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[demolite]

Hi, I'm tracking down vacuum leaks on my X25XE.

I'm in the process of opening up the plenum soon, but have a quick question for you V6 owners. In theory, on non-DBW engines, actuating the rear multiram (as in closing the valve) on idle should starve cylinder bank 1 of IAC air and thus make the idle very bad. On mine, turning the valve closed does absolutely nothing on idle. This leads me to believe that there is a bad leak on bank 1.

Could someone test their rear multiram and see what happens on idle?
This is to know if I should be extra rigorous on checking bank 1 when I open it up.

Thanks in advance!

[minifreek]

The multirams only effective at fast air speed not at idle...

You can close both at the same time, or open them at the same time at idle and there will be no effect...

[Doctor Gollum]

Seek and ye shall find...

http://www.omegaowners.com/forum/index.php?topic=90513.0

This place is a mine of information if you can be bothered to look

[terry paget]

On a 2.5, plenum ram valve should be open at idle, closed between 1000 and 'high speed'. I think its default setting is open so engine will always run if it fails. It doesn't matter where the front ram is, engine will always run, so I suspect that defaults closed.

[terry paget]

Seek and ye shall find...

http://www.omegaowners.com/forum/index.php?topic=90513.0

This place is a mine of information if you can be bothered to look

Thank you Doctor. Some cars have variable valve timing, achieving much the same thing. I wonder how well they perform after 16 years and 200,000 miles service.

[Webby the Bear]

I think it's worth hooking up a vacuum gauge. Not only do you get an insight in to the engines workings but also if you actually have a vacuum leak. Reason I ask is cos I was chasing a leak for ages having checked and rechecked vac line routings and replacing plenum o rings / top hat o ring etc. All to find out I didn't have a leak in the first place. Vac gauge reading was bang on and didn't fluctuate one bit.

Just my humble opinion :-)

[Nick W]

Thank you Doctor. Some cars have variable valve timing, achieving much the same thing. I wonder how well they perform after 16 years and 200,000 miles service.

On a Honda or Toyota that's had basic servicing? As good as when they were new.
BMW, Fiat and others weren't so well designed.

[Diamond Black Geezer]

I think it's worth hooking up a vacuum gauge. Not only do you get an insight in to the engines workings but also if you actually have a vacuum leak. Reason I ask is cos I was chasing a leak for ages having checked and rechecked vac line routings and replacing plenum o rings / top hat o ring etc. All to find out I didn't have a leak in the first place. Vac gauge reading was bang on and didn't fluctuate one bit.

Just my humble opinion :-)

Will see if I can dig one out from fathers/a mate's garage 

[demolite]

I'm soon off to see what I can find. The reason I'm suspecting an air leak is that idle fuel correction factors are +30% for bank 1, while bank 2 is about 0%. Part load correction for bank 1 is only 2-3%, bank 2 is 1-2%. When revving parked, bank 1 correction goes from 30% towards the 2-3% when throttle is opened more.

What's the theory on the rear multiram not affecting idle? As I understand, it's the only air channel between the two banks. Only thing I can guess is that it's not very air tight closed so idle air can go around it?

[Kevin Wood]

I have a feeling (although not looked at the plenum for a clockwork throttled car for a while) that the ICV feeds both sides of the plenum through a couple of passages in the casting, not just into the 2,4,6 side.

[Doctor Gollum]

I'm soon off to see what I can find. The reason I'm suspecting an air leak is that idle fuel correction factors are +30% for bank 1, while bank 2 is about 0%. Part load correction for bank 1 is only 2-3%, bank 2 is 1-2%. When revving parked, bank 1 correction goes from 30% towards the 2-3% when throttle is opened more.

What's the theory on the rear multiram not affecting idle? As I understand, it's the only air channel between the two banks. Only thing I can guess is that it's not very air tight closed so idle air can go around it?

Did you read Dtms guide to how the multiracial work.

[Kevin Wood]

Hmm. we'ses got predictive textses in middle earth, then? Precious!

[Doctor Gollum]

Hmm. we'ses got predictive textses in middle earth, then? Precious!

Oops stupid bloody gayphone

Multirams it is...

[frostbite]

When I had my 2.5 cdx it had broken vac tanks nipples that the P/O tried gluing to hide it rendering the multiram useless so bought spares from a vectra

Always worth a check then snap the TB shut and you should see if they work