VVT / VCT / VCA help pleeease - what does it do????

[olethalb]

hi chaps, i know i no longer own a icr but now have a aum k04'd bora.

i have been suffering stalling on idle particularly when the engine is cold, i've changed the temp sensor, genuine maf, inlet mani gasket, cleaned and alligned the tb, pressure tested the charge pipes, check all (new) vac lines etc etc.

after all this stalling still happened until i disconnected the VVT solinoid, now it hasn't stalled in 3 days (usually 6 or 7 times a day) it runs rough and idle still fluctuates but hasn't stalled.

so can anyone tell me the function of VVT? there is no info in the haynes manual on it's function, searched the net and forums to no avail.

all i can find is this small description from vortex;

What is VVT?
VCT or Variable Cam Timing. Synonymous with Variable Valve Timing. The VCT in later 1.8T's is simply for emissions purposes. It has only two states - normal and massive overlap. The overlap is used to draw exhaust gasses back into the cylinders at startup.

can someone tell me how it adjusts cam timing?

what will happen if i remove the solonoid?

if i do remove it do i need to add a resistor to the loom like n249 bypass etc?

any input will be greatly appreciated.

Thanks, Olly

 

[DJ-LIAMC]

I think VVT is Varial Valve Timing Not sure how it works though

 

[warren_cox]

http://en.wikipedia.org/wiki/Variable_valve_timing

 

[olethalb]

thanks for the replies, i understand how vvt works and what it does but it seems to have a different purpose on the 1.8t and need to know for definate when it comes into play and what are the effects of not having it?

Olly

 

[warren_cox]

I thought it was used to reduce emissions in the low rev ranges, and to increase outright power at the top end of the rev range.

By having the cams run in two states it means you get the benefit of a consistent idle at tickover (extreme profile cams run very rough at idle), and increased fuel economy.

Then when you are further up the rev range the cams are 'lifted'(???) changing the profile / duration of the cams which means you get better performance.

That's pretty much why VVC was invented, so I don't think the VAG group has anny real magic / alternative agenda for their system.

 

[Shaunyboy]

The VVT is mainly used at low revs to improve power, Im not actually sure what unplugged the solenoid will do as i have never tried it, is there any cam position error codes?

 

[andycupra]

VVT 1.8Ts remap about 10 bhp moreo than non VVT

 

[Shaunyboy]

If you get rid of VVt and use diffrent cams and map it, power will be better, but its expensive as it would need custom mapping to get rid of the vvt.

 

[csd_19]

I'd always understood the VVT on the 1.8t to only be an emissions control system at startup and idle. From what I remember it runs at the same time as the secondary air pump (where fitted), and by introducing overlap between the inlet and exhaust valves it allows for some of the exhaust gas to be drawn back into the cylinder to be burnt again. This reduces the amount of unburnt hydrocarbons going down the exhaust.

You're right about it running either massive overlap or normal, the solenoid acts on the guide plate under the cam chain on the two cams at the gearbox end of the engine and increases the distance the chain has to run between the cogs, hence introducing overlap.

Unfortunately its not a performance system like Honda's VTEC, Rover's VVC or Toyota's VVTi, purely emissions.

 

[Shaunyboy]

I'd always understood the VVT on the 1.8t to only be an emissions control system at startup and idle. From what I remember it runs at the same time as the secondary air pump (where fitted), and by introducing overlap between the inlet and exhaust valves it allows for some of the exhaust gas to be drawn back into the cylinder to be burnt again. This reduces the amount of unburnt hydrocarbons going down the exhaust.

You're right about it running either massive overlap or normal, the solenoid acts on the guide plate under the cam chain on the two cams at the gearbox end of the engine and increases the distance the chain has to run between the cogs, hence introducing overlap.

Unfortunately its not a performance system like Honda's VTEC, Rover's VVC or Toyota's VVTi, purely emissions.

Aswell as that, it also improves torque low down in the rev range, no performance gains what so ever, same as renaults F4R engine, their system is for lowdown torque and as you say emissions control, hence why the cupra r has it, but doesnt have no EGR or SAI.

 

[Cuprar72]

talking about this valve mine has a slight oil leak from where it is screwed on, theres 2 torx screws im assuming it has a gasket or seal behind this? can it be replaced and is it just unscrew 2 screws replace gasket and refit? thanks