5.0 to GT40 upgrade. Which MAF, plugs and coil? Using A9L and 19lb injectors

LawsonP

Member
Sep 20, 2021
16
3
13
60
Kansas
My engine idles rich, yet the plugs show lean. I’ve been reading extensively no one article seems to cover everything. Here is what I think I know.

- 1989 5.0 motor.
- Used GT40 intake and heads from an explorer.
- The heads are ported. Upgraded springs and a mild cam for torque.
- The MAF housing is from a 93 fox body. It is 70mm.
- I am using the 94-95 MAF sensor which I understand to be comparable with 19lb injectors. The part number is F2VF-12B579-A2A
- The intake is 65mm from the explorer.
- I retained the 19lb injectors. I don’t believe I am hitting horsepower issues.
- I am using the plugs and coil for 93 GT.
- the computer is the A9L, which was used through 93.

This motor is in a 1975 Bronco. So not all sensors are utilized, but I have done what I can.

Basically the truck idles very rich. After a 9 hour drive it was running poorly so I changed the cap and rotor, cleaned the MAF with MAF cleaner, and changed the plugs. A man who knows 5.0 said the plugs showed signs of running lean. I also know my gas mileage is suffering. I did unplug the computer for 30 minutes or more to reset the computer after changing the plugs and coil.

So logic is, A9L is looking for 19lb injectors data and other components of that period, cap, rotor, plugs, coil, and MAF for 19lbs.

I haven’t checked my timing yet, or pulled OBD 1 data, but that will follow. I understand 12-14 degrees is the target, and to back off a few degrees if things are running lean.

So at idle I’m rich, and 3,000 rpm I’m lean. Anything I should revisit here? I also sprayed around the intake looking for vacuum leaks, but nothing.

Thank you for your help. I don’t want to upgrade to 24lb injectors as I think that requires the injectors, special adapters. Another computer, and a different MAF. I’m close, runs ok, but not quite there. Also seems a bit flat on power on long grades upwards. Hard to hold speed without giving a lot of gas.
 
  • Sponsors(?)


Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
31,944
13,239
234
Box behind Walmart
www.stangnet.com
I haven’t checked my timing yet, or pulled OBD 1 data, but that will follow. I understand 12-14 degrees is the target, and to back off a few degrees if things are running lean.

Do both of these things before moving on. Start at 12*. Be sure to remove the timing lockout plug when setting. Check fuel pressure at idle.

Start with those codes then work Engine On codes.

It's probably running in limp or open loop.
 
  • Like
Reactions: 1 user

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,526
12,477
224
Massachusetts
- The MAF housing is from a 93 fox body. It is 70mm.
- I am using the 94-95 MAF sensor which I understand to be comparable with 19lb injectors. The part number is F2VF-12B579-A2A


Is this a 1993 cobra MAF housing? The standard 93 maf housing was 55mm. Do you have a pic to confirm?


Those electronics will work fine in the 1993 cobra MAF housing which is the same as the 91-93 thunderbird MAF housing. I run this combo and it should work fine.

But we should conform you do have the correct housing as those electronics in a 55mm housing would cause you to run lean.
 

KRUISR

5 Year Member
Apr 16, 2015
929
353
83
51
How do you know you are rich at idle / lean at 3000 RPM?

I agree with Mustang5L5, that the A9L is looking for a 55mm MAF. 70mm MAF without some sort of calibration factor will give the ECM a reading of less air than actually going into the engine (will give lean condition). Increasing fuel pressure could help to a point (depends what current setting is).
 
  • Like
Reactions: 1 user

mikestang63

SN Certified Technician
Aug 27, 2012
10,612
7,424
204
In the garage
"The MAF housing is from a 93 fox body. It is 70mm.
- I am using the 94-95 MAF sensor which I understand to be comparable with 19lb injectors. The part number is F2VF-12B579-A2A"


if you are using the MAF HOUSING from a stock 93, it is 58MM not 70MM
If you are using a 94-95 MAF SENSOR, that is for a 70MM HOUSING
You need to find a corresponding 94-95 MAF HOUSING that is 70MM in diameter
 
  • Agree
  • Useful
Reactions: 1 users

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,526
12,477
224
Massachusetts
He did say 70mm MAF, didn't he?

He did, but just want to confirm this as it is important and we don’t want to make any assumptions.


Vast majority of 93 Mustangs got 55mm MAF so just want to make sure he has the correct cobra housing


93 cobra housing and 94-95 electronics will work fine. If that’s what he has, then we can carry on.

Didn’t mean to make a big deal about this :shrug:
 

WhiteCobra95

5 Year Member
May 2, 2006
399
66
49
He did, but just want to confirm this as it is important and we don’t want to make any assumptions.


Vast majority of 93 Mustangs got 55mm MAF so just want to make sure he has the correct cobra housing


93 cobra housing and 94-95 electronics will work fine. If that’s what he has, then we can carry on.
You guys are 100% correct. This is the place to start. Mixing the wrong parts together will guarantee endless debug work.
 
  • Agree
  • Like
Reactions: 1 users

LawsonP

Member
Sep 20, 2021
16
3
13
60
Kansas
Is this a 1993 cobra MAF housing? The standard 93 maf housing was 55mm. Do you have a pic to confirm?


Those electronics will work fine in the 1993 cobra MAF housing which is the same as the 91-93 thunderbird MAF housing. I run this combo and it should work fine.

But we should conform you do have the correct housing as those electronics in a 55mm housing would cause you to run lean.
Is this a 1993 cobra MAF housing? The standard 93 maf housing was 55mm. Do you have a pic to confirm?


Those electronics will work fine in the 1993 cobra MAF housing which is the same as the 91-93 thunderbird MAF housing. I run this combo and it should work fine.

But we should conform you do have the correct housing as those electronics in a 55mm housing would cause you to run lean.
How do you know you are rich at idle / lean at 3000 RPM?

I agree with Mustang5L5, that the A9L is looking for a 55mm MAF. 70mm MAF without some sort of calibration factor will give the ECM a reading of less air than actually going into the engine (will give lean condition). Increasing fuel pressure could help to a point (depends what current setting is).
I never got any emails about posts so I’m playing catch-up. Posted photos. The mass air is 70mm and the intake is 65mm from explorer. Sounds like I put the wrong year for the MAF. I’ll see if I can’t track down the source again, but photos uploaded. Thanks!
 

Attachments

  • 0111FA59-7753-418B-8E1C-3ADCDB8EA023.jpeg
    0111FA59-7753-418B-8E1C-3ADCDB8EA023.jpeg
    710.9 KB · Views: 25
  • 3EE44CDC-4BB1-4E48-B6B1-B6E93448EBD7.jpeg
    3EE44CDC-4BB1-4E48-B6B1-B6E93448EBD7.jpeg
    764.3 KB · Views: 26
  • ACEF3CCB-E8C4-45FC-A321-5C3D87B9AED9.jpeg
    ACEF3CCB-E8C4-45FC-A321-5C3D87B9AED9.jpeg
    651 KB · Views: 28

LawsonP

Member
Sep 20, 2021
16
3
13
60
Kansas
How do you know you are rich at idle / lean at 3000 RPM?

I agree with Mustang5L5, that the A9L is looking for a 55mm MAF. 70mm MAF without some sort of calibration factor will give the ECM a reading of less air than actually going into the engine (will give lean condition). Increasing fuel pressure could help to a point (depends what current setting is).
About rich and lean. I am blasted with fumes at idle. And a mechanic I showed the plugs to said they looked lean. I had just driven 9 hours at highway speeds on a C4 with 4.56 gears and 37” tires. No tach, but running high rpm. I’ll hook up a tach to be sure. Sounds like I have a few things to follow up on. Thanks everyone. I’ll see what I can get done tomorrow.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,526
12,477
224
Massachusetts
That is a 94-95 MAF. It works fine with a9x and 19# injectors. I run the same MAF.



However, this is not helping

23EEF67F-79F8-41D7-B659-C573BAC1637F.jpeg
 
  • Like
Reactions: 3 users

LawsonP

Member
Sep 20, 2021
16
3
13
60
Kansas
I checked the fuel pressure and it is running at 33psi at idle.
The spark plugs are AFSF32PM Spark plugs.
The timing was set to about 10 degrees, I bumped it to 12 degrees.
I ran an OBD1 test and have the following results. I reset the computer while I was changing the plugs and coil, so these setting should be relevant.
KOEO
31 - EVP or PFE circuit below minimum voltage car only. EGR valve control sensor fault trucks only ex.V8. EVAP valve control sensor fault. ex.V8
81 - Air diverter solenoid fault, intake air control circuit fault/air injection diverter
82 - Air diverter solenoid circuit fault or supercharger bypass circuit fault. Integrated relay control module.
85 - Cars Only Canister Purge Solenoid circuit failure. Adaptive fuels limit reached - lean. Canister purge circuit failure. Shift solenoid 4/4-4/3.
84 - EGR vacuum regulator circuit failure. EGR vent fault.
95 - Fuel pump secondary circuit fault.

KOER
6 - For whatever reason, the reader seems to think this is a 6cyl engine.
94 - Air diverter solenoid circuit fault.
44 - Thermactor air system fault.
31 - - EVP or PFE circuit below minimum voltage car only. EGR valve control sensor fault trucks only ex.V8. EVAP valve control sensor fault. ex.V8

I do not have an EGR.
I do have a VSS sensor.
Can't think of anything else at the moment.

I might re-run all these settings after I reset my computer again and take it for a short drive so I have absolutely current information.

Thanks.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
36,526
12,477
224
Massachusetts
To be honest, that port wide open could be the source of all your issues. It’s letting unmetered air into the engine under load, which would make it lean under load and then rich at idle.
 
  • Like
  • PlusOne
Reactions: 2 users