling and soldering the printed-circuit board not in the components for this circuit. Edited to say: If the tacho is reading at 50%, did you change from a wasted-spark system to a normal-spark system as that would also account for the difference? The tachos have tiny switches on them which can be set for normal or wasted-spark ignition and the number of cylinders. Chris 2003 1.8K SV 140hp see it here Edited by - Chris W on 4 Jul 2006 10:17:05 Link to comment Share on other sites More sharing options...
Graham Perry Posted July 4, 2006 Share Posted July 4, 2006 Webcon actually sell such a device. When you fit a new Alpha kit there is a one page section in the manual about sorting out the tacho, and they give you the various parts to make it work depending on the tacho type. The instructions are however a little vague, and when I installed my Alpha it was the one area where I was not confident in what was required (everything else was easy) even though I had the parts, so I had someone who knew which bits went where do it and it only proved a 5 minute job Link to comment Share on other sites More sharing options...
graham bass Posted July 4, 2006 Share Posted July 4, 2006 Has anyone got a copy of a Webber Alpha manualor can you tell me what colour the tacho feed is on the ecu wiring? On a slightly different note but semi related to the above, I recently fitted an SPA tacho on my 1860 crossflow but connected it to the conventional point on the coil. Unfortunately this appears to be giving me an erratic needle movement (rev fluctuation of +/- 400 rpm in some instances) which doesn't help setting the shift lights! I've tried the usual fixes, swapping wires over and seperating out the loom but to no affect. I was going to try and connect the tacho to the rev counter feed on the ecu to compare but reading the above this may not provide a cure in light of comments made. My other option is to try refitting my old tacho to compare the performance which I'm now at the point of and would identify if the tacho is at fault or I have a wiring problem Any info would be appreciated Regards Graham Link to comment Share on other sites More sharing options...
Chris W Posted July 4, 2006 Share Posted July 4, 2006 Graham can you tell me what colour the tacho feed is on the ecu wiring?It's white/black. On my ECU (EU3) it's pin 55 on the smaller ECU connector. Chris 2003 1.8K SV 140hp see it here Link to comment Share on other sites More sharing options...
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