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dpuma8

Megasquirt Relay Board with Bosch 044 fuse blowing

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Hi everyone,

I have a Carter P4070 feed pump that feeds into a surge tank that has a submerged Bosch 044 fuel pump.  I have had a problem where after shutting off the car for 30 minutes, the fuel pressure will drop to around 10 psi.  I have read on the internet that the Bosch needs a 10 gauge wire but the Megasquirt relay board doesn't have an opening large enough to connect the 10 gauge wire to it.  So after realizing this, I have the 14 gauge wire connected to the relay board and after a few inches, it connects to the 10 gauge Bosch wire.

So after doing this, the problem I am having is either the fuel pump fuse or the main fuse will pop immediately.  I changed the fuel pump and the main fuse to 30 amps for both but after a few minutes, those fuses will pop again.

1) Fuses didn't pop when I had 14 gauge wire connecting to the Bosch pump but now it does.  I changed the ground wire from 14 gauge to 12 gauge and is now connected to the same frame grounding bolt as the Carter pump.  Is grounding both pumps to the same frame bolt a bad idea?

2) The recommended main fuse for the Relay Board is 20 amps but do I need a larger main fuse?  Or do I have other issues?

 

 

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18 hours ago, dpuma8 said:

Hi everyone,

I have a Carter P4070 feed pump that feeds into a surge tank that has a submerged Bosch 044 fuel pump.  I have had a problem where after shutting off the car for 30 minutes, the fuel pressure will drop to around 10 psi.  I have read on the internet that the Bosch needs a 10 gauge wire but the Megasquirt relay board doesn't have an opening large enough to connect the 10 gauge wire to it.  So after realizing this, I have the 14 gauge wire connected to the relay board and after a few inches, it connects to the 10 gauge Bosch wire.

So after doing this, the problem I am having is either the fuel pump fuse or the main fuse will pop immediately.  I changed the fuel pump and the main fuse to 30 amps for both but after a few minutes, those fuses will pop again.

1) Fuses didn't pop when I had 14 gauge wire connecting to the Bosch pump but now it does.  I changed the ground wire from 14 gauge to 12 gauge and is now connected to the same frame grounding bolt as the Carter pump.  Is grounding both pumps to the same frame bolt a bad idea?

2) The recommended main fuse for the Relay Board is 20 amps but do I need a larger main fuse?  Or do I have other issues?

 

 

Ok, the Bosch 044 pump draws around 18A at full Load..so essentially a 20A fuse is cutting it a bit close. You need to size the fuse to protect the wire and the device. IF you use 10AWG the wire is rated for 40A, 14 AWG is rated for 25A. If you are popping this fuse there may be an underlying connection issue or a faulty pump.

I would remove battery power and check the following:
Resistance between the relay board contact and the fuel pump... This resistance should be very low (less than 1-2 ohms). If not, check wiring, connections

If that is good check the resistance between the pump negative terminal and ground..If this is low then your ok, if not, check wiring, connections

Check the resistance between the Relay board ground/neutral and the Pump ground/neutral. If this is not low, resecure the relay board to ground

Remove the Positive and negative from the fuel pump and Relay board. Check resistance between the two wires. If this value is low you may have wiring grounding out or burnt through insulation...

 

If you have any more wiring questions don't hesitate to ask.

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Another thing I thought of is check your Battery Voltage. Make sure its not low, Lower voltage will cause a higher current to produce the same power.

In addition fire up the pump and measure the voltage on the Fuel pump...If its low..check your battery, charging circuitry and possibly the connection you made with 14 to 10 awg.

Do not use crimp connectors for connections like this. Solder connections.

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Dropping fuel pressure is fairly normal after the car is off. Without the pump energized it just kind of flows back through the impellers.

That does seem like a wiring issue. Can you show us pictures of the connections? I fear you might be shorting it somewhere. Is it running in the cabin? Is it grommeted as it passes through the trunk floor?

Alternatively it could be a plumbing issue. Are you returning to the surge tank? Are you dead heading the pump? What size are the fuel lines? 

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I am using the stock fuel lines for a 75 280z.  My issue I was having was fuel pressure would be near 10 psi all the way home making it a difficult drive.  The next day when I start the car up again, the same scenario happens where fuel pressure is fine until I shut down and restart the car.  I think maybe my battery is low because when trying to start my car, the engine fan kept turning on when really it doesn't work until the engine is 200 degrees.

The return line from the front of the engine flows back to the surge tank so that it doesn't go dry.  There is another return line from the surge tank back into the gas tank so I don't think it is a plumbing issue.

 

I pulled the fuel pumps, gas tank, and surge tank from the car and I am making changes to my wiring.  I am skipping using the Megasquirt relay board for fuel pump control since it seems like 30 amps is pushing the board.  Redoing my ground locations and adding two relays for both fuel pumps.  Few more days and I will know if this all worked.

Thanks for the help, guys

 

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All kinds of different things are getting mixed up and blended here.  Retaining pressure when the pump's not running, maintaining pressure while driving, fuses to protect the wires (the device, the pump, is actually a current limiter and protects itself), low battery causing driving problems (what's the alternator doing while the engine is running?).

You need to separate out and work on single problems.  And get the cause and effect right.

Here's a few things - the fuel system is designed to hold pressure for quite while (weeks or months have been seen in wrecking yard cars) after the pump shuts off.  There's a back-flow valve in the pump, and the regulator is a pressure relief valve.  Aftermarket regulators are almost all poor at holding pressure.  If you have low pressure while driving it's probably an obstruction in the lines or a bad regulator.

When the engine's running the alternator will supply enough voltage to run everything properly.  It might overwork itself if the battery is dead but it will still put out current as long as RPM are up.  The voltmeter reading will be a clue.

Are you running two pumps on one circuit?  The low pressure Carter pump counts too.

There's a lot of backyard advice in the thread.  Be careful and check multiple information sources.

 

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Hmm, while checking multiple sources is never a bad idea. I don't see anything wrong in this thread in the advice offered.

All three of the responders are noting he is pulling too many amps. A single 044 pump should not pull that many amps under normal operation. Granted if both pumps are indeed running off the same wire that may be a problem. The ECU really only needs to trigger the surge tank pump, the carter pump can and should be triggered via accessory on so that it fills the surge prior to the other pump kicking on.

The only thing that would be suspect are the suggestion to only use soldered connections, and my statement of the fuel pressure dropping with the 044 pump.

Personally I would disagree with only using soldered connections. I think a good crimp connections is just as good if not better in certain situations.

If you are referring to fuel pressure dropping being normal, it is. The 044 pump usually comes with a check valve to keep the pressure up. In aftermarket applications almost no one runs them. It is pretty common for the pressure to bleed down once the pump is off, or even between prime and crank. 

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1 hour ago, seattlejester said:

The 044 pump usually comes with a check valve to keep the pressure up. In aftermarket applications almost no one runs them. It is pretty common for the pressure to bleed down once the pump is off, or even between prime and crank. 

People are making general comments that just aren't specific and not quite right.  It's just confusing an already confused situation.

The check valve is installed in the fitting at the outlet end of the pump.  You'd have to disassemble the pump and intentionally remove the valve, for no apparent reason (just checked the internet and I see that people actually do that - for no apparent reason, apparently, except that they think it's "not needed".  Maybe weight savings?...see last comment below...).  The leak-down problem with aftermarket regulators is just the result of cheap engineering and low-cost manufacturing.  The guys that make them will tell you it's a design function, to allow high-flow, but that's BS.

When people get in to the putting these systems together they almost always go overboard on the simple irrelevant stuff and miss the basics.  As you pointed out, his pump is way overkill for the rest of the system, and for the engine he's running.  One of the basics of DC pumps is that they pull more amps as they work harder.  So, with a flow restriction he's going to pull more amps and get low fuel pressure.  The signs are there that his fuel system is out of balance, and over-spec'ed . He'd probably do well to get a lower flow pump, and fix his flow restrictions.  Wouldn't be surprised if he has one of those tiny anodized fuel filters in-line, probably choking flow.  No offense dpuma.  But avoid the hype and the bling, and do the proper math is the way to get things working right.

https://www.rceng.com/technical.aspx

K&N filters.  Cold air intake.  Bosch 044.  Turbo injectors.  Electric fans............

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Hmm it seems then that your problem was with my statement, I think that is fine. I thought everything else was really leading towards the right area , so was surprised at the comment.

Honestly I don't know what to tell you, that is just how the pumps come unless you take them off of an OEM application. If you buy the pump itself it just comes with the threaded ports, no check valve. Most aftermarket suppliers will sometimes even offer the basic kit which provides the clamps and adapters to AN, but they still don't come with check valves. So no disassembly in my case, and most people who buy them, buy just the pump and not the assembly so they just don't get it with the check valve. 

I agree though you need to set your fuel system for your needs. I think you are choking the pump either on the output or the intake or both.

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The problem is general.  Some of the answers, and the overkill application of the pump.  It's just bad system design. 

Here's a nice collection of data in one spot.  https://www.highflowfuel.com/i-13775895-genuine-bosch-044-320lph-inline-fuel-pump-includes-an-fittings-of-choice-0580254044.html

 

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Don. I've seen several comments from experienced builders that don't like the Relay boards. For High amperage draws they simply can't flow enough current.  Connectors  and PCB traces are simply too small for big amperage electric pumps and even some cooling fans.   Moat builders with high amp draw pumps and things like Nitrous solenoids build their own Relay boards with appropriately sized Relays and wiring. . 

12 Gauge is the recommended minimum size for any High Performance Fuel pump. Do not run the Main pump and scavenge pump off the same circuit. Each electric fuel pump should have it's own relay ( 30 or 40 AMP continuous duty for the Bosch 044. 30 Amp for the Carter scavenge pump ) and separate +12v feed. 

So it looks like you are headed down the correct path with the modifications you are planning. Dual HD relays and separate 10 or 12 gauge wiring feeds to each pump is a good idea. I'd even go 10 gauge to the 044 pump. It's a long run. 

 

Edited by Chickenman

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Don, it is very common for aftermarket Fuel Pumps and particularly Aftermarket FPR's to lose rail pressure after sitting for some time period, as others have mentioned.  Perfectly normal. The stock FPR controls most of the pressure loss. Aftermarket FPR's due to the nature of their design are less concerned with Rail leak down than OEM designs. 

 There is a setting in MS to  Prime the fuel lines before cranking the engine. By default this is off. Set it to 1.5 or 2.0 seconds. Then you can turn the key to " On " the fuel pump will run for the set time to pressurise the fuel rail. Then you can crank the engine. the Fuel pump will " Turn Off " after the time period is exceeded if the Ignition switch is left in the " On " or Run position ( Safety feature ). 

Picture attached with setting to change circled in Red: 

Priming Pulse ScreenShot002.jpg

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If this is the engine that I think it is, Don is running a GT3076 Turbo with 550cc injectors  So the single Bosch 044 is definitely NOT overkill for his project. And they are only good for about 450 HP on a single pump on Petrol. If he goes E85 later he will have to go to an even bigger pump or dual pumps. 

Don give me an E-mail. I've recently updated some of the AE tables. Would like some feed back on how the Tune is working if possible. 

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I was running my bosch 044 through a nitrous relay box. They have higher rated amps and relays, cheaper, and more sanitary, so I can't comment on the actual relay board. I did run 12 gauge on mine, just because I had it.

Over 20 amps still seems really high.

Real street did a test that said with boost an 044 pump should flow enough for 800hp in theory. People usually say if you try to break 600 you want dual. One guy got 700ish I believe in application on a single 044 pretty well documented as well. 

http://realstreetperformance.com/Fuel-Pump-Comparison-Test.html

Curious why it is only good for 450hp? I understand with E85 the fuel usage increases so makes sense, but in gas tests it seems the 044 should be good if it is fed through the appropriate sized lines (3/8 is what many people suggested, AN6).

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Actually I was thinking of the Walpro 255 figures. A 044 will push a bit more .   This is taken from real life testing on Big Turbo Audi's and VW's.  You never want to push a fuel pump to 100% , particularly in Road Racing. The testing done above does not take into account performance loss by pump electrical heating, fuel heating,  and line loss ( through bends and fittings ) . That all adds up and takes a toll on efficiency in the real world. Pumps also get weaker with age. Particularly when you drive them near 100%. 

And while mathematical calculations look great on paper, real world seldom  ( at the Amature and DIY level ) approaches the efficiency levels tested in theory.  It's always smart to leave an overhead for variables.  

One variable is the AFR. A lot of Big Boost Turbo guys would get very nervous at a 12.0 to 1 AFR ratio. Depending on the engine you often see 11.5 or 11.0 for AFR. Again especially in Road Racing ( Which is my background ). You get much more heat build up in a Road Race engine or Hillclimb engine than a Drag car.

AN-6 is getting a bit small in the 450HP to 500 range IMHO.  It should be noted that the Audi's I mentioned are all 4 bangers and in the 2.0 liter range. Those would be working a lot harder to make 450 HP to 500 HP than an L28. No replacement for displacement. 

I tend to be conservative when estimating values or fuel systems. That's just me... YMMV 

 

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That makes a bit more sense. I appreciate a good margin as much as the next guy. I was just curious if the theoretical peak hp was really double the real world hp expectations of a pump. I mean Real St builds some really high hp JZ motors so I was curious if their recommendation was off or no one bothers to actually convert to inline.

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Reading this whole thread make me believe their may be multiple issues going on.  Inconsistent FP from one start to the next makes me believe of a blockage somewhere in the fuel system.   How are your filters?   Where and what are they?  As stated above, FP dropping after shutdown is pretty normal for aftermarket pumps/reguators.  Bosch, should hold pressure, but wha regulator are you running?

Has this fuel system ever worked properly for you? 

 

I think everyone has you covered in the wiring department.   

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Hi guys,

Let me clarify my situation better and what I am running.

L28et with GT3076r, MS2 with relay board, RC Engineering 550cc injectors with inline resistors, and Aeromotive Fuel Pressure regulator.  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.

I set fuel pressure to be 36psi with the aeromotive FPR vacuum line off, reattached the vacuum line to the FPR, and then drove around to tune with Chickenman's tuning start points.

I will drive around for an hour, turn the car off for 30 minutes, restart it, and then struggle home with fuel pressure at 10 psi.  I am now adding a Bosch relay to my car and hooking the Bosch 044 directly to that rather than going through the MS relay board.  The Bosch 044 was wired to the relay board with smaller gauge wire and the fuses did not pop. Since I have had the car in the garage for some time, the battery might be low so I will charge it tonight.

My Bosch 044 came with a check valve but I did not install it with the pump.

 

Edited by dpuma8

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I would install the check valve first of all and see what that does. Without the check valve in the pump the Fuel Pressure will definitely drop. The FPR alone won't stop the pressure drop off. 

However, if I understand you correctly. After a 30 minute stop ( and Heat soak ) the fuel pressure only comes up to 10 psi. How long does that last?  A heat soak issue ( fuel percolation )  should clear itself pretty fast.  Within a minute or so maximum. 

It may be possible that the Fuel Pump is losing it's prime with out the check valve installed. Where is the fuel pump located? It should be at the rear of the car, close to the fuel tank and mounted as low as possible. Make sure the Fram G3 sure is not plugged or restricted. A 100 Micron filter ( Aeromotive makes a good pre-filter )  with a fairly large surface area will work well.

Do not put in a Post pump filter ahead of the pump.  These are typically 40 Micron or smaller and restrict fuel too much when used before the pump. Edit: Actually, thinking about it, the Fram G3 is a post pump filter. It is designed to be used under pressure.. not suction. With the added volume of the Bosch 044, sometimes the paper elements collapse. It also does not flow enough for you application. I'd have a close look at that G3 filter. 

Other possibilities. FPR may have a bit of debris stuck in the seat or the valve is sticking open. Take it apart and inspect. Aeromotive FPR are usually very high quality, but even the best quality parts are sometimes defective. Check for any kinks or restrictions in fuel lines.

Another possibility, and this can be a SOB to find, is that the fuel tube in the Fuel tank feed is rusted and has perforations in it. This can suck air and cause the FP to olose prime. Usually happens below a certain fuel level in the tank. 

But the first thing I'd do is put that check ball back in place. Simple and it may do the trick...

 

 

Edited by Chickenman

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The surge tank wiring and plumbing also need looking at .

The  Carter scavenge pump should be on it's own separate Bosch relay  ( Not on  the MS relay board ) and needs twelve gauge wire as well. Where is the surge tank located. Again it should be located close to the fuel tank and as low as possible. All electrical pumps work best as pusher pumps. They do not work as well as puller pumps. 

The Surge tank should have a vent line leading back to the fuel tank. With out a vent line, you could create an air lock in the surge tank.  

One other thing. Does the Carter fuel pump have enough volume to keep up with the Bosch 044 pump?  It must be able to supply MORE volume than the 044 can push out at maximum capacity... otherwise it just becomes a restriction and the surge tank will run low, causing cavitation in the Bosch 044 FP. 

Edited by Chickenman

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Echoing above, what's the carter fuel pump rated to? Do you have a fuel return back to your fuel tank once the surge tank fills? Can you hear it trickling back? Do you have a vent line back to the tank or to atmosphere? If the bosch pump pulls more then the carter pump you are going to have an imbalance in pressures if you have a sealed system for the most part.

What kind of lines are you running? Have you checked the fuel filter? I know bosch pumps don't like a fine filter in front of them. Some people even suggest running without one for pump longevity.

The check valve would keep fuel in the initial startup, but once the car is running if it continues to make 10psi then you have another problem somewhere.

This is where video or pictures are worth a lot more. Are you running the bosch pump dry? Do you have a sock on the pump? Is it cavitating? Without the pictures and information this discussion really fair to try and have.

 

 

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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.

 

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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.

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