mrkimpreza

Yesterday I had two runs logged with DeltaDash.

A normal run up to about 5500-6000rpm. No knock correction, no knock, boost curve up to 1,1bar, lamba high expect for known lean spot till ~3000 rpm.

Same run however with tube to boost sensor (next to solenoid) disconnected. DD, so ECU, sees zero, 0, non boost.

Boost peak is slightly higher (up to 1,2bar and still lowering at high revs), no knock, lamba still high, still solenoid activity. Not much difference. Naturally I don't have a boost curve from DD because the ECU sees no boost at all. However my gauge shows a slightly higher peak (1,2 vs 1,1) and DD still shows a lowering duty cycle of the solenoid.

So I'm wondering, what does the ECU do with the boost signal ?


Mark.

dowser

Certainly, when the MAP sends too high a signal the ecu cuts fuel

Richard

john banks

The ECU will reduce the duty cycle if it detects you are over target boost. So to increase boost using the factory boost controller you need to fool the MAP sensor AND adjust the restrictor - see my log using a Dawes 16 PSI on the log is really 19 PSI and I still have a 20.2 PSI fuel cut or thereabouts.

But it uses a load (mainly MAF based I think) vs RPM table for looking up a guess duty cycle - hence it still drops boost at high RPM even if it does not know what the boost is

The ECU seems to work on open loop boost control unless you go too high and then it compensates the duty cycle down hence you get a momentary peak in cold weather/hard driving/with downpipe/high octane etc. If you fool the MAP sensor you end up with slightly higher held boost as well in these conditions.

[Edited by john banks - 4/25/2002 1:02:44 PM]

mrkimpreza

So what are the risks of running with the tube to the ECU boost sensor disconnected ?

It still has a "guested" duty cycle, limiting my boost to 1,2b (just right I think), it still drops at higher revs and it still monitors lambda and knock and consequently does air/fuel correction and knock correction.

Seems like a rather simple and riskless mod.... What do you think ?
(I'm not sure yet, I just did one run and connected the tube again)


Mark.

MattRus

Did you block off the tube when you disconnected it? If not the ECU would supply to much fuel (run richer)as air will leak from / be drawn into the inlet manifold via the tube. Are you certain that you removed the MAP (pressure sensor) tube and not one of the other boost control ones. Sorry, to doubt you but the MAP is more than a safety device to detect over boost and does effect other ECU parameters along with the atmospheric pressure sensor (depends on MY though)

Cosie Convert

With the pipe disconnected there's going to be no problem measuring atmospheric

Interesting findings ! If using a MBC this could make FCD's redundant

I really wanted to but I wasn't brave enough to try this

Intersted to hear if anyone else has tried it ?

ps I'm aware of the dangers of overboost

john banks

Come on guys do it properly! Rather than disconnect the air feed to the MAP sensor you could shell out all of 6p on a zener diode if you want no fuel cut, or less than a fiver making a proper (safe) fuel cut lifter with three components. When a fuel cut is so easy to raise it seems a bit daft.

mrkimpreza

@Matrus: I did not block the tube.

Look where the solenoid is. The solenoid has two rather thick (1cm) tubes. Leave them just a they are. Near the solenoid there is also a thin tub running from somewhere behind the solenoid to a sensor with a wire connected. The sensor, in my case says "denso xxx".


Mark.

MattRus

That's the MAF. Usually held on by just one bolt!
Appologies for doubting you!
Interesting findings though, just goes to show how useful the EciTek software is! I will be trying it on my car soon hopefully.

mrkimpreza

MAF as in Mass AirFlow sensor ???

Don't think so, then it makes no sense that I read no boost in DeltaDash (MRP, Manifold Relative Presure). I have to check the logs but if it's the MAF you should read no MAF voltages and boost (MRP) correctly

Mark.

Paul_H

It's not the MAF sensor, it is the MAP sensor (Manifold Absolute Pressure)

A fuel cut lifter as described above, in conjunction with a carefully chosen revised restrictor size is a pretty good tuning solution.

You get extra power (of course ), retain a higher fuel cut for protection, and keep the driveability and sophistication of throttle response, and it doesn't break the bank.

I think it is also much kinder on the turbo/engine/gearbox than a Dawes, because it is more progressive i.e. the boost doesn't arrive with such a sudden thump.

[Edited by Paul_H - 4/26/2002 5:56:43 PM]

[Edited by Paul_H - 4/26/2002 5:58:20 PM]