ECU fault code 31 solved

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abovetherim
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ECU fault code 31 solved

Post by abovetherim »

OK peeps, if you have read some of my other recent posts you will know I have been doing an engine swap, rev 4 into a rev 1.

Now yesterday I got it to run, albeit badly and there was an EML which gave the code 31 on diagnosis.

Code 31 points to MAP sensor (vacuum sensor) on a 3sge n/a engine so this is where i went poking around.

Now I am using a rev 1 MAP sensor and am told the rev 3+ engines use one with a different part number so I did consider this to be my issue but as it was late Saturday and I also had today off work I thought I would do some checks to rule out any other possibility.

First thing to do was find the testing procedure in the BGB, which is for the 91 rev1 but should still stand for the later revs. This gave me the ecu pin labels the MAP sensor uses.

Next I opened up the rev 4 ecu (rev 4 engine loom being used) and the rev 3 ecu (this is the ecu running the car) and checked the pins were in the same location. I was hoping they wouldn't be as this would be a simple fix. But alas they were positioned identically.

Next Follow the bgb check procedure. This showed no voltage between VC-E2 and PIM-E2 both of which should show voltage with ignition on (around 5V).

Next as neither showed voltage then the common terminal was E2 so I checked continuity between the MAP sensor plug and the ECU plug. Thats where the problem was, no continuity.

At the plug end the loom is pinched by some loom clips where it is attached to the diag port and MAP bracket. This shouted at me to be the place to start and low and behold that is where the wire was broken.
Quick bridge with some wire soldered and heat shrink and all is good.

So now the EML is out and the car is no longer overfueling.

Sorry about all the wordy detail but I thought this post may prove useful to anyone that gets that code especially as that part of the loom is pinched.

Now just got to try and get the engine to idle a bit lower as when warm it still sits at 1100-1200.

:cheeky:
Edited as I posted wrong fault code


1991 rev 1 T Bar n/a 3sge import. A work in progress!!!

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