will a9p computer work with 5 sp car
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The A9P will work just fine, however, you MUST use an automatic 02 sensor harness or you will burn up the ECM. Also, you may get an occasional hanging idle when you push the clutch in when coming to a stop, 1500 rpm or so.
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I have an A9P but I had no idea about the automatic o2 sensor harness.
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His car is already a 5spd car if I read correctly. The O2 sensor harness is wired differently between a 5spd and auto. When I did my 5spd swap I kept the A9P and the harness, no issues other than the hanging idle.
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me too.
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How is the O2 wired differently? It is just 3 wires. The ground, 12V for the heater, and the low voltage signal wire. Are you saying that the O2's in an automatic have a different pin out on their harness. I seriously doubt that. What exactly is different? Is the signal wire going to a different pin on the computer so the harness you are talking about is the one between the connector on the O2 and the plug on the ECM?
Very strange. Why would they do that?
Very strange. Why would they do that?
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543 Posts
Let me try to give you an explanation:
Its not that the O2 sensors - or their function - is any different between MT and AT cars, its that the O2 sensor harness is different.
The EEC uses many sensor inputs to determine strategies for engine operation under various conditions. One input the EEC uses to determine idle, and idle down (ie 'dashpot'), strategy is transmission gear. The EEC is 'signaled' by 'grounding' pin 30 so it 'knows' whether the transmission is in gear or not. For MT it uses the NGS (mounted on the top cover of the T-5) and CES (mounted on the clutch pedal) which connects pin 30 to pin 46 (SIG RTN, an EEC internal 'ground'). For AT the NSS is used to signal that it is P or N by using the same circuit that is used to connect the starter solenoid to the ignition switch. When the AT is in P or N pin 30 is grounded thru the internal 'coil' of the starter solenoid.
Ford essentially used two sets of circuits (wires) to deliver the MT or AT signals from the respective transmissions to the EEC processor. Presumably for cost/commonality reasons both sets of circuits are contained within the main EEC harness. The determination of which circuit is used is made via a specific 'jumper' wire. The jumper is different for MT and AT. Ford put the jumper in the O2 sensor harness, therefore there are 'MT O2 harnesses' and 'AT O2 harnesses'. From arms length (and even closer) the MT and AT O2 harnesses appear identical but under close examination of the 8-pin connector where the O2 harness connects to the main EEC harness you would see a difference in the pinout position of the jumper wire. So although we all call this harness the 'O2 sensor harness' it actually contains more functionality than that. Just for the record the 'O2 sensor harness' also contains the wire for the 'low oil' sensor which is mounted on the oil pan and also has nothing to do with the O2 sensor function.
The A9L vs A9P processor issue has to do with the fact that on AT applications the pin 30 ground signal in P or N uses the same wire that is used to supply battery voltage thru the ignition switch to the starter solenoid during START. So during START pin 30 will see battery voltage because the AT transmission 'signaling' circuit is wired that way. But its only wired that way when the AT specific O2 sensor harness is used. I cannot verify that certain processers are 'immune/vulnerable' to having battery voltage on pin 30. I have read that the AT processors (ie A9P, etc) are 'immune' and that MT processors are 'vulnerable' (A9L, etc) to being 'fried' when battery voltage is put to pin 30. That is why it is said that it is OK to use an AT processor in a MT - because in an MT car (with an MT O2 sensor harness) pin 30 does not recieve battery voltage in START, but not visa versa. More importantly though is that when the 'wrong' O2 sensor harness is used (ie an MT harness on an AT car) the EEC will not recieve any signal at pin 30 because the correct jumper for the necessary AT circuit will not be there. And that can/will cause issues with idle and idle down (ie rough idle, stalling, etc). That is why I feel it is incorrect when it is said that all you need to do is use matching processors and O2 sensor harnesses - regardless of the actual trans in the car. For example if you have a car that has an MT and you use the EEC processor and O2 harness from a donor car that was AT although the processor and O2 sensor harness 'match' the processor will not receive the transmission signal at pin 30 because the jumper in the AT O2 harness is incorrect. The best way is always to match the transmission, O2 sensor harness, and EEC processor.
I hope this explanantion was helpfull.
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there should be no reason he needs to change the o2 harness just to swap the computer
all the computers are PIN'd the same
the o2 harness need to be matched with the TRANSMISSION,not the computer..
what happens when the "wrong" o2 harness is used,is the previously mentioned jumper wire send 12v to PIN 46 SIGRTN when you turn the key to start the car
as of now,his computer is not getting fried
swapping another computer in its place,without changing anythign else,will still NOT get fried
been there..fried one..repaired it..still running..A9M(auto,same as a A9P) with a 5spd car..came from the factory that way..when i did my 4cyl swap,i had to re-pin the jumper wire on the o2 harness. i put a 1992 5spd o2 harness into a 1988 EEC harness..jumper was in the wrong spot
there are 4 factory o2 harness configurations:
87-89 auto
87-89 5spd
90-93 auto
90-93 5spd
easiest way to check:
5spd car..
remove EEC
clutch down,crank engine
DVOM on PIN 46
if voltage is present while cranking,clutch down,then the jumper wire is in the wrong place. fix it.
no voltage=slam the EEC back in and go do a burnout
all the computers are PIN'd the same
the o2 harness need to be matched with the TRANSMISSION,not the computer..
what happens when the "wrong" o2 harness is used,is the previously mentioned jumper wire send 12v to PIN 46 SIGRTN when you turn the key to start the car
as of now,his computer is not getting fried
swapping another computer in its place,without changing anythign else,will still NOT get fried
been there..fried one..repaired it..still running..A9M(auto,same as a A9P) with a 5spd car..came from the factory that way..when i did my 4cyl swap,i had to re-pin the jumper wire on the o2 harness. i put a 1992 5spd o2 harness into a 1988 EEC harness..jumper was in the wrong spot
there are 4 factory o2 harness configurations:
87-89 auto
87-89 5spd
90-93 auto
90-93 5spd
easiest way to check:
5spd car..
remove EEC
clutch down,crank engine
DVOM on PIN 46
if voltage is present while cranking,clutch down,then the jumper wire is in the wrong place. fix it.
no voltage=slam the EEC back in and go do a burnout
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Thanks for the info guys!
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Im gonna jump in and jack this thread!
I have been messing with these car since they were new and have done a few 5.0 swaps and have used every ecm under the sun.
I never knew there were different O2 harnesses... Goes to show you learn something new everyday and never know it all.
That being said. I just did a swap on a 90 4cylinder with a 90 computer harness and have a CEL that has NO codes.It is a solid light. Also when I release the clutch at idle ,in neutral the car stalls.
Now this has me wondering if I have the wrong O2 harness??
Any feedback would be helpful.
Thanks
I have been messing with these car since they were new and have done a few 5.0 swaps and have used every ecm under the sun.
I never knew there were different O2 harnesses... Goes to show you learn something new everyday and never know it all.
That being said. I just did a swap on a 90 4cylinder with a 90 computer harness and have a CEL that has NO codes.It is a solid light. Also when I release the clutch at idle ,in neutral the car stalls.
Now this has me wondering if I have the wrong O2 harness??
Any feedback would be helpful.
Thanks
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3,382 Posts
Let me add that I used the proper T5 trans harness,removed the jumper and plugged in the intermittent clutch switch.
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the no codes condition is most likely the result of a fried computer. the trace on the #46 SIGRTN,to be specific..
open up the computer,take the board out and look underneath for a burned spot. it should look just like this:
take a small piece of some thin wire,like 24 ga, and carefully solder it between the two ends of the burned spot..fixed..
even though you may have used a 5spd harness,it may have been from the wrong era
more info here
http://forums.corral.net/forums/showthread.php?t=1094179&highlight=sigrtn&page=5
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never heard this before!
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This information is false. First of all the 5 speed 02 harness goes from 87-90 not 87-89. And the other set of 5 speed 02 harness's range from 91-93 not 90-93. Pin 1 and 5 are jumpered on 87-90 and Pin 1 and 6 are jumpered 91-93.
Also the AOD 02 harness is the same accross the board from 88-93 (88 california only). Pin 5 and 6 on the connector is the jumper wire.
Lastly there is a 4th 02 harness. Its a speed density harness. Its the same 02 harness as the above harness's but its missing the jumper wire.
I can provide pictures off all of these things. I own about 10+ 02 harness's and i have carefully marked everyone of them when they came out of the car. I fixed a car on the dyno recently. They were trying to tune the fox but it wouldnt change or learn the tune. He complained about the 02's not working and i checked this on the guys car after i found out not only was he using a speed density 02 harness but it was an 87 car converted to mass air.
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This is what your above table should have looked like. Keep in mind, there was NOT any mass air harness's in mustangs in 87. So 87 had its own NON jumpered 02 harness. I only put 88 there because in california when there was a mass rush of vehicles sold to that state they put the 8LD computers and mass air harness's in those cars. So they would be jumpered.
88-90 5 speed [pin 1 and 5 jumper]
91-93 5 speed [pin 1 and 6 jumper]
88-93 AOD [pin 5 and 6 jumper]
87-88 Speed Density [NO jumper present]
88-90 5 speed [pin 1 and 5 jumper]
91-93 5 speed [pin 1 and 6 jumper]
88-93 AOD [pin 5 and 6 jumper]
87-88 Speed Density [NO jumper present]
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I'm pretty sure that automatic ECMs (A9P etc) have a diode for pin 30 in the circuit board that prevents the 12 Volts that is applied to the starter solenoid while starting from entering the ECM and frying the circuit trace. Manual trans ECMs do not contain this protective diode.
This diode will still allow pin 30 to sense the ground condition through the solenoid when the neutral safety switch is in gear.
It's kind of weird and hard to understand at first, but it's really a pretty slick way of doing it.
That's my understanding of it anyway.
This diode will still allow pin 30 to sense the ground condition through the solenoid when the neutral safety switch is in gear.
It's kind of weird and hard to understand at first, but it's really a pretty slick way of doing it.
That's my understanding of it anyway.
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what type of driveability issues will this cause
Anyone know what to do about the 86 harness with no jumper? It looks like it will not matter auto or 5-speed o2 harness because the computer side of the 86 harness has no wires in these spots.... Switched to MAF and new style o2 harness with the smaller o2 plugs and trying to figure out if it matters which trans harness...??? Thanks..
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