Fuel regulator adjustment

[Steve M]

My Westy failed its emissions on the co reading 4.6 (limit 3.5) but passed on hydrocarbons at 120 ( limit 1200)

I'm going to reduce the fuel pressure slightly to hopefully get it below the 3.5 limit

My question is do I turn the adjustment screw anti clockwise to reduce pressure or clockwise ?

[Kingster]

I can check tomorrow if no one else knows as mine has a gauge on it.

Might get time later today with luck.

Could also give you a rough guide as to how much too.

[Dave Eastwood (Gadgetman) - Club Chairman]

If you have to do it that way, make a mark of where it's set now before disturbing it.

 

Drive it like that the bare minimum to pass the MOT, try not to labour the engine under load, don't use high revs or lots of throttle.

 

Remember you're fuel map will now be out, and worse, out on the lean side. Adjust it back again as soon as possible.

 

It's normally clockwise to increase, and anti-clockwise to decrease the fuel pressure.

 

Again, though, myself, I wouldn't like to do it without a fuel pressure gauge, so I definitely knew what it was on, and what to reset it too.

[Steve M]

Thank you Kingster & thanks to you Dave

Excuse my ignorance, but by lowering the fuel pressure, what damage would it do ?

[Kingster]

Lean out the fueling. Do too much and you could hole a piston, but you'd need to thrash it to get that far in my experience (only done it once!)

Will be in the garage in a hour or two by the way...

[Kingster]

I'm no expert but might be better to edit the map and then when done load the original back in.

You should be able to lean it out at the mot rev range to help reduce emissions. Happy to be corrected

[Dave Eastwood (Gadgetman) - Club Chairman]

The fuel injection system uses a series of tables to choose how much fuel to squirt into the engine in any given circumstance.

 

The main table will be something like: the position of the accelerator pedal up one side of the table, and the rpm across the other. So when the engine is being set up - known as being mapped. The tuner will fill in a figure, for each square on the table. This figure, effectively is how long the fuel injectors need to squirt fuel for at that accelerator position while the engine is at that particular rpm.

 

Put your foot down, and the table will show the new accelerator position at that same rpm as needing a longer injection of fuel. The engine then starts to spin faster to match the amount of fuel you're now injecting, the ecu sees this new accelerator position/rpm combination and realises that it only needs a certain amount of fuel to maintain that, and alters what it's injecting to suit.

 

Likewise, when you lift off, it realises you don't need as much fuel, and will shorten the time the injectors fire to match.

 

The point is, unless you're engine is equipped with a Lambda sensor, it doesn't actually know how much fuel is really going in. It just knows how long to fire the injectors for.

 

By changing the fuel pressure, you're changing how much fuel goes into the engine at each and every "load site" - position on the map.

 

You're not talking about changing it much, so at low accelerator openings, and a low rpm, you'll probably get away with it. But at wide open throttle and high rpm, too lean can be dangerous. At it's simplest, it can cause the combustion inside the engine to run extra hot. (Think of the fuel as helping to cool the process a little). Too hot, can melt things! Additionally, too lean can cause a sort of missfire, The extra heat encourages this too. The fuel starts to burn before it should, again, this causes internal damage - ultimately in extreme circumstances it can burn holes through pistons.

[Kit Car Electronics]

It'll lean out the mixture everywhere, not just at idle, so will be potentially very damaging at high load.

 

Fuel flow varies with the square root of pressure, so for example to reduce the flow by 10% (0.9) you need to reduce the pressure to 0.81 of it's current value (that's differential pressure across the injector, i.e. absolute rail pressure minus intake manifold pressure).

 

Here's a typical emissions plot to give you an idea of what you're aiming for - a slightly leaner (less rich) mixture at idle:

[Kingster]

So much more eloquently put and easier to follow Dave!

[Dave Eastwood (Gadgetman) - Club Chairman]

I'm no expert but might be better to edit the map and then when done load the original back in.

You should be able to lean it out at the mot rev range to help reduce emissions. Happy to be corrected

 

Exactly what I was going to add in the next post!

 

Really, you should just edit the problem area of the map.

 

A couple of questions though, is this sudden new behavior? What happened last MOT? Was the engine properly warmed up. (There was no chance it wasn't right up to temp, as it could still be on a rich warm up map otherwise).

 

Is the car running OK otherwise, no hesitation, flat spots etc.

 

Bear in mind that if the fault isn't simply it running rich, then artificially leaning it off can cause other emissions parameters to go out...

 

If it is a new development, it could really do with sorting out properly, rather than just trying tofind a work round. Otherwise if it's the start of an issue coming on, it could come back to haunt you.

[Dave Eastwood (Gadgetman) - Club Chairman]

So much more eloquently put and easier to follow Dave!

 

Without wanting to sound patronising, was trying to keep reasonably non-techy! (Difficult for me, but I do try!)

[Kit Car Electronics]

It'll lean out the mixture everywhere, not just at idle, so will be potentially very damaging at high load.

 

Fuel flow varies with the square root of pressure, so for example to reduce the flow by 10% (0.9) you need to reduce the pressure to 0.81 of it's current value (that's differential pressure across the injector, i.e. absolute rail pressure minus intake manifold pressure).

 

Here's a typical emissions plot to give you an idea of what you're aiming for - a slightly leaner (less rich) mixture at idle:

Obviously that's a Toyota plot, Ford engines normally just emit pure Essence of Springtime

[Dave Eastwood (Gadgetman) - Club Chairman]

It'll lean out the mixture everywhere, not just at idle, so will be potentially very damaging at high load.

 

Fuel flow varies with the square root of pressure, so for example to reduce the flow by 10% (0.9) you need to reduce the pressure to 0.81 of it's current value (that's differential pressure across the injector, i.e. absolute rail pressure minus intake manifold pressure).

 

Here's a typical emissions plot to give you an idea of what you're aiming for - a slightly leaner (less rich) mixture at idle:

 

Ooooooh, and that trace shows beautifully how changing one parameter to reduce say CO, can make NOx and ultimately the HC spike!

[Dave Eastwood (Gadgetman) - Club Chairman]

Obviously that's a Toyota plot, Ford engines normally just emit pure Essence of Springtime

 

That's my coffee all over the work bench; off to make fresh     

[Steve M]

It's the first mot with the car in my ownership, for its last mot the engine would of been pretty much standard zetec

I've always had issues with the cold start since it came back from N.motorsport ( that's in no way having a dig at them, I was offered the chance to bring the car back up, but as its a 5 hour round trip, I declined )

By the way the car drives superb, no flat spots etc

I took the car to interpro, who did the best they could with the cold start, they did say prior to them adjusting it, it was very rich at idle.

I've turned the adjustment screw on the fuel regulator 1/4 turn anti clockwise, I'll see how I get on from there, I'll also raise the tick over to 1200 rpm from its current 1000 rpm, fingers x'd that will be enough !

Massive thanks once again for the help !!