DIYPNP Map Sensor Reading Off
 

Hi all,

Some of you guys have seen by car in the build threads section. Fast forward a few weeks ago, I did a shakedown run at Pacific Raceways where my car broke down.

I ended up towing the car back up to Canada and going over everything it seems like my map sensor is reading off. Thinking that the DIYPNP MPX4250AP died, I swapped it out for a GM 3bar. No luck either.

So I ended up pulling off the connector to the map sensor, and weird thing is, with the sensor unplugged, and the ecu powered ON, I am getting a weird back back feed voltage off the signal wire. It reads about 1-1.3v.

With everything completely soldered off the board (NO MAP SENSOR), I am seeing voltage on the map sensor signal pad with my meter. I go into Tunerstudio and it's telling me I'm at 20kPa but slowly rises to about 120kPa over a course of 5 minute. WTF. I shouldn't be reading anything here (or 20kPa, the "0 voltage" signal. This is with NOTHING plugged in at this point.

Any thoughts? Did my DIYPNP just died on me?

For reference, this is the video when it just went to shit on me:



Im obviously not doing anything to the DIYPNP when this happens on track.

It's hard to troubleshoot without schematics.

Everyone should tell DIY that they should publish the schematics.

No kidding. One interesting thing we found out today by probing around is that the ground for the map sensor goes through the microsquirt module. Seems like a lazy way of doing things versus finding an alternate way to route the trace.

This is normal behaviour. There is some voltage from the processor's ADC circuit, which rises as time goes by. You'll find that the same thing happens to the TPC is if you disconnect it.

Still does not say why, or give any clue as to why the DIYPNP is reading map incorrectly despite which map sensor is plugged in. Not sure if you saw the video but I would say that is pretty random behavior.

Quite frankly I'm lucky I didn't run super lean and totally kill my motor.

you say it was off, but how off was it?

Your video embed is teh brokenz.

Key on, engine off - when it should be reading atmospheric, it reads roughly 124-125kPa

Fixed now, my apologies! Skip to about 4:00 for broken diypnp

so it reads 124-125kPa at atmo, does it react in vacuum and boost as normal albiet 24-25kPa too high?

As indicated previously by Reverant, your voltage readings are normal and customary. The input is floating without input from an actual sensor. In fact, your readings show that the ADC circuit is likely to be working correctly.

The map sensor receives VREF and Ground directly from the same power supply as the processor in order to minimize any potential offsets. If you feel this is in error, please tell me a better way to route the traces between the map sensor and processor, and I will pass your suggestion on to engineering.

Did you calibrate the MPX4250? Did you calibrate the GM 3 bar? DId you take voltage readings from the sensor?

You seem pretty quick to point fingers, but so far I'm not seeing where our product is to blame.

You can say that there are almost 3 different reactions I get, depending on what mood the DIYPNP is in:

1) No reaction, stays at 125kPa at vacuum while revving

2) Some reaction if I do light revs, but the behavior is not consistent with engine behavior (vacuum does not increase)

3) Some reaction if I do light revs, but the behavior is consistent (vacuum does increase, goes to roughly 112kPa)

with both sensors?

I was simply asking the question if this is normal, and yes it seems that it is. So if we can write this out of the equation then lets look at other potential problems with this situation.

As for sensor calibration, yes I calibrated both. I confirmed that as well by looking at the data sheets. I did take voltage readings off both sensors and the sensors are fine.

Did you not see the video? Sudden power loss. I managed to tune on this fine on the dyno, by a respectable tuner at that. I'm quick to point fingers because my car suddenly died on track, and I was left with a towing bill due to an ECU fault. So far

Obviously no one was touching the DIYPNP at the time. I hope there is a better explanation than "did you calibrate the sensors".

Yes, with both sensors.

so it's suddenly reading high, and not reacting much at all to inputs. how did you install the 3bar?

I know the stock one can crap out, itll typically happen after a cold winter and condensation was allowed to form in the MAP line and it fubars the circuitry inside.

Take a couple of pictures of the DIYPNP, both sides (top and bottom) and post them here.

I just followed what they had here:3-Bar MAP sensor

As requested here are some shots of the DIYPNP front and back. Note, there is no mica filter on the transistor on the back because I pulled it off while probing around.

https://www.miataturbo.net/attachmen...ine=1371010213

https://www.miataturbo.net/attachmen...ine=1371010213

https://www.miataturbo.net/attachmen...ine=1371010213


Here is one of the logs that I did in the pit while going through two gears in the pit at Pacific Raceways. Note that at 6800rpm, it says Im at 137kPa (19.xpsi), there is no way my rotrex is boosting this much as much as Id like.

Just shows how all over the place the map signal was.

https://www.miataturbo.net/attachmen...ine=1371010213

137 kPa = 5.5 psi of boost at sea level.

It seems you are very laser focused at an alleged map sensor problem, and I think that's throwing you off from your real problem.

I don't see any other suggestions here for any other problems. The point being is that the car went to shit randomly. Not sure if you even saw the video, but I don't see a response to something just occuring out of the blue.

Maybe because the reason is that this product is terribly unreliable. I made it down to Washington twice, once to tune and once to track. This thing obviously died on me out of the blue but I see refusal to admit that nothing but the DIYPNP died on itself.

Also looking at the log you can see that MAP increases before RPM does. I got some response from DIY Autotune stating that all you guys see is "moderately slow throttle response" which is utter bullshit. I'll post the log showing TPS vs MAP later tonight.

With the ignition on, what's the voltage on pin 3 on the white PCB? Obviously with the MAP sensor soldered on the board.