Req_fuel & injector settings

[pete95zhn]

How will I set my req_fuel, I get different answers from different sources.

MegaSquirt calculator http://www.megamanual.com/v22manual/mfuel.htm gives with inputs

Engine Displacement (cubic inches) 183
Engine Displacement (cubic inches) 4
Number of Injectors 4
Number of Squirts 2
Injector Flow (lbs/hour)
per injector 86
Injector Staging alternating
Fuel Type Gasoline

an answer of

Req_Fuel
(ms) 5.6
Downloaded
Req_Fuel
(ms) 5.6

And if I change Injector Staging = simultaneous --> Downloaded
Req_Fuel
(ms) = 2.8

OTH PhatBob manual  http://www.vems.hu/wiki/index.php?page=MembersPage%2FPhatBob%2FUserGuide :

req_fuel = 6.49 * (D / N / I)
I injector flowrate (cc/min)
D engine displacement (cc)
N number of injectors (eg. 4 for a 4 cyl port injection)
 
req_fuel = 6.49 * ( 3000 / 4 / 903 ) = 5.4

No separation between batch or sequential or which divider.

I'm using divider=1 and sequential injection.



Finally I'd like to confirm that when using Low-Z -injectors ( 2.35 ohm ) with ballast resistors and the box has 30V Flyback, then PWM will be disabled like this:
 
*Inj open time should be 0,
*Inj rampup_battfac must be 4080 (which diables the feature)

What are right values ( or a good starting point ) in this window:



PS. How in h*** one marks a topic as new??

[rob@vems.co.uk]

You can see threads as new if you dont post on them.

From the top...
Go with req_fuel from my manual, we have a different injector strategy to MegaSquirt

Have you really got a 3000cc four cylinder engine?

divider=1 and sequential injection is fine.

Inj open time @ 13.2V should be zero
Inj effective rampup try starting with 1000
Inj rampup_battfac should be 4080
battfac try 512
Injpwm DC should be 100
Injpwm DC added @6V can be anything as it cant add to 100%
Injpwm peak time can be turned off by using 25.5

[pete95zhn]

Have you really got a 3000cc four cylinder engine?

Yeah, those crazy Porsche engineers...       

[rob@vems.co.uk]

I really had no idea... can't wait to see the results of your work

[pete95zhn]

OK, now it started like never before...but only afted I doubled the req_fuel from 5.4 to 10.8 . Although then A/FR was 10-11:1 even after warm-up enrichment didn't interfere.
I made the VE-table with tools: Generate table and used these ( hopefully someday's ) figures: 500lb-ft/4200rpm, 500hv/6200rpm, max 7200rpm @ 2,0bar = 300kpa. Top row has then numbers in excess of 160, so I can't just double the tables' values ( >>It is common practice to then half this number and to double the values in the VE table, as this means that the VE table's resolution effectively doubles and allows finer grain tuning.<< ) to get req_fuel back to 5.4 .
Highest PW I noticed was 1.3ms @ 2000rpm, @ idle it was 0.9 . So there is altogether something to do, but what?

[rob@vems.co.uk]

It started like never before?  Where did it fall over before?  Dont forget that req_fuel has no effect on priming cranking afterstart.

If you want to double values start there, followed by the warm-up enrichments.  Your engine is only in that area for a very short time, so you should really concentrate on getting the req_fuel and VE numbers right for the normal warmed-up operation of the engine.
Also bear in mind the effect of the target lambda decrease the number where you are at 160VE and you'll find that the PW increases and that means you can bring the VE value lower.

[pete95zhn]

It started like never before?  Where did it fall over before?  Dont forget that req_fuel has no effect on priming cranking afterstart.

How come then if I don't change anything in priming/cranking/afterstart and play just with req_fuel it either doesn't even promise, just starts but then dies, starts but dies a bit later sunning stumbling or starts and finally idles like it's going to win LeMans 24hrs... Req_fuel amounts are then ( about ) 5.4-> 7 -> 8 -> 9 -> 10.8

If you want to double values start there, followed by the warm-up enrichments.  Your engine is only in that area for a very short time, so you should really concentrate on getting the req_fuel and VE numbers right for the normal warmed-up operation of the engine.

Yes, this is the goal. I just tried with doubling the VE-table and halfing the req_fuel. When warm, I had to subtract 15 units from VE-table to get A/FR near stoichiometric. Still PW remained below 1.0. OTH Inj effective rampup was still 1000. I haven't yet tried to play with that, it's next thing to do.

Also bear in mind the effect of the target lambda decrease the number where you are at 160VE and you'll find that the PW increases and that means you can bring the VE value lower.

[rob@vems.co.uk]

It started like never before?  Where did it fall over before?  Dont forget that req_fuel has no effect on priming cranking afterstart.

How come then if I don't change anything in priming/cranking/afterstart and play just with req_fuel it either doesn't even promise, just starts but then dies, starts but dies a bit later sunning stumbling or starts and finally idles like it's going to win LeMans 24hrs... Req_fuel amounts are then ( about ) 5.4-> 7 -> 8 -> 9 -> 10.8

Then you must have cleared the afterstart phase then!  What sort of warm-up enrichment value does it settle on?

[pete95zhn]

It started like never before?  Where did it fall over before?  Dont forget that req_fuel has no effect on priming cranking afterstart.

How come then if I don't change anything in priming/cranking/afterstart and play just with req_fuel it either doesn't even promise, just starts but then dies, starts but dies a bit later sunning stumbling or starts and finally idles like it's going to win LeMans 24hrs... Req_fuel amounts are then ( about ) 5.4-> 7 -> 8 -> 9 -> 10.8

Then you must have cleared the afterstart phase then!  What sort of warm-up enrichment value does it settle on?

WUE is flat 140% from -40C to +5C, then linear to 0 at +70C. A bit rich though, but engine runs. I'll adjust it when this PW issue is solved. If I multiply VE-table by two ( ignoring boost area ) and divide req_fuel by two, PW drops to 0.3, increasing to 0.7 @ ~1600rpm. I played a little with Inj effective rampup, it's now 400. I'll get it lower, but I ran out of gas just when I rememberd that I can datalog all this...
IAC ( Bosch pwm -style ) is another question. It seems that I have to use pretty low % to control idle. 30% gives 1300rpm idle, 20% ~1000rpm...TB ( 65mm ) doesn't apparently close fully. Engine idles now @ 57kPa, which is better than before ( ~70 ).

[pete95zhn]

OK, I'm getting now pissed and I have to admit that I have looked for fully commericial EMS's...

*Whatever I do, I can't get the PW higher I've earlier written. I've tried req_fuel from 5.4 to 22.0 with matching VE-table, engine idles and can be tuned close to 14.7:1 A/FR, but PW stays well below 1.

*It also doesn't rev above 2k, dies just below. Acceleration speed has no effect. I have checked all settings but haven't found yet any bugs, because it looks like ther's some kind of limiter on...or the trigger just can't handle higher rpm. Acceleration enrichments have little effect.

*One issue, probably related to previous ones is that when trying to open the thottle very slowly ( and if it doesn't die ), A/FR goes to very rich ( 10:1 with black smoke ), rpm down to 800 and intake pressure to 90 kPa.... ie it idles stumbling and shaking. Even after closing the throttle again this continues for 3-5 seconds, then is suddenly jump back to 1300 rpm/65 kPa/14:1 A/FR. Only good part with this is that EGT goes down too...

Is it possible that all this is related to some hardware issue? Can I check eg PowerFlyback's funtionality? My ballast resistors are 6R8's ( 6.8 ohm ) and injectors 2.35Ohm.

[rob@vems.co.uk]

Its clearly chucking more fuel in, else you wouldnt get black smoke out...

Please download your configs and tables and send them to me.  What Firmware are you running?

Rob

[hilly]

You haven't got your overrun fuel cut set to something like 2000rpm have you ??

Hilly

[rob@vems.co.uk]

Failing the full config and tables can you post a picture of the the warm-up enrichments.

[Jorgen]

We were looking at this and one thing sticks out. You wrote: WUE is flat 140% from -40C to +5C, then linear to 0 at +70C.

We argue about what this means but I get the impression that you have 0 in the 70C cell. That means that you remove all fuel and that the engine only runs on some end of scale rounding error.

You should have 100% in the 70C bin. That means that the warm up enrichment is turned off.

Jörgen

[pete95zhn]

You haven't got your overrun fuel cut set to something like 2000rpm have you ??

Hilly

IIRC no, but I'll check.