Dynotech Tuning

iTrader: (12)

Someone asked how the SD setup accounts for EGR changes on a speed density setup in another thread and it was a point I had never thought of before.

I don't believe there are any fuel compensation tables for EGR since the MAF is the component that can tell when the EGR is flowing. I need to do some testing but MAF HZ seems to be the best indicator of how much EGR flow is actually filling the combustion chamber. If the MAF shows 100Hz at cruise with the EGR fully enabled (and is functioning properly and isn't clogged at all), one would expect a higher MAF Hz when the EGR is disabled. Since the MAF Hz would be higher at the same RPM with the EGR disabled, I would guess that the LOAD would increase as well.

Now, on our Speed Density patch, I don't believe there is anything that can compensate for this at all. If so, most would tune their vehicles at full operating temperature when the EGR system is activated. This will make the cruise areas lean when the engine is cold and the EGR system isn't activated yet. One might think that using the Fuel Enrichment vs. Coolant Temp tables would work but it would add fuel to all of the map and make other areas too rich. I'm not too sure how much leaner it would make the cruise areas but I would imagine that a SD tune that is already a bit lean in the cruise areas would become a bit hesitant if things became too lean. Lean AFR + cold engines= poor fuel ignition.

I thought it was a topic worthy of discussion since the EGR system is something that is still very important to a lot of people who prefer the advantage of fuel economy and have very strict emissions visual inspections in their states.

-Jamie

ExViTermini

iTrader: (25)

I thought the purpose of the map sensor in the stock setup was EGR related?

Dynotech Tuning

iTrader: (12)

That is true but I would imagine its only to activate/deactivate the EGR solenoid. I would need people to chime in about how the system compensates for the fuel requirement changes.

Do the 9653 equipped evos come from the factory with EGR systems? I know they don't use a MAP sensor from the factory.

-Jamie

todd6027

iTrader: (10)

90550001 evo7 had mdp sensor in manifold and egr stock , it was called manifold differential pressure sensor rather than map sensor

Dynotech Tuning

iTrader: (12)

Yes, they are ALL called MDP's and almost all roms use a MDP and EGR. As far as I know,only the 9653 rom variants didn't use any MDP or MAP.

Nimpoc

iTrader: (17)

Thanks for starting the thread for me.

In the case of a MAF car, I don't think there is any change in LOAD or MAF output as the exhaust gas is inert, and therefore doesn't require any fuel because it doesn't make any power. To maintain a given vehicle speed (power level) the throttle angle stays the same, though manifold pressure increases, and the same amount of fuel should be going in to mix with the good air. Ideally the fueling should go down a little as the higher manifold pressure reduces pumping losses, improving BSFC. You also get to add timing since the mix isn't so volatile, plus combustion temps go down which really is the whole point of EGR (NOx reduction).

I'm just guessing here, still learning the Mitsu system.
I'd guess on the stock ECU that the MDP (MAP) sensor is monitoring EGR flow via the delta in pressure as a function of EGR valve PWM signal. As it's a 1-bar sensor, y'all can chime in if the tables allow EGR under boost, probably not.

Now about the SD situation... As EGR is introduced to the inlet stream behind the TB, the MAP sensor just sees it as more good combustible air, which it's not. This would result in excess fuel if not accounted for. The EGR flow is also likely to have an impact on IAT that isn't seen by sensors not mounted in the intake manifold. At this point I'm not sure how OEMs account for this, which is why I asked.

211Ratsbud

iTrader: (1)

Retract those questions lol.

Dynotech Tuning

iTrader: (12)

I did a quick test at 2k rpm cruising in 3rd gear on the dyno today. With EGR enabled at 60kpa, the fuel trim averaged -1% on SD. With it disabled it averaged +4% at the same 60kpa. So it appears that its not accounting for the lack of inert gases occupying some of the combustion chamber with the EGR off. I will do more extensive testing when I get the opportunity before I make a final judgement. I will try and test it on MAF and then on SD as well.

-Jamie

mrfred

iTrader: (50)

Highest load for EGR is 80 KPa. The transition from vacuum to boost happens right at about 90 KPa.

mrfred

iTrader: (50)

Additional thought - if EGR operation produces a drop in MAP, then for a SD load measurement routine, wouldn't that would produce a proportionate load and fuel reduction? And since the Mitsu EGR OBD routine looks for a pressure drop when EGR is active, there is apparently some pressure drop (although I've never been able to detect it).

Nimpoc

iTrader: (17)

I think it's a wording issue; as EGR is introduced, the IMAP increase (less vacuum). Thus the SD ECU's perceived load on the system goes up despite the additional gas being inert.

Would you be willing to explain how the Mitsu EGR logic works?

mrfred

iTrader: (50)

You are correct, IMAP does actually increase relative to absolute when EGR opens, so SD would call this an increase in load and thus add more fuel. It fact it appears to be a multiple effect, less O2 and higher perceived load.

The EGR PWM values are totally passive, i.e., there is no feedback based on IMAP, but there are several flags that control whether EGR operates. Since I was never particularly interested in EGR except in how to turn it off, I haven't put any effort into tracking down those flags, but I do know that none of those flags are related to IMAP.

211Ratsbud

iTrader: (1)

Is the fact of more load = more fuel a rule? Closed loop will just run off the o2 sensor and inert gases will just take up space.

mrfred

iTrader: (50)

The baseline response will be for the ECU to add more fuel when load increases, but the STFT+LTFT will compensate (subtract fuel) to keep AFR at stoich.

Dynotech Tuning

iTrader: (12)

I believe there is an Evoscan Custom Request that would allow the EGR valve to be opened while cruising. It might be interesting to set the duty cycle tables to zero and then log the car at a constant speed on the dyno and see how the IMAP changes when it switches on.

The EGR opening is quite small (about 3/16" diameter) but I could see that being enough to show a change in vacuum. I wonder if someone is running a stock location MAP sensor and has the Tephra MAP sensor averaging option enabled if it would register the change fast enough?


-Jamie