scout4bta

This adventure started out with the engine not starting after setting for a few days. It would start after priming with the lift pump but without bleeding. I temporally installed a 0-15 psi analog gauge at the banjo bolt to the filter to check the pressure.
It has good pressure at cold idle (8 psi) and a small bit of throttle it would climb to 12 psi and just after shut down the psi would climb past 15 psi (18psi?), wrap the needle all the way around and then slowly drop to zero psi. This can't be normal!

My guess is the IP (VE) if feeding the pressure back to the top of the lift pump. But why, how?
Ideas, suggestions?
The lift was replaced July of 2017.

oliver foster

I bet when the FSS closes it is causing a back pressure for a quick moment while the LP is still producing pressure.
Resulting in a slight spike in pressure.

This is just a guess, as I don't run a fuel pump on my 1st gen trucks all the time. I just install one for diagnostic purposes when needed in the shop.

scout4bta

Yes could be that the IP still rotating is causing the spike. Never thought of looking at the gauge during shutdown until now, could have been happening all the time.
I'm not using the FSS just the emergency lever if that makes any difference.

maybe368

I think that this is probably normal, especially because your gauge only goes to 15 lbs. I bet that if you put one that goes to 100 pounds, you wouldn't even see it. Also, I don't think that it can blow out the front seal, because the FSS is gutted, there is nothing stopping a little back pressure as you mentioned. I say party on and don't worry about it...Mark

scout4bta

Found a new in the box gauge same make etc, it reads 5 lbs less. Pressure still spikes after shutdown but only goes to 12 psi.
Engine had set for 3 days, had to prime it before it would start.

maybe368

Sounds like you have an air leak on the suction side...Mark

oliver foster

You took the words right off my keyboard....

scout4bta

Yea I've fought that monster before and now it's back.

edit: Really makes me want to replace all the flex lines with stainless steel braided hose........

maybe368

Ha! You should have better protection for your keyboard, the alpha thief strikes again...Mark

edwinsmith

Does this last longer than regular hose? I figured it was just more rugged and resisted cutting and abrading.

maybe368

The usual advice may not be good, because yours is in a scout. It may still be worth pressurizing the fuel tank with a few psi's to see if it shows up. Did you just plumb directly into the scout tank? or is it a transplant?...Mark

scout4bta

The spiking lift pump pressure isn't.
The previous test was done on a cold engine, did the test with a hot engine, NO spike. False alarm.
Why the difference no idea.

maybe368

Did you find the leak?

scout4bta

Besides all you mentioned it eliminates push on slip fittings. Every connection is via flared AN fittings.

scout4bta

Just beginning. Looking at the obvious first, cracked flex lines etc.