I am trying to catch up with engine control by electronics, and hope someone will put me straight here.

I understand that an FCD delays the fuel cut by fooling the ECU into thinking that the boost is less than the engine is really running at. In that case, will the ECU underfuel dangerously for the actual boost that the engine is experiencing?

I see that there are both pressure and electronic FCD's. Is there a difference in how each suppresses the fuel cut and which is the best to use.

Les

 

Best to use electronic for precise control and having a new predictable fuel cut.

MAF based cars (like Scooby turbos) have only a small input to fuelling and timing from the MAP sensor so they don't underfuel until the fuel pump or injectors top out.

 

John

I have to disagree slightly

I've recently installed a mechanical FCD on my MY99. Whilst running 18psi boost with defend at 14.5psi I saw a lot more knock correction and knocklink activity with AFR voltages down to 0.88V.

Now I know this isn't "lean" as this equates to an AFR of 11:1 but the ECU was also fooled into running an inappropriate degree of advance which, in combination probably with the reduced cooling effect of less fuel, lead to increased knock. This was whilst using optimax + NF.

IMHO you have to be very careful where you set your defend point with a FCD. Mine is now set at 15.5-16psi doesn't produce much KC or KL activity with 18psi boost. Doesn't go too bad either

Cheers

Simon

 

Fair enough, but try taking 0.3V off a 4.4V MAF reading and see the effect compared with 0.3V off the MAP value.

In practice this is what an APS induction kit does, and it represents a 25% difference in airflow and hence fuelling and massive extra advance.

But a knocklink is always a good idea (nay mandatory) with a FCD.

I think by far the biggest issue on your car is timing in the base map is not right for 18 PSI. You get similar results if you take a standard ECU and raise the fuel cut in the ECU. So the ECU sees the full MAP voltage and dets like a *******.

11:1 is still rich, although for a TD04 running high boost and top mount about right. The biggest issue really is the timing.

[Edited by john banks - 5/21/2003 4:00:28 PM]

 

Yeah I think things are pretty much on the limit. Makes a nice drive though, but for how long

I know I am seriously eating into my safety margins, but hopefully my KL will keep me atuned to mischief on the det front, and my AFRs are now 0.895V.

Les, I think the bottom line is FCDs are "fun" but risky whether electronic or mechanical, but if you can retain a higher fuelcut, this can only be an advantage (to the electronic sort).

It seems a lot of people on scoobynet use them, particularly with MY99/00 cars, reasonably safely. But my feeling is that this is largely due to the TD04 not being able to sustain more than 1 bar at 5500-6000rpm, thereby preventing a lot of high rev/boost det, which is a certain killer.

Cheers

Simon

 

Thanks JB and Simon, makes it all a bit clearer. My car is a MY94 STI and I just want to be able to increase the boost a bit. I have got Knocklink,AFR and Boost gauge on the car now.

Les

 

Les

In that case you would need to be pretty careful as the jap imports are mapped for 100+RON fuel standard so run a lot of advance. In addition, the TD05 will sustain 1.5bar boost at 6000rpm.

If your boost control is standard you could try a Dawes MBC as this will allow your big turbo to spool a little quicker and hold a bit more at the top. I use the Dawes FCD too although I'd be very cautious about raising the boost too much.

I think the scoobyecu remap might be suitable to your car and would be another option. See [www.scoobyecu.co.uk]

Simon

 

Thanks again Simon, that was one way I had in mind. Didn't realise that my JDM had more ignition advance as well. My indicated boost will go up to 1 bar plus a little with the PE T75 turbo back system, and I will shortly fit a ported header system and H&S up-pipe. I have had fuel cut once when trying WOT for the AFR. I have got a Dawes and was going to try it as you say to get a quicker spool-up. Sounds like the Scooby ECU map would be best for me.

Les