[Skodapilot]

OK, from the hiss, I know it's vacuum related, and that is why I'm only getting base boost.

The sound is coming from the left hand side speaker grille. It appears to be the fat vacuum hose that runs from under the dash through under the fuse box toward the cruise control.

What does that hose plumb into, and what is the easiest way to get to that hose. I've tried going in through the speaker grille, but can't find enough room to work and remove/repair anything under there.

 

[adrian]

Hi Meatball you'll need to take the lower dash out. Take central console out, heater ducts and then drop lower dash - two nuts in engine bay at the sides hold the lower dash at the sides. The tube in question goes to the diaphram that operates the throttle (housed under the dash next to the heater box) and to the clutch and brake pedal cruise switches.

 

[Skodapilot]

Cheers. Figured that was what I was going to have to do. Wasn't sure where the mounts for it were. You cleared that up nicely.

It's an '84/'85 T16 so I think it is only the Brake with the Switch. I hope the Diaphram is OK, or all the acres of pipe work for everything else vacuum related. Might have a go at the switch pedal adjustment while I'm at it, see if I can get cruise to work again.

 

[Skodapilot]

Well, I had a go at dropping the lower dash. Fund the two outside bolts below the windscreen.

Bloody socket extension isn't long enough. Typical.

Ended up having to try again through the speaker grille. Sweated blood but replaced loads of pipe-work.

Still leaks, only shows a quater boost on the gauge. Hiss goes on and off like a valve. Some hiss on low throttle, no hiss on mid throttle/revs, loads off hiss on big throttle/boost.

Whie I was in there, I pulled on the cruise operating chain, and that worked fine, revs rose.

Then under the bonnet, sucked on one of the cruise controller pipes and again the revs rose.

Someone else suggested the pressure transducer, what does that do? is it an expensive part, does this really mean a dash off job to replace?

 

[wrighar]

I went through 4 overpressure switches on my old C900 T8 (but no APC pressure transducers)

The overboost switches seem quite prone to leaking. luckily with the right nack they can be changed without removing any dash bits as the have a little clip like that that holds the oil filler neck in place, and you can just get your hand up from below

Andrew

 

[9000CS23T]

Originally posted by Scaero (ecopower stg0):
[qb]I went through 4 overpressure switches on my old C900 T8 (but no APC pressure transducers)

The overboost switches seem quite prone to leaking. luckily with the right nack they can be changed without removing any dash bits as the have a little clip like that that holds the oil filler neck in place, and you can just get your hand up from below      

Andrew [/qb][/b]

Yes I've replaced one of these before, symptoms were pretty much the same as yours. You can get it by lying on your back in the pass footwell and looking up behind the glovebox. I believe from memory it has two vacuum pipes and two wires on it.

 

[Skodapilot]

Guess it is time to start crawling arround in the footwell then.
Wonder if I could disable it temporarily, and see if that is the problem.

Do you plug the Hose(s), and join the wires I've heard? Does yours still have all the foam rubber hanging down? that seems to block a lot of the view.

 

[bambo]

I had symptoms similar to what you describe and on mine, it was the pressure transducer which is like the overboost switch but has no wires going to it.

My Boost reading didnt go to 'base' though, so is it possible that your problem is the vaccum pipe running from the guage to the transducer rather than it or the over-boost switch?

 

[Skodapilot]

I'm only getting a peak mid orange in bursts, but a normal 1/4 to 1/3 orange normal boost.

When I was swapping hoses, I managed to knock one off the overboost (I think). the hiss suddenly got louder. I'm going to disable that first. if that doesn't do it, then In shall move onto the transducer.

I am going to crack this, and get back my

 

[Skodapilot]

Biggy update:

Tonight, wrestled below the Dash, and through the speaker hole.

Removed the two two hoses from the over boost fuel cutoff.

Joined them directly. Left the electrical wiring on the cutoff for now.

Started the engine, no hiss.

Took it out for some welly.
Was giving 1/4 yellow on the APC gauge, now giving 2/3-3/4 and holding solid.

No annoying hiss, and sounds absolutley beautiful when the Bailey recirc dumps back, now I can hear it through the RaceX conefilter.

Guess I should really go about getting base boost checked now, and doing a little APC tweaking.

Not too much now, with no Overboost.
Might see about linking the wiring tomorrow, see if that pushes me a little higher.

Whoohoo.

 

[wrighar]

MbT,

That's good and pretty much what I ended up doing several times.

This now means:-

Your seeing real boost at the dash (Possibly no more than you were getting anyway
You getting an acurate APC figure to the APC box and probably better fueling (richer) under boost now leading to longer engine life and possibly more power/boost.

My old 8v would run a bit sick and stutteer under hard high rev boost when the overpressure switch was leaking as the APC wasn't seeing boost figures.

Andrew

 

[Skodapilot]

That figures. It seems to come instronger now, but not that much faster if you get what I mean.

The idle position for the needle is about the same as it was. That hasn't changed at all, but appears to boost higher.