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Author: Subject: EFI fuel pressure confusion
CTLeeds

posted on 17/4/19 at 06:02 PM Reply With Quote
EFI fuel pressure confusion

Hi guys,

I'm a bit confused about the fuel pressure on my car. It's a BMW engined car and should have 3.5 bar approx at the fuel rail when it's under load. I've recently changed the fuel pump as when I took it for a run on the rolling road the fuel pressure was dropping right off after 5000rpm and the guys said it was the fuel pump. It was a cheap ebay 044 copy which I've replaced with a genuine Bosch 077 unit. The pressure is now 2.5 bar at the rail all the time. Doesn't matter what revs the engine is at, whether the vacuum line to the regulator is connected or not it's 2.5 bar. I've replaced the regulator as well with a new BMW 3.5 bar unit. I've also checked the results using two different gauges. I also removed the filters to check it wasn't that either.

I'm confused! The engine seems to be running okay but maybe a bit lean as I'm getting a few pops in the exhaust...

Advice appreciated...

Chris

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big-vee-twin

posted on 17/4/19 at 10:10 PM Reply With Quote
077 is a Diesel pump with an operating pressure of 1.5 bar.





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CTLeeds

posted on 18/4/19 at 05:27 AM Reply With Quote
quote:
Originally posted by big-vee-twin
077 is a Diesel pump with an operating pressure of 1.5 bar.


Apologies, my mistake. It's an 070.

Thanks,

Chris

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big-vee-twin

posted on 18/4/19 at 01:16 PM Reply With Quote
That pump operates at 3.0 bar, so with a few losses in your system like filters and bends these would reduce this.

So I don't think your going to get 3.5 bar.

The 044 gets up to 5 bar.

[Edited on 18/4/19 by big-vee-twin]





Duratec Engine is fitted, MS2 Extra V3 is assembled and tested, engine running, car now built. IVA passed 26/02/2016

http://www.triangleltd.com

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CTLeeds

posted on 18/4/19 at 01:32 PM Reply With Quote
Is pressure not dictated by the regulator and/or other restrictions? The Bosch website says the pump flows 168 lph @ 3 bar to 135lph @ 5 bar with a maximum operating pressure of 7.2 bar. I have a 3.5 bar regulator so the pump should be operating at 3.5 bar giving a flow of approx 150lph.
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BaileyPerformance

posted on 18/4/19 at 03:08 PM Reply With Quote
pressure is set by the regulator, not the pump UNLESS the pump is not capable of maintaining the regulator pressure.

lockout pressure on a Bosch 070 is 7bar, so shouldnt be an issue assuming the pump is genuine bosch and it has a solid 12v supply (or more) and the feed to the pump is 12mm bore NOT ADAPTED TO 8mm. The pump is gravity fed, so it must be below the tank, outlet at the base of the tank.

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CTLeeds

posted on 18/4/19 at 04:16 PM Reply With Quote
quote:
Originally posted by BaileyPerformance
pressure is set by the regulator, not the pump UNLESS the pump is not capable of maintaining the regulator pressure.

lockout pressure on a Bosch 070 is 7bar, so shouldnt be an issue assuming the pump is genuine bosch and it has a solid 12v supply (or more) and the feed to the pump is 12mm bore NOT ADAPTED TO 8mm. The pump is gravity fed, so it must be below the tank, outlet at the base of the tank.


Yep, that's what I thought and is my setup exactly. Only 2.5 bar at the rail though.

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BaileyPerformance

posted on 18/4/19 at 05:22 PM Reply With Quote
quote:
Originally posted by CTLeeds


Yep, that's what I thought and is my setup exactly. Only 2.5 bar at the rail though.



Are you using a basic capillary type gauge? Removing vac pipe has zero effect?

What fuel filter are you using - 2 connections? (in/out)

Pump has a constant tone?

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CTLeeds

posted on 26/4/19 at 03:46 PM Reply With Quote
quote:
Originally posted by BaileyPerformance
quote:
Originally posted by CTLeeds


Yep, that's what I thought and is my setup exactly. Only 2.5 bar at the rail though.



Are you using a basic capillary type gauge? Removing vac pipe has zero effect?

What fuel filter are you using - 2 connections? (in/out)

Pump has a constant tone?


Hi, apologies for the delay in coming back to you, I wanted to double check a few things before replying.

I'm using a Sytec gauge, I think it's a capillary type. Removing the vacuum pipe has little effect. There's definitely vacuum present at the end of the tube but I don't have a vacuum gauge to check the amount. The pump does have a constant tone with no signs of it struggling at all. I've removed the filter whilst testing to ensure that's not restricting flow pre-rail.

The pump has 13.5v with the engine running.

I'm still in the dark as to what's going on!

I'm thinking about trying an aftermarket pressure regulator to get me where I need to be.

Cheers,

Chris

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Schrodinger

posted on 27/4/19 at 07:18 AM Reply With Quote
One thing you haven't answered is what are the pipe sizes?





Keith

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CTLeeds

posted on 27/4/19 at 08:56 AM Reply With Quote
quote:
Originally posted by Schrodinger
One thing you haven't answered is what are the pipe sizes?


8mm. Same as the original donor pipes.

Cheers

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BaileyPerformance

posted on 28/4/19 at 09:06 PM Reply With Quote
quote:
Originally posted by CTLeeds
quote:
Originally posted by Schrodinger
One thing you haven't answered is what are the pipe sizes?


8mm. Same as the original donor pipes.

Cheers


Pump feed pipe must be 12mm

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CTLeeds

posted on 28/4/19 at 09:48 PM Reply With Quote
quote:
Originally posted by BaileyPerformance
quote:
Originally posted by CTLeeds
quote:
Originally posted by Schrodinger
One thing you haven't answered is what are the pipe sizes?


8mm. Same as the original donor pipes.

Cheers


Pump feed pipe must be 12mm


Feed to pump is 12mm. 8mm after pump.

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theduck

posted on 29/4/19 at 12:21 PM Reply With Quote
What pressure regulator are you using?
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CTLeeds

posted on 29/4/19 at 12:24 PM Reply With Quote
quote:
Originally posted by theduck
What pressure regulator are you using?


New BMW 3.5 bar regulator. I think it's a Bosch manufactured part.

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