Fuel pressure - is this okay?

adamnreeves · Post by **adamnreeves** » Wed Jul 01, 2009 6:49 pm

Westfield SEiGHT RV8 4.6. Fuel pump is bosch 044 which has an external non-return valve. I have a FSE power boost valve regulating the fuel rail.
New bosch injectors from the states, standard install on a Mustang apparently (231cc/min)

I have installed a pressure guage on the regulator. On pump priming it registers 3bar. Once priming finished it starts dropping. After 30 seconds there's no pressure.

With engine running the pressure is 2.5Bar.

stevieturbo · Post by **stevieturbo** » Fri Jul 03, 2009 9:50 am

2.5bar with vac connected, or disconnected ?

Doesnt sound too unreasonable if its with vac connected.

adamnreeves · Post by **adamnreeves** » Fri Jul 03, 2009 12:14 pm

Vac connected. Its an adjustable regulator but set up to match standard settings. I was more concerned fuel pressure dropping off after 30 seconds off priming, this is without engine running.

stevieturbo wrote:2.5bar with vac connected, or disconnected ?

Doesnt sound too unreasonable if its with vac connected.

stevieturbo · Post by **stevieturbo** » Fri Jul 03, 2009 2:24 pm

If the engine isnt running..it doesnt need any fuel pressure lol.

I'd be more worried if it dropped off while the engine was running

adamnreeves · Post by **adamnreeves** » Fri Jul 03, 2009 2:45 pm

No but if the fuel pump has a non-return valve, the regulator will not fuel return if below 2.5bar then fuel must be flowing somewhere; leaking injectors? although it seems to be idling between an AFR of 13 and 13.5.

Maybe I am being paranoid again

stevieturbo wrote:If the engine isnt running..it doesnt need any fuel pressure lol.

I'd be more worried if it dropped off while the engine was running

stevieturbo · Post by **stevieturbo** » Fri Jul 03, 2009 5:00 pm

If the injectors were leaking, you'd know about it.

I dont see why people want the system to remain under pressure when the engine is not running....it seems daft to me.

adamnreeves · Post by **adamnreeves** » Fri Jul 03, 2009 5:12 pm

Cool, I'm being paranoid then. I don't specifically want pressure when the engine is not running but was curious.

stevieturbo wrote:If the injectors were leaking, you'd know about it.

I dont see why people want the system to remain under pressure when the engine is not running....it seems daft to me.

CastleMGBV8 · Post by **CastleMGBV8** » Fri Jul 03, 2009 5:58 pm

Adam,

I was leaving this to others who are more familiar with the EFI system.

It is my understanding that with ignition on the pump will prime the system, but the pump will turn off again untill the ecu senses cranking and then after a slight delay for oil pressure to build the pump runs and (hopefully)the engine fires and the pump will then run continuously until the engine is switched off.

I think it's also a basic safety device in that if the engine is not running but ignition is on, that in the event of an accident fuel will not escape from pressurised ruptured fuel lines but I could be wrong.

Kevin.

CastleMGBV8 · Post by **CastleMGBV8** » Fri Jul 03, 2009 6:10 pm

Adam,

I've forgotten which ECU and system you are running, it could be that if your running injectors with a higher flow rate then unless there is some adjustment made to the ( not sure of the technical term) but the time period that the injectors are open then it will run richer than required, if its megasquirt or similar then it can be corrected.

Kevin

adamnreeves · Post by **adamnreeves** » Fri Jul 03, 2009 6:17 pm

Injectors are 231cc/min which are good for 300 bhp. I am running megaquirt and have already done the fuelling, well at least for idle, running at 13.0-13.5 AFR which is what the RV8 is supposed to idle best at.

The priming of the pump is also done by megatune which is configurable. I have it priming as soon as the ignition is one and then 2 seconds later, this is too ensure that the injectors are primed. I have also played around with the initial enrichment for the first 10 seconds. Then I have another enrichment setting going on in stages up to coolant of 71degrees. Yes spent hours doing this and thats on top of the base map provided by cobratone.

CastleMGBV8 wrote:Adam,

I've forgotten which ECU and system you are running, it could be that if your running injectors with a higher flow rate then unless there is some adjustment made to the ( not sure of the technical term) but the time period that the injectors are open then it will run richer than required, if its megasquirt or similar then it can be corrected.

Kevin

stevieturbo · Post by **stevieturbo** » Fri Jul 03, 2009 6:20 pm

13.0-13.5 is pretty rich, I'd be surprised if it would pass MOT at that.

Eliot · Post by **Eliot** » Fri Jul 03, 2009 6:50 pm

I run a bosch 044 pump with no non-return valve - I have no pressure when the engine is off. Never had any issues with starting.
To set the basline fuel pressure you need to override/bypass the fuel pump relay so its running when the engine is off and adjust the regulator to get 3 bar (assuming thats your baseline).
After that and once the engine is running at idle you will see you fuel pressure is much lower - which is expected assuming you have a vac line going to your FPR.

CastleMGBV8 · Post by **CastleMGBV8** » Fri Jul 03, 2009 7:14 pm

Adam,

13-13.5 does sound a bit rich as Stevie suggested but is the figure that apparently JE sets his idle at, although clearly the rover can be made to idle at a weaker setting it may raise engine temps so you may need to be careful.

Don't get paranoid about the paranoia, it's perfectly normal and sets in as soon as you put the ignition key in on start up of a new engine

Kevin.

stevieturbo · Post by **stevieturbo** » Fri Jul 03, 2009 7:19 pm

Any modern RV8 fitted to a fuel injected car would have idled at 14.7:1 as the CAT and emissions rules dictate.

Pretty sure that when I had mine, it was idling well into the 14's

Having a rich idle, is taking the easy way out. All engines will idle very rich, and idle well.

And probably fail MOT, and use loads of fuel, and have more chance of fouling plugs.

The biggest hindrance to a good clean idle...is camshaft. But even then it needs to be farily big to make the idle sloppy.

adamnreeves · Post by **adamnreeves** » Fri Jul 03, 2009 9:09 pm

I had actually set my idle AFR to 14.7 but then I read my Des Hamills tuning book and it suggested that the factory set them between 12.8 to 13.2 and JE sets to 13.5. Yes my plugs are black. I think I'll lean it up again. I do have a fast road cam with more overlap but I am using bleed down lifters anyway. I shall give it a go. I guess this is for the older engines.