Experienced newb here (Not my first Miata. Definitely my first megasquirt.) and I'm stuck beating my head against a seemingly simple problem.

MS2PNP on a nearly stock 1.6 (just a light flywheel). I've go it starting and idling smoothly, and driving pretty well through any steady acceleration, but it has a mean lean stumble at tip-in, especially from idle. No VTPS sensor, so accel enrichment is just MAPdot. I've tried idle air fuel ratios from 14.5 down to 12:1, idle timing from 12 to 17 degrees, and accel enrichment as high as 25%, but no matter what I do, tip-in always makes it spike lean and then stumble.

Any idea what I'm missing here? Doesn't seem like I should need TPS signal for this. The stock ECU gave good throttle response on this exact engine without VTPS or even a MAP sensor. MAPdot is at least a faster signal than the MAF door swinging...

 

More information is needed. Most people recommend posting your tune and a log with your problem.

 

If you ask me, MAPdot treshold too high.

It sees high map (tip in), goes way lean, injects fuel too late, then goes way rich for way too long.

 

Shouldnt you unplug the TPS and be 100% map on the slider scale considering you essentially have no TPS?

I've since moved onto 1.8's but i remember screwing around with something like that on my 1.6's.


You can 3d print an adapter and run a Kia TPS sensor that plugs right in and will work great with the MS. thats what i did.

 

Yeah, that makes sense. I just noticed the same thing. I think I had been misunderstanding that x-axis position of the first dot on the MAPdot chart should determine the start of enrichment, but clearly the MAPdot threshold setting is blocking it from even using that chart. I'll try that when get back out to the car...

 

I do have the slider all the way left, to be 100% MAPdot. So I don't think unplugging the TPS is needed.

I'm guessing that Kia TPS might be the same as the atuomatic transmission Miata TPS. I have one of those, but the throttle body itself is different, and won't even bolt to my manifold! So yeah, I'd probably need to made some adapter too. I'm not convinced I need TPS yet, though...

 

Yes, you do.

 

Oh!
So TPS is needed to get decent tip in on a stock 1.6? Any idea why? Just curious how Mazda was able to do it without one and we can't.

If needed, I'll get to work on that. Any reason the AT 1.6 TPS won't work? That's my current best choice.

 

I think TPS is less critical on the MAF based system Mazda used.

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My best guess is that maybe you need the MAPdot threshold so low to work that normal fluctuations in map are constantly triggering accel enrichment. TPS could allow you to keep the MAPdot threshold high enough to avoid that. Gotta play around this afternoon...

 

How many 1000s of hours have you put into your tune? Cause Mazda put in many. But yes, your map dot threshold should be around 25, not 250. And yes, you need TPS.

 

That was definitely it! Dropped from 250 to 50 and now its actually driveable! Runs at least as well as a poorly-carbureted car now!

Thanks for the help!

 

If you have a MAF or AFM well before the intake manifold, the sudden change in airflow can be detected pretty early thus negating the need for the acceleration enrichment by the TPS. Ie the MAP signal has both a lag as the sensor is not on the manifold but further away and the by the time the MAP sees the change, the extra fueling is probably overdue.

 

I've always wondered this. I realize it's extra wiring, but why is it so uncommon for people to run an external map sensor and mount it under the hood with say 6" of hose to the manifold rather than multiple feet like we all have now? I'm sure we're talking about a fractional increase in latency with the vacuum hose length, but still.