Electrical Maf Conversion On An 87 W/ 89 Harness Question

[87notcher]

Hey guys,

Im sure I will take some heat, but I have spent days reading through old posts and am just still having some questions about what I need to do to make my MAF conversion correct so please be gentle lol!

I have an 87 coupe that I converted from speed density and AOD to MAF and 5 speed back in 2004. Back then I purchased an 89 engine harness/computer and just swapped the complete thing versus installing the MAF plug kit. Im pretty sure I just plugged my stock (87)oxygen O2 sensor harness back in and I know I didn't do anything about the VSS, which my car already had, being a cruise control car. I have a tweecer RT on the car and some mild engine mods, AFR 165's, Crane 2020, GT 40 Intake, 24 lb injectors, etc.....and always had some nagging hanging idle issues that I just assumed were tuning problems but never could quite fix. I hardly drive the car so never worried too much, but lately it has gotten much worse. It starts a surging idle that kills the car when stopping and sometimes even right when starting, both with a/c on and off which all sound like VSS and perhaps O2 issues. After reading a ton of threads I realize my O2 problem is due to me still having my 87 O2 harness so I am already on the hunt for an 89 with the loop on it to take care of that part.

I have read through all the posts I can possibly find and everyone mentions connecting the 2 wires for the VSS and adding pins in the harness for them. I took my computer out and looked at my harness and see that I have no wire in the #3 position, but there is a green wire in the #6 spot. Do I need to just connect one of the VSS wires to that existing green wire and then add the other to the #3 position, or is the green #6 already connected somewhere? I guess I just always assumed swapping the entire 89 Engine harness fixed everything and I was pretty ignorant of the other items.

Sorry for the long post and for rehashing issues that have been talked about to death on here apparently. Just seemed like most post I read referred specifically to when people modified their original harnesses instead of just swapping them. I have been out of the scene for awhile and just kind of catching up again and want to get my car completed correctly after all these years if it isn't!

 

[jrichker]

In order to fix your O2 sensor problem, you need a O2 sensor harness from 88 to 93 5.0 Mustang that matches the type transmission you have installed in the car.

Diagrams courtesy of Tmoss & Stang&2birds

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

In order to fix the VSS problem, you are going to have to run another wire from the VSS to the computer.

O2 sensor wiring harness

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring; http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

94-95 Mustang wiring diagrams
http://www.veryuseful.com/mustang/tech/engine/#95-95Diagrams

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

Mustang 5.0 Lights and Radio schematic, by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif tang/tech/engine/images/mustang88VertTopMotorCkt.gif

 

[87notcher]

Yea, that's a lot of solid information, thanks for sharing. I used the attached 88-91 sensor diagram to locate the wires for the VSS. Is it possible my wires are different for some reason? What is throwing me off is that I have a green wire in my #6 position currently instead of the orange and yellow referenced above. Are you saying I should look at my VSS and see if the same green wire runs the that plug as well and then add just the wire to the #3 location? Should these wires be run from the VSS plug or the speed control box/unit on the drivers side of the dash by the clutch/brake pedal as I have seen referenced?

 

[jrichker]

The same VSS sensor wiring forks off in 2 directions, the engine control computer and the VSS computer.

The wire colors may change at some point. If they do, the most likely place is the VSS computer. Use a DVM or multimeter to check for continuity between the engine control computer and the VSS sensor wiring at the transmission.

If you already have a working cruse control it should be a matter of identifying the two wires on the speed control box/unit that go to the VSS sensor. Then you splice in more wire to connect them to the engine control computer.

 

[87notcher]

That helps a lot, I should have realized the wiring goes in 2 directions from the sensor back.....I will trace them this evening and check continuity to locate what I have versus what I need. Thanks!

 

[Mustang5L5]

Intercept the vss wiring in the drivers kick panel. It's an 8 wire plug. Colors vary.

As for the o2 harness. Grab an 88+ harness wity the jumper, and make sure the pin layout jives with the computer you have.

Keep in mind your former AOD car lacks a harness for the NSS on the t5. Without this, and the jumper on the o2 harness, you basically have no nuetral sensing circuit in your wiring. The jumper on the o2 harness has nothing to do with the o2 sensors. It's just a convienent spot ford chose to jump out the nuetral sensing circuit. This is why your idle hangs. Car doesn't know clutch is in, it trans in nuetral, so it acts as if it has a load

You'll need to change the trans harness and jumper the o2 harness

I made a thread on this a few weeks ago.

http://www.stangnet.com/mustang-for...o-mass-air-02-harness-differences-etc.892849/


The differences in the 1987 wiring is not frequently talked about due to it being a 1 year issue. So it's not fully understood


Sent from my big ass iPhone 6 using Tapatalk

 

[87notcher]

Thanks Mike, not sure how I missed it but that thread is huge, will be referencing that for awhile! I had no clue I had to do anything with the transmission harness at all. I have no switch on my clutch pedal I know, and the NSS on the trans is not plugged in either obviously and I never thought twice about that. I didn't even know there was a different harness I guess. I will start searching for one asap!

With regards to my VSS again, I looked last night and my original post is wrong bc I screwed up and was looking at the EEC harness wrong of course. See the attached pic (#1 is the pin on the top right)....I have the correct green/white wire, and orange/yellow in the correct pin 3 and 6 locations I guess because I used an 89 engine harness. I have also included a pic of one of the plugs for my cruise control module which I believe to be the same wires....I will try to ohm them this evening to check. Is there any way my VSS is already connected due to my 87 having cruise originally and the 89 harness having these wires going to the EEC already? If not, am I looking at the correct wires on the drivers side? You mentioned an 8 pin plug in the kick panel and this plug is neither so im guessing I am incorrect? I had no clue there were so many differences in my 87!

 

[87notcher]

Also, I have an A3M computer if that matters for my transmission harness situation at all. I believe that is a 93 5 speed computer. Will I have to repin an 89 O2 harness differently to accommodate this at all?

 

[Mustang5L5]

VSS is not wired into a Speed Density computer. It's only used for cruise control in the 86-88 cars. That's why cars that don't have cruise control don't even have the VSS. 86-87 cars even have a different trans harness that doesn't even have the pigtail for the VSS.

Usually during the typical MAF conversion, the two wires are added to the EEC harness at the kickpanel, and just run under the dash over to the driver's kick panel where the trans harness comes up from under the car. That harness is the one you'll need to replace if you want to get the proper NSS pigtail that connects to the T-5. This switch on top of the T-5 is wired in Parallel with the clutch switch, so either clutch in, or trans in neutral, sends a signal to the EEC and idle logic changes. According to what you've said, you have none of this, nor the jumper on the O2 harness.

I have pics of the trans harness connector in the other post, where I show the lack of 2 wires for the NSS. Two wires in that harness are also for the VSS, and you can intervept them there and run them to the computer and add then to th EEC connector if you have the proper pins (they are available for sale, although I don' have a source of the top of my head). The VSS tells the EEC vehicle speed, so it doesn't stall out when coming to a stop.

You'll need to grab an 88+ O2 harness as well. Since you changed the engine harness to an 89 harness, then the proper wires should be there. Basically where the O2 harness connected under the MAF, there should be 8 wires connecting to the engine harness. 1987's and early 1988's only get 5. Where they route the NSS wires is still a mystery, but when converting to a MAF computer, it's been observed to have issues when using this 1987 harness, which fortunately you don't have. Once you have the O2 harness with jumper, you'll need to pay attention to where the jumper is, and repin it if it's incorrect.

Once you change out the O2 harness, the trans harness, wire up the VSS, the car should idle properly and run smoother. Some people simply ground pin 30 (the NSS circuit) and fool the car into thinking it's always in neutral. You can do this, but I prefer to do things correctly.

Not a whole lot of people are aware of the differences in wiring of the 1987 cars, nor the need to swap the trans harness for proper operation of the NSS.

 

[Mustang5L5]

Also, I have an A3M computer if that matters for my transmission harness situation at all. I believe that is a 93 5 speed computer. Will I have to repin an 89 O2 harness differently to accommodate this at all?

Best way to tell. Plug the O2 harness in. Removed the EEC. Crank the engine over and test Pin 46 to ground. If you have power, you need to repin in. If there is no power, it's correct.

 

[87notcher]

I cant thank you enough Mike, I am getting excited about getting this thing where I enjoy driving it again. I read your reply several times and are you saying I should still run VSS connector wires from my EEC connector to the new trans harness I will install to get my signal? Im hung up wondering if my 89 engine harness, which already has the correct wires for the VSS pinned into the EEC connector, will get the correct signal from the new transmission harness that I will install anyway? Do you have any idea where the EEC pinned wires in my 89 harness run to currently? I mean at the end of the day though I guess an extra connector wire will not hurt anything anyway just spliced into the existing wires even if they do connect through all the new harnesses somehow lol.

 

[87notcher]

https://lmr.com/item/LRS-8793MTH/Mustang-Manual-Transmission-Harness-87-93-50L

also, it appears this is the correct trans harness correct? Does is have the clutch safety switch plug as well? Is there an additional shorter trans harness needed beyond this? I am thinking about grabbing this instead of scrounging for an old one, and picking up an O2 harness and then seeing if I have continuity between my VSS and the EEC once these are in place. Then can run the connector wires if needed....or are you positive already they will be needed? Sorry for all the questions....im almost there!

 

[Mustang5L5]

Im hung up wondering if my 89 engine harness, which already has the correct wires for the VSS pinned into the EEC connector, will get the correct signal from the new transmission harness that I will install anyway? Do you have any idea where the EEC pinned wires in my 89 harness run to currently? I mean at the end of the day though I guess an extra connector wire will not hurt anything anyway just spliced into the existing wires even if they do connect through all the new harnesses somehow lol.

That's all still an unknown. The trans harness plugs into the dash harness. From there, it's not currently known how the VSS wires run to eventually make it back to the EEC. That would require dismantling the harnesses, and tracing wires and studying wire diagrams. The 87 dash harness may not even be wired correctly with regards to the VSS due to it only being needed for cruise control that year. A lot of these wiring changes came out in 1988 with the addition of MAF on the cali cars.

It's just way easier to run two wires over to the driver's kick panel and tap the VSS there, and pin it into the EEC.

 

[Mustang5L5]

https://lmr.com/item/LRS-8793MTH/Mustang-Manual-Transmission-Harness-87-93-50L

also, it appears this is the correct trans harness correct? Does is have the clutch safety switch plug as well? Is there an additional shorter trans harness needed beyond this? I am thinking about grabbing this instead of scrounging for an old one, and picking up an O2 harness and then seeing if I have continuity between my VSS and the EEC once these are in place. Then can run the connector wires if needed....or are you positive already they will be needed? Sorry for all the questions....im almost there!

Yes. That's the harness.

It does not have the clutch safety switch plug though. Do you have that on your pedal? If you crawl up under the dash, you will find the plug for this. There are two plugs, and a jumper in one of them. They are really buried up there, and when I did my AOD to T5 swap, I really had to hunt for them. But they are there.

When you find them, remove the jumper, and plug both into the clutch switch on the clutch pedal assembly.

https://lmr.com/item/LRS-11156A/86-93-Mustang-Clutch-Pedal-Safety-Switch

I actually didn't have the switch on my quadrant when I did my install, so I used a 5A blade fuse in both plugs to jump them out, until I got my hands on one.

One plug is for the starter, which should be jumped out from the factory. My gut tells me the other is for the NSS circuit. Nothing is in it, because the AOD doesn't need it as it's wired in parallel with the AOD trans harness under the car (the small 1 foot long one that physically plugs into the AOD).

 

[87notcher]

I know I do not have the clutch safety switch on the pedal still, I completely remember removing it back in 03 when I did the swap thinking it would just keep me from starting the car with the clutch in. Pretty sure I have one on an extra pedal assembly I have though, if not ill pick one up as well. At this point I really want this back correct with all the factory systems working together. Im glad to know the wiring for that is already in my harness.....Ill do some digging for them.

Last belabored VSS question now is I assume that the 8 pin connector in the kick panel I need to connect to is the one from the trans harness then where it connects to the dash harness? I wont worry about any of the connections I was looking at anymore that plug into the cruise control module bolted to the left of the pedals correct?

 

[Mustang5L5]

You can tap into the VSS wherever you'd like inside the kick panel. I'd probably prefer to connect to it dash side, in case you ever need to remove the trans harness again. You shouldn't, so ultimately it doesn't mater.

You'll just need to identify which of the two wires go to the VSS.

It's just easy to do because it's right here in the open, vs tucked up under the dash.

I believe the part number for the EEC terminals that plug into the EEC are E7EB-14461-BA. pricing varies on this. I found one site selling them for $11 a pin!