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| Fuel Pump Cavitation https://slantsix.org/forum/viewtopic.php?t=51844 |
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| Author: | Lobster1 [ Thu Apr 25, 2013 9:08 am ] |
| Post subject: | Fuel Pump Cavitation |
I am about to tackle my fuel pump problem and thought I'd throw it out to the Forum before I drain the bank again. I installed the Powerjcection 3 bolt on EFI and it works really well except when it does not. When the car is warmed up and idling the fuel pump starts to cavitate, kind of like vapor lock in the pump. Why would the thing generate more heat under less load? This is the return-less system and a control module turns the pump off and on to keep the fuel pressure between 40 and 50 psi. Check list; fuel tank clean, pump is below tank and primed, pump has big heat sink, is shielded from exhaust, filter is new, and tank vent is not blocked. When I Google search Powerjection fuel pump I find dozens of blogs and complaints similar to mine, but I find people with other brand having issues as well. I am fairly positive my problem is cavitation. I hear the pump spinning high rpm's with no resistance, I watch my air fuel ratio shoot way up, and my fuel pressure drops to zero. This is my attempted solution, open up fuel tank vent. Currently it is a fuel line int the trunk with a tiny hole in the end. Can I safely open it up? Replace fuel pump with a Bosch 044 and replace filter. What else have I over looked? Any thoughts? Frustrated in EFI Land, Barnaby |
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| Author: | Matt Cramer [ Thu Apr 25, 2013 11:48 am ] |
| Post subject: | |
You mentioned the pump is below the tank, but where exactly is it located? Is it literally directly underneath the tank, in front of the rear axle, or what? |
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| Author: | Lobster1 [ Thu Apr 25, 2013 11:50 am ] |
| Post subject: | |
It is slightly forward of the tank on the frame rail. Lower than bottom of the tank and about 6 inches in front. |
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| Author: | ceej [ Thu Apr 25, 2013 9:49 pm ] |
| Post subject: | |
The pumps have an internal return for systems like these, and they will create a lot of heat when internally bypassing fuel. At idle, a slant doesn't use much fuel. I have a Holley red pump that works the same way. Even it is overkill for most slant engines. It will get hotter at low fuel demand than at high usage. If your going to run without a return system, think about a smaller pump. Probably not what you wanted to hear, but I hope it helps.  CJ |
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| Author: | Lobster1 [ Fri Apr 26, 2013 9:09 am ] |
| Post subject: | |
What I want to hear is not always what I need to hear... Thanks CJ! After digging through as many blogs and threads as I could find pertaining to this topic I found that the Bosch 044 was the the third best option and will be my attempt to fix. Others have had solved cavitation with the Bosch. The best solution is the in tank tank pump. I am not comfortable cutting a 4 inch hole in the top of the tank. And getting it flush to seal and line clearance issues between the tank and floor? The next best solution is adding a return line. I spent good money on the returnless system... One more thing and please let me know if this is logical. How about mounting the pump vertically? If ti cavitates the bubbles would float up and away. Cheers, BT |
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| Author: | ceej [ Sat Apr 27, 2013 8:01 am ] |
| Post subject: | |
Cavitation often defies gravity. It's not nearly the force we make it out to be. If the fuel reaches a boiling point, gravity goes right out the window. Orientation of the pump won't play a big part in it. CJ |
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| Author: | Lobster1 [ Sat Apr 27, 2013 10:20 am ] |
| Post subject: | |
Absolutely correct Ceej, I called Bosch yesterday and left a message and buckle your seat belt... I got a call back from technical support. Talk about earning my support, very impressed! They told me to mount it horizontally below the fuel tank. One more question; is it reasonably safe to open up my fuel vent? Or how can I safely ease the restrictive ventilation on the tank? Cheers, Barnaby |
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| Author: | ntsqd [ Tue Jul 02, 2013 2:55 pm ] |
| Post subject: | |
Fuel pump vapor lock or cavitation, whatever you want to call it, is easy to achieve with too much restriction in the suction line. What is "too much" depends on the whole system. I looked it up once for a list post and don't recall the particulars, but if you look up gasoline's boiling point vs. pressure you will find that a slight reduction in pressure (suction vacuum) from ambient results in a dramatically lower boiling point. So "too much" restriction might only be a very tiny restriction. Factor in fuel that is more being heated by cooling the pump than it is being consumed and vapor lock seems more like the goal rather than the curse. I'd consider installing a metered "bleed" downstream of the pump, bypass some of the fuel back to the tank all of the time. Find a check valve with, say, a 40 psi cracking pressure and tap a hole in it to 1/4-32 which will allow you to screw a Holley main jet into the hole. Rock Auto had a fuel pick-up for my '65 Valiant with a return fitting for not a lot of coin. For the air vent into the tank you can go to any size that you want. The key is to place it such that you can't spill raw fuel out of it. Keep in mind that small critters like to find openings like what you're proposing. I would suggest putting a cheap, carb type fuel filter in the end of the hose. That will keep critters and dirt out of the vent. |
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| Author: | Lobster1 [ Tue Jul 02, 2013 4:49 pm ] |
| Post subject: | |
Resolved, and thanks Thom, I upgraded to the Bosch 044 fuel pump with an-08 input and an-06 to the EFI and an-06 return. Running the return line was easier than I anticipated after I got over the dread of drilling a hole in my gas tank. Ouch! The fuel pump supplied with the kit is notorious for cavitation. Even with the return line many Powerjection customers ditch that particular pump. The returnless system is marginal at best and also contributes to the cavitation. Electric fuel pumps like constant flow essentially the fuel removes heat. And absolutely Yes, bigger lines on the suction side help. This was my fault. I read countless blogs and reviews of the Powerjection system and the warnings about their fuel pump should have convinced me to run the Bosch or Walbro in the first place. Return line too... Cheers, Barnaby |
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| Author: | Sam Powell [ Thu Jul 04, 2013 2:45 pm ] |
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Sound like you are making good progress. Keep up the good work! Sam |
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| Author: | Lobster1 [ Fri Jul 05, 2013 9:29 am ] |
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Thanks Sam! Learning the hard and expensive way and doing everything twice...  Now it's turbo time. I hope do do this only once.Cheers, Barnaby |
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