[T3] Getting Ready for the Gathering

[jadney at vwtype3.org]

My '71 Square has been parked in our garage since last year's trip to Cincy, so last weekend 
it was time to get it out and get it ready for the Gilmore Aircooled Gathering in western 
Michigan.  

A month or so ago, I'd been driving the rusty '73 back from a friend's shop about 20 miles 
south of here. I was just over a mile from home when it started to buck, backfire, and 
generally not want to go any farther. Well, I managed to nurse it home, and later I discovered 
that the vacuum hose had fallen off the Pressure (MAP) Sensor. I figured it had just fallen off, 
so the fix was easy.

Unfortunately, a couple weeks later, I drove it again for some local errands, and had to stop a 
few times to let it recover (cool?) so it would drive another half mile. Checked that same 
hose, but it was okay this time. Now I'm thinking the hose just blew off when the car 
backfired, but the root problem must be something else.

So this got me thinking about other possibilities, and could any of them be things I should 
check/fix on the '71 before the trip to Michigan. I figure there are three possibile problems 
with the '73 that could cause these symptoms, which appear to be excessive richness or bad 
injection timing: FI trigger point gaps, Pressure (MAP) Sensor drifted out of cal, or that weird 
non-venting problem with the fuel pressure regulator that causes fuel over-pressure.

Well, I went thru the '71 distributor last year, so I can cross that off the '71 list.

I had a couple '71 MAP sensors here to check their calibration, so I pulled the sensor out of 
my '71 to check it while I was set up to do it. Well, it was running a bit rich, so mine got 
adjusted at the same time. Unfortunately, by the time this happened, the '73 was put away in 
the garage and filled with all the crap that gets stored in whatever car is stored there. So that 
will have to wait for another day.

Finally, I decided to pull the fuel pressure regulator out of the '71 and drill the tiny vent hole 
that will prevent the over-pressure problem from ever happening. Drilling that little hole is 
easy, but getting that regulator out of the car took most of a day. In the end, I had to put the 
car up on jackstands unbolt the rear engine supports, and lower the engine a couple of 
inches. This was all due to the fact that the factory installed hose clamp was in such a 
position that it was unreachable from any direction with the engine fully in place.

What an unnecessarily nasty job!!!

The problem with the fuel pressure regulators is that the only vent for the air side of the 
internal diaphram is via the helical path around the threads of the adjusting bolt. After a few 
decades, corrosion seals this path and the air chamber becomes a sealed volume. Once that 
happens, the pressure regulator can't respond to changes in pressure due to altitude and it 
starts to respond to a warm engine compartment by increasing the fuel pressure. I wanted to 
fix this potential problem on my '71 before this trip.

If you want, I can do the same mod on anyone else's regulator very cheaply. If you want to do 
it yourself, use a 0.051" carbide drill to make a very small, but reliable, hole on the bottom of 
the regulator body. Be sure to drill the hole in the AIR side of the regulator!

If you don't touch the adjusting screw, the regulating pressure won't be altered.

I'll do the same fix on the '73 after we get back from Michigan. I figure that's the most likely 
cause of it's problem, since it seems to show up only as the engine compartment gets hot.

I'll add the regulator mod to my price list. I figure $5 would do it, or $10 if it needs to be 
cleaned. So most of the cost will be shipping, unless you have other things for me to do at 
the same time.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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