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rocklizzard91

Troubles with Modeled fuel strategy

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Hello everyone, I am having some troubles with getting my v9 EJ207 to run on the modeled fuel strategy. I can get it to run on the stock ECU and I have run the car on the traditional mode as well.

The car is basically stock aside from Injector Dynamics 1000cc injectors and a walbro 255lph pump. I am using the "spec-c" intake mounted IAT, factory ECT and factory V9 MAP sensor. I have a PLX SM-AFR wideband (not yet hooked up to the ECU, I have lambda corrections turned off so I assumed this will not affect the ability to run the car). 

 

As far as the map goes I have left everything as it comes from LINK aside from adjusting the PS voltage code, Tacho fix, switched to modeled in the "Fuel Main" tab added injector size info, latency and injector short PW adder tables. Number of cylinders is correct, engine size is correct, VE table is the LINK factory table, I'm running 91oct fuel, so I left the fuel density as from the factory as well. Fuel pressure is 43.5 as well. I can only get the car to run when I size the injectors at ~400cc, as I raise the injector size, the lamda leans out. Alternately I can lower the fuel pressure to ~20psi and it will let me raise the injector size closer to the true size, but my factory fuel pressure regulator is not a 20psi regulator.

 

Does anyone have any pointers? I have included the map I am working on. 
I'm much more familiar with megasquirt and I'm sure I am overlooking something easy, any help is appreciated!

1000cc Modeled WRX V9 G4+ Xtreme Plugin.pclr

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That base map was originally running traditional fuel map right? The numbers in the fuel table are way too low for a modelled VE table. as a starting point, multiply everything in the table by 1.7 so that the number at ~3500 @ 100kpa is around 100.  This lines up with most of your symptoms too : changing injector size to 400 means the ECU basically doubles the fuel amount. I assume you mean changing the refernce pressure in the ECU rather than acutally changing your pressure reg? In that case, same thing, ECU thinks you've got half the pressue so double the pulse time (ie double the fuel)

The numbers arent quite double because of a dead time etc but you get my point. Also, the manual says to disable IAT calibration to start with when using modelled fuel

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As CJ has hinted, In modeled mode your Fuel table numbers are Volumetric efficiency.  Numbers will typically range from about 50% at idle to 100% at peak torque.  In traditional mode the numbers in the fuel table are just "% of master fuel".  You cannot change from traditional mode to modeled mode without building a new "VE" table.  

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Thank you guys for the help!

Yes the map was originally for the traditional fueling mode, that does make sense that I need to treat it as VE not as % fuel! I will play with that tomorrow! CJ you are correct, I was manipulating the pressure in the map, not physically changing it via regulator. I did manage to get it to idle with the VE values a bit higher earlier today, but saw it was limited to 150 so I felt like I was going to run out of resolution quickly, good to know I should be ok!

 

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I played with the VE table a bit today, just revving the engine in the driveway from idle up to about 3000rpm and input values that got me close to stoich. 

Is it normal to see such high values for VE down low in the MAP? I am positive I have the injector data and engine size set correctly, I did notice the fuel pump is not fully driven at idle, its reduced to 33%, could that be the reason I see such high VE values? ( I just interpolated values out past 3000rpm and 0psi, I do not plan to use them as input)

ve1.png

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I would expect numbers closer to 50% around idle.  Usually if you have un-realistically high VE numbers that means the engine is getting less fuel than the ECU thinks it is supplying.  fuel pressure would be the first check.

Is the MAP reporting realistic vacuum at idle?

Also turn off your IAT trim table, that should normally not be turned on in modeled mode.

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According to the last recorded value in the log you posted, your IAT's are about 60deg C. At this temperature, your IAT correction is pulling between 0.5 and 8% of fuel so disabling this should get your VE quite a bit more accurate.

Heres a pretty generic sample image of a VE table. No idea what engine this is from (first result from google), but it shows you the general shape that most engines will want. It looks like the left column is MGP.

sdtable.png

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Right on, I will check fuel pressure this weekend, I was looking at the help file and it says to set the base by running the pump with the engine off. The ECU does account for the pressure drop in vacuum correct?

 

I did turn off my IAT comps per CJs first suggestion post, it did seem to help a bit. Adam, are you saying that the modeled fuel mode should always have IAT comp tables off? Or only while setting up the VE initially? How will the ECU fuel correctly without adjusting for air density?

 

Thanks again!

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I did turn off my IAT comps per CJs first suggestion post, it did seem to help a bit. Adam, are you saying that the modeled fuel mode should always have IAT comp tables off? Or only while setting up the VE initially? How will the ECU fuel correctly without adjusting for air density?

IAT table should always be off unless there is some special need for extra compensation on top of the automatically calculated air density.

The ECU uses "charge temp" to calculate the air density.  The charge temp approximation table uses a blend of IAT and ECT to approximate the temperature of the air entering the combustion chamber.  This approximated temperature is then used to calculate air density based on the idea gas law.  

The reason you use the charge temp approximation instead of just IAT is that IAT isnt always a good indication of the temperature of the air entering the combustion chamber  - after the air passes the IAT sensor it is usually heated more by the manifold and port walls etc, the amount of this heating effect generally varies with load and engine speed.   At low speed the charge temp is closer to ECT, at high speed the charge temp is closer to IAT.

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Hi,

sorry for hijacking this thread, but I'm just wondering about some of the same.

-effects of this charge temp and this stuff.

reason being that my engine feels like its varying on power, and the injector duty cycles varies between 62 and 70%

Afr is fine.

Engine was mapped in an engine dyno without any airflow to filter or anything.

Question is, if some settings are wrong and engine stills run fine on afr.

-could this be because of the modelled mode?

Will it compensate automatically for what it thinks is right, and not see anything on afr, since the duty cycle varies that much?

Could airflow to filter affect this?

Duty cycle should theoretically be a result of power, and 8% is a big difference, same with injector pulsewith.

-having a hard time to explain :)

 

It is a na separate itb engine, bmw s14,with quite aggressive cams and overlap.

 

sorry for hijacking your post, trying to understand more about tuning

 

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Adam, that does make sense, just to verify, I can turn off IAT in the IAT fuel correction tab and select off? Or should I just zero out the fuel trim table? 

In the future i do plan to run water injection, is that something to consider using the IAT table for? Or will the ecu still do just fine with the charge temp table still?

Again, thanks for the help!

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Jo can do both, same effect. No IAT correction is applied.

I usually reachen the mixture a bit up on the iat table on very high IAT, to help with cooling. 

I would suggest to use a 4D or 5D table for water meth corretion and activate it trough a DI input or virtual aux while spray is active. 

 

 

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Alright! I checked my fuel pressure and I was correct at 43.5psi base and mid-high 30's at idle. Is there any other reason I might have such high VE values with everything else in the injector info entered correctly? I am using the factory 3-bar Version 9 STi map sensor, and I did calibrate it and I do think it saw relatively reasonable values at idle.

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It will if your injectors dont flow the rate you have input . If they flow less you end up with artificially high VE numbers . At least thats what i found . I set my engine up and had a similar issue with high VE numbers at idle and ofcourse from there up as well . As a work around i input the flow rate at half what they were supposed to flow ( 1200 down to 600 ) and multiplied the whole fuel map by 50% - halving the VE numbers . Worked for me .

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LINK don't state at what fuel temp the the cc should be measured at. It should be in the help file. Some test at 20DegC while Injector dynamics test at 52DegC. The software should allow for the temp it was measured at to be inputted.

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Any idea where the parameter for fuel temp for injector flow is? Spent a while last night trying to find it and I could only find the inputs for fuel density and cooling coefficient.

You'd think the hotter the fuel is, the more it will flow? So I should see slightly less for injector size at the "regular" fuel temp test?

I just don't want to "work around" to get them to flow correctly, it makes me feel like something else is wrong

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I have not yet got this sorted out. I did rough-in the map to 10psi and 8000rpm and see values start is 70 (idle) up to 120 (peak torque) and down to just under 100 at redline. I am running a rather small turbo, could this be boosting my airflow at low rpm enough to bump up the VE of the engine at idle?

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