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Thread: Smiths gauges and aftermarket ecu

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  1. #1 Smiths gauges and aftermarket ecu 
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    Electrical question. I have smiths gauges in my cabrio and I'm overhauling an ST170 engine to go in. I've looked at various loom and ECU options (including OEM) but I cannot find any answers for how any ecu (to keep the VVT) can work with basic gauges rather than a full-modern dial cluster (which I don't want). Any ideas?

    It is as "simple"as splicing a sensor feed to the gauge and to the ecu, so the ecu gets its information it needs yet the gauge also gets sensor information, rather than an ecu outputting the information back? The car was using an Omex600 & carbs on a 1800 zetec. A previous owner has made a beautiful loom and superb wiring diagram (attached) and I guess that the sensors reported to the Omex AND the gauges. The wiring diagram is attached for reference.
    I have zero comprehension of vehicle electrics right now. Many thanks in advance.
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  2. #2 Re: Smiths gauges and aftermarket ecu 
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    My guess would be to wire each gauge to its own sensor. So you would need two temp sensors for example, one for the gauge and one for the ECU.
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  3. #3 Re: Smiths gauges and aftermarket ecu 
    Club Member lil_red_roadster's Avatar
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    Quote Originally Posted by scott h View Post
    My guess would be to wire each gauge to its own sensor. So you would need two temp sensors for example, one for the gauge and one for the ECU.
    Indeed...my old Rover T-series had 2 temp senders, one for the gauge & one for the ECU. When I stuffed it into the Roadster I replaced the gauge sender with one to match the Marina clocks and used the Emerald ECU to provide an input to the tacho.
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  4. #4 Re: Smiths gauges and aftermarket ecu 
    frequent forum contributor Club Member jon_cox's Avatar
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    According to your wiring diagram the only wire from the ECU to the instruments is feed (yellow) for the tacho. There appears to be 2 temp sensors on the diagram. Not surprising. Chances of have a temp sensor that matches both the ECU input signal needs and those of the Smiths gauges is pretty slim. Also, depending on the ability of the ECU, apart from needing the temp to adjust the mixture map it is using the coolant temp to trigger the electric fan at a pre-set temperature. However, on your wiring diagram there is a separate circuit being fed from Fuse 08 to manage a manual override switch on the dashboard along with a coolant temp switch located somewhere under the bonnet, probably within a hose.
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  5. #5 Re: Smiths gauges and aftermarket ecu 
    frequent forum contributor Club Member chris_cussen's Avatar
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    Having fitted an Omex ECU to a Zetec engine(using the Omex loom) I can confirm that there are two temperature sensors, one is used by the ECU and the other is wired directly to the gauge. The ECU has a tacho output.
    Other sensor inputs to the ECU are (or can be) air temperature, lambda sensor. Crank position sensor is a definite requirement.

    If the VVT is controlled electronically (i.e. via a solenoid) the Omex ECU does have an auxillary programmable output. You may want to contact Omex on how to set it up so it operates above a specific RPM.
    Cabrio, Omex 2.0l 150bhp Zetec blacktop, Omex ECU and wiring loom.
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  6. #6 Re: Smiths gauges and aftermarket ecu 
    frequent forum contributor Club Member jon_cox's Avatar
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    Hi Kieran

    Looking back at the original engine installation pictures from eBay you can see the 3 different temperature senders that are fitted. This corresponds to your wiring diagram as previously suggested.
    I have labeled it for you on this picture. Your wiring diagram shows a green / grey wire going from the ECU to the temperature sender hence the arrow for ECU going to the sender placed into the thermostat housing.
    Cabrio.JPG
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  7. #7 Re: Smiths gauges and aftermarket ecu 
    frequent forum contributor Club Member chris_cussen's Avatar
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    Just s further note, the Omex ECU has outputs for the fuel pump and fan. These need relays as the current taken by both is large.
    Cabrio, Omex 2.0l 150bhp Zetec blacktop, Omex ECU and wiring loom.
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  8. #8 Re: Smiths gauges and aftermarket ecu 
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    Quote Originally Posted by lil_red_roadster View Post
    Indeed...my old Rover T-series had 2 temp senders, one for the gauge & one for the ECU. When I stuffed it into the Roadster I replaced the gauge sender with one to match the Marina clocks and used the Emerald ECU to provide an input to the tacho.
    This. I've been in contact with Motorsport electrics (ME221 ecu favoured option once I've overhauled engine) and they said exactly the same - so I guess I can continue to use the existing loom for the gauges and install duplicate sensors - effectively two looms - one for gauges and one for ecu. I'm sure I'm not the first to face this, but I cant find anyone supplying a wiring loom that has duplicate wires in to address this...

    Thank you jon_cox for the image (you recognise my ability and have drawn me a diagram [thumbs up]), and everyone else for taking the time to help a dumb noob out.
    Last edited by kieran78; 31-01-2020 at 09:06 AM.
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  9. #9 Re: Smiths gauges and aftermarket ecu 
    frequent forum contributor Club Member jon_cox's Avatar
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    Hi Kieran
    Just in case you have not come across this and for completeness of this thread for any other members that might be considering an ST170 engine swap, you should read in full all the information that can be found over on the locostbuilders forum.
    There is a member on there that goes by the forum tag of big_wasa. He has documented a way of getting the ST170 engine running in a kitcar using the existing wiring loom and ECU. http://www.locostbuilders.co.uk/view...php?tid=174681
    There is also a video on youtube https://www.youtube.com/watch?v=gjsu8mMp0kw
    There is also a couple of people on eBay offering to supply a converted loom. https://ebay.us/FmwHZv
    There is also the RX8 gearbox adaptor plate available on eBay https://ebay.us/Kh8ZiU

    So in theory, an easy, quick and budget friendly modern engine conversion for anyone wanting to upgrade. The only downside I can see to this is the probable need to modify the transmission tunnel to fit the RX8 gearbox in and where the gear lever ends up.
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