MicroSquirt.com read only forum (Jan.15,2018)

Need some input on this situation...

This is how I currently have the plumbing hooked up

Tank pickup to a brass tee, one side of tee to fuel filter, to pump (walbro gsl392), to fuel rail, to regulator, and other side of regulator loops back into the second end of the tee mentioned previously. Tank and filter are strapped to subframe near rear tire.

Has been running for several thousand miles like this w/o issues for my mpfi setup. Previous to that, similar plumbing with a gsl395 pump for tbi had no pump issues.

Recently this issue has cropped up. Upon initally starting the car that day after sitting overnight, everything is fine, pump sounds normal. After the drive, the pump sounds very screachy, not healthy at all, but engine runs ok all seems well otherwise. Pressure is maintained according to underhood gauge.

Every now and then, very hard to duplicate consistently - when the temps start to climb in stop and go traffic, the pumps screach gets even louder and louder, pressure drops until the engine stutters and dies. Try to restart, same issue, engine shaky, pump screachy... after few attempts to start and keep the car running, and traffic traffic lets up, get back to speed, all is normal and well.

I can sit idling in the driveway with the pump screaching, w/o issue. If, after sitting, and before driving the car for the day, I take 12v to the pump and run it w/o engine on for 15 min, there is no screaching.

I think I may be overheating the pump by taking the hot fuel return to the pump input instead of the tank (don't have provisions for fuel return to the tank, but thats in the works now....) What are your guys thoughts ont he situation? Is it possible for the pump to get noisy only when its hot, and aren't they designed to pump warm/hot gas? Should I replace the pump as well just incase it may of gotten permanently dammaged?

It sounds like your pump is cavitating, probably due to hot fuel at it's low pressure side. They'll pump warm liquid fuel just fine but when said fuel flashes into vapor you get symptoms as you describe. Your plan of returning to the tank is an excellent idea. Let us know if that solved the problem. If it was me, I would have a reduced level of comfort with that pump and relegate it to spare part status and get a new one.

-Mike

It'll also help if you put the fuel filter after the pump instead of before it.

A low throttle openings most of the fuel fed to the fuel rail is not used but returned to the tank. It wont take much to heat up whatever quantity that is held in the pump, high pressure line and fuel rail. You need a return line to the tank! Try to keep it away from the pickup point, or you may get cavitation problems at that end.

Kendall.

Ok, so it seems unanimous that return to pump input isn't a good idea. Thought I read about someones install where it was a success - not in this case apparently. I also thought it would help with fuel sloshing in the tank because the pump would be recieving most of its input from the return and not the tank - now I may have to worry about this

About the filter being infront or behind - is there an offical stance on this? Some say put behind pump so that dirt won't harm pump as sock on pickup isn't good enough, others say only infront.... kind of confusing.

pierre71 wrote:About the filter being infront or behind - is there an offical stance on this? Some say put behind pump so that dirt won't harm pump as sock on pickup isn't good enough, others say only infront.... kind of confusing.

Filters always should go after pumps. This is because if they plug, after the pump is a much safer location. Ahead will cause cavitation, whereas after will cause reduced pressure and flow, but no pump damage.

jib

jib

Happy to report that did the trick ... I got a sending unit that included both a pickup and return line, then sent the return from the regulator into that. No more pump screaching!

I still am running the existing pump with filter before - I may change this later but for now it will have to do. Perhaps some sort of surge tank system....

pierre71 wrote: Recently this issue has cropped up. Upon initally starting the car that day after sitting overnight, everything is fine, pump sounds normal. After the drive, the pump sounds very screachy, not healthy at all, but engine runs ok all seems well otherwise. Pressure is maintained according to underhood gauge.

I had a screechy sounding fuel pump in the Jag, just like you indicated. Turned out that the tank had rust floating around and it would collect on the fuel input sock and start blocking the inet. Jag XJ-6 had the tank filler tube located on the top of the trunk area, where water eventually gets in.

A new tank fixed the problem, as did a new filler tube sealing gasket.

- Bruce