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Old 10-22-2015, 08:28 PM   #1
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Default Sequential vs. semi-sequential fuel in MS3

I just had an FM turbo, Reverant-built MS3, and Fab9 Coil-on-plug kit installed by Tork Motorsports in Kent, WA on my 1995 with the stock 1.8L engine. John at Tork is a very experienced Megasquirt tuner and he's worked diligently to get everything running.

I understand from Dimitris that his MS3 can run sequential fuel timing. John has semi-sequential timing configured now. We searched the internet but couldn't figure out the difference between the two.

Can somebody clue us in? Is this even something that's worth worrying about?
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Old 10-22-2015, 08:54 PM   #2
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Originally Posted by aceswerling View Post
I understand from Dimitris that his MS3 can run sequential fuel timing. John has semi-sequential timing configured now. We searched the internet but couldn't figure out the difference between the two.

Can somebody clue us in? Is this even something that's worth worrying about?
All MS3s can use fully sequential fuel and ignition.

The difference, with regard to fuel is this:

In a semi-sequential configuration, also known as batch-injection, the ECU has two active injector drivers. The injectors are paired together (typically 1/3 and 2/4), and each pair squirts twice per cycle. At each squirt (assuming correct phasing), one injector is firing at an intake valve which is just about to open on the intake cycle, and the other is firing at a valve which is closed, as that cylinder is in the compression/expansion phase, and then on the next squirt, the opposite.

Most TPI engines in the 1980s and early 1990s were configured this way, including the '90-'93 Miatas ('90-'92 in California).

(For engines with 6/8/10/12 cylinders, replace "two" or "four" with the appropriate multiple.)


In a fully-sequential configuration, there are four injector drivers, with one injector each. Each injector is timed to its specific cylinder, squiring once per cycle, just before the opening of that cylinder's intake valve. All modern engines are fully sequential.


The fundamental idea of fully-sequential injection timing is that, by preventing an injector from squiring at a closed valve, we decrease the likelihood of fuel precipitating out of atomization, clinging to port walls, etc. It allows for marginally more precise mixture control.


The benefits of fully-sequential injection timing are apparently only at idle and low-load cruise, and consist primarily of slightly decreased emissions and slightly improved idle stability, by allowing the mixture to be held closer to the target AFR.

At higher RPM and load, the benefits of sequential injection decrease. The reason for this is that as injector duration increases and cycle period decreases, injector duty cycle goes up. Once duty cycle exceeds 25% (ish), we are now guaranteed to be squirting at a closed valve. Properly-designed ECUs mitigate this by starting the squirt sooner and sooner as RPM increases, so that the end of the squirt always happens in time for that fuel to be drawn in before the end of the intake cycle.
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Old 10-22-2015, 09:15 PM   #3
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Thanks for the information, Joe. So you're saying that semi-sequential on the Megasquirt is the same as the standard batch fuel control provided by the stock ECU. Have I got that right? in the Engine and Sequential Settings box, I see a drop down box called Sequential On that has three settings: Off, Semi-Sequential, and Fully Sequential. I though that Off would be the same as the standard batch fuel control. No?

My idle quality has always been a little rough on this engine so I'd like the sequential fueling. Can I just switch the configuration in the Engine and Sequential Settings box from Semi-Sequential to Full Sequential and expect it to work?
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Old 10-22-2015, 09:26 PM   #4
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Semi-sequential is timed batch fire on a miata, which would be a downgrade on your 95. If you don't have a dynamic injector timing table configured you are basically untimed batch injection, except it's fixed at a specific time.

Untimed injection = batch fire injection non sequential
Sequential/Semi-sequential = Injection is timed to specific crank angle, either once per rev (semi) or once per cycle (sequential)

I went through all the trouble of wiring my 1.6 car up for full sequential injection, so I think it's worth it. I also think it's beneficial to have one squirt per cycle with large fuel injectors, because if you have two of half the pulse length it's easy to go way too low on pulsewidth.

eg: on 91 I idle around 1.8ms w/1 squirt per cycle. If I have 2 squirts a cycle, that's two .9ms pulses, super close to deadtime on my new injectors, way past it on old junk. Injectors aren't as linear down low which is why you usually have to idle rich as well.

Untimed or fixed time sequential would be better than what you have now, you wouldn't even really need to tune a dynamic timing table. That's well into the point of diminishing returns IMO.
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Old 10-22-2015, 09:34 PM   #5
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Originally Posted by aceswerling View Post
Thanks for the information, Joe. So you're saying that semi-sequential on the Megasquirt is the same as the standard batch fuel control provided by the stock ECU. Have I got that right?





Quote:
Originally Posted by aceswerling View Post
in the Engine and Sequential Settings box, I see a drop down box called Sequential On that has three settings: Off, Semi-Sequential, and Fully Sequential. I though that Off would be the same as the standard batch fuel control. No?


Off means one injector channel. This would be for a TBI application.

Semi means half the number of channels as cylinders, aka batch, which is the same as the early OEM ECUs.






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Originally Posted by aceswerling View Post
My idle quality has always been a little rough on this engine so I'd like the sequential fueling. Can I just switch the configuration in the Engine and Sequential Settings box from Semi-Sequential to Full Sequential and expect it to work?
It's been a few years since I've intimately grokked an MS3, and so I'm not going to give this answer with 100% confidence.

I can't remember.

Check your injector wiring. If you have four injector wires connected to the ECU, then yes, you can just flip the software setting. The caveat here is that I can't remember if running four drivers in batch mode is a valid setting, so even if you do have four wires, I can't say with certainty that there's not some hidden pairing somewhere.

If you have only two injector lines hooked up, each with two injectors on it, then the answer is obviously no, until you re-wire.
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Sequential vs. semi-sequential fuel in MS3-80-yes_05a5fa0412207aa099e1ded86e9c9421231a1e21.jpg   Sequential vs. semi-sequential fuel in MS3-80-no_07ff371331a8ff37a2852356d6b6e283866fa6bd.jpg  
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Old 10-22-2015, 09:35 PM   #6
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Thank you for the help.

I checked the Injector Timing Table and see "360" across the board, which tells me it hasn't been configured.

I'm hearing that it would be best to go Full Sequential if possible or turn off Semi-Sequential and go back to regular batch if not. It sounds like the Semi-Sequential is the worst of the three options. Is that right?

OK, so I'm hearing the wiring needs to change to get to full sequential injection. The MS3 was configured using the standard ECU wiring, which doesn't sound like it would drive 4 injectors without additional wiring. I'm hoping somebody can clue me in on how to do that and how to configure the Injector Timing Table to get this working properly.
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Old 10-22-2015, 09:47 PM   #7
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You are in batch now, there is no lower to go. If you wanted you could try to create an injection timing table on semi-sequential, but I wouldn't till you make it full sequential.

94+ cars and cali 1.6 cars have 4 injector drivers stock, so I don't think you have to change any wiring. MS2 was able to switch between semi and full sequential using all four spark drivers with no wiring changes so long as "use additional drivers" is still selected

So no, probably no wiring changes. It had 4 drivers natively and your car had 4 separate wires/channels. Change it and go for it, I say.

Or ask Rev, that would probably be best.
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Old 10-22-2015, 09:53 PM   #8
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Originally Posted by aceswerling View Post
I'm hearing that it would be best to go Full Sequential if possible or turn off Semi-Sequential and go back to regular batch if not. It sounds like the Semi-Sequential is the worst of the three options. Is that right?
Off would be the worst of the three options. Semi-sequential (same as batch) is in the middle, and fully-sequential is best



Quote:
Originally Posted by aceswerling View Post
OK, so I'm hearing the wiring needs to change to get to full sequential injection. The MS3 was configured using the standard ECU wiring, which doesn't sound like it would drive 4 injectors without additional wiring. I'm hoping somebody can clue me in on how to do that and how to configure the Injector Timing Table to get this working properly.
Let me back up and ask a question:

I'm not familiar with Reverant's MS3s. Is yours an MS3X? (Does it have two DB37 connectors, or just one?)

If two, you have an MS3X with eight injector drivers and you're probably already wired for full-sequential. So you can probably flip the switch.

If one, then you have a base MS3 and are using the on-board drivers on the original 1980s-vintage "3.0" main board, which has only two channels.


But, yeah, ask Rev. He builds so many different styles of ECU it's impossible for me to know with certainty what's in yours.
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Old 10-23-2015, 02:18 AM   #9
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It's got a single DB-37 connector in addition to the connectors that hook into the OEM wiring harness. I take that to mean I have the base MS3. I'll send Rev an email and see what he says.
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Old 10-23-2015, 05:10 AM   #10
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All (and I mean ALL) my MS3s have full sequential injection and ignition hardware.
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Old 10-23-2015, 09:51 AM   #11
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Joe,

I might be misunderstanding, but I think you're possibly confusing semi-sequential and Batch injection

Batch injection is completely untimed, whereas semi-seqential is batch injection, but timed to inject at a certain point in the engine cycle.

Semi sequential is an improvement over batch, albeit marginal.

In this case setting semi-sequential to off would mean the injection event is untimed, presupposing the injectors are wired for batch fire, I'm not sure how it would work if set to off whilst the injectors are wired for sequential.
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Old 10-23-2015, 11:58 AM   #12
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Different people use different words to describe similar concepts. In the V8 community, it's not uncommon to use the term "batch" to refer to a situation where two drivers control four injectors each, and the term "Semi-sequential" to refer to four drivers with two injectors each.


For our purposes, with a 4 cyl engine, Batch and Semi-Sequential are functionally indistinguishable. There is no such thing* as "untimed" injection. The timing may not be user-adjustable, but that's irrelevant in a situation where the injector is firing twice per cycle. I've seen people with MS1/2 ECUs (two-channel) wire up the injectors with the wrong phasing altogether (pairing 1/4 and 2/3, as though the injectors were supposed to mirror the ignition coils) and you could barely tell the difference.

* = excepting systems like Bosch K-Jetronic CIS, where the injectors spray continuously and fuel delivery is is controlled by varying pressure.

Based on what Rev has said (that all his units ship with the capability for full-sequential injection) and what aceswerling has said (that his ECU is one of the custom ones with a plug-n-play connector), he's good to go for the switch to full sequential operation.
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Old 10-23-2015, 08:22 PM   #13
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I'm happy to share that the car runs great after switching from Semi-Sequential to Full Sequential. As suggested, the idle quality improved and the car feels smoother across the entire rev range. Thanks to everybody for the pointers.
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Old 10-23-2015, 08:35 PM   #14
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You can actually run a megasquirt with 1 injector driver. My buddy fried a driver on his ms1 and needed to drive to my place for a spare. He was able to wire all of his injectors to 1 output and change some settings to make it run off 1 driver for all 6 injectors.
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Old 10-23-2015, 08:43 PM   #15
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Aidandj, that's interesting. Was your buddy basically firing the injectors for all 6 cylinders simultaneously?
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Old 10-23-2015, 08:45 PM   #16
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Yes. It ran horribly. Wouldn't recommend.
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