Tip-in stumble
#1
Tip-in stumble
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...
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...
#4
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.
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.
#5
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...
#6
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.
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.
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...
#12
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...
Thanks for the help!
#13
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#14
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.
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