Engine KOER OBD1 Test on 5 speed

Is this the same problem you are talking about here?

@Mustang5L5
Please give this a quick sanity check. There has some questions in my mind about the connector drawings.

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Sorry, but it's incorrect for the manual trans. There are two

In 5-spd application, the lt blue/yellow wire connects to the purple/yellow wire
In AOD applications, it's white/pink to the purple/yellow.

1987/early 1988 only harness for both 5spd and AOD (no jumper at all)
later 1988-1990 5-spd harness (jumper from pin 1 to pin 5)
91-93 5-spd harness (jumper from pin 1 to pin 6)
later 88-93 AOD harness (jumper from pin 5 to pin 6)


Your diagram is the early versions. 88-93 AOD and 88-90 5-spd.

91-93 5-spd looks like this. Pin 1 to 6



My recommendation is to always check the wiring that the loop is connecting. Simply following that is easier than figuring out the loop location

Barron91lx said:

Thank you. I will go through the dump code procedure. Last weekend I put an A9L computer in it to see if there was any difference and I get the 91 code with it too. I think the O2 harness is the original aod. Should I get a 5 speed sensor harness? Would that hook right up to the main harness? I think I'm going to try swapping the O2 sensors this weekend. I just put them on new a few months ago.
Thanks for your help

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Unless you make some changes in your AOD harness, you really shouldn't put an A9L in the mix here as you can fry your expensive A9L easily.

When 5-spd swapping a car, there are a few wiring changes that need to be made if you intend to run the 5-spd ECU. If you keep the AOD ECU none of this needs to be done, but the AOD ecu will sometimes have a high idle because it usually expects to idle against the load of a converter. .

Under the dash, there are two plugs hanging by where the clutch pedal usually is. In an AOD car they are taped up and one has a jumper in place. This is the NGS circuit and starter circuit. These connect to the clutch pedal switch. If you don't have a switch, leave the jumper in one and install a 5A blade fuse in the other. This will allow you to run the codes now.

As for the rest of the wiring, there is a transmission harness that should be changed. The AOD harness does not have the provision for the NGS on top of the t-5. You need the harness that runs from driver's kick panel to the trans tunnel and out to the car. LRS sells it for about $100. That will allow you to plug in the T5's NGS which does affect idle strategy slightly.


Second thing, is to verify the o2 sensor jumper matches the ECU you are using. You need to repin the jumper to match. See above post for wiring. Here's a thread I made on repining the o2 harness if you intend to run the A9L. It's very easy, but if it's it's not your speed LRS sells this harness also for about $100.


or for purchase