Fuel Regulator Vacuum Switching Valve needed or not?

[Tonyd]

After almost 4 years, two house moves, one house and garden rebuild, a change of job and multitudes of lifes hiccups I finally have my part built Lexus powered Cobra back in my garage, in my house, next to my beer fridge, and I can work on it again. The donor of the engine was a June 1990 manufactured LS400.

Back in the day I removed all the EGR stuff, replacing with blanking plates, but I left the Vacuum Switching Valve beneath it connected between the plenum and the fuel rail regulator in position.

Three questions.

1. What is the purpose of the electrically operated valve between the fuel pressure regulator and the intake plenum ?

2. Can I remove it and connect the fuel pressure regulator direct to the plenum ?

I'm not concerned about fault codes, as long as the engine performs as normal I'll be happy. The fuel pump runs at 12v permanently as I've dumped the fuel pump ecu if that has any bearing on the issue.

3. Eventually I want to put a reasonable amount of boost into the engine say 10psi plus using a piggy back ECU and secondary injectors. As the original fuel rail regulator is not designed to see positive inlet manifold pressure should I disconnect it from the intake plenum totally at that time?

Cheers,

Tony

 

[Zuffen]

Tony,

The solenoid is usually plumbed into the chrome vacuum line on the plenum then goes to the charcaol canister to purge the fuel vapours from it.

You can discard it and hook the fuel pressure regulator direct to the plenum.

If you want to run boost, discard the factory FPR (just use a shrter banjo bolt in it's place and use an external/remote FPR.

You don't need secodary injectors as you can use bigger capacity injectors that blot straight in and plug into the existing loom. Much easier and neater than fabbing up secondaries.

I recomend a tachometric relay on the fuel pump to stop the pump running when the engine stals/stops or you are involved in an accident. Google it. Peugeots use them and there's a dirty way to do it with the oil pressure switch and acouple of relays. Bosche make the relays and I know you can get them of UK eBay.

 

[Tonyd]

Thanks Rod,

I take off the valve. I'll be putting a gravity/ shock activated cut off switch to disable engine and fuel pump electrics in case of accident etc.

Re adding boost if I'm using bigger injectors will the standard fuel rail be able to cope with the increased fuel flow requirements, similarly standard LS 400 fuel pump.

I'd convinced myself that I'd be using a seperate boost level activated fueling system ( seperate injectors, seperate fuel rail and seperate pump) run by piggy back ecu whilst retaining the OEM ECU to run the engine when off boost and to run the auto box ( until I knacker it).

Spark would be managed by the OEM ECU at all times as its got knock sensors.

Could the standard ECU manage bigger injectors and boost within its standard maps? If so it'll save me the piggy back problems and expenditure.


Cheers,

Tony

 

[Zuffen]

The stock fuel rails will support well over 600FWHP.

The standard pump will run out of puff with boost. Remember you're asking it to a) flow more uel and b) flow it at a higher pressure. Go for an aftermarket pump. I used twin Bosch 044's but that was overkill. One of those will support 600+hp but they can be a bit noisy.

The concept of a stand alone fuel system sounds staightforward until you get into the transition from no boost to boost. A bit like sequential turbos. Good idea, if you're the factory and can spend heaps getting it right.

I'd go straight to a stand alone ECU and you'll most likely get better results.

 

[Tonyd]

The stock fuel rails will support well over 600FWHP.

The standard pump will run out of puff with boost. Remember you're asking it to a) flow more uel and b) flow it at a higher pressure. Go for an aftermarket pump. I used twin Bosch 044's but that was overkill. One of those will support 600+hp but they can be a bit noisy.

The concept of a stand alone fuel system sounds staightforward until you get into the transition from no boost to boost. A bit like sequential turbos. Good idea, if you're the factory and can spend heaps getting it right.

I'd go straight to a stand alone ECU and you'll most likely get better results.

Thanks for the advice, I'll get the bits together for when its through its IVA test, God knows when that will be though.

Cheers,

Tony

 

[Lextreme]

Guys, I want to resurrect this old thread and see about getting fresh input to the original questions posed in this thread.

Why do I ask?

A '96 owner interested in the EGR Delete Kit noticed on the product page that David (the original Lextreme) wrote that a feature of the kit is that the Fuel Pressure VSV (FPR) can be removed.

Is this true of the '96?

More insight on this, fellas?

 

[ivan129]

Guys, I want to resurrect this old thread and see about getting fresh input to the original questions posed in this thread.

Why do I ask?

A '96 owner interested in the EGR Delete Kit noticed on the product page that David (the original Lextreme) wrote that a feature of the kit is that the Fuel Pressure VSV (FPR) can be removed.

Is this true of the '96?

More insight on this, fellas?

Might help to post a picture of the part your referring to

 

[P Bateman]

My understanding is that the Fuel Pressure VSV will open when the cold-start injector is switched on, to drop FPR line vacuum and cause a fuel pressure increase. Cold-start injectors don't normally pulse like a cylinder injector - they turn on and spray like a fire hose. The pressure leak would ordinarily affect the cylinder injectors so by bumping the pressure, they are unaffected. It's mostly an emissions thing and I would imagine the engine may not run 100% with the valve deleted.