VIS Motor / Inlet Manifold / Fuel Comsumption

[Tasng4]

I know alot of what follows has been covered eslewhere but the info is very fragmented, perhaps someone could confirm my understanding of possible cause and symptoms of VIS motor & inlet manifold problems.

A few weeks ago the engine warning light came on in my ZT-T 160 the garage said I needed a new inlet manifold. After researching on the forum I found the following:

1. VIS motors can wear and become full of oil & dust which affects performance. The symptoms of performance problems are poor low or mid or high range power. I've tried flooring it and I can't appriciate any power issues.

2. The butterfly valve bearings in the manifold can wear and this results in the 'death rattle', the manifold should be changed as the valves may fall into the engine. I have no 'death rattle' yet.

3. Fuel comsumption can be increased due to incorrect VIS motor actuation. I DEFFINATELY seem to have increased fuel consumption - 30 miles from an eighth (1 segment on the gauge) of a tank.

4. The throttle body can become dirty and affect performance and fuel consumption. The throttle does stick at low temperatures, I'm about to try to clean the throttle body with carb' cleaner.

Could anyone confirm my understanding and possibly suggest any ways forward to fix or at least aleviate my problems.

I have a big trip to the UK (I live in France) and I'd at least like to get the fuel consumption back as close to normal as I can. I'm happy to replace the inlet manifold and I've seen new ones on E_Bay for between £300 and £480, does anyone have experience of these? I've looked at 2nd hand ones but this seems a false economy as most cars have done quite high mileage and the same problems may re-occur.

Please help!

[Typhoon190]

I can recommend this seller. I'm sure they are a genuine X-part centre.

http://cgi.ebay.co.uk/MG-ZS-ZT-V6-KV...item1e5aa0e9dd

I had a faulty balance VIS motor and power motor. IMHO I didn't notice much difference with the power VIS fixed, but the balance motor certainly seemed to make a difference to the power at just over 3000rpm, and improved the economy.

[Nelspeth]

Sounds about right i think, mine is exactly the same especialy the fuel consumtion! mine varies tho, yesterday i put £15 in and got about 25 miles!!..other times it can be quite frugal.
I bought my Zt about a month ago with the noise from the manifold, at first i thought the noise was a worn tappet or cam but more investigation shown the manifold was goosed!
I tried fitting a spare set of VIS valves but turned out these were faulty too, Iv now give up on repairs and i waiting for the spare cash to get a new manifold...as you say buying a second hand one is just false economy.
Also when you do fit a new one fit a catch tank to the crank case breather! this will stop any more oil build up in your nice shiney new manifold.
As for the new manifolds on E-bayhere
a few on the Xpower forum have bought them and they seam to be as stated.

Paul...

[stocktake]

Just to be clear. The faulty VIS motors will NOT bring the engine light on

[SD1too]

Hi Neil,

Originally Posted by Tasng4

A few weeks ago the engine warning light came on in my ZT-T 160 the garage said I needed a new inlet manifold.

I don't see how that diagnosis can follow from the symptoms. As Stocktake says, a faulty VIS actuator will not illuminate the engine warning light. Ask the garage to tell you the fault code which led them to their diagnosis, and we can look up that code for you.

1. VIS motors can wear and become full of oil & dust which affects performance. The symptoms of performance problems are poor low or mid or high range power. I've tried flooring it and I can't appriciate any power issues.

Many owners don't realise that their VIS actuator is faulty until after it's repaired. Then they notice that the engine's performance has improved.

2. The butterfly valve bearings in the manifold can wear and this results in the 'death rattle', the manifold should be changed as the valves may fall into the engine. I have no 'death rattle' yet.

You probably don't need a new manifold chamber then. (Note that the inlet manifolds are the aluminium pipes. The black plastic moulding containing the VIS actuators is the inlet manifold chamber.)

3. Fuel comsumption can be increased due to incorrect VIS motor actuation. I DEFINITELY seem to have increased fuel consumption - 30 miles from an eighth (1 segment on the gauge) of a tank.

Your method of measuring fuel consumption is extremely inaccurate. You cannot use a small portion of the fuel gauge. Let the tank empty until the warning light illuminates, then do a brim-to-brim calculation.

4. The throttle body can become dirty and affect performance and fuel consumption. The throttle does stick at low temperatures, I'm about to try to clean the throttle body with carb' cleaner.

Good plan.

From what you've said, I think you'll be wasting your money replacing the inlet manifold chamber. How many miles has the car covered? When was it last serviced? What's the air filter like, and the plugs? Is the exhaust leaking? Do you do a lot of short journeys or urban driving? All these things have a detrimental effect on fuel consumption, and the V6 is not the most economical engine to start with!

Hope this helps.

Simon.