mdb4879

A friend and I have a new project that he bought from his cousin a couple years ago. I'm not sure how relevant the details of the build are for this, but we're getting the car together and hoping to go to the dyno soon. The car had a GM 3 bar MAP sensor on it which I replaced with a Hondata 4 bar (bought the car not running and have never been able to get it running worth a crap). I made sure everything was wired carefully, but it struck me as odd that the signal wire was getting 4.4 volts. I've made certain all three pins are wired correctly. We go to start the car on the basemap from our tuner and it won't start. MAP reads as 24.5" vacuum. I go back and double and triple check the wiring. I check continuity between the ECU end and the sensor end of the harness and everything is correct. MAP sensor is still getting 4.4v to the signal from the ECU. I check for continuity between ECU pin D17 and there's no connection to any other pin. It's not grounding or shorting out. I unplugged just the D connector and test pins D17, D19, and D21 with the ignition on. D21 is grounded, D19 is producing 5v, and D17 is producing 4.4v. Remember, this is directly testing the pins in the ECU with connectors A and B plugged in and ignition on. I thought something was wrong with the ECU so I grabbed a virgin P28 from another car and it tests the same. Has anyone run into an issue like this before or have any ideas what I should be checking? Am I correct in thinking that the signal pin is supposed to be an input to the ECU from the sensor and not a power output from the ECU? I would really like to not have to either sort through the existing wiring or create an entirely new harness. Right now all I can think of is start adding grounds anywhere and everywhere. Any ideas or comments are welcome. Thanks.

JRCivic1

MAP sensors are not simply interchangeable... they must be scaled in the tune for the MAP sensor that you intend to use. You cannot simply exchange a GM 3-BAR with a Hondata 4-BAR... or a stock OE 1.7-BAR... each of these scales the 0-to-5v voltage range differently.

There is a possibility that the Hondata 4-BAR sensor is damaged... but I suggest trying this first:

Since you have wired up the engine harness to accept the stock 3-pin round MAP plug style, use a stock style ECU and factory MAP sensor and see if you get the same voltage of 4.4v on the signal wire. If your wiring is working properly, the value should be between 2.5 and 2.9v.

mdb4879

I'll try to clarify. The basemap I have has parameters set for the 4 bar MAP sensor. I'm not getting 4.4v returning from the MAP sensor. The ECU is supplying 4.4v to the MAP from the signal pin. The ground pin and 5v source for the sensor are working as they should. Somehow the ECU is producing the 4.4v from the signal pin (D17). This has been confirmed both by testing the pins at the MAP sensor connector on the harness with it unplugged from the MAP sensor and also at the ECU with the "D" connector unplugged from the ECU.

mdb4879

After much testing and swapping ECUs and other components around I came to determine the new Hondata MAP sensor was bad. I sent it back to my tuner for him to test and he confirmed it and sent it in for an RMA. I was so hung up on the fact I was getting voltage from the signal pin on the ECU I thought it wasn't supposed to. Apparently that's how it operates. So for anyone wondering in the future, there you go.

JRCivic1

If you tested the signal wire at the ECU with the MAP sensor unplugged... and you still measured 4.4V... how is this proving you have a bad MAP sensor ??? Hondata tests every MAP sensor that they sell to make sure it works... what are the chances that it goes bad during the trip from their facility to your hands ???

mdb4879

So from my personal testing, it was that it tested with positive voltage from the signal wire in this car, tested the same with the same ECU in another car, with the car running didn't read any change to the MAP with the 4 bar sensor, and with a stock sensor and parameters changed to match that and it did show changes as it should with the stock sensor that lead me to determine the MAP sensor was bad. I then shipped the sensor to my tuner, who I bought it from, to test and he concluded the same and sent it to Hondata for an RMA. He said before this he's only had one sensor be bad from Hondata, so it would seem that I'm the unfortunate second. It's highly unlikely to happen to someone else, but it is possible and if would seem that is what happened to me.