03whitegsr

iTrader: (8)

Has anybody broken down the code section that figures out how the cam and crank signals relate to ignition and fuel timing?

JohnBradley (Aaron) has noted that cams that have the dowel pin off on the cam seem to effect the ignition and fuel timing.
https://www.evolutionm.net/forums/ev...ble-build.html

I've always assumed that since there is a crank signal, it would base the timing on the crank signal and the cam signal was just for identifying which cylinder it was on. With what Aaron has noted though, it makes me wonder if the exhaust cam timing can impact the ignition and fuel timing?

donour

iTrader: (6)

This question seems to get asked a lot -- recently by me even.

https://www.evolutionm.net/forums/ec...nk-sensor.html

d

03whitegsr

iTrader: (8)

Damn newbs

Very interesting and suprising. I have no idea why you would use the cam for timing when you have a crank trigger. Seems stupid.

This draws two questions then:

1. Is there a timing advance offset table based on RPM? On the 1G, I believe there is such a table to deal with timing belt stretch.
2. Is there any kind of offset value that could be adjusted so that when you change exhaust cam timing X degrees, you could adjust your base timing to compensate instead of changing the entire map X degrees?

Ceddy

The Crank Trigger wasn't added til 95, because of OBD2 and Emissions laws mandated in 96.

One of the laws was that Timing can not be advanced. A stationary Crank Trigger prevents this.

Mitsu kind of went over board with this and put Inverted Signal CAS on 95-96 USDM cars, but then switched back to a normal CAS for 97+.


I think they went with the CAM location because of space and a cleaner environment.

The older style adjustable CAS are timed off the Crank Pulley, so with Adjustable CAM Gears your timing is still correct. But emissions laws and the addition of the Crank Trigger ruined this for us.


Edit:

In the Timing Map Header there is a value that adds 20*(0x14) to the looked up value.

JohnBradley

iTrader: (30)

Here is a couple pics of the crazy timing maps. Both of these are 2003 VIIIs and I havent seen this problem in the 04s. Only 3 2003s and 10-11 2005s. I have a problem car here right now, and will be redynoing it after fixing some other issues. The car had all the classic problems and then I verified cam position and the intake cam was 2 teeth off. The true problem cars are definitely not like that, so redynoing this one might not necessarily let us know. I will locate another problem car (I know where one is and who owns it) and then verify it as I soon as I can get it in.



Aaron

03whitegsr

iTrader: (8)

Interesting, my timing map is very aggressive with low 20s in the high RPM 160-200 load range. Cam timing is dead on with the timing marks.

Time to get a timing light and see if something funny is going on.

Edit: JB, is that the stock timing map or is that a map that you tuned and found it needed that much timing advance?

JohnBradley

iTrader: (30)

Here is a normal 92 octane timing map for the standard BPU 2003 for comparison-

JohnBradley

iTrader: (30)

So I verified that the car has stock cams (the map listed as weirdcams) and the base timing is indeed at 0* advance when I have 5* BTDC locked in. I doublechecked versus my car to make sure that 5* was 5* and it is in fact where it is set. Anyone that has ever owned a DSM knows all this already but on the Evos without a CAS its not well known.

After fixing the timing belt, i took the car back to the dyno and made 316whp. This is the timing/fuel map. It is stock injectors too by the way.



With this timing map the car made 252whp, this map on a car with identical mods made 306 only a half hour before this was on the dyno. The owner of the first car was actually watching since I had talked to him about this while we were working on his.



Here are the results overlaid-

03whitegsr

iTrader: (8)

Very interesting.
With OBD-II requiring a crank trigger, I have always assumed the crank trigger drove the actual timing events, on the 2G and the EVO. The fact that it uses a cam trigger actually makes me want to go over to a standalone a little now with a crank trigger. Some day, until then though, the stock ECU is pretty kick ***.

I realize you seem to have to tune the cars differently, but do these cars with the "weird" cams have different stock maps then cars with "normal" cams? Is this possibly something the factory knows of and has properly accounted for it in certain ROM versions?

JohnBradley

iTrader: (30)

Other than a possibility of background maps being different, the normal fuel and timing map are identical. The car had a stock 0015 ROM in it when I dyno'd it. Its base pull was 228whp on a totally stock map.

Mods-

3" Intercooler
Piping
AEM intake
3" exhaust with testpipe
255

all the normal stuff.

FYI on the fuel map-

MAF scaling isnt the problem since the idle and cruise seem relatively unaffected. I can rule out the filter causing the problem and making the car behave abnormally. I am not worried about this so much since even with an AEM, timing errors and issues related to the crank and cam sensors can and do happen. The stock ECU probably has the best way of dealing with them in comparison to other options though. I would presume the fuel map is goofy since the injector phasing is off because of the dowel. That also accounts for the erratic nature of the power graph. Firing on a closed valve doesnt hurt power but it makes it look choppy.

Aaron

03whitegsr

iTrader: (8)

A few degrees on injection angle shouldn't do much on the fuel, unless you are saying it's 180 cam degrees out?

I don't see a "weird" fuel map in your posts above, just the map after you changed the cam timing.

I'm less concerned about compensating for it then wondering if there is something different in the background between ROM versions that we haven't yet noticed.

JohnBradley

iTrader: (30)

Here is the back to back comparo. Both resulted in the same AFR, the offset in the map is about the same. Stock injectors with 255 on both cars, lean spool off. No really quantifiable trim difference in closed loop, the only difference seems to be open loop.

Ceddy

I have been looking closely at the CAS and Crank code, trying to get the 95/96 DSMs working with a Flashable ecu.


I stated before that the CAS is used for scheduling events, this is incorrect. The Crank is used for scheduling events. Some info and nomenclature off an old site had me confused. I apologize for misinforming people.



A few uSec after the falling edge of the Crank wave, the CAS wave is checked. If it is positive, it denotes cylinder #1 is TDC on power stroke, and the Cylinder Index is reset.

Crank Trigger is used to schedule events: Spark, Fuel, and count RPMs.

CAS is used to denote TDC.


Very sorry for the confusion.

merlin.oz

Ceddy, can you confirm the crank angle for fuel start pulse?
I presume its set to trigger on or just after the 61* crank trigger signal??

Ceddy

I believe fueling starts on the falling edge of crank signal of the next cylinder.

If order is: 1, 3, 4, 2

Fueling for cylinder #1 would start with cylinder #3 crank trigger.

This gives maximum fueling time.
(Fuel is delivered during the Exhaust and Intake stroke)



Its main purpose is Cylinder Index reset when cylinder #1 is TDC.

But there is a lot stuff going on in this small section of code, the CAS could have a secondary use or side effect.


Another possible issue if you have Adjustable CAM gears or timing is off a tooth or three, is the TDC signal arriving at the wrong time.

If you look at the CAS signal it has a big pulse for Cylinder #1 and a small pulse for Cylinder #4. If the CAS and Crank where out of phase enough the Cylinder #4 pulse could trigger TDC, or the Cylinder #1 might not trigger.

If something like this would happen, it would be like a 1G CAS with a 95 DSM ecu. Fueling would be 180* out of phase, car still runs ok, but has some issues.

But thats just a guess.