Same car, 1989 LX convertible with a toasted AOD automatic. I have read a lot about doing the AOD to T5 conversion but one thing is not clear. Will I need to replace the engine ECM (or chip) and harness to get it to work with the manual transmission? Thanks.
You don't have to change the harness or the computer. I've adapted the stock wiring harness from a 1989 Mustang into a 1978 Fairmont, and the computer just wants to know what the transmission is and the connector on the transmission will tell it. You can always do a search for questions in this forum and several posts will come up, but asking here is ok also. It helps refresh my memory! Good luck, good wrenching!
When it comes to a Foxbody Auto To Manual transmission swap,the #1 rule thats good to go by is to NEVER use a Manual (A9L) ecm in combination with an Auto (A9P) O2 sensor harness.Ive heard of guys running this combo before and claiming to have never had issues,but theyve just been very lucky.If it ever takes more than a few seconds of cranking time to get the engine started,you can be sure the combo mentioned above will damage the ecm.
Long story short,when you run a Manual ecm in combination with an Auto o2 harness,the 12 volt starting voltage will heat the Signal Return (pin 46) trace up on the ecm board and burn it in two (open circuit),as soon as you press the clutch pedal down & turn the key to start.The damaged trace can be easily repaired by soldering a piece of 28-30ga wire in place across the short,but the problem will occur again if you dont swap the correct o2 harness in place.Another thing you can do is locate the o2 harness near the maf sensor and look at the looped wire.You need to make that looped wire connect the purple/yellow wire to the blue/yellow wire.If you do that,you can keep the Auto o2 harness in place.Pictures of this harness shown at the bottom.A description of why the trace burns is listed in the last paragraph below.Tmoss is the source for that information.
From everything Ive read,other than a couple instances,you can use any of the other combos without issues.
That being said,your combo should work fine.I believe the A9P ecm has more aggressive timing settings than an A9L,so thats most likely why some guys keep the Auto ecm in place when swapping to a Manual.
ECM O2 HARNESS
Auto/ Auto =Y
Auto/ Man =Y
Man/ Man =Y
Man/ Auto =N
(AUTO TO MANUAL SWAP-ECM & O2 HARNESS)
If you do a Auto to Manual transmission swap & you decide to keep the Auto ecm in place,you'll have to do one of the following things.If you dont do this,theres almost a 100% chance youll cause damage to the ecm.
1st choice= remove the AOD O2 harness & replace it with a T5 O2 harness.
2nd choice=convert the AOD O2 harness to a T5 O2 harness.
An AOD O2 harness can be converted to a T5 O2 harness in 5 minutes.Simply unplug the O2 harness connector located under the MAF sensor in 89+(88 Cal.)5.0 mustangs.Use a small flat head to remove the red plastic insert inside the connector which locks the pins in.With a tiny flat head,bend the plastic locking tab back that holds the pin in and use a straightened paper clip or something to push the pin out.You'll notice the AOD harness has one unused pin slot and the gray rubber section does not have a hole for this unused pin.Use a small drill bit to poke a hole in this soft rubber.Now move the purple/yellow looped wire from the AOD position to the T5 position.This must be done to every AOD to T5 swap to prevent future damage.
The confusion is due to the Auto ECM/O2 wiring harness is setup via the pink-white wire to detect when the starter is cranking on pin 30.The Manual ECM does not care if the starter is cranking and instead uses pin 30 jumped to the blue/yellow wire to detect clutch and neutral engagement by sensing if the blue/yellow wire is grounded to pin 46 (black/white wire) or not.
The Auto purple/yellow jumper wire in the O2 harness sends +12v to pin 30 while cranking.Moving this jumper to the Manual configuration will instead send the status of the clutch and neutral safety switch to pin 30.I haven't confirmed this yet,but the Manual ECM might be missing (or the Auto harness might have) a protection diode, which explains why when an Auto O2 harness is used with a Manual ECM,it fries pin 46 ground trace with 12V from the starter which is shorted against pin 46 black/white sensor ground while cranking.
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