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!

 

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....

 

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.

 

Something magical is happening at 6k rpm and 5k rpm....doesnt seem to happen anywhere else.

 

What is the plug gap?

 

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.

 

Here is the MSQ we are currently using.

 

Anyone?

 

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!

 

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.

 

This is probably an obvious question and I'm a noob for asking it, but how did you log the misfires?

 

did you ever changed out CAS or Crank angle sensor wire ? make sure it is shielded.

 

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.

 

Shielded wires fix my high rpm stumble.

 

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.

 

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.

 

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:

 

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!!

 

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.