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Old 08-02-2012, 06:45 PM   #1
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Default Misfire log, what to check next? MSPNP N/A car

Car details.

92 Miata with 94 1.8(2001 bottom end)
Intake
Stock header
exhaust
MSPNP 90-93 no maf

Misfire occurs most often between 5800-6200. Sometimes it'll get a blip at 5k. Very noticeable on the dyno graph. Changed coil, igniter, wires also tried adding grounds etc. Plugs are gaped correctly. Timing is staying true while watching with a timing light, however the light flickers differently during the misfire. Ive updated the firmware of the MSPNP, I have another PNP in another car im going to try also.

Log is from a 4th gear pull on the dyno


Thanks in advance!
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File Type: xls misfire4th.xls (53.0 KB, 84 views)
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Old 08-03-2012, 12:45 PM   #2
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Sorry. Gotta ask the obvious question. You've changed pretty much everything else. Did you change the plugs? Sometimes they look perfectly fine, but aren't....
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Old 08-03-2012, 12:52 PM   #3
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Update:

Changed CAS
Changed MSPNP
moved grounds for coil and injectors..

Same issue.

stefanst,

The plugs are new and I've pulled them to inspect them and they look fine. I however just ordered another set from a local parts store and am going to swap them for a try.
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Old 08-03-2012, 12:53 PM   #4
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Something magical is happening at 6k rpm and 5k rpm....doesnt seem to happen anywhere else.
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Old 08-03-2012, 01:00 PM   #5
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What is the plug gap?
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Old 08-03-2012, 03:09 PM   #6
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Gap at .035 on new set of plugs was at .042 on last set. No change.

Anyone have a MAP for a 1.8 we can try, please post up. No meter.
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Old 08-03-2012, 03:35 PM   #7
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Here is the MSQ we are currently using.
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File Type: msq 1990 18.msq (35.0 KB, 68 views)
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Old 08-04-2012, 12:56 AM   #8
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Anyone?
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Old 08-04-2012, 01:20 AM   #9
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Please keep in mind that I have 0 experience running MS - I still am missing important engine parts.
But it looks like your MAP is all over the place. Almost 20% deviation. That may trigger enrichment and leaning out pretty much randomly. Also your O2 sensor doesn't seem to work...

Of course I may be wrong!
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Old 08-04-2012, 11:57 AM   #10
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We're not using an O2 sensor, as for the map we pretty much put the car on the dyno to do WOT tuning first. Haven't spent much time on anything else.

I loaded a map from another 1.6(my old setup) car and added some fuel and it did the same thing in the same spot.

Being we've swapped near everything I imagine it's a harness/resonance issue.

One thing that seems odd to be is not only is the map flickering up and down, but so is the injector duty cycle during a pull.
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Old 08-05-2012, 10:16 AM   #11
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This is probably an obvious question and I'm a noob for asking it, but how did you log the misfires?
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Old 08-05-2012, 01:01 PM   #12
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did you ever changed out CAS or Crank angle sensor wire ? make sure it is shielded.
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Old 08-05-2012, 10:10 PM   #13
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The CAS sensor was extended but it appears to be with non shielded wire, never been an issue in other swaps I've done but defiantly worth a shot.

The car doesn't run a crank sensor.

I'm going to try a few other simple things when I can get the car back on the dyno. I'll report back if we find it.
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Old 08-06-2012, 02:06 AM   #14
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Shielded wires fix my high rpm stumble.
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Old 08-06-2012, 03:05 PM   #15
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I'm seeing the AE trigger a lot at full throttle and some major MAP spikes. Where is the MAP sensor plumbed up to? You may need to try plumbing it to a different spot on this particular engine.
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Old 08-06-2012, 11:49 PM   #16
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Bell,

Which wires?

Matt,

I appreciate your reply, something so simple for us to not to think of trying. I hope to have the car back on the dyno tomorrow afternoon. I do believe its routed on one of the nipples under the 94-97 manifold, I'll have to check with the car owner as he installed the MS.
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Old 08-06-2012, 11:58 PM   #17
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I feel pretty confident that's it after thinking how the live gauges on the megatune are acting. The duty cycle jumping around etc....

:Crosses fingers:
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Old 08-07-2012, 12:52 AM   #18
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Its plumbed to the port on the firewall side bottom of the intake manifold next to EGR (usually caped except I think its used on Auto cars).) Will let you know tmw.

Thanks!!
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Old 08-07-2012, 11:35 AM   #19
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You might want to try putting it on a tee on the line to the fuel pressure regulator.
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Old 08-07-2012, 10:28 PM   #20
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Quote:
Originally Posted by Matt Cramer View Post
You might want to try putting it on a tee on the line to the fuel pressure regulator.
:bowr ofl:

Thank You Sir. Moved that reference line for the MAP and all problems cured.
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