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Old 04-07-2010, 03:10 AM   #1
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Default Question dealing with injector timing

OK so for our FSAE team, we are using the honda cbr600rr engine, with a performance electronics ECU. We run a 14 tooth missing 1 tooth gear (if I remember right) on the crank for the ecu pick up.

Now, we just noticed that the PE ECU requires that the pick up sensor be directly over the missing tooth when cylinder 1 is at TDC. With the stock RR gear with a tooth ground off, the missing tooth is actually 10 degrees off of the sensor when at TDC.

AKA, the ECU thinks the engine is rotated 10 degrees more than it actually is.

We had fuel and engine tune issues last year, and we think this might be part of it. What I want to know is how much of an issue do you think this is?

Technically, this means the injectors fire 10 degrees before they should, which in theory should allow fuel to escape the combustion chamber during valve overlap.

My question is, when does the ECU usually tell the injectors to fire anyway? I see no ability to change injector timing with either the PE or Megasquirt, so how do the ECUs compute when to fire?

And finally, does the 10 degrees make that much of a difference? Would it really cause a big hit in fuel econ and performance like we had last year?

Does the ECU just fire the injector the same time it fires the coil? Or is there a prescribed degrees BTDC? If it is with the coils, then it shouldn't be a problem, our spark map will just be 10 degrees higher (retarded) everywhere to account for the error.

I know noone can answer for Performance Electronics, but answers about megasquirt can help me understand this whole problem.

=)
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Old 04-07-2010, 12:26 PM   #2
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also, the guy at PE couldn't really give us a good answer lol.
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Old 04-07-2010, 03:16 PM   #3
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I know nothing about the honda engine or your ECU. However, if I knew my ECU was 10* off, my first thought would be that the loss of performance was due to ignition timing being off, rather than injector timing.

Most MS'ed miatas run batch injection. Two banks of two injectors, and each bank squirts twice per engine cycle. I don't have tunerstudio on this computer so I can't look at the menus or default settings right now, but with MS2 and MS3 you can run sequential and you can control the squirt timing. MS1 didn't have that capability.

In my reading on setting up sequential fuel I came across some info on the jbperf website (JB makes expansion boards for MS) that covers the settings in MS. Don't know if that would be of any use to you, but here it is. One thing you can glean from that is the injector timing is usually held fixed, whereas spark timing is dynamic. So if you are asking if the injectors fire at the same time as the spark plugs, the answer would probably be no, or at least "not always." If you merely adjusted your spark map 10* to account for the sensor placement, that probably didn't fix your injection timing.

It sounds to me like you should just sync up your ECU to the motor and that would fix both, assuming your ECU controls both fuel and spark. For example with MS we tell the ECU to give a fixed 10* ignition timing, then using a timing light we adjust the trigger offset in the software such that there is actually 10* at the crank. Your sensor/tooth discrepancy wouldn't matter if the offset could be adjusted by your ECU to sync it up with the motor.

The only discussion I recall seeing here about injection timing was from the few people running sequential injection. Maybe one of them will pipe up with some more useful info. Most of us are running batch and haven't messed with it.
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Old 04-07-2010, 03:40 PM   #4
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The only issue is performance electronics has no adjustment for when the injectors fire, so while we can just adjust the ignition map to account for the 10 degree error, the injectors are still firing 10 degrees too soon.

If anyone else wants to chime in that would be great!
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Old 04-07-2010, 04:10 PM   #5
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That's why I said you should sync up the ECU with trigger offset (NINJA: as opposed to a blanket 10* adjustment to the spark map alone) if you can. The sync doesn't just sync up the spark; it allows the ECU to know exactly where in the cycle your motor is, and affects every other timing-based parameter that the ECU controls. Assuming your ECU is controlling both injection and ignition, that basic sync operation would also get injection back to where it would be if your sensor/tooth setup wasn't 10* off. If your ECU works like that then you don't need independent injection timing control. Or am I just not understanding the problem? Wouldn't be the first time.
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Old 04-07-2010, 04:59 PM   #6
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well part of the issue is there is no way to "sync" it, like you can with the MS. I talked to the guy, and it seems the PE just fires the injectors when it passes the missing tooth on the crank trigger (when cylin 1 is at TDC). I think its retarded there is no way to change that.
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