Itinerant Air-Cooled

Psucamper wrote:So I made up a new 'harness' of ground wires for everything including the brown wires from the double relay and sent them all to a common point on the block.

Gauge pressure was no more than 15 psig!
current suspicion is the FPR is partially stuck/faulty open and won't permit a pressure buildup to a nominal 28 psig. Hate to pull the FPR if there's a diagnostic that will clarify the situation. Next? Bob L.

At idle, remove vacuum hose to fpr and see if it improves. Reapply vacuum hose and see if pressure drops from whatever the hose-off number was. We are looking for variation as a proof of function.
Now get a pair of vise grips or your fuel hose clamping tool and, at idle, block the hose to the fpr while looking at the gauge. If the pressure reaches 50-60 psi, release! clamp! now! your fuel pump is able to create pressure,

As a general rule, if pump is being starved badly enough to drop the pressure to 15 psi, it will not be able to drive down the street. Inlet line from tank to filter is a very likely culprit. You remove the hose at the inlet of the filter and see that it drains with alacrity. Better yet, if you are unsure, remove the hose from the tank, quickly stick a hose-blocked-with-a-bolt on the tank nipple, and remove, blow through, inspect, replace hose ends, re-install after a quick check of tank outlet itself for any rust or obstruction.
Colin

Did it pass the "volume test"?

1 L in about 30 seconds.

Success!! Found the culprit. All diagnostics led to a very thorough re-examination of the bus harness in the engine compartment AND under the bus. The ground wire from the dbl relay at the fuel pump was intermittent (at best) and led to false conclusions on many levels. Made a quick temporary fix and fired up the engine. It's alive and well. Cold start OK and handover from fuel pump relay to power relay perfect. Thanks to all for pertinent advice. Now on to the real work. Bob L.

Good detective work!

Psucamper wrote: handover from fuel pump relay to power relay perfect.
Thanks to all for pertinent advice.

For the record, there is no "handover" from the fuel pump relay to the power relay. They are utterly independent of each other.

It is the fuel pump relay that is initially energized from starter through 86a:


. . . . . . and the same relay is subsequently energized from AFM through 86b:


Thank you for your consideration of this exceptionally important point in this most technical of all forums.
Technical Managing Editor

Colin....I dig. Clarification duly noted and appreciated. Bob L.