All those issues were dealt with. O2 sensor, temp in sensor etc all checked, grounds, connections, resistances.

 I think I mentioned that a while back when I first posted about this bucking issue. You might recall that this issue only occurred 3 time previously, about 18 months apart, only in summer, and 3 of the 4 times was on logging roads.

The issue I was trying to get across was that I now have the bucking happening, not as severe as it sometimes is, on regular streets AFTER I swapped in a different fuel pump. And that I noticed the fuel pressure not holding when tested tonight.

Alistair

On 2013-08-27, at 9:12 PM, Dennis Haynes <d23haynes57@hotmail.com> wrote:

> 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
>