Engine miss fire doesn’t stay running.

Chasg302 · Aug 11, 2019

I bought a 87 Gt 5spd with an 90 rebuilt motor in it with mass air flow BBK headers trick flow upper and lower intake and 70mm throttle body. Car also has well had an 89 automatic computer in it which is fried for sure. Wires from mass air flow were connected into the plug to computer (ecm). Question is should I remove the mass air flow and get the stock 87 computer also will this work? Or do I have to get a 1990 computer and leave the mass air flow on for the 1990 motor to run properly? Btw 89 ecm is definitely fried. It smells burnt and it got wet.

jrichker · Aug 12, 2019

Mass Air and the original Speed Density computers are not interchangeable without moving some of the computer connector pins around.

Mass Air computer A9L was used between 89-93 in 5 Speed Mustangs.

Chasg302 · Aug 12, 2019

So I will need an A9L for it to work right? They had the mass air sensor tapped into the pins of the plug to the pcm. Or would the car run ok if I got a new 87 pcm and disconnect the mass air?

Chasg302 · Aug 12, 2019

If I was to get the A9L I’d have to tap the wires from mass air into the pcm plug again?

Blown88GT · Aug 12, 2019

Chasg302 said:
So I will need an A9L for it to work right? They had the mass air sensor tapped into the pins of the plug to the pcm. Or would the car run ok if I got a new 87 pcm and disconnect the mass air?

If I was to get the A9L I’d have to tap the wires from mass air into the pcm plug again?

1. You can't use the '87-88 ECU (speed density) unless you still have the 19 lb injectors.
2. You can't use the '87-88 ECU (speed density) with a MAF.
3. There are some wiring mods that might be needed.
4. SD vehicles had a BAP sensor which is likely configured incorrectly.

In order for your or us to proceed, you need to determine exactly what you have now :
1. ECU part number and/or pic.
2. Injector part number and/or pic.
3. MAF part number or details and/or pic.

Chasg302 · Aug 12, 2019

Hi I like I said I do not have a ECM. It had a 89 auto ecm in it which was fried. What I am asking is which one will work everything is stock as far as mass airflow and injectors go.What the person did before was put a reman 90 gt stock motor in a 87 manual. I’m assuming they figured a 89 auto ecm would be compatible. The wires from mass air flow were tapped into the pins on the ecm plug.

General karthief · Aug 12, 2019

Loose the maf, get a bap sensor and a sd computer. Make sure it still has 19lb injectors.
that would be a start.
you should also get a ford assembly manual for wiring diagrams. There may be more wiring issues the previous owner did.

Chasg302 · Aug 12, 2019

General karthief said:
Loose the maf, get a bap sensor and a sd computer. Make sure it still has 19lb injectors.
that would be a start.
you should also get a ford assembly manual for wiring diagrams. There may be more wiring issues the previous owner did.

Chasg302 · Aug 12, 2019

What is an SD computer? Does it not already have a bap sensor besides the map sensor.? Sorry for the questions I’m a chevy guy and the fords ive had were all carburetor car s. I’m not going with a carb on this one. Determined to figure out what some basically dumb ass did to this car. Also to tell you how stupid they are first thing was timing was 180 out.

Steel1 · Aug 13, 2019

SD = Speed Density computer, this style would have come with your 87 non maf car.
Speed density cars came with a bap sensor mounted on firewall, no map sensor.

Red50Fox · Aug 13, 2019

Hello, I only know enough to keep myself in trouble but... From LMR and CJPony, they it is different from what you mentioned above. Just looking for clarification.

Applications:
- 1986-1988 5.0L MAP Sensor (Manifold Absolute Pressure Sensor)
- 1989-1993 5.0L BAP Sensor (Barometric Air Pressure Sensor)
and
Manifold Absolute Pressure Sensor for your 1986, 1987 or 1988 5.0L Mustang or a Barometric Air Pressure Sensor for 1989, 1990, 1991, 1992 or 1993 5.0L Mustang

Steel1 · Aug 13, 2019

Red50Fox said:
Hello, I only know enough to keep myself in trouble but... From LMR and CJPony, they it is different from what you mentioned above. Just looking for clarification.

Applications:
- 1986-1988 5.0L MAP Sensor (Manifold Absolute Pressure Sensor)
- 1989-1993 5.0L BAP Sensor (Barometric Air Pressure Sensor)
and
Manifold Absolute Pressure Sensor for your 1986, 1987 or 1988 5.0L Mustang or a Barometric Air Pressure Sensor for 1989, 1990, 1991, 1992 or 1993 5.0L Mustang

You're correct my bad.....that's what I get by responding before I've had my coffee!

Chasg302 · Aug 13, 2019

Steel1 said:
SD = Speed Density computer, this style would have come with your 87 non maf car.
Speed density cars came with a bap sensor mounted on firewall, no map sensor.

Chasg302 · Aug 13, 2019

so this will work with my 1990 motor correct?

Boostedpimp · Aug 13, 2019

Red50Fox said:
Hello, I only know enough to keep myself in trouble but... From LMR and CJPony, they it is different from what you mentioned above. Just looking for clarification.

Applications:
- 1986-1988 5.0L MAP Sensor (Manifold Absolute Pressure Sensor)
- 1989-1993 5.0L BAP Sensor (Barometric Air Pressure Sensor)
and
Manifold Absolute Pressure Sensor for your 1986, 1987 or 1988 5.0L Mustang or a Barometric Air Pressure Sensor for 1989, 1990, 1991, 1992 or 1993 5.0L Mustang

Yeah two different part numbers but they are basically the same.

if you have speed density you have to hookup the vacuum port on the sensor making it a BAP. If you have mass air you disconnect this vacuum port and leave it open making it a MAP

Sounds like you already have the car converted to MAF and have everything in place just need a computer. I would look at the o2 sensor harness and verify which one is in the car auto or manual wiring. From there you then start the painful process of locating a A9L or A9P or one of there variants for a decent price because if you have the wrong harness it will fry the ecu

General karthief · Aug 13, 2019

For once I didn't start the 'misinformation train', I just got on board and road all the way to stupid town!
it's easy to get BAP and MAP turned around. And to muddy the waters even more the MAP sensor can (allegedly) be used as a BAP sensor just by removing the vacuum source.
those two sensors are not exclusive to 5.0 mustangs, they were also used in 5.0 cars and trucks for many years and rarely go bad.

Chasg302 · Aug 13, 2019

Boostedpimp said:
Yeah two different part numbers but they are basically the same.

if you have speed density you have to hookup the vacuum port on the sensor making it a BAP. If you have mass air you disconnect this vacuum port and leave it open making it a MAP

Sounds like you already have the car converted to MAF and have everything in place just need a computer. I would look at the o2 sensor harness and verify which one is in the car auto or manual wiring. From there you then start the painful process of locating a A9L or A9P or one of there variants for a decent price because if you have the wrong harness it will fry the ecu

General karthief said:
For once I didn't start the 'misinformation train', I just got on board and road all the way to stupid town!
it's easy to get BAP and MAP turned around. And to muddy the waters even more the MAP sensor can (allegedly) be used as a BAP sensor just by removing the vacuum source.
those two sensors are not exclusive to 5.0 mustangs, they were also used in 5.0 cars and trucks for many years and rarely go bad.

Ok the car has a 90 motor in it with a MASS AIR FLOW ON IT.

Chasg302 · Aug 13, 2019

I just want to know if I disconnect the MASS AIR FLOW and put a BAP on it with a 1987 gt manual ecm (sd computer) will this application work. Or do I have to get a 1990 computer and jump the mass airflow sensor into the plug

Chasg302 · Aug 13, 2019

Chasg302 said:
I just want to know if I disconnect the MASS AIR FLOW and put a BAP on it with a 1987 gt manual ecm (sd computer) will this application work. Or do I have to get a 1990 computer and jump the mass airflow sensor into the plug

Ok I know there is a MAP sensor is there a BAP too?

General karthief · Aug 13, 2019

Ok, let's help you get things straightened out.

How To Install Fox Body Mustang Mass Air Conversion (86-88)

Easily install your Fox Body Mustang mass air conversion with the help of Late Model Restoration's installation instructions!

lmr.com

This should show you if your maf conversion is done correctly.
I would say to keep the maf if you can.

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