problem with injection timing

[Vicoor]

I've been experimenting with injection timing. I really don't understand the dynamics of it, but as is indicated by almost all of the info I can find, the engine likes to have the fuel injected on a closed intake valve. Obviously with a properly sized injector at a maximum duty cycle near 80%, all the fuel cannot be injected while the intake valve is closed. In order to end the injection pulse in a manner to get "this cycle's" fuel in during "this cycle" it is necessary to transition from ending the pulse at about -340deg during light and moderate loads, past -360/360 to values somewhere in the vicinity of 230deg to 250deg at 80% duty cycle.

The problem is, when the transition from negative to positive occurs the interpolation takes the values the "wrong way" around, resulting in values that go past 0deg to get to the positive values. and results in "bobbles" in performance.

Is there some way to arrange the settings to avoid this, or is this just the way it is?

It seems to me( in my limited way of thnking) that it would be better to have settings based on a full 720deg cycle, instead of one negative revolution and one positive revolution.

Victor

[davcol]

I too am having trouble figuring out how to tune the injection timing table , i start out with it idling at

800rpm -310 degrees
1000rpm -305
2500rpm -285
3500rpm -280
5000rpm -275
6000rpm -270

do you think i have these settings right, it also set on end of pulse , i am trying to advance the injection timing as the rpm and load increases .

[jsmcortina]

It seems to me( in my limited way of thnking) that it would be better to have settings based on a full 720deg cycle, instead of one negative revolution and one positive revolution.

That's exactly what the code does (now) for exactly the reason you found. Add 720 to your values.

James

[racingmini_mtl]

Victor,

The ini has been changed (quite a while ago) so that you can enter values from -360 to 720 degrees. This way, any one can find a 720 degree range that will not have a discontinuity. So you can just change your values to fit the 0-720 degree range.

Jean

[davcol]

It seems to me( in my limited way of thnking) that it would be better to have settings based on a full 720deg cycle, instead of one negative revolution and one positive revolution.

That's exactly what the code does (now) for exactly the reason you found. Add 720 to your values.

James

could you respond to the above question please, is my setting O.K.

[racingmini_mtl]

It seems to me( in my limited way of thnking) that it would be better to have settings based on a full 720deg cycle, instead of one negative revolution and one positive revolution.

That's exactly what the code does (now) for exactly the reason you found. Add 720 to your values.

James

could you respond to the above question please, is my setting O.K.

No one can answer this but you. It depends on a multitude of factors such as the intake and exhaust shape and size, the cam timing, the injector size, position, angle, type, and a bunch of other things. Anything that has an impact on how fast the air and fuel are moving will also impact the ideal injection timing but these are likely only part of the equation.

So the only way to really know is to try different values and see if the engine runs better or not.

Jean

[paulpug]

Hi Jean,

Are there any underline principle to follow ,any rule of thumb,

Paul

[James]

How much does AFR change when adjusting injector timing?

I am just thinking if this adds in another thing to tune on the dyno what is the best strategy…? fuel, spark, injector timing, fuel, spark, injector timing

[Vicoor]

Adding 720 to the negative values got the injection timing working correctly. No more "bobbles". Now I just need to spend more time dialing it in to get the most responsive/lowest pulsewidth for a given speed/load range.

Thanks for the quick replies. and to James Murray....

Don't you ever sleep?

[hassmaschine]

How much does AFR change when adjusting injector timing?

I am just thinking if this adds in another thing to tune on the dyno what is the best strategy…? fuel, spark, injector timing, fuel, spark, injector timing

in my admittedly limited testing, not much - there seems to be a wide range of "ok" timing, and a narrow range of "bad" timing where the engine runs much worse (squirting directly into an open valve, usually). but within the range of "good" timing, +/- 100 degrees barely made any difference on my motor. Haven't tested on a dyno yet but I will soon.

[davcol]

is there a way to have 12x12 injection timing table for better interpolation for MS2 ,instead of 6x6.

[jsmcortina]

Does your injector timing change is a highly non-linear manner?

James

[racingmini_mtl]

is there a way to have 12x12 injection timing table for better interpolation for MS2 ,instead of 6x6.

There is no space available for this. Moreover, there should not be a need to have that many slope changes. But I'm willing to be proven wrong and if it happens then I'll have a look to see what could be done to make more space but that would likely mean some major work.

Jean

[davcol]

O.K. i was just asking.

[tpsretard]

Injection timing is normally VERY liner.
I have no problem on my STI

or the high rpm rally engine i use MS2 on

[wheelman]

I started out trying to use negative degree values in the table, the engine ran rough and I noticed surges from time to time.
After adjusting the values by adding 720 so all were positive the issues seem to have disappeared.

I also had to adjust the required fuel when switching from non-timed to semi-sequential. I read that the number of squirts set on the engine parameters form was ignored so I didn't adjust anything. First start after switching to semi-sequential my AFRs were super rich. I adjusted the number of squirts to match the the timed injection table, this cut my required fuel in half. Since then I've been driving around using VE Analyze live, most of the VE settings have dropped from what they were when running non-timed injection. The VE table has also flatten out a lot.

Wheelman (Ken Wheeler)

[Asteris]

So, in a 4 cylinder engine with 2 MSII Injector drivers, you need to set 2 squirts alternating, right?

[racingmini_mtl]

So, in a 4 cylinder engine with 2 MSII Injector drivers, you need to set 2 squirts alternating, right?

If you want to use semi-sequential injection then you need to set either 2 squirts simultaneous or 4 squirts alternating. That's the equivalent of one squirt per rev which is what you need. Setting 2 squirts alternating (or 1 squirt simultaneous) is for full sequential injection with 4 injector drivers.

Jean

[Asteris]

Understood. Thanks.

[Vicoor]

Still working on final settings while running, but I just wanted to post what I have found for cranking. I had been using 295deg(end of pulse) for cranking and was frustrated that I had maxed out the cranking pulsewidth and prime pulse and still could not get my truck to light on the first try when temperatures were 25deg F and below. I tried other settings while the valve is closed to no avail. I was thinking about where I should put the cranking injection timing to try to help this and remembered that I found I could get a really good idle (hideous drivability) by injecting at 180deg (bdc intake), so I tried this and found that it will start reliably so far down to 20degF.

Always the one to wonder why. I speculate that by shooting the fuel into the open valve just before it closes puts the fuel in the top of the cylinder for more reliable ignition at cranking speeds?

I think it would be good to start some threads about settings everyone has found to work along with specific engine setups, like; 2.4l 4cyl, ported head, 10.5:1 comp ratio, modified intake manifold. 280deg .440 lift cam with 57deg overlap, etc... and maybe we could get a handle on a direction to go with different settings like injection timing.