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