Hi all, so I was looking at the owner's manual and stumbled upon the air injection system diagram, and it doesn't make sense to me. From what I see, the fresh air (from the air filter box) is under some negative pressure (from the engine pulling through the injection plate) and the exhaust ports would be under positive pressure so it looks like all it does is take a little exhaust gas and recycle it although it's stated purpose is to inject a little clean air into the exhaust. Are the exhaust injector ports angled so that a low pressure is achieved across them?? Thanks, Lester Image Unavailable, Please Login
I only have a guess, that would be venturi effect. The exhaust gasses rushing past the port draw in air. There is a one way check valve on each bank that doesn't allow pressure to go in the opposite direction. Those valves do go bad and the corrosive exhaust gas is usually the cause of rotting out a T in the system. Some suggest the check valves are something that should be replaced at a 30K service as a maintenance item.
+1 But it's more due to the exhaust valve closing and the inertia of the exhaust pulse moving away from the exhaust port causing a low pressure area to form behind it -- i.e., the exhaust pressure of a single cylinder is not constant (where the air injection nozzle is located). Occasionally in the cycle, it drops below the pressure in the air box, and air is drawn (or really pushed) into the exhaust stream (of course, only when the engine is "cold", and the cutoff valve is open).
My "T" was completely rotted out requiring replacement but I really didn't give the valves consideration for replacement. I wonder if I should given they have 50K on them and due to the state of the T in the system? Probably a $500 part at this point, anyone replaced these? I don't recall Rob of Robzworkz testing or replacing these when he redid the lines as I'm doing....
The valve is $20 at Autozone. And the T is $100 at a dealer. I have seen T that would work at a plumbing shop.
Yes, I did a search here in the past when I had one go bad. It might be called an air injection check valve? It's a GM part and available at the chevy dealer or general auto parts stores. I no longer have the part number but I got it at Napa. I wasn't aware of the changing them at service idea. I only found mine when my engine got noisy. Traced down the noise and found a crack, within a few days it had broken as you see. The rear one had been replaced in my car. There was a decent write up I recall that I followed that I found here somewhere, probably in the 3X8 section. I think the first picture illustrates pretty well the corrosiveness of the exhaust gases. The male end there was longer on the replacement, it had rotted to crumbs. The pics are taken of my Mondial 3.2 through the passenger compartment hatch. (to avoid confusion) Image Unavailable, Please Login Image Unavailable, Please Login Image Unavailable, Please Login
When I replaced mine in 2009 the direct replacement was a Niehoff FE476 which I purchased for $16/ea from Shucks (now Orielly's). My air injection came off 3 years later and the tips were already rusted but the valves still worked. Image Unavailable, Please Login
Thanks! That's only three years worth of rust? I don't know if mine were changed ever so makes sense to change since I'm replacing the hoses. Hopefully they come off easily.......
Ettore, Did you plug the ports with Verrell's bolts? I've been thinking of taking this system off for years, but I didn't know if the plugs could be installed with the engine still in the car.
Yep, used Verrell's air injection plugs. I was able to do it with the engine in the car but I had the fuel distributor out at the time which made things much easier on the rear bank. I was able to access all the fittings from above on the rear bank and from the wheel wells on the front bank. Image Unavailable, Please Login Image Unavailable, Please Login
Looks like you had your exhaust test ports out as well, which I'm sure also made it easier. What did you use to plug the outlet on the air filter box?
Richard, one of the gas analyzer tubes was corroded completely through and the fittings on two others were pretty bad so those came out and got plugged as well (see post #4 for details on that: http://ferrarichat.com/forum/showthread.php?p=141578012#post141578012) . As far as the air filter box, I used a 22mm vacuum cap from HKS to plug the port. I left the smaller vacuum line from the throttle body to the electrovalve connected and just clamped off the hose that previously connected the electrovalve to the air injection valve. Image Unavailable, Please Login Image Unavailable, Please Login
