Fuel starvation, cavitating fuel pump.

[dgbeatty]

We had fuel cavitation problems in the middle of Nevada. I changed the pump and filter in a McDonald's parking lot in Fallon, NV (pavement temp 153°f). The problem reoccured 50 miles later. We spent the night and scurried home early the next day while it was still cool without further problems.
Once home we installed a new tank believing that to be the problem. Upon inspecting the old tank with a remote camera it was spotless inside (the original OE tank). At this point my hypothesis was the the screens assemble or the internal plastic line(s) had failed in an area I was not able to inspect. I installed a fuel resistant clear hose on the fuel pump intake to observe. Sure enough it was continuously cavitating with a full tank at idle.

CONCLUSION Two factors created the problem.
1. We use LFP batterys and as such our alternator is set to 14.8 volts.
2. We use a Pierburg fuel pump. These pumps have essentially the same specs but are renowned for their toughness. They do provide a very slightly higher delivery quantity.
Combined these two changes increased the fuel delivery quantity to the point where it exceeded the ability of the tank to deliver a solid stream of ETHANOL. On pure non California gasoline the problem does not come into play.

SOLUTION.
Reduce the pump speed. A 30amp PWM speed control set to 10 volts achieves the specified return fuel flow. Cost $10. Never doing anything simple I installed a PSC (pump speed control) that calculates pump speed based on RPM. Cost (you don't want to know).

This has been a problem for the past three years with various changes made. It was my punishment for not following the full test procedure
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Schau in das Buch

[MarkWard]

What size outlet did your replacement tank have?
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[dgbeatty]

The van is an 87 Westy. Both the OE and replacement tank are 12mm outlets.
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Schau in das Buch

[dobryan]

I cannot believe the outlet at 12mm could be the issue. Something else in the tank system must constrict the flow.
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Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

"To travel hopefully is a better thing than to arrive." Robert Louis Stevenson

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[DanHoug]

[MarkWard]

I think the point was that the alcohol added to the fuel was lowering the vapor point that in conjunction with the higher efficiency pump was causing the cavitation. Not an actual restriction per say. It makes sense to me.
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[DanHoug]

[dgbeatty]

Perhaps I was not clear enough.
It continued to occur with a NEW tank.
YES the pump is cavitating caused by lack of solid fuel stream.z
No there are no fuel or air leaks.
Yes I have measured the pressure at the pump inlet, it is negligible.
Yes I have measured the tank pressure, essentially 0 differential.
Vehicle speed does not appear to be involved.

Somethings that I should have made clear.
It was August in Nevada, I was over 4000 elevation. It has never occurred at lower temps or elevation. 12,000 is fine as long as it is cold. 110f is fine in death valley. It is the combination of altitude, temperature and running time (minimum of 1 hour).

When it occurs the pump becomes much warmer. No the pump is normally quiet. It just occurred to me to perform some testing with a swirl tank installed. BTW this a known problem with the WRX-STI crowd. Many go so far as to add a surge tank with a swirl device and a second pump in the trunk. There is also a documented problem of fuel heating with recirculating fuel injection systems.

Dan Beatty PE
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Schau in das Buch

[DanHoug]

ah, thanks for the clarification Dan. you've done your homework. sound like you need an ice can cooler for the fuel line! better yet, a 2-tap chill plate in an ice chest with one line for nut brown ale. NSF approved, of course.

back in the day, my dad said they'd pee on the fuel line if the car vapor locked from high under hood temps.... probably be multiple obscenity charges today with the ethanol fuels.
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-dan
60% of what you find on the internet is wrong, including this post.

'87 Westy & '89 Westy both 2.1 4spd

Past projects can be found at--
www.thefixitworkshop.com

[Wildthings]

Sure your fuel tank is venting properly? Perhaps a ventilation hose is blocked or the carbon canister is a mess inside.

[dgbeatty]

Dan Houg ,thanks for looking this little problem. I am on a test drive this afternoon. Sacramento to Weed as fast as I can go with a couple idling stops on the hottest asphalt i couId find. The van has run well, the pump has stayed cool and quiet. When I replaced the tank I insulated the front and top sides to protect it from radiator heat. That and the PSC appears to have hopfully cured my self induced problem. Just need to find a higher and hotter road to be sure. What has worked in the past is to load the van with the wife and dog and have a definate place far away as the destination.
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Schau in das Buch

[Wildthings]

Other people drive these vans in all kinds of weather at all kinds of altitudes. If yours will not do what other vans do, your van must have some part of its fuel system that is out of factory spec. Finding what it is and getting it back to factory condition would most likely be the best policy in the long run.

[letsrig]