My question relates to the much-discussed fuel pump/prepump/relay/regulator issues.

Car is 1986 245 manual trans.
Symptoms are:
1. an intermittent loss of fuel pressure, often will be triggered when accelerating the car through the gears
2. sometimes will recover after a "blip", but sometimes will not recover and you are stranded
3. the car will idle almost normally, and can even rev a little in neutral, but cannot deliver enough power to move without stalling
4. possibly my imagination, but I believe the problem is much more likely to occur when the tank is about 1/4 to 1/3 full

What I have done so far:
1. new in-tank pump, hose and sock - pump now runs but original problem not fixed
2. new fuel filter - not fixed
3. new fuel relay (at passenger footwell location) - seemed fixed for a couple of weeks, but then problem recurred when fuel got low again (?)

I am now thinking that the fuel pressure regulator may be intermittent, but I have yet to prove that the main fuel pump and its electrical supply are completely OK. One important question for anyone who knows:

If the main pump is completely off (no power supply), can the in-tank pump provide enough fuel flow through the turned-off main pump to allow the car to idle? If the answer is no, then I don't need to keep looking at main pump electrical supply and relay problems. If the answer is yes, then I still have a number of candidate problems to work through.

Can the FPR show intermittent stuck-open (low pressure) behavior like this? Why would the fuel level in the tank affect this problem if the in-tank pump and hose are fine?

Thanks for any ideas.

Joel
'61 - '94 544, P1800, 122S, 1800ES, 164, 245, 850