Did I fry my ECU?

Tiny
MRMEXICO66
  • MEMBER
  • 1998 NISSAN MAXIMA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 228,000 MILES
I unplugged my MAP sensor to see if it would drive any better it did not so I pulled over and plugged it back in with the car running as soon as I plugged it in the car shut off. I restarted it and it was misfiring on all cylinders with a MAP sensor code. I replaced the MAP sensor but it did no good. So what did I do to my car by plugging in the MAP with the car running?
Monday, April 30th, 2018 AT 9:36 PM

7 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
In theory it should not have hurt the ECU. The MAP sensor uses three connections. Power ground and signal. In function it works like a potentiometer. With it unplugged the ECU falls back to baseline programming and uses other sensor inputs. When you suddenly plugged it back in the system now had an input that it had to use. That may have scrambled it a bit.
Try disconnecting the battery for a few minutes to let the system forget the input and see if it clears up.

What is the issue you are trying to correct that prompted you to pull the MAP? It is possible that it is the root cause for the misfires.
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Monday, April 30th, 2018 AT 10:59 PM
Tiny
MRMEXICO66
  • MEMBER
  • 4 POSTS
I had a misfire code for number five cylinder and a knock sensor code but the weird thing is it ran fine until it warmed up then it would start to idle erratically and stumble while taking off. So someone said on YouTube to unplug it see if it ran better or not. That is why. Now the car is unforgivable but I am going out right now and unplug the battery I will let you know what happens. Thank you for responding I am at my wits end with this craziness.
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Wednesday, May 2nd, 2018 AT 8:20 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
MAP normally would not effect either of those. However, the knock sensor and a single cylinder misfire together would cause some stumbling as the engine uses the KS to adjust the timing and the misfire would throw the ECU off on its own.
Try the reset and we will go from there. Do you know the last time it had plugs or any other work done?
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Thursday, May 3rd, 2018 AT 5:32 AM
Tiny
MRMEXICO66
  • MEMBER
  • 4 POSTS
No idea about the plugs I just bought the car. I tried disconnecting the battery it did not work. What baffles me is as soon as I plugged in the map sensor the car shut off immediately and as soon as I restarted it it ran like really bad. So if the battery trick did not work I have no idea what it could be other than the ecumenical was damaged. Any other ideas would be appreciated and I will try them all. Thanks for your help.
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Thursday, May 3rd, 2018 AT 5:01 PM
Tiny
STEVE W.
  • MECHANIC
  • 15,233 POSTS
The hope was that the system would flush out bad data. The thing is that if you still have the misfire the engine will run bad, shaking and rough.

Is the part in the first picture what you unplugged, it is at the bottom of the other picture or was it the unit out in the intake tract? Just realized we may not be talking the same part.
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Sunday, May 6th, 2018 AT 1:52 PM
Tiny
MRMEXICO66
  • MEMBER
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Yes, it was the mass airflow sensor I unplugged. I also noticed when I was pulling codes by turning the dial on the ECU there were no lights lit up on the side of it. What does that mean if anything?
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Saturday, June 16th, 2018 AT 11:35 PM
Tiny
STEVE W.
  • MECHANIC
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Okay, that is a bit different. The MAF on Nissan vehicles does not like to be plugged in with the power on. The MAP that you referenced earlier would be okay, but the MAF is a different animal. With that it is possible that it damaged the ECU.
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Monday, June 18th, 2018 AT 11:55 AM

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