Boost and fuelling.

[HedgehogSandwich adi]

Hi all..wonder if anyone can help.

 

Heres the situation..

 

1JZ engine (virtually identical to 2JZ for the purposes of this thread). Recently fitted hybrids..now hitting boost cut on stock boost. I want to get rid of boost cut and run 18 psi if poss (stock turbo 1JZ boost is 10.5 psi, boost cut 1bar, standard MAP maxes at 1.1 bar i think, same as yours).

 

How do i do it?

 

1) FCD- Fitting an FCD to increase boost cut will make the engine lean??? Im assuming this as the MAP signal is altered to fool the ECU into thinking pressure is still below 1bar. Hence no extra fuel will be added to compensate at higher pressures...obviously leaning out the engine. If i ran 16-18 psi with an FCD i'd be getting lean ..is that right?

 

2) S-AFC an S-AFC also fools the ECU into thinking different amounts of air is entering the engine...and obviously the ECU compensates in the way of fuel...but can an SAFC richen the mixture whilst running higher boost on stock injectors? Can it also effectively remove boost cut?

 

3) What should i do??? I'm confused

 

Points to note.

The stock 1JZ fuel system supplies enough fuel for 400 bhp.

 

I hope i've explained what i mean..if you need nay more info just tell me what.

 

Cheers

adi

[Branners]

I believe Pete Betts knows a fair bit about the fuel cut on the 2.5tt. Best bet is to give Pete a call, he's working at building up his business so he may be able to work directly on your car. Hes based in Warwickshire I believe.

 

JB

[Steve W]

EDITED

 

Just realised I'm talking CO**LERS ! !

[HedgehogSandwich adi]

yep..spoke to pete last week..i was just wondering what the findings were of people who'd been in a similar situation (albeit on a 2JZ).

 

I'm prob ordering an FCD off pete next week.

[Justin]

I just de-catted together with a FCD and am running at 18 psi for the first time. Unfortunately it looks like I am running lean now and have to drive 2 1/2 hours to see CW to see what he says. I didn't expect this to happen and it seems strange to me that no one else has mentioned it with similar spec cars and exhaust set ups. I am no expert so I will reoprt back CW's findings tomorrow.

 

[Adam W]

What you do is rely on the fact that the car will be running well rich from the factory, so you can go a bit leaner than that by tricking the ECU (exactly as you describe) and still be safe. Get it checked on a wideband to be sure though, especially as you have an unusual engine.

 

An AFC adjusts the fuel mixture by adjusting the airflow signal to the ECU, so if you tell the ECU there is less air going in than there actually is you will raise the fuel cut limit, but the ECU will also inject less fuel, very similar to how an FCD would work. For example, you couldn't fit an FCD and then try to richen the mixture with an AFC, as the first would lower the air flow signal, then the second would raise it again!

[HedgehogSandwich adi]

Apparently Pete reckons you can fit his FCD with an S-AFC , as long as the FCD is closest to the ECU in the line.

 

Regarding the S-AFC though..Obviously i need to richen the mixture at the same time as fooling the ECU into thinking i'm still running under 1bar.

 

SO......

 

leaving the FCD aside for a minute...If i fit a 2bar MAP sensor, fit an S-AFC....

 

no ..its no good..its a complete head f**k. Im totally confused..

 

 

I've got to do something sharpish though..i hit boost cut three times today and it cant be doing my engine any good.

adi

[Ian C]

You are ultimately limited by what your ECU is mapped for. If it's map goes to 1.1bar, then anything over that will 'clip' at 1.1bar and get that fuel map. As the air flow measurement is seen by the ECU as a voltage, putting in a 2bar map sensor would be a terrible thing to do, as it probably gives the same voltage for 2bar as the old one does for 1bar, therefore the ECU would see a value representing half the actual airflow it's getting across the pressure range.

 

Anyway, I'm sure you didn't actually intend on putting one of those in

 

The AFC is best used when trimming overfuelling down. If you put in 25% bigger injectors, you use the AFC to tell the ECU that it's getting 20% less air so it fuels 20% less and you are back at the status quo. But then, at the higher boost levels, you set it to, say, 0% correction so that you are now adding 25% more fuel than stock. Of course, the ECU will still only map to 1.1bar, but at 1.1+bar of pressure you can be adding 25% more fuel.

 

There is some trimming you can do with throttle position and revs, but it's best to run safely rich.

 

Hope that is all reasonably understandable!

 

Of course, this all needs setting up by someone with the experience and the hardware necessary. Speaking of which, I'm interested to know how Justin gets on, getting his fuelling checked by CW

 

-Ian

[Adam W]

You could put in a 2bar MAP sensor, AND 1100cc injectors.

 

The sensor would read say 1bar, but output the voltage that the old sensor used to output at 0.5bar. Therefore the ECU thinks that there is half as much air going in as there actually is, so it tells the injectors to stay open for half as long as they actually should. However, as the injectors are twice the size, the two things cancel each other out.

 

It's a pretty common mod for Mk3 Supras, only instead of going 100% bigger, we use a 25% bigger air flow meter, and 25% bigger injectors with an AFC to trim it (not that it needs much adjustment though).

[HedgehogSandwich adi]

I think this needs a lot more thought before i do anything..

 

For now i'll fit an FCD and just slightly raise the boost cut to stop it happening, then get it checked out to make sure im in no danger of leaning out. I think that even with the altered signal to the ECU i should still be okay regarding fuel, as the 1JZ runs rich anyway (mine is running way rich at the minute, so much so i can smell it).

 

There is someone else on the soar*r list (edited for diplomatic reasons) that has just fitted the same turbos..so i think i'll wait and see what he does. It looks for now like the way to go eventually will be a 2 bar map sensor and something like the power FC, the problem being there is that the power FC doesnt like autos (particularly the 1JZ) and therefore i cant use it. arse.

 

 

This is all extremely frustrating..i've got an engine that can provide enough fuelling as stock for 400+bhp, two turbos that can take pressures of 28 psi and i cant even push them enough to raise a tickle !

 

This has been a bit of an eye opener...what is boost cut on the mkiv (17 psi?). How do you lot running 20 psi get around it ?

 

adi

PS Adam, i'm ashamed to admit the 1JZ injectors are a measly 370cc, even less than the 7M, but they do a damn fine job!! Its also extremely difficult to fit larger sizes because of the design.

 

 

 

[Ian C]

We run 20 psi one of three ways:

1) remapped aftermarket ECU - rare and expensive

2) fuel controller based on revs and throttle position - imperfect as it has to be mapped for 'worst case scenario' boost levels and therefore always runs safely rich

3) wing and a prayer - cheapest and yet the most expensive long-term

 

Runing rich at idle is no guarantee whatsoever of the fuelling at full chat, but I'm sure you know that. It's good to see someone taking the sensible approach of seeing what the car is up to and then sorting out adequate fuelling before upping the boost!

 

What design are the 1Jz injectors? Top feed or side feed? Can my spare 440's fit? They are side feed, high impedance.

 

-Ian

[HedgehogSandwich adi]

The stock injectors are side feed..although i think low resistance..i'll have to check.

 

But if you use a fuel controller based on revs and throttle, then how does it alter fuel? by altering the MAP input to the ECU? But this maxes out at 5V and 1.1bar so how on earth does the AFC tell it to *add* more fuel over pressure of 1bar? I can imagine it tells it lower down the rev range that more pressur is being applied than it actually is, but when we start reaching max pressures and voltages i cant see how it works..

 

does anyone have an idiots guide to the S_AFC and all things MAP?

 

[Ian C]

You pick your maximum boost, say 1.4bar.

 

You install a new fuel setup, i.e. bigger injectors. Let's go from 440 to 550, as it's an easy-to-work-with 25% increase in fuelling capacity (and a relevant figure)

 

So, with nothing between the sensor and the ECU, we run, up to 1.1bar, 25% richer than normal - the injector pulses deliver 25% more fuel each time, but the ECU doesn't know this, all it does is open and shut the things according to the map it has stored.

 

Now, the AFC steps in and fudges this airflow figure. We need to drop it by 20%. Yes, only 20%, because percentages are like that (125% of 100 is 125, but 80% of 125 is 100, so it's 20% less, OK? )

 

That means 1.1bar on the sensor is sent to the ECU as 0.88bar, as then it supplies 20% less fuel, tadaa, the fuelling is correct with the bigger injectors in place.

 

Once you get above 1.1bar, the sensor clips at 1.1. The AFC now 'fills in the blanks' by using throttle position and revs to calculate what boost you probably are running, and feeds this to the ECU as a fudged figure between 0.88 and 1.1bar. The ECU uses it's fuelling map to deliver 1.1bar's worth of fuel through 25% bigger injectors and you get mapped fuelling up to just about 1.4bar.

 

Two things 'wrong' with this approach. One, it's not as accurate as a good airflow meter - you can't know exactly what boost you have just from throttle position and revs. So you need to set it up to 'worst case scenario' boost levels - this means that, at these pressures, anything less than full throttle on a cold day and it's 'wasting' fuel because you have it set up for full throttle on a cold day.

 

Two, once you get beyond 1.4bar you need to overfuel even more, e.g. if you intended to run 1.6bar you need to run 1.6bar's worth of fuel when the ECU thinks it's at 1.1bar, and the factors involved above mean that you need to be fuelling for 1.6bar of boost even when you are only running 1.4bar actual boost, as at this point the ECU is at it's 1.1bar area of the fuel map anyway - it delivers the same fuelling between 1.4 and 1.6bar.

 

Wow - see if that makes any sense. This is why CW needed my car a couple of days to set up

 

So you see, the AFC doesn't tell the ECU to add more fuel, it tells it to add *less* by fooling it into a lower part of it's fuel map, thus stopping *overfuelling* by the bigger injectors. Which is why AFCs are reasonably useless without bigger than stock injectors to trim down...

 

-Ian

 

Edited post-proofread

[HedgehogSandwich adi]

wahey..cheers Ian, nicely explained..got it now.

 

so in the above scenario...what would happen if i fitted a 2 bar MAP sensor (same voltage ratio obviously). I could then effectively map the fuel without the guesswork of revs and throttle?

[Ian C]

Dunno mate! The AFC I have doesn't have it's own boost sensor, so I don't know how it would deal with a non-stock sensor.

 

Without an AFC, the ECU would probably underfuel by about 50% as it's voltage range is now 0-2bar instead of 0-1bar, so 0.5v* will be 1bar actual boost, but the ECU will deliver 0.5bar of fuel. Great if you have 880cc injectors! But it's still not an exact science, so you'll still need an AFC to fine-tune the results to ensure safe fuelling and nothing mickey mouse at the lower end of the throttle/revs/boost spectrum. Still a lot of tweaking and road time with a decent O2 sensor.

 

*I don't know what the actual voltage range is, this is assuming 0.0-1.0v for clarity

[HedgehogSandwich adi]

okay..cheers for all the info ..much appreciated.

 

adi

[Justin]

Went to Chris Wilson today about my problem. False alarm, it wasn't me running lean it was simply down to knackered spark plugs. He closed the gap on them and the problem went away so running 18psi is no problem for my J-spec de-catted FCD TT. I just need some new cooler grade plugs.

[HedgehogSandwich adi]

Originally posted by Ian C

What design are the 1Jz injectors? Top feed or side feed? Can my spare 440's fit? They are side feed, high impedance.

 

-Ian

 

Ian, i may well be interested in taking a set of your 440's off you.. the 1JZ injectors are side feed high impedance.. let me double check a few things and i'll get in touch with you soon.

 

cheers

adi

[HedgehogSandwich adi]

yes they do fit straight in.. and they do a nice job of sustaining the fuel at higher boost...Would you be willing to let some go in a couple of weeks or so?

[Ian C]

You have a private message awaiting...

 

-Ian