Date: Wed, 28 Aug 2013 00:12:13 -0400
Reply-To: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
Subject: Re: Fuel pressure anomaly
In-Reply-To: <C6985859-F0DD-4783-830E-727EF403415F@shaw.ca>
Content-Type: text/plain; charset="US-ASCII"
Getting bad gas is very rare with todays tanks and fuel distribution
network. The Syncro having a high mounted plastic tank makes it rare to have
a fuel storage problem on the vehicle itself.
The short pump inlet and overall design of the fuel delivery system also
makes issues like vapor lock and other weirdness's rare also. The ability of
the system to hold pressure after shut down is not much of an issue like it
was on the CIS systems. If the pump has enough capacity to make pressure and
the regulator is working all is good. Leaky injectors are easy to check.
Remove them, jump the pump and look for leaks. Then get them to spray and
check the spray patterns. A bad injector will be obvious.
Intermittent bucking and poor running can indicate an over rich condition
which is most likely being brought on by an O2 sensor problem. Easy test is
to cycle the ignition while the problem is happening. If the problem
immediately clears up for short while you have an O2 sensor or wiring
problem. Besides the sensor and wiring to it a common problem is a bad
ground. On the early Syncros the ground wire for the distributor harness was
usually connected at the base of the oil breather tower. This connection is
also the ground reference for the O2 sensor. The plastic tower makes for a
lousy connection. Relocate this ground and also check the connection to that
ring terminal.
If the O2 sensor test does not indicate a problem there than the next thing
to check is the temp sensor. These sensors themselves rarely go bad but the
connector and wiring is often a problem. So is the ground in the harness.
Get your ohm meter and check the ground connection (brown wire) from the
sensor to the chassis. If you can measure any significant resistance add
another ground to this wire. It is common to see 10-20 ohms here. Should be
almost "0".
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Alistair Bell
Sent: Tuesday, August 27, 2013 11:24 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Fuel pressure anomaly
I have posted about my intermittent bucking and poor running with my 86
syncro, something that occurred only sporadically, in summer, and all but
one time on rough logging roads. Until the last time I was putting it down
to bad gas.
Last weekend I had the chance to swap in a used fuel pump. I drained the
tank while doing this and did not find any crud or water. After the swap the
van exhibited the bucking and missing behaviour. I checked other things, arm
track, connections etc etc.
I had checked the swapped pump delivery rate out of the van and it seemed
ok, but tonight I decided to check it again by the book.
I got 600 ml in 30 seconds, Bentley says min rate of 500 ml in 30 sec.
Then I checked pressure, all to spec. So I turned off engine and went
back... Saw the pressure gauge dropping fast. That's not right, it should
hold pressure. I started engine again and turned it off, pressure held.
Started again and off again, pressure dropped. I tried clamping off return
line and it did slow the rate of press loss.
Then I started van again, no clamps, pressure held. Held to spec. Only
dropped 2 psi ( 33-30) in 10 min.
The pressure drop occurrence could not be replicated consistently. I do
suspect the fuel press reg but I need to rule out a leaky injector ( mind
you, no gas smell from exhaust on restart).
Dennis, what do you think?
Alistair
