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1973 bus - engine photos and questions.
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Amskeptic
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Joined: October 18, 2002
Posts: 8568
Location: All Across The Country
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PostPosted: Sun Feb 14, 2010 3:41 pm    Post subject: Reply with quote

WestyPop wrote:

BTW there's a nice info piece on your bus's emissions control systems right here on the Samba http://www.thesamba.com/vw/archives/manuals/73emissions.php

Good luck solving the mysteries.


Here's some too, fresh off the press . . .
Very Happy

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EMISSIONS EQUIPMENT

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Most of these systems are no longer mandated. You want to disable some that pose a risk to your engine's health, and you
want to keep those that work. This diagram will help you identify any unknown wiring and switches and plumbing that have
managed to hang through the years with your engine. Perhaps it will help answer what that strange sensor is languishing
over the battery (yes, that would be the 4th gear only vacuum advance temperature sensor #25), or the switch on the '74
cooling flap shaft that shuts off the EGR when the engine is not fully warmed up (#16)

Evaporative Charcoal Canister and hoses (Diagram 4 #4, #8, #11, #12) and particularly the tee #11, should be intact and functional.
This system serves up some nice fuel fumes when starting off after a sit. Better that the engine enjoy them, than the cabin full of your friends and the dogs.

Crankcase Ventilation is a good system to have. The crankcase breather hose should be inspected for kinks and deterioration. If you have lousy rubber it will sag shut. Then someone will tell you that you need an overhaul because oil is blowing out your dipstick. The breather box should be cleaned at least once every ten years or so. The '72-'74 system is passive but effective.

Preheat Intake Air (Diagram 2 E), keep! Can be checked by applying vacuum to the end of the hose at the thermostatic switch on the underside of the right air horn. Follow this hose to the valve itself on the air cleaner/filter intake. It should close off the fresh air under vacuum. The thermostatic switch in the right air horn should "sing" quietly when
warm. Your mixture reference hose's day job is to provide vacuum to the preheater when intake air is under about 55*.

Your air filter intake fresh air supply should be hosed in from just above the battery. It is a big diameter (38mm?) pleated black paper/aluminum hose.

Thermostat and flaps, keep. These are engineered to work with your chokes, enrichment device, fast idle time, and EGR temperature switch, and they really help the oil from getting contaminated with cold combustion byproducts that encourage sludge. Make it all happen as the factory designed it. As thermostat supply dries up, we need to create a
robust idiot-proof alternative.

The EGR is a potentially dangerous system if it develops fresh air leaks. Exhaust is inert and "cool" to the engine. It has been asked to recirculate to cool down combustion, but if there are any leaks in the EGR plumbing or valves, oxygen gets in there and heats up the combustion due a lean mixture that burns your exhaust valves. I disabled my EGR in 1980,
lugged the inlet to the balance pipe right at that "Vac Valve" (for '74 only) on the Diagram 4, sealed the EGR valves at the vacuum nipples (Diagram 4 #21) in case the diaphragms should ever leak, and blocked off the muffler's EGR flange.
My last California smog test NOX emissions were well-within specs without it. If your system is intact all the way to the muffler, you can test the EGR valves for proper closing by pulling a hose and applying vacuum to the end of the valve. It should slow the engine down, then recover when you stop applying vacuum. Make sure your EGR plumbing is air-tight from the muffler take-off all the way to the balance pipe.

The Air-Injection system is an accessibility obstacle course (#22) and I deleted it as well, plugged the heads where the injection pipes (#19) thread in, and I blocked off the central idling anti-backfire valve port at 3, and kept the pump as a momento only. Air injection has a major downside to it, it raises exhaust temperatures through the roof and
promotes cracking in the valve port/seat area. These air-cooled engines are pushed to their limits with air-injection and, much like a mis-fire that overheats a catalytic converter, a rich main or a mal-functioning choke because the wire fell off or something, will heat those exhaust ports as detrimentally as a leak in the EGR will heat the combustion chambers,
in both instances, the heads suffer. The anti-backfire valve (#23) has to work if you're keeping it. The control hose (it tees into the "Mixture Reference Hose") opens the air pump outlet to the central idling circuit every time there is high vacuum, i.e. when you shift, so that the afterburners don't backfire like mad. If any of these connections leak, you are introducing air that will burn up your engine under load. Pull the hose off the air pump-to-check valve (#1) also. It won't give you vacuum leaks, but it will give you noise, soot, unwanted heat, and exhaust fumes waiting to get sucked into the cabin through the heater blower.
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