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Megasquirt Relay Board with Bosch 044 fuse blowing

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5 hours ago, HuD 91gt said:

His HP Bosch 044 should run through the FPR and have a return back to the surge tank.   The frame G3 is filtering the fuel from the fuel tank, to the surge tank correct?   It is filtering LP fuel from the carter pump.  I don't see issues there.  The LP fuel pump doesn't have to keep up with the 044 unless he is running the 044 to it's limits at all times and the surge tank is too small to be used as a buffer for changes in fuel burn.

 Make sure vent and return hoses from the surge tank and fuel tank are clear and make sense.  Positive differentials between the two could cause you issues if they aren't venting properly.  Despite how much thought and engineering I went in with my surge tank development, when I was filling up I was only able to get a 1/2 tank of fuel.  I realized my venting was way off.  Like they say above.  Let's get some photo's of your whole system.

 

Sorry... but I disagree with that. The  feed pump absolutely MUST keep up with the main pump under all conditions and keep the main pump submerged in the Surge tank. You run the Ffel level in the surge pump too low and the Bosch pump will cavitate and you can kiss it good bye in a hurry. But likely you will have melted a piston by then.

Feed pump does not have to be high pressure. But it must be high volume. Think of a Surge tank as a float bowl. Yes, there is some reserve, but with a GT3076 and 550cc injectors you can suck a Surge tank down pretty fast. Also depends on mounting locations of pumps etc. Pictures will definitely help. 

G3 Fram filter is definitely a restriction on a motor of this potential. I've run into problems with a G3 pre-filter. on a hot day on my NA motor. Switching to a Aeromotive 100 Micron filter. 

BTW, have a look at the 280Z stock fuel line hose sizing to and from the Fuel pump. Inlet is 11mm ID ( 7/16"  ) . Outlet from pump is 9mm ( 3/8" ) That should tell you something. The feed from the fuel tank to the scavenge ( or main pump )  pump and the feed from the scavenge pump should always be larger than the outlet size from the Main Pump. If Main pump is AN-6... inlet hose should be AN-8.

Edited by Chickenman

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Quote from Aeromotive on this exact problem. Could definately be Pump cavitation. 

Quote

3.) After 30 minutes or so of driving, fuel pressure starts to fall, then the fuel pump gets louder and/or seems to quit running altogether.  What’s wrong, is my pump going bad?

You may be experiencing EFI vapor lock.  Even though the fuel is recycling through the car, eliminating localized hot spots, the recycled fuel is still being exposed to under-hood engine heat.  Fuel in an EFI bypass system does slowly warm up as it is recycled through the chassis, the fuel rail(s), engine compartment, and finally back to the tank.  The longer an EFI engine runs, the higher fuel tank temperatures can become. Unlike the more common carburetor vapor lock, where fuel is heated to boiling in the float bowl(s) or fuel line(s) under the hood, EFI vapor lock is often caused by hot fuel in the tank.

Excessive pump noise along with fluctuating or dropping fuel pressure often indicate that fuel temperature is high enough to cause hot fuel handling problems.  A combination of high fuel temperature and low pressure can result in cavitation, where liquid fuel changes to vapor.  In a return style EFI fuel system, the most likely place for these conditions to exist in the same place, at the same time, is at fuel pump inlet.  Once cavitation starts, it will feed upon itself.  As vapor enters the pump, it displaces liquid fuel required to lubricate the mechanism, allowing metal to touch metal, creating even more friction and heat.  Once the pump begins to super heat, a complete vapor lock will develop. 

In order to prevent cavitation and vapor lock, correct fuel system design and installation are vital.  Ensure supply lines and inlet filters meet hi-flow, low restriction requirements and are kept clean.  Keep the tank full on hot days.  Reduce fuel pump speed and recycle rate with a fuel pump speed controller during low load, idle and cruise conditions.  Carefully route fuel lines and plan component placement to avoid exhaust heat. Do not overlook proper tank ventilation, if the vent line or vent valve do not allow ample air to move freely in both directions, fuel delivery problems will never fully resolve.  Any conditions that restrict the pump’s access to fuel in the tank must be addressed. 

 For more detailed information on installation issues that can result in premature cavitation, hot fuel handling problems and vapor lock, see Aeromotive Tech Bulletins TB-101, TB-102 and TB-802, all of which can be found at www.aeromotiveinc.com under the Tech Help, Tech Bulletin section.

I would definitely be looking at replacing that G3 and checking hose sizes. Further info on Pre-Filter restrictions. Read this:

http://aeromotiveinc.com/wp-content/uploads/2014/12/TB_101_InletFilter02.pdf

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1 hour ago, HuD 91gt said:

Random thought.  But how accurate are FPR gauges in the low end?  I searched the Carter pump and it says it operates at 4-8psi.  Pending how the surge tank is plumbed (Not the way I believe he had it in my post above), is it possible your 044 is not operating and the pressure you are seeing is directly from the Carter pump?   

Just a random thought, and it completely depends how your system is hooked up.

That is a possibility. Relay could be overheating on Relay Board. May have Thermal protection and relay is opening. Or some other intermittent electrical disruption. 

Or Bosch pump is cavitating badly and it takes a while to cool it down. Pump cavitation can do nasty things to a pump in short order. Fortunately the Bosch 044 is a roller vane design, which are much more robust than a Ceramic Turbine design. 

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Yea without pictures/video/audio this is rough. Looking it up an 044 pump will push 4LPM. Depending on the surge tank size and design that might be too much. I've seen kits in the past where people used oil filters as surge tanks. While it works you could empty it before it started refilling to capacity if you weren't careful.

Also without seeing the surge tank setup one can only guess how it is pulling fuel. I've seen some pneumatic pump designs where the suction is so strong and the tank material so weak that it pulled the bottom of the tank towards the pump inlet and cut off flow. When you shut the pump off it would relax. Took forever to find out what was going on.

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4 hours ago, Chickenman said:

Sorry... but I disagree with that. The  feed pump absolutely MUST keep up with the main pump under all conditions and keep the main pump submerged in the Surge tank. You run the Ffel level in the surge pump too low and the Bosch pump will cavitate and you can kiss it good bye in a hurry. But likely you will have melted a piston by then.

Feed pump does not have to be high pressure. But it must be high volume. Think of a Surge tank as a float bowl. Yes, there is some reserve, but with a GT3076 and 550cc injectors you can suck a Surge tank down pretty fast. Also depends on mounting locations of pumps etc. Pictures will definitely help. 

G3 Fram filter is definitely a restriction on a motor of this potential. I've run into problems with a G3 pre-filter. on a hot day on my NA motor. Switching to a Aeromotive 100 Micron filter. 

BTW, have a look at the 280Z stock fuel line hose sizing to and from the Fuel pump. Inlet is 11mm ID ( 7/16"  ) . Outlet from pump is 9mm ( 3/8" ) That should tell you something. The feed from the fuel tank to the scavenge ( or main pump )  pump and the feed from the scavenge pump should always be larger than the outlet size from the Main Pump. If Main pump is AN-6... inlet hose should be AN-8.

If the return from the injectors goes back into the surge tank it will not matter if the LP pump can outflow the HP pump.   Any residual fuel which is not used by the engine will be returned to the surge tank (Which 70+% of the time is a majority of the fuel pumped).  In addition to this return fuel, will be the fuel supplied from the LP pump from the fuel tank.  As long as the LP pump can supply enough GPH for the engine to use, the surge tank will never be low no matter the size of the HP pump.  If the LP pump could not keep up with the GPH required by the engine then you would start to see the level of the surge tank decrease.  Since the engine is never operating at max power 100% of the time, as long as the surge tank is large enough, and of a decent design it offers a buffer.  But besides that point the Carter P4070 is a high flow LP pump.   Pumping around 72GPH.   Plenty to feed this setup in it's current tuning state i'm sure. 

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What we have so far....

"My fuel system is Tank>>Fram G3 fuel filter>>Carter Fuel Pump (wired to my EZ Wiring kit, no relay, 14 gauge wire)>>External Surge Tank with submerged Bosch 044 (Wired to the MS Relay Board)>> Engine>> External Surge Tank>> Tank."

 

What we really need to know:

Flow:

Stock tank > hose (size) > Fram G3 fuel filter > hose (size) > Carter Fuel pump > hose (size) > external surge tank (model, link, picture) > inlet mechanism (sock, fitting, sump) > bosch 044 pump > hose (3/16) > fuel rail in (fitting size) > fuel rail > fuel rail out (fitting size) > hose (size) > aeromotive fpr inlet (fitting size) > aeromotive fpr > aeromotive outlet (fitting size) > hose (size) > surge tank > hose (size) > fuel tank.

Vent:

Then we need to know the vent situation. The surge tank should have a vent, and the fuel tank should have a vent. 

Then the electrical. What Hud brings up is interesting. If the bosch 044 pump is blowing the fuse and not working and your fuel rail is only showing 10psi, you might be seeing the carter pump pushing fuel. The problem with that then is the surge tank is not doing what it should be doing if you are generating pressure that means you are filling up the surge and pushing fuel past the bosch pump which shouldn't happen, it should just be returning to the fuel tank.

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 Further reading on Fuel Pump Cavitation and starvation caused by restrictive Pre-Pump filters.  

http://aeromotiveinc.com/wp-content/uploads/2014/12/TB_101_InletFilter02.pdf

http://aeromotiveinc.com/wp-content/uploads/2014/12/TB_802_Tanks_Sumps_Stealth_02.pdf

 

Aeromotive has some excellent Tech Articles. Well worth reading them all.

https://www.aeromotiveinc.com/tech-help/tech-bulletins/

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Holy Hanna... I finally found some specs on Fram G3 filters. They are rated at 5 Microns. That's far too small to be used as a pre-filter for ANY EFI pump. Let alone a high volume pump such as a Bosch 044. Get rid of the G3 and put in a recommended Aeromotive pr pump filter which are 100 Microns in size. 

Fine filters should only be installed post pump.

Thanks Atlantic Z for perpetuating this incorrect information. :angry:

I was wondering about this ever since I installed a Fram G3 before my Airtex 8312 EFI pump based on the Atlantic Z article.. It's a Ceramic turbine pump, so it does need a pre-filter according to Airtex. In Tank pumps have a sock to catch the coarse stuff, but an inline pump doesn't. Would have been nice if Airtex had recommended a proper inline Pre-filter... but they don't. 

My pump had been getting growly and noisy during hot weather. Worse when fuel  tank was below 1/2. Mkaes sense now as this is a Textbook case of a restrictive fuel filter being installed before the pump ( Fram G3 ) . G3 is going bye bye and I'm ordering a proper Aeromotive 100 Micron SS filter from Summit ASAP!!! 

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