Bypassing The Immobiliser (Ignition Only)

[ChimpOnGas]

ianl said:

Bit of a thread resurrection as I've now got an immobile Griffith 500.
Having done all the diagnostic checks mentioned in this excellent thread, I'm confident the immobiliser is my issue & so have emailed Dave (ChimpOnGas) for his instructions on bypassing it. Pretty please Dave.
Can't go anywhere anyway but I see it as my TVR's way of giving me something to do whilst in lock-down.
All the best.
Ian

Hi Ian,

I've responded, you now have my instructions.

Meta relay 1 is only rated at 10a, so was intended for the low amp ECU circuit, remember it's the ECU that switches the fuel pump relay.

Meta relay 2 however is rated at 25a, so was intended for the far higher load drawn by the starter motor solenoid.



TVR got these circuits back to front, this means the high amp load of the starter motor solenoid is passing through the lower rated 10a Meta relay 1, a starter motor solenoid will typically pull between 8 to 10a so while Meta relay 1 could handle the load for a while it was always doomed to fail.

If you make a relay work to its rating all the time it'll work for a while, but because every time you crank the car it's right on the edge of it's capacity, eventually it will fail. Inside a relay is a set of contacts that get pulled in to close and connect the high amp circuit, like wire gauge the size of these contacts is critical, if you continually load a thinner than ideal wire with too many amps it will fail.

A wire is path for electrons to travel but it's also a resister, the thinner the wire the greater the resistance, a starter motor pulls by far the most amps on a car's electrical system, that's why your starter/charge cable is massively thicker gauge than all the other wiring in your car. If you tried to use a thin cable to supply the high amp side of your starter motor it would have huge resistance and all that would happen is it would glow red hot for a millisecond and vaporise, actually this is exactly how a fuse works.

The problem is the same inside a relay, make the contacts too small and eventually they will burn out, the problem is exacerbated in a relay because every time the contacts make and break a small amount of vapourised material will be transferred from one contactor to another and some is lost to the atmosphere, this is exactly the same for ignition points and why they had a limited life.

The so called 'Hot Start' problem is mostly caused by the back to front way TVR wired the Meta immobiliser, had TVR wired the ECU through the 10a relay and the starter solenoid through the 25a relay as Meta had intended the problem would never had existed. Well not quite actually, because not content with making this Meta wiring gaff TVR went on to cheap out on the thickness of the main stater/charge cable, add in some internal corrosion under the insulation of this string thin cable over the years and the inevitable bad earths created by trying to use the rusty chassis as the earth return, and you've got yourself a no-start situation just waiting to happen.

I recommend the following:

1. Bypass the Meta system on the starter solenoid circuit

2. Run a new starter solenoid wire using a 30a relay triggered by the cranking terminal on your ignition switch, let the high amp load run from your battery through the high amp relay circuit to effectively create a direct connection from battery to starter solenoid

3. Upgrade the starter/charge cable that runs from your alternator, through the 100a fuse, onto to the starter motor, and finally ending at the positive battery terminal, use the thickest cable you can!

4. Using the same thicker gauge cable connect one end to your engine block using a stout bolt, connect the other end to your negative battery terminal so you now have a proper copper cable engine earth rather than relying on TVR's idea of using the chassis as part of the earth return circuit, because a circuit is a loop the earth path is as equally important as the positive

If you do all all four things your TVR will crank like you would never believe it could, don't waste your money on the so called 'Hot Start Kit', it's creator failed to understand the true reason for the problem. The 'Hot Start Kit' is just a relay as I describe above in point 2, while it's true TVR never fitted a dedicated relay on the starter solenoid circuit this was because they thought they could rely on the one in the Meta system, this idea could of worked had they just wired the system correctly through the higher rated Meta 25a relay circuit.

This is why with the immobiliser now bypassed it's recommended you fit a dedicated 30a starter solenoid relay to protect the contacts in your ignition switch (sprung cranking position), please also note with the immobiliser bypassed on the starter solenoid circuit the car will be still protected against theft. This is because the ECU will still be disabled until you deactivate the immobiliser, with the immobiliser bypassed on the starter solenoid circuit the car will crank on the key even if you haven't deactivated the immobiliser, but the engine won't start because the ECU will not have activated the fuel pump and it will not open the injectors.

Just follow my four upgrade steps above and you'll never have another cranking issue again, however do keep in mind even with a bypassed immobiliser, improved high amp cabling/engine earthing, and a starter solenoid relay.... you still need a good strong battery and a healthy starter motor!

Kind regards,

Dave.

[ChimpOnGas]

ianl said:

All sorted. Many thanks to Dave & Mark.