I just ripped on the car and in 4th and 5th I'm getting a mystery hiccup where the tach drops 500-1000rpm in an instant and it feels like the car misses. 11.5:afr, very conservative spark table...so I'm not really sure what to do next. Its not showing in the logs either (and my notebook decided not to boot today). WTF is going on?

I suspect this is engine management related due to the tach behavior similar to "burning" when using MS.

Thoughts?

 

new plugs btw

 

Loss of CAS/CKP signal?

 

Mine did that last summer, I beefed up every ground I could find, but Joe had offered some other fixes if you search for the thread.

 

Let's see those logs!

 

The log shows nothing. I can't post the log because the computer won't boot.

 

https://www.miataturbo.net/megasquirt-18/losing-spark-tach-5000rpm-under-load-36299/

Joe mentioned this was one of the reasons he went to a trigger wheel.

 

I can't think of anything that wouldn't be in the logs... Before the plugs it ran fine? The A/FRs don't change during the hiccup?

Edit: The above post/thread sounds logical.

 

What year miata is this, and is it running a factory-style ignition system?

 

1991 with MSPNP9093 running savington's cops on the 1.6 cam angle sensor. It did this before randomly...maybe once or twice per month or once or twice per track event. . The plugs are fairly new.

AFR will jump from 11.5 to 12.0 or so during this hiccup.

I'd kill for a crank trigger/hall setup right now. I've wanted one for a long time but I can't do the math nor do I have the brain to design what I need. I can run a hall and trigger wheel on MSpnp, right?

 

Got a spare CAS? If not I can send one.

Mine went away with a reflash, but the CAS did randomly die a few months later.

 

I do not have a spare. I may take you up on that offer, but I'm going to bug someone to send me a hall wheel...thanks for the offer.

 

Yeah, this does sound very familiar.

Cap mod done?

Moar ground wires to head?


If you're serious, I'll PM you a name and a city, it's all I've got to go on right now. Send me your shipping address and I'll ship you my crank trigger setup. Do a good job on this, and some associates of mine may be interested in retaining your services.


You can use any sensor with an open-collector output. Most aftermarket trigger wheel pickups are VR, which would require a little re-wiring, but an NB crank sensor would put out the correct signal.

 

I have not modified the board because I've never soldered or played with a circuit board and I'd rather not start on a $700 computer that makes my car "work". I guess I could send it to DIY and get the TPS mod done too.

I can add a few more ground wires to the intake plenum and chassis.

Link to details on NB crank wheel? I want to fix this with the most simple method possible because I don't really know what I'm doing with electronics and configuration.

 

edit: I bought tuner studio.

I guess when I feel better I'll try to improve the grounding points with some cable and rings.

 

OK, you need to get a datalog of this happening. There very well may be a clue, even if it's subtle. The fact that your tach drops out is very telling, since your tach is driven directly off your coils.

Something like a loose main power or ground connection to your coils would do this.

Does manifold pressure have anything to do with it--can you pull to high rpm at 100kPa without a problem? The other very real possibility is a misfire due to not enough ignition energy. New plugs and/or smaller gap would solve that, or hotter coils.

 

I'll make another log tomorrow if its dry.

I'll check the connections tomorrow since this is fairly new in terms of frequency.

Yes, it won't misfire at low MAP. I have .045" plug gap and that's worked fine previously even at the track. The plugs are roughly 300-miles old.

 

+1 for spark blowout

 

Too much gap for the coils and MAP.

 

Reduce gap or get LSX/ MSD coils. Sounds like the cops are starting to slowly take a downward turn