I have an AEM installed in my 94 Miata with an AEM 3.5 bar MAP sensor. For some reason, the MAP Volts signal gets erratic above 5000 rpm when under boost (boost is set to between 8 and 9 psi). With MAP Filter set to 4 as it was in the initial startup cal, Engine Load drops to around 4 psi. The boost gauge and the dyno's map sensor confirm that boost does not drop when this happens. Obviously it is bad for the MAP sensor to be not reporting pressure correctly at positive pressure and high RPM's. I have swapped MAP sensors, vacuum source, 5 volt, and sensor signal wires to the sensor trying to figure this out. I have also verified, using the boost gauge and the dyno's map sensor that the vacuum line Im using has the right vacuum. Nothing has helped. The car drives great under 5000 rpm.
The tuner I took the car to (Tony Szirka at UMS Tuning in Meza, Az) got the AEM tech rep on the phone and they decided it must be the AEM box that was doing something strange, so I sent it back for troubleshooting and repair. They could not find anything wrong with it, but replaced the guts based on Tony's recommendation. I have it back in the car and nothing has changed. I'm desperate at this point. Does anybody have any experience with this kind of problem and the AEM EMS?
What I've done recently:
1) ran a 4 gauge grounding wire from the battery to the engine block, alternator, and other 16 gauge wires to all the stock grounding locations from the 4 gauge wire at the block.
2) Replaced my stock coils with toyota COP's. Stock units split open and died. I read on here how people had seen reduced noise with them.
3) Installed a filter to the stock 12v permanent power wire to the ECU.
4) Verified that the sensor ground is not shorted to chassis. It is not.
See this post for additional information:
Map signal going crazy