Engine Starting/Tuning/Troubleshooting Discussion

[jlangholzj]

Originally posted by Mbirt:
Excellent post, John. I've got a few things to add.

The stoichiometric AFR for the E10 gasohol at competition is closer to 14.1:1. Some ECU's might place greater priority on this parameter than others. For E85, it's 9.76:1, but who knows if we'll get E75, E82, or what. It'll be numerically higher than 9.76.

I was ball-parking the numbers earlier...should probably go back and change that. I always try and shoot for 1 lambda and it seems like the close loop control will account for any variance in the quality and octane. This last year at comp I wasn't seeing a change in our logged lambda-load maps from comp vs testing here at home.

I liked your idea about cutting injector power while calibrating the cranking PW. To further fine-tune it from there, you'll know it's too much fuel if significant throttle opening helps it start. If it doesn't start regardless of throttle opening, it's too little fuel.

I got the idea from my experience with flying. Having a mixture knob on the dash is always great! closest i could get without making it super technical was the switch It also works great if you're having trouble starting and suspect it might be flooded out. Also we usually kill the engine with it to keep fuel from pooling up on the back side of the valve. Kind of nice to have it, i use it more often than not.

Teams not running 600/4's will want to exercise extra care when formulating an ignition base map. Check out the chapters on ignition and EFI in A. Graham Bell's "Four Stroke Performance Tuning". Your engine isn't running as restricted as a 600/4 and will not be as tolerant of over-advanced spark timing and lean running at high load. Our single on E85 likes less advance than the stock bike's module gave at "all in".

Question for you guys: Do you have any rules of thumb for timing the injection event? Our ECU has a nice, big load vs RPM map for the start of injection angle, but it can't be calibrated in real time. Changes must be made offline, a new ECU program must be compiled and flashed--tedious. I can, however change the phase angle of the entire map and it made a significant difference on the engine dyno by shifting trouble spots at various loads to new speeds. I would really prefer a calibratible end of injection angle map.

As previously mentioned we're running an M84 (little brother to the M400) and I've got the option to adjust INJ timing real time but just eliminated the table axis and set it at 300*BTDC. I haven't had the chance yet to fully exploit that ECU and tune it in as well as it should be. I've got to design our cooling, electrical and get a running engine in one year so it gets a little crammed I did have another Sparky join up though and a few other Mechy's so I'm hoping I'll have a little more dyno time this year.

[Tilman]

Heyho,

great post! Please add a section with abbreviations used, this will make it much easier to read for any non-native speaker.

Some things the manual of our ECU suggests:
1) Measure injector dead time. Our ECU does this by switching between sequential (4-stroke) and non-sequential (2-stroke) injection each 5 seconds with battery compensations switched off. Then one varies the injector dead time until there is no lambda change anymore between 4- and 2-stroke-injection.

Is it possible that what you refer to as battery compensation is the same as injector dead time? However, you should tune this as early as possible, because if you don't, your injection maps might depend on a wrong injector dead time. This will not hurt you unless you have to change injectors ...

2) On injection timing: The DTA S Series manual states "Some engine builders think this is a very important number, others think it is of no importance". I think you might go with the latter until you have tuned everything else ...

3) Air inlet temperature compensation: Our ECU's manual states that "There is only one set of correct fuel compensation figures for this [air inlet temperature] shown below." and I back this because the ideal gas law does quite a good approximation of air density. This might be true for absolute barometric air pressure compensation, too.

I think one should set all compensations at least to good approximations / well educated guesses before trying to tune the engine ... However, I never tuned an engine myself, so this is just from my understanding of these topics.

[B Lewis @ PE Engine Management]

I just thought that I would add some things to the earlier comments based on our experience.....

1) Measure injector dead time. Our ECU does this by switching between sequential (4-stroke) and non-sequential (2-stroke) injection each 5 seconds with battery compensations switched off. Then one varies the injector dead time until there is no lambda change anymore between 4- and 2-stroke-injection.

Is it possible that what you refer to as battery compensation is the same as injector dead time? However, you should tune this as early as possible, because if you don't, your injection maps might depend on a wrong injector dead time. This will not hurt you unless you have to change injectors ...

Injector dead time is the same as battery compensation. The method mentioned above will work but only for 1 battery voltage unless you repeat the test multiple times at different voltages. The best way to get battery comp numbers is to test the injector on the bench at multiple values with the same ECU that you will be running on the engine. The battery voltage compensation is a function of where the flyback voltage is clipped in the injector driver. I could give a whole dissertation on why the battery compensation is important but basically it linearizes the response of the injector to open times which makes manual and adaptive tuning in the ECU MUCH easier.

FSAE teams can get free injector characterization from us when they purchase a PE3 system.

2) On injection timing: The DTA S Series manual states "Some engine builders think this is a very important number, others think it is of no importance". I think you might go with the latter until you have tuned everything else ...

I agree this should be left as the last thing to study when tuning the engine. Injector timing is very important for 2-strokes and can be important for idle quality and for part throttle drivability and emissions. We have never seen much gains at WOT on small displacement engines by changing the injector timing.

3) Air inlet temperature compensation: Our ECU's manual states that "There is only one set of correct fuel compensation figures for this [air inlet temperature] shown below." and I back this because the ideal gas law does quite a good approximation of air density. This might be true for absolute barometric air pressure compensation, too.

On the surface, I agree with the statement above, however, depending on the engine this is not always true. With some air temperature installations, the sensor itself can become heat soaked. In this case the sensor is not reading actual air temperature but rather some combination of air temperature and sensor body temperature. This is very common in some production engines and can lead to a lot of head scratching when tuning if you are not aware of this. The 5.0L Ford engine is a great example of this problem.


As always, the PE phone lines and inbox are always open to FSAE teams. Give us a shout if you have any questions.

[jlangholzj]

for those of you who weren't able to or didn't know about the ford PT webinar that was put on this last week, there was some good engine basics that they covered.

Couple of things that I picked up that i thought was interesting (or just made me think)

1) When you're spending lots of time on your fuel/ign map, look at a histogram of the TP (or map) and RPM ranges that you're in the most. This is where you should be focusing the most time in the map on. Its a no-brainer when you say it outloud, just never really thought of it before.

2) Even with signal smoothing and filtering a MAP based fuel map can be troublesome. Its not that it doesn't work, but they were reporting 2-3 inches of water fluctuation in the unfiltered MAP signal. Something that me an last years TL have been talking about is switching over the alpha-n. Just seems to make more sense with the restrictor and everything.

I'll have the slides hopefully within a week and I'll try and find a spot to post them up.

[Cardriverx]

Just to chime on injection timing:

It really doesn't matter for us. The thing is, at high duty cycles changing the timing really doesn't affect much since the injector is already spraying for 75-90 percent of the cycle.

Now, if you were to say run 600cc injectors on a 600rr, it would matter a lot since your max duty cycle would be around 30 percent.

Also, I am a supporter of alpha-n for our cars. With the restrictor the MAP signal is hard to get reliably without variance. Of course if you run a turbo you at least need MAP comp. but in my experience alpha-n is the easiest route to go.

[Mbirt]

Originally posted by Cardriverx:
Just to chime on injection timing:

It really doesn't matter for us. The thing is, at high duty cycles changing the timing really doesn't affect much since the injector is already spraying for 75-90 percent of the cycle.

Now, if you were to say run 600cc injectors on a 600rr, it would matter a lot since your max duty cycle would be around 30 percent.

Also, I am a supporter of alpha-n for our cars. With the restrictor the MAP signal is hard to get reliably without variance. Of course if you run a turbo you at least need MAP comp. but in my experience alpha-n is the easiest route to go.

The issue that I suspected to be attributable to injection timing was on a single with its only injector in the "high-mount" location spraying into the runner's bellmouth. The uncooperative load point was less than 80 kPa MAP at the speed of greatest intake ramming. Operation at this point has been much improved by moving the injector closer to the cylinder head--along with a big-time reduction in POT fuel consumption.

Also, I'll second the posts above in favor of alpha-n mapping. I'm a believer after trying it on a whim. After only a few hours on the chassis dyno modifying the original SD map for AN operation, it did great things for our idle and POT operation.

[jlangholzj]

Originally posted by Cardriverx:
Just to chime on injection timing:

It really doesn't matter for us. The thing is, at high duty cycles changing the timing really doesn't affect much since the injector is already spraying for 75-90 percent of the cycle.

Now, if you were to say run 600cc injectors on a 600rr, it would matter a lot since your max duty cycle would be around 30 percent.

Also, I am a supporter of alpha-n for our cars. With the restrictor the MAP signal is hard to get reliably without variance. Of course if you run a turbo you at least need MAP comp. but in my experience alpha-n is the easiest route to go.

you better not be that high on your duty cycle. By the time you get up to 75-80% you start to lose resolution in your fuel map. Typically 85% is "maximum" duty cycle. That's something else that I didn't put in on the initial post. When your duty cycle start getting that high, its no different than just leaving the injector wide open. I try to be at the 60% mark maximum. Otherwise its hard to be sure exactly what the injectors are doing.

[Teranfirbt]

I'm not entirely sure what injectors you're using, but we've got maps on ours showing complete linearity up to 90% duty cycle.....

[jlangholzj]

Originally posted by Teranfirbt:
I'm not entirely sure what injectors you're using, but we've got maps on ours showing complete linearity up to 90% duty cycle.....

I've never had the opportunity to test ours, they're just the stock primary injectors from the R6. I guess I've just always been told to try and keep it under 80% as a rule of thumb. Really with our restrictors you'd have to be running some crazy low pressure to see in that range anyway.

[Cardriverx]

The only reason to restrict using more than 90% duty cycle is to prevent the coils in the injectors from overheating. They will flow linearly beyond 90% in most cases. Running around 65-85% is where you should be at WOT.

For example check out the ID725, it will stay linear till 90% even at 15000rpm

http://www.injectordynamics.com/ID725.html

I would also read some of these articles, they are very well done.

http://www.injectordynamics.com/tech.html

Originally posted by jlangholzj:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Cardriverx:
Just to chime on injection timing:

It really doesn't matter for us. The thing is, at high duty cycles changing the timing really doesn't affect much since the injector is already spraying for 75-90 percent of the cycle.

Now, if you were to say run 600cc injectors on a 600rr, it would matter a lot since your max duty cycle would be around 30 percent.

Also, I am a supporter of alpha-n for our cars. With the restrictor the MAP signal is hard to get reliably without variance. Of course if you run a turbo you at least need MAP comp. but in my experience alpha-n is the easiest route to go.

you better not be that high on your duty cycle. By the time you get up to 75-80% you start to lose resolution in your fuel map. Typically 85% is "maximum" duty cycle. That's something else that I didn't put in on the initial post. When your duty cycle start getting that high, its no different than just leaving the injector wide open. I try to be at the 60% mark maximum. Otherwise its hard to be sure exactly what the injectors are doing. </div></BLOCKQUOTE>