TVIS Question

[nwpsb52]

Hi there

My question is "Can I bypass the VSV switch on the TVIS?"

As far as I can see connecting the vacuum hose directly from the reservoir to the actuator will simply mean that the TVIS is disabled, am I right.

I need to do this as I have broken one of the pipes on the VSV checking for a vacuum leak and still want to run the car whilst I source a replacement.

[crazylegs]

i am sure it will run but will run like poo. ok if you are doing 10 mph but what about pulling away? your acceleration will be very limited. i think never tried it. tell us how you get on.

[nwpsb52]

Hi Kev

Understand where your coming from, but reading Mr T's Engine Repair Manual at low revs there should be vacuum between the VSV and actuator 4,350 revs for a 1A and zero vacuum above, this leads me to believe that the TVIS is activated by the VSV closing off the vacuum, thus if vacuum is present all the time all that I would be losing is top end performance.


Saw your post about your new motor, hope you've been able to get out and enjoy over the last couple of days sunny weather down here.

Paul Bone

[gpk]

You are right, the vacuum holds the tvis butterflys closed (below 4300ish), when there is no vacuum they are open (above 4300ish). I haven't tried the car with the valves closed all the time so I can't comment on how it will run in that situation but I have ran the car with the vsv disconnected so the valves were open all the time and it ran fine. There were no noticable problems in either pulling away or normal driving at low revs and at high revs it acted as it normally did.

[System-G]

When we did my engine swap last year we accidently got a couple of hoses the wrong way round and TVIS was inactive. Not sure if it was permanently open of permanently closed, but it had a shed load more torque low down than what it does now we have plumbed the hoses the correct way around.

But there was no "boost" at 4300 - 4800rpm where TVIS usually kicks in and also top end speed was somewhat restricted. The car would only rev to 6200rpm and no higher. Total loss of high rev torque and speed.

The car is still driveable like that (in fact I even did half a day at anglesey before realising the difference!!!).

[waynestoyotamr2]

Just wondering, and sorry for the thread hi-jack, but is there any way you can change the point TVIS comes on???

[Lauren]

Just wondering, and sorry for the thread hi-jack, but is there any way you can change the point TVIS comes on???

No you can't. There isn't any point really.

[nwpsb52]

Just wondering, and sorry for the thread hi-jack, but is there any way you can change the point TVIS comes on???

Although Lauren in right in as much as there is no adjustment which sets the point at which the TVIS activates because the activation is controlled by the ECU.

You have two options for changing the point at which it activates and those are to reprogram the ECU or replace with a later ECU which will mean that TVIS will activate at 4650 RPM not 4350 as per MK1A's

As Lauren says it would seem to be a pointless exercise .


Paul

[System-G]

Paul, don't the different ECUs have different connector blocks on them?

I know the wiring looms are completely different, but haven't compared the connector blocks themselves.

[JMR_AW11]

Paul, don't the different ECUs have different connector blocks on them?

I know the wiring looms are completely different, but haven't compared the connector blocks themselves.

You can certainly fit the earlier ECUs to the later mk1b (the one that normally uses 89661-17140 ECU)

The connector blocks/pins are physically the same for types 89661-17030 and 89661-17070 and 89661-17140.

I have tried this many times. However, you are right that the actual wiring is slightly different. The mixture screw input uses a different input pin on the earlier ECUs and this means if you swap, tweaking the mixture screw will not do anything.

Otherwise the car seems to run fine. I wouldn't recommend it as a long term thing though. Best to stick with the correct ECU.

Changing the TVIS opreating point doesn't really achieve anything other than it sounds more sporty IMO at the mk1a setting of 4350rpm.

[kpm]

Do the TVIS valves open fully as soon as they are activated or do they move to adjust air intake with revs/load etc,
If the car was being used for racing/Trackdays etc, and not on the road Would there be anadvantage to keeping the valves open, and allowing as much air in as possable, If they are simply open or closed this would not help I suppose?

Cheers

[nwpsb52]

Do the TVIS valves open fully as soon as they are activated or do they move to adjust air intake with revs/load etc,

With the TVIS it is either on or off there is no in between and as far as I am aware it is entirely dependent on the Revs as to when it comes in.

Paul