[T3] Getting Ready for the Gathering

[Keith Park]

When I ran into the fuel pressure regulator problems, 
The pressure would spike on startup, making for hard starts,
Then slowly come down.. it would run rich but still ran OK.  Sometimes it
would 
Be high for a while driving around but the only symptom would be the hard
starts, and of course,
Slightly less gas mileage.

Keith


Topnotch Restorations
topnotch at nycap.rr.com
http://www.topnotchresto.com
71 Squareback  “Hothe”
65 Notchback  “El Baja Rojo”
93 RX7  “Redstur”
13 Subaru Outback "Blendin"

-----Original Message-----
From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> On
Behalf Of jadney at vwtype3.org
Sent: Friday, June 9, 2023 1:10 AM
To: type3 at vwtype3.org
Subject: [T3] Getting Ready for the Gathering

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.

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

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