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MGCT (V7iii)

dale decrescenzo

Tuned and Synch'ed
Joined
Sep 4, 2020
Messages
62
Location
Mo
So, just how does this system work ?

Im asking as i had an unusual episode this morning, I left for work and the noticed that the front tire was low. So i returned to the garage and pumped it up. then every time i accelerated away from a stop, the MGCT light flashed and the engine missed.

After a couple of stop signs, i woke up and turned the MGCT off, and thus the engine missing stopped.
so im guessing that MG determined that shutting the motor down is a good way to regain traction. ??

After getting to work, I read the owners manual (Brilliant) and discovered that inflating my tire may have taken the MGCT out of calibration !?

So i am wondering if inflating my front tire did truly negate the MGCT calibration, and does the MGCT system interrupt the ignition, or does it do something else, and thus I have a different issue ??
 
Yes, changing air pressure (especially on a single tire only) can affect MGCT calibration. The system detects rear wheel slip by comparing rotation speeds of the front and rear wheels. If the rear wheel is discovered to be spinning faster than it should be, relative to the front wheel, then it assumes the wheel is spinning and cuts power to try and bring it back under control.

By increasing the pressure of the front tire, it causes the front to naturally spin slower, as the effective diameter of the tire is now larger. So based on the previous calibration, it thinks the rear is now spinning too fast (relative to front). So, assuming both tire pressures are now correct, a recalibration may be needed.

__Jason
 
Yes, changing air pressure (especially on a single tire only) can affect MGCT calibration. The system detects rear wheel slip by comparing rotation speeds of the front and rear wheels. If the rear wheel is discovered to be spinning faster than it should be, relative to the front wheel, then it assumes the wheel is spinning and cuts power to try and bring it back under control.

By increasing the pressure of the front tire, it causes the front to naturally spin slower, as the effective diameter of the tire is now larger. So based on the previous calibration, it thinks the rear is now spinning too fast (relative to front). So, assuming both tire pressures are now correct, a recalibration may be needed.

__Jason
Thank you Jason...
now the last question, when the system sees the rotation discrepancy, i would assume that it backs off the throttle, regardless of my input. i would also assume that it would not cut the ignition. But thats what seemed to happen this morning. So this makes me wonder if i have another issue beyond a calibration issue..
 
Dale, carefully note kwt's message of "assuming both tire pressures are now correct" -- did you check and set both?
 
dd -- most fuel injected vehicles without drive-by-wire throttle (eg V7 III) control engine operation via various fuel limitation protocols. Older and simpler ECUs turn off all injectors at once which can upset the suspension. Newer and more capable ECUs turn off individual injectors as needed for smoother deceleration. Turning off the ignition without turning off the fuel has many adverse side effects due to unburned fuel as well as emissions compliance. The only example of ignition-only control that I'm aware of is MSD which is done carefully rotating among cylinders as needed. This was acceptable for carburetored race vehicles which was the intended application.
 
Dale, carefully note kwt's message of "assuming both tire pressures are now correct" -- did you check and set both?
to be honest... i was running late, first corner from the house i noticed that the front was soft, so back to the house for a shot of air. I just shot some in the front until it felt good.

I did catch kwt's comment, and i get the effect of a diameter change, but i was a little put off by the engine oddly missing-out every time the track control light flashed. and i am further confused as this only seemed to happen during mild acceleration. i could get to speed and hold it there without the fault light or the miss.

So my simple mind finds the two following conditions

1.) If wheel speed difference is detected
and operator is asking to accelerate
MGTC cuts injector.

2.) if wheel speed difference is detected
and operator is only maintaining speed
MGTC thinks all is well.
 
dd -- good analogy just like ABS only kicks in during braking. But to confirm find a icy road and report back. Just kidding. Same thing happens to me on San Diego's buckled asphalt. I just drive through it.
 
to be honest... i was running late, first corner from the house i noticed that the front was soft, so back to the house for a shot of air. I just shot some in the front until it felt good.
Nope, do not do this. TC is very sensitive to tire pressures. Set them both properly, and I'd bet your issue goes away. Despite the post above, TC is spark kill, not fuel. Same as the rev limiter. TC2 is far too sensitive. My last post on this.
 
GTM -- thanks for the correction on spark vs fuel control although it's surprising for emission-compliant engines with catalytic convertors.
 
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