Checking over the engine in the 90 and noticed a couple of things.
Firstly, I have a blanked hose on the RHS of the plenum. Is this a problem? Normal modification?
Where should that hose be connected?
Secondly, there is a pinched hose under the air inlet ducting. What is the purpose of the hose and what are the implications of it being pinched/kinked?
Paul,
Looks like a GTV6 plenum. There are slight differences between early and late engine plumbing setups. Not really a problem unless you want to make it look original.
You should probably change the kinked hose. Try your local speed shop for some silicone hose. Even comes in colours and most places will sell it by the metre these days.
Cheers
Steve
Adelaide.
Regarding the plenum, I've noticed when flipping through the 75 workshop manual (Fuel System section), there is reference to that sort, with connections to a 'vacuum regulating valve'; both the blocked-off vacuum port and your unused small port at the front. The purpose of which is to reduce exhaust emissions and thus unrelated to performance. Ensure both ports are properly blocked if you leave them unused.
With the kinked hose, whilst not ideal, it's unlikely to be completely blocked, and should still function fine. It simply supplies air via the auxiliary air valve during cold start-up. But for sure, replace it when you can.
:)
That small 'unused' port at the front actually has a hose. It had come loose and was hiding among all the other rubber spaghetti in the engine bay.
I guess I'll simply start pulling stuff off the engine until it affects performance..... ;)
I do have a full GTV6 manual somewhere, I really should dig it out.
Here's a comparative photo from my '83 GTV6. Same plenum, but the external components are in different places.
That's the one - the vacuum regulating valve is shown. 8)
On my 75, that short 'port' off the top of the throttle body also provides vacuum advance for the distributor. I don't know if that's relevant in the GTV6.
:)
Yep it's for the vacuum regulating valve. Also went to the small diam port on the front of the plenum - make sure that is blocked too. I had a mongrel of an idle issue on my '83GTV6 that took about 6 months to track down to that little sucker. I think it was blocked with oily goop so that it took a fiar bit of heat to allow it to start playin up and effecting the idle. Leave it off! It's supposed to relieve excess vacuum when you back off suddenly from high load for emission reduction. I figured that given how much oil my car was burning (or pumping straight past the rings) that a little excess vacuum was irrelevant. It also had a 3rd hose going in to the intake pleated tube on the drivers side near the Throttle Position Switch on my car, so you want to make sure that is blocked too.
The other small diam port at the front of the plenum provides vacuum to the fuel pressure regulator.
Early GTV6 (my 1983 at least) didn't have vacuum advance on the dizzy. Still surprises me - but I guess ALFA knew what they were doing. In the top view photo of the '83 you can see a small diam length of brass tubing on the top of the throttle body that was intended to supply (draw?) vac to the dizzy. have a close look at the end and there is a brass plug in it and the end is polished, so you see a circle in the brass.
Quote from: shiny_car on August 13, 2013, 07:35:41 PM
On my 75, that short 'port' off the top of the throttle body also provides vacuum advance for the distributor. I don't know if that's relevant in the GTV6.
:)
yeah ok shiny_car already explained the dizzy port. Sorry.