Artifex

It's my first time, so be gentle. I've had my ms3 pnp pro in the car for a couple of months now and the car is running quite well. The car is a '91 1.6 N/A, the only performance related thing done to it is the MS.

From the beginning, I've had this issue. When under WOT, MAP decreases as RPM increases. The decrease in MAP isn't substantial, but it's about 5-6 kpa lower at redline than at ~3000. For example, WOT 3k rpm I'm at 95 kpa. Kpa gradually decreases all the way to redline where I end up at about 90 kpa. Does anyone have any idea what could be causing this? I posted a log of a 1st and 2nd gear pull to show what's going on. In the VE table of my tune you can see that the 100 kpa cells never gets touched from 5k to redline from VEAL. I've tried searching for anyone else that has encountered this but no luck.

This also brings me to another (maybe) related observation, the max MAP I see at WOT is 95. I understand that as altitude increases, ambient pressure decreases but I live at 900-1000 ft above sea level. According to Google, that's 98 kpa. Last week I helped a friend install his ms3 and under WOT in his '93, MAP was reading 98.7 the whole time.

Could this be as simple as a bad MAP sensor or some random setting being wrong? The car pulls great under WOT, granted it's N/A.

If my search skills suck and there exists hundreds of threads of this issue, feel free to belittle me for being the noob that i am.

sixshooter

iTrader: (12)

With the car not running you should see proper ambient MAP readings. When it is running you will almost always see less than ambient MAP readings at WOT when naturally aspirated because of restrictions in the inlet tract. These can be things like air filter, piping, elbows, interfooler, the throttle body, and possibly the chosen location on the intake manifold for the signal line.

If you have improper readings with the car not running, ensure the proper MAP sensor is selected in TS and the power and ground sources are adequate.

Artifex

Thanks for the insight, reduced MAP readings due to restrictions in the intake makes perfect sense. My car does still have the stock MAF in place.

What got me really thinking about this and pushed me to post about it was that my friend's car has the same setup as me, 1.6 n/a stock maf, and he had normal MAP readings at WOT. Could the length of vacuum line to MS cause an error in MAP readings? Mine's quite long, it's routed from the FPR through the firewall on the driver's side and across the dash into MS.

I'll double check TS settings and finally order an air filter to delete the MAF. Maybe that'll fix it.

sixshooter

iTrader: (12)

It relies on voltage and resistance as well as the air pressure itself. Make sure your grounds are clean and your splicing is good, too.

Artifex

I figured I should post a follow-up, as my weird MAP readings are now fixed.

MAP readings were fine with the car on engine off. ~98 kpa

I finally deleted the AFM with a cone filter and that solved the MAP dropoff passed ~4k rpms. MAP reads 95-96 to redline.The restriction in the intake tract from the AFM was the culprit. It's like you know what you're talking about or something, Six. Thanks again for the help.

The car drives great now with most of the quirks ironed out and after the AFM removal. The butt dyno shows a noticeable amount of torque increase from 2.5-6k. I can even accelerate on hills now! 10/10 would recommend for any N/A stock Miata.