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Old 10-06-2012, 04:52 PM   #1
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Default Misfire under boost

I've just started trying to tune more than just idle and very light load, and am getting misfires above 3k rpm and more than very slight throttle. If I feather the throttle, I was able to take it to 4k without any misfire.

When I look at logs, the one weird thing I notice during misfires is that the injector pulse width is spiking up and down, but have no idea why it is doing this. Rev limiter and overboost are turned on, but it's not anywhere near either limit.

General car info:
04 VVT engine
MS3X
stock injectors running sequentially
FM's old style 300cc/min staged injectors in batch mode
For now boost control is just on the ~6 psi wastegate until everything else is sorted

In the attached log, there is one misfire in second gear and then several in third gear between 3770 and 3780 seconds. Any ideas about how to fix this or just general improvements would be greatly appreciated.
Attached Files
File Type: msl 2012-10-06_13.09.18.msl (1.10 MB, 98 views)
File Type: msq Matt's CurrentTune.msq (176.5 KB, 153 views)
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Old 10-07-2012, 02:16 AM   #2
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What are your plugs gapped to?
Your VE table is awful.
You're log shows AFRs tell a story of tragedy and extreme lean-ness.
Your spark table is more advance than I'd start with on a 10:1 engine.
How can you have "stock injectors running sequentially" and "FM old style batch mode" injectors? Which one is it?

Take the plug gap down to .024", possibly replace the plugs.
Make a drivable VE table.
Roll spark back another 3-5*
Let us know how that drove.
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Old 10-07-2012, 07:34 PM   #3
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I guess I should have explained the setup a little bit more. I put the drivetrain from an 04 VVT into my 90 Miata. In the original car, it had the Link Piggyback with the stock ECU controlling the stock injectors, and the piggyback controlling 4 more injectors on the intake manifold. When I put the drivetrain in my car, at least for now I've kept that (slightly odd) second set of injectors and am controlling everything with the MS3. The stock injectors are running sequentially, and all 4 staged injectors are running in batch mode.

The misfire is still there, but here's what I've done today:
I went ahead and put in a new set of spark plugs gapped to 0.24 (old ones were at 0.036 when I pulled them out, but not sure how old they were).
I switched to using a more conservative timing table you posted in an earlier thread. (Didn't really check the one from Frank's example tune until now.)
I switched to the richer AFR map y8s posted
Reverted to the original VE table from Frank's example tune to throw out all my earlier changes and then spent an hour or so driving around with VE Analyzer running. How's the <3500 rpm half of the VE table looking now?

At the end of the hour of driving, I recorded another log with the same backfire happening. The AFR right before the backfire seems better controlled, but not perfect yet (12.7 when target is 12.1).

Thanks! - Matt
Attached Files
File Type: msq 2012-10-07_17.27.12 VEAL round 2.msq (176.6 KB, 136 views)
File Type: msl 2012-10-07_17.21.49.msl (1,005.7 KB, 82 views)
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Old 10-07-2012, 08:12 PM   #4
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Does it mis/backfire when using only part throttle?
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Old 10-07-2012, 08:18 PM   #5
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I had a similar problem once, years ago, and I believe I added some 8AWG ground wire from the body to the engine but I don't think it fixed the problem. I'm out of brain, maybe someone else can help.
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Old 10-07-2012, 09:40 PM   #6
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Does it mis/backfire when using only part throttle?
Yeah, I didn't want to go full throttle much until part throttle was sorted out, so most of these runs have been at 30-40% throttle. I checked and it does do it at full throttle too. However, with very slight throttle it is possible to keep revving smoothly.

It does seem somewhat rpm dependent. It runs smoothly at under 3k at any throttle angle, including up to a few pounds of boost.

Just because this is the same rpm that the VVT goes active, I tried temporarily setting the VVT demand angle to 1.5 everywhere with no effect on the mis/back fire.
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Old 10-08-2012, 01:40 AM   #7
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Look at the overboost protection window. 110kpa on the low setting. Make that 200kpa and see what happens.
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Old 10-08-2012, 03:25 PM   #8
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Sorry for the dumb question, but where's this 110 kPa Overboost entry that needs fixed? I'd feel so stupid if it was just cutting fuel for misconfigured protection logic this whole time. I've been searching for it (and even opened the .msq in a text editor to search for every overboost and "110" entry).

The only overboost window I know of is in Advanced Engine > Boost Control Settings, and that one only lists a 200 kPa entry with a 10 kPa deadband.

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Old 10-08-2012, 03:50 PM   #9
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how did you swap the ingition? are you using the 04 coils or 90 coils?
did you verify timing with a timing light?
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Old 10-08-2012, 07:44 PM   #10
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Quote:
Originally Posted by MatthewakaMatt View Post
Sorry for the dumb question, but where's this 110 kPa Overboost entry that needs fixed? I'd feel so stupid if it was just cutting fuel for misconfigured protection logic this whole time. I've been searching for it (and even opened the .msq in a text editor to search for every overboost and "110" entry).

The only overboost window I know of is in Advanced Engine > Boost Control Settings, and that one only lists a 200 kPa entry with a 10 kPa deadband.

Apparently I opened that in the wrong project.
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Old 10-08-2012, 11:10 PM   #11
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You sound like you're pretty on top of it, but I'm suspicious of your fuel system. Simpler is always better. I'm not sure that VE Analyzer can work as advertised with your sequential/batch hybrid setup. I could be 100% wrong on this, but I would go to one good set of properly sized injectors and use a single mode in the MS3.
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Old 10-09-2012, 12:29 AM   #12
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Quote:
Originally Posted by hornetball View Post
You sound like you're pretty on top of it, but I'm suspicious of your fuel system. Simpler is always better. I'm not sure that VE Analyzer can work as advertised with your sequential/batch hybrid setup. I could be 100% wrong on this, but I would go to one good set of properly sized injectors and use a single mode in the MS3.
Now I'm suspicious of my fuel system too! I went back and checked all the logs I've taken for this, and the MS3 is trying to suddenly stage the injectors (and consequently cut the primary PW in half). I never looked closely at what the secondaries were doing until now because the primary duty cycle was only 40% and was nowhere near where I thought it would or should kick in. However, it sure looks like in completely misunderstood what the 80% Duty Primary Staging Threshold meant. A couple quick runs with different settings changed when and how it was having problems, so I'm pretty sure that's the culprit.

Now that I know what to concentrate on, I'll try to actually understand the staged injection control. Once it starts transitioning correctly, I'll certainly keep a close watch on what VE Analyzer does in that region. If I don't get the hang of it pretty quickly, I'll just grab a set of bigger injectors and simplify my life immensely.

Thanks so much to everybody for all the great advice!
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Old 10-09-2012, 01:09 AM   #13
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Dem EV14s.
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Old 10-22-2012, 01:00 AM   #14
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I seem to have fixed one problem and found or caused another. I switched to using the table based injector staging, and so far that seems to be doing what it should. The second set of injectors smoothly come on line, and there isn't any noticeable change when they come on or off.

However, as soon as I switched to the table staging, I started getting misfires where it would lose sync (always error 31: Miata 99-00 - 2 cams not seen) and RPM would momentarily drop to zero. It doesn't do it as consistently as the sudden staging misfire, but generally will happen when in boost at 3k+ RPM.

I also started getting a bizarre problem when it is idling. Sometimes after it has been idling for a while, the RPM will suddenly shoot up and then it will do constant rev limiter style cutting in and out until I shut it down. During this, both the MegaSquirt rpm and the Miata tach (driven by the MS tach output) will go crazy and jump around. I attached a log of it doing it. I couldn't tell anything from the ignition logger, but here that is too.



So far I've replaced the cam and crank signal wires with shielded ones grounded at the MS, tried turning the MS noise filtering on and off (though didn't do too much with noise settings), tried a couple different sets of spark plugs (since I switched them at the same day this started happening), and tried different staged injection settings all to no effect. At this point I'm at a loss for what is going on and how to fix it.
Attached Thumbnails
Misfire under boost-syncloss.jpg  
Attached Files
File Type: msl 2012-10-21_12.32.19.msl (424.3 KB, 86 views)
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Old 10-22-2012, 10:58 AM   #15
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what happens when you change skip pulses to 3 from 1?
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Old 10-22-2012, 10:38 PM   #16
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I just tried that, and didn't see any noticeable difference.
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Old 02-12-2013, 11:38 AM   #17
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Quote:
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I just tried that, and didn't see any noticeable difference.
any updates to this issue? running into something very similar myself.
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Old 02-12-2013, 12:23 PM   #18
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Oh yeah. Because I bought a pre-assembled MS3, I skipped all the installation instructions. The VR Pot thresholds on the cam and crank signal hardware weren't set, and it was ignoring the signals when I went under boost. Once I went back and did that step in the instructions, that fixed all the signal loss problems.

If you haven't already set them, check out the VR sections of Megasquirt-3 MS3 Tach input and ignition outputs
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Old 02-12-2013, 12:24 PM   #19
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Thanks man will do!
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Old 02-12-2013, 12:30 PM   #20
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you're going to adjust the VR pots you dont have?
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