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Old 09-16-2012, 02:55 PM   #1
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MAF conversion non-functional without 89 harness???

reposting this in a different area because it wasn't gettign many views where it was at. 87 GT AOD 5.0, previously converted to T-5. Did an interactive systems and technology MAF conversion including the VSS and FPM2 wires. I think I installed it all correctly. Havnt driven it, and can't for awhile, (body work in progress) but it idles and revs fine, no surging or anything. When researching the MAF conversion and AOD to T-5 conversion, I came across this:

Oxygen sensor Harnesses - Manual/Auto differences and year differences

So, for quite awhile, I was concerned I was going to fry my new A9L ECM if I tried to start it with the original 87 speed density AOD oxygen sensor harness. So I found a 5 spd 89 O2 harness and was ready to install it. Anyone familiar with this issue will know, that what makes the oxygen sensor harnesses different (AOD vs T5) is just a simple little loop on one plug. On maf car, this "loop" completes and returns a circuit (beyond my understanding really). In Speed Density cars, there are fewer wires on the plug that connects to the oxygens sensor harness. So, I contacted a longtime and respected board member here asking his opinion. Paraphrasing him, he said not to even bother trying to do an MAF conversion using the SD harness, to get an 89 MAF harness and just plug it in. He went on to say that it will just run in limp mode without swapping to an 89 harness. again...paraphrasing. So, that kind of threw me for a loop/ People have been doing MAF conversions, adding the pigtail, changing some pins around for nearly 20 years. Yes, I understand if done INCORRECTLY it will run in limp mode, but he seemed to be saying you cannot convert an 87-88 to mass air without upgrading to an 89 harness.

Below is the question and answer to the member (Iam not identifying him). Any comments on this anyone, or can help clarify, or prove/disprove this???


Originally Posted by 1983Ttop5.0
"Alright, I'm fairly new to the forum, but I've read alot of your post in the threads, and can tell you are knowledgable, and have good advice. I'm not new to mustangs, just new to this in depth of knowledge needed for what I'm doing. I'll give you the short version of what I'm doing. 1983 T-top car, factory 5.0 & T-5. Installed a 1990 roller cam engine. Used a wrecked donor 1987 (5.0 AOD) and transplanted ALL chassis, engine and dash wiring, harnesses, interior, etc. Swapped in a manual trans harness. Car ran good temporarily as speed density. I immediatly proceeded on MAF conversion. MAF conversion is all wired in including FPM2 and VSS. Using A9L computer. I've known about the O2 sensor harness issue for months. Theres a few issues that have come up though. Speed density cars have a very basic O2 harness, and do not have that loop (at all) for the signal return. Whats more, on the ECU side that plugs into the O2 harness, even if the O2 harness had the jumper/loop, there are no pins in the factory SD harness for it to connect to. From what I understand, that signal was routed elsewhere in speed density cars. Where? And how do I deal with this? I have checked for voltage at pin 46 while cranking and get less than a volt (.3), so negligible. But.....the sensor that goes on the top of the T-5 trans, is missing (was removed while car was carbed), and I dont know if that can affect any of this. I need to know what I need to do to make it "safe" to plug in my A9L without fear of frying it. Help! Next....I understand there is a jumper in some kind of plug under the drivers side of the dash I need to unplug that was jumpered whiel the car was AOD? How do I identify it/where exactly? Next, what plugs get plugged in at the pedals? If you can help with any of this, man you'd save me a bunch of stress and headaches! Thanks!"

Answer
"First off i know you dont want to hear this but the 87 speed density harness your trying to convert wont work. You are right when you said it doesnt have the proper plumbing for that loop signal return which will cause havoc on the mass air car and not have an 02 signal at all. Which equals limbo mode. Car will still run but will be rich and run very slow. Because its in safe mode. Metaphorically ever see a desktop computer run fast and efficient in "safemode" when it boots up? thats what your computer would be doing. Safe mode.

Do yourself a favor if you can. Get rid of the "conversion" kit you spent money on. Get an 89 mass air harness OR you other option is to find an 88 speed density harness that has already the proper plumbing to convert to mass air and use the kit you have. 88 was the first year they made mass air in california only so most of those harness's already came equipped with the proper plumbing to convert to mass air regardless if it was speed density or not.

As for the 02 harness thats easy one. If you dont have the proper looped wire for mass air after you fix the problem with the engine harness then make your own! Basically head to the bone yard and find an old ford EFi dont matter what it is. Cut the 02 cannon plug out (or take the whole thing) cut 2 wires out of the cannon plug back about 2 inches and unclip them from the cannon plug itself. Solder the 2 cut wires together and clip them into the proper locations needed for 5 speed 02 mass air harness. Which in your case would be the far right top and bottom (or number 1 and number 5 location if you numbered it top and bottom left to right staring at the pins. You already know those pins will "click" right into place because it used the same plug on all fords. All that matters here is the loop wire. The other 5 wires found in 2-4 and 7 & 8 locations on that very plug are all the same mass air or speed density.

As for the dash loop its easy to find. Its near the radio on the dash frame. It should have a red and green stripped wire looped in a 2 wire plug. Thats the pedal position switch that tells the computer where the clutch position is when you press and depress. I have seen people run w/o it no problems but why not hook it up as if it were stock right? "
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Old 09-16-2012, 03:22 PM   #2
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Run the codes with your mass air computer. See if code 67 shows up. The wires for CPS switch are there. They just run straight to the computer on an SD harness, rather than the 02 harness like the MAF cars. Your harness can and will work on a MAF conversion. And it won't be in FMEM(limp mode)!!! Code 67 is not even a code that puts the ECM in Limp Mode. So I have no clue what he is talking about.

Regardless, if you have an issue, I will help you get it squared away WITH the SD harness. You already checked for voltage at PIN 46. It was fine, and you won't burn the ECM up. So run the codes, if you have code 67, we will look into it. But you shouldn't if everything is correct. And that means the SD harness is fine.
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Old 09-16-2012, 03:58 PM   #3
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That member is speaking from years of experience. You can tell just by the way he calmly explains it like he has done it 175 times.

He understands what most techs understand. That if you don't go all the way with a conversion, and just splice wires here and there. Eventually you will encounter more issues than you are willing to deal with.

ESPECIALLY WHEN IT COMES TO SMOG!

Here in Krakifornia, we all fall in line and do whatever it takes to pass that friggin test only every 2 years!

So I would say 1,000,000 thank you's to the guys who have put in many years of doing what you are doing and are willing to go into so much detail to help you out!
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Old 09-16-2012, 04:53 PM   #4
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Quote:
Originally Posted by liljoe07 View Post
Run the codes with your mass air computer. See if code 67 shows up. The wires for CPS switch are there. They just run straight to the computer on an SD harness, rather than the 02 harness like the MAF cars. Your harness can and will work on a MAF conversion. And it won't be in FMEM(limp mode)!!! Code 67 is not even a code that puts the ECM in Limp Mode. So I have no clue what he is talking about.

Regardless, if you have an issue, I will help you get it squared away WITH the SD harness. You already checked for voltage at PIN 46. It was fine, and you won't burn the ECM up. So run the codes, if you have code 67, we will look into it. But you shouldn't if everything is correct. And that means the SD harness is fine.
Well, I do want to run the codes, trust me. Two problems with that though. The Neutral gear switch (top of the T-5) has had the pigtail chopped off, (this T-5 is a z-code Cobra WC). The car is actually an 83 T-top, that I have transplanted ALL 87 harness/dash/interior/etc. When the car was carbed, I didnt need that switch. So I think I need to source a Neutral Gear Switch otherwise I WILL come up with code 67 indefinetly. I think its also called a Neutral Sensing Switch. Anyone have one for cheap? For the tiem being, can I just jump the pins at the connection in the trans tunnel? I'm new to EFI as you can tell, and its a steep learning curve. I'll have to spend an hour or two doing a little research, because....I dont even know how to do KOEO/KOER yet. (though I've heard it isnt hard.) Oh, the neutral gear switch on the tranny....does it have ANYTHING to do with the O2 sensor harness issue.....meaning....should I re-test for voltage at pin 46 AFTER I either get the neutral gear switch installed or jumper it? Thanks Chris
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Old 09-16-2012, 07:05 PM   #5
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Yes, both the clutch switch and Neutral switch work together. And go to the same place. Even if the Neutral Switch is not hooked up, the test can be done. Its just to show that the circuits in the harness actually will produce the results you are looking for.


So.....run codes, verify code 67. Hold clutch down and hold it. Run codes again. Code 67 should be gone. They way the two switches are wired, either one can override the other. So pushing the clutch down will still send the correct signal regardless of if the Neutral Switch is wired up or not.
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Old 09-16-2012, 07:10 PM   #6
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Mustang Mass Air Conversion StangNet

ive done an 87 & 88 using the factory harness with no issues. just adding wires for the MAF and relocating others as per the directions above. no changing or messing with the o2 harness. if your chassis was a factory auto, the harness in the trans tunnel will only have a plug for the VSS and the reverse lights. i have a TKO in my 88, and not having the Neutral switch created any issues.... it was a factory auto car.

fwiw, i know you mentioned living in cali..... here in MD cars that are registered as "historic" or "antique" no longer have to report for emissions. we only have to show for 1 visual state inspection at the time of registration. just something to look into considering your car is almost 30 years old, not sure if cali has anything like that for older vehicles.
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Old 09-16-2012, 07:45 PM   #7
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Exactly. I have no clue why that guy would say it wouldn't work. He obviously has never did the conversion, or didn't know what he was doing.

I even gave him the same link for the conversion you did. Just in a PM a few days ago.
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Old 09-16-2012, 10:46 PM   #8
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Hey Joe, the switch I'm referring to isnt the pair in the pedal assembly, the clutch safety/neutral safety, I'm referring to the one on top of the T-5 that senses when you are in gear, or neutral so the car dosnt start in gear, only neutral.
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Old 09-16-2012, 10:47 PM   #9
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And, I think the "collector car" plates I can get here in Colorado are at the 30 or 35 year mark, and means I only have to get emissioned once every five years. I'll research that.
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Old 09-16-2012, 10:58 PM   #10
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Quote:
Originally Posted by 1983Ttop5.0 View Post
Hey Joe, the switch I'm referring to isnt the pair in the pedal assembly, the clutch safety/neutral safety, I'm referring to the one on top of the T-5 that senses when you are in gear, or neutral so the car dosnt start in gear, only neutral.
There are two connectors on the clutch switch. One is for starting, the other is for neutral sensing. Then the switch on the trans is for neutral sensing also. The sensors for neutral sensing have nothing to do with starting the car in or out of gear like an Auto transmission car.
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Old 10-18-2012, 05:07 PM   #11
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I just want to add my thoughts. My 88, from what I've read, does not have the correct O2 harness. With a high-flow BBK converter pipe on it, the emissions place told me it was one of the cleanest cars they've put on their machine. So, emissions wise, not quite sure what the difference would be.
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