MAF Upgrade - Lessons Learned Thread

Many know that I have just completed a 408 Stroker build with MAF Upgrade. Seattle FSB 408 Stroker Build

What an experience! After hours and hours of research and many questions it has all finally come together. Although challenging at the time, the fun part was problem solving. Check this out, my tuner believes that I have reached my goal of 500+ Ft/Lbs Torque at the flywheel. He estimates a 30% loss of HP & TQ through the drivetrain to the rear wheels. I more conservatively estimate a 25% loss. The best part is a smooth running engine and no codes!!!

I wanted to share some issues that crept up which created significant learning opportunities. I hope that this can provide some clarification to others that are contemplating a MAF Upgrade. If I am mistaken in any area, please correct me. If you have some personal Lessons Learned with your MAF Upgrade, please post them here for all to see.

A MAF Upgrade is something that requires a lot of research, preparation and problem solving. In my case, my 1990 EFI 5.8L Speed Density E4OD Bronco required a EEC-IV/OBD-I/E4OD/MAF Powertrain Control Module (PCM) which can only come from a 1995 Ford Truck PCM, unless I chose an older non E4OD Ford Mustang PCM which would require a separate Transmission Control Unit (TCU).

No matter which computer you use, a proper "tune", or reprogramming of the PCM, is in order for your specific build. Many will attempt to do a MAF Upgrade on the cheap with a closely matched PCM, such as the 5.8L BIO0, attempting to end up efficient. But unless you provide a custom tune, or install a on-board tuner, you will be settling for "good enough" which may never become efficient.

How did I ever become convinced that I had to have a 5.8L "BIO0 PCM" or a "AKCO Lightning PCM"? With a knowledgeable, experienced custom tuner all can be made near perfect for your application even using a 5.0L MAF PCM. Mail order tune? Blah!!! Get on the Dyno and get the most out of your build!!! A tune can even benefit an aging EFI vehicle, with or without upgrades, to create a much more efficient system (i.e. more power and better mpg).


Here is what I ended up with:

MAF Upgrade

1995 Ford F150 5.0L PCM - WAY1 (F5TF-12A650-JB)
Pro-M Racing 75mm Mass Air Meter
RJM Injection Technologies Truck MAF Conversion Harness
Distributor Mount Gray "Push Start" TFI-IV Ignition Control Module
Single Narrow Band Oxygen Sensor
DynoJet Performance Tune w/Custom Chip

287.85 - Peak Rear Wheel Horsepower
392.11 - Peak Rear Wheel Torque :twotu:
13.00 - Air/Fuel Ratio (Flat @ WOT)

Air/Fuel Ratio - 14.7 Idle, 13.0 WOT
Fuel Pressure - 42 psi with 40 lbs/hr Fuel Injectors
Base Timing - 12.5 BTC
Compression Ratio - 9.546:1




MAF Upgrade - Lessons Learned

HEGO - The Oxygen Sensor (O2 Sensor) assists the PCM in determining if the Air/Fuel Ratio is rich or lean by measuring the percentage of Oxygen in the exhaust. In Closed Loop, (idle/ low load cruising), the PCM continuously adjusts the Air/Fuel Ratio according to input from the Oxygen Sensor. In Open Loop, (acceleration/high load), the PCM ignores the Oxygen Sensor and relies on a programmed Fuel Map to provide a more rich Air/Fuel Ratio. This is how EFI provides economy (Closed Loop) and performance (Open Loop).

Modern Oxygen Sensors are typically Heated Exhaust Gas Oxygen (HEGO) Sensors, having a heating element to quickly bring the Lambda (Oxygen) Sensor into operating range instead of slowly waiting for exhaust gases to heat the sensor. There are 4-wire and 3-wire HEGOs. The only difference is the 3-wire HEGO uses a common ground for both the internal lambda sensor and heater element. Older non-heated Oxygen Sensors have only 2 or 1 wire.

I got caught up in the "you have to install 2 HEGOs with your MAF Upgrade" threads. Furthermore, my Ford Fuel Injection Truck Computer Pin-out Chart indicates a Left and Right HEGO on Pins #43 & #44. So I had 2 new bungs welded in the appropriate locations on my Bassani Y-Pipe and I was ready to go. Then I saw a post on FSB where someone stated that they only needed one HEGO with their WAY1 PCM MAF Upgrade. Totally confused, I decided that it just wasn't clear from all the threads and builds that I have read. So after hours more of researching, I determined the following:

Bronco MAF w/OBD-I (WAY1/VEX1/AKC0) only requires 1 HEGO.
Bronco MAF w/OBD-I (BIO0) requires 2 HEGOs.
Bronco MAF w/Mustang PCM (A9L/A9P) requires 2 HEGOs
Bronco MAF w/OBD-II (1996) requires 3 HEGOs

Look at the wiring schematics in your Chilton or Haynes manual. I have finally figured out that the Ford Fuel Injection schematic only says for a "1994-95 Mass Air V8 Truck". It doesn't say what kind of PCM, I'm left guessing. Clearly a A9L or A9P. If you install a second HEGO with a WAY1/VEX1/AKC0 PCM, the right passenger side HEGO will be in the incorrect location and the left drivers side HEGO will not function at all.


ACT/IAT - This is the Air Charge Temperature Sensor (ACT) or Intake Air Temperature Sensor (IAT). It provides Intake Air Temperature for the PCM to determine proper air/fuel mixture considering the density (temperature) of the air. On Speed Density systems, this sensor is located on the driver's side lower intake manifold. On Factory MAF, it is located in the air intake tube after the filter and before the MAF Sensor. In either location, the same sensor is used.

With a MAF Upgrade, we have been advised to relocate this sensor to the factory MAF location. I believe this is due to the new MAF PCM being programmed to look for different temperature parameters due to the sensors expected location. Clearly the intake manifold will have warmer air than the air filter box.

I did not relocate my ACT/IAT Sensor and left it in the intake manifold. With my custom tune, we programmed the PCM for the specific ACT/IAT Sensor temperature parameters for the intake manifold location. Heh, if you have an on-board tuner or are getting a custom tune, why not? My tuner insists that this will work fine.


TFI - The Thick Film Ignition (TFI) Module, aka Ignition Control Module (ICM), works electronically with the PCM to control ignition timing and dwell. There are two types of distributor mounted TFI ICMs used in Broncos, the gray "Push Start" TFI-IV Module and the black "Computer Controlled Dwell" TFI-CCD Module. These are not interchangeable unless harness wiring modifications are made. Due to the TFI ICMs propensity for heat related failure, Ford relocated a redesigned module in the 1996 Bronco to a remote location. The remote mounted TFI-CCD Module is not interchangeable with either distributor mounted modules.

I was prepared to upgrade my Distributor Mounted TFI Ignition Module from TFI-IV Push Start (Gray) to TFI-CCD Computer Controlled Dwell (Black), but I have stayed with my original "Push Start" TFI Ignition Module. Even though my new WAY1 MAF PCM was designed to be used with a TFI-CCD, I have had no CEL or dwell issues. My PCM receives proper signals and adjust timing perfectly. I currently don't see a problem. What are the differences between the two? Well, lets review...

Both TFI-IV and TFI-CCD send a Profile Ignition Pickup (PIP) Signal to Pin #56 of both Speed Density and MAF Computers.

Both TFI-IV and TFI-CCD send a Ignition Diagnostic Monitor (IDM) Signal to Pin #4 of the PCM - the TFI-IV from the negative terminal of the ignition coil (filtered through a 22k ohm resister) and the TFI-CCD from Pin #4 of the TFI (internally filtered).

Both TFI-IV and TFI-CCD use the ECM Spout Signal from the PCM to control the ignition timing.

The main difference between these two Ignition Modules is that TFI-IV Ignition Dwell is controlled by the TFI in relation to engine RPM and 12v Start Relay Signal. The TFI-CCD Ignition Dwell is controlled by the PCM through the Spout Input. I still don't see a difference, same input just a different way of getting it. Heh, my computer is happy and efficient.

Edit: My engine eventually developed a ping when warm and under load. This was remedied by a distributor upgrade to a remote mount CCD TFI ICM. I am not sure whether this is due to the increased heat from the performance engine or the content of the signal. I would now recommend this upgrade to anyone who is using a PCM that was originally designed to use a Black CCD TFI ICM.


VSS - I was initially confused regarding the Rear Anti-lock Brake System (RABS) Sensor located on the rear differential and the Vehicle Speed Sensor (VSS) located on the Transfer Case. This was largely due to terminology where the RABS Sensor is also commonly called a VSS. This caused significant E4OD shifting problems until I figured it out.

The VSS is critical to the electronic E4OD. It sends an AC Frequency Wave to both the Cruise Control Module, and more importantly to the PCM indicating vehicle speed. In relation to the E4OD, this signal allows the PCM to determine shift points. Additionally the VSS Signal provides input to the Anti-Lock Braking System (ABS) on 1992 and newer Broncos.

1990-1991 Broncos have mechanical speedometers connected to the Transfer Case Tailhousing by cable and gears. The VSS is part of this system and sends a usable AC Frequency separately to the Cruise Control and PCM which controls both engine and E4OD functions. It is important to note that electrical schematics show one VSS wire going to PCM Pin #3 (VSS+) and the other wire going to PCM Pin #6 (VSS-) and what I believed to be a Chassis Ground. Also note that there is a separate ABS Sensor on the Rear Differential solely for RABS Module Input, which also measures vehicle speed.

1992 and later Broncos upgraded to an electronic speedometer connected to a Programmable Speedometer/Odometer Module (PSOM). The speedometer cable and VSS were removed from the transfer case and the ABS Sensor on the rear differential became both the VSS and ABS Sensor. The signal goes through the ABS Module to the PSOM, for speedometer/odometer functions, and is then sent to the Cruise Control and PCM. It is important to note that electrical schematics show one VSS wire going to PCM Pin #3 (VSS+) and the other wire going to PCM Pin #6 (VSS-) with No Chassis Ground.

This is where my dilemma occurred following the Ford Fuel Injection 1994-1995 MAF V8 Truck EFI Harness schematic. The FFI schematic clearly shows (what I believed to be) a VSS Chassis Ground on both Speed Density and 1994-1995 MAF PCMs. Knowing this, we left the 1990 VSS in place during re-pinning as the schematic and instructions indicated and installed a chassis ground on the VSS-. Subsequently, the E4OD would not shift correctly at all. After a week of searching, I finally found that a Chilton's wiring schematic showed no Chasis Ground for 1995 PCM Pin #6 (VSS-). We removed it and it worked! Clearly this was my mistake in not recognizing that the VSS- on PCM Pin #6 was a reference ground which does not include a chassis ground. The schematic ground symbol on VSS- threw me off.

The point is that there is a difference between the 1991 & 1992 Bronco VSS and without it being correct your E4OD will be very unhappy.

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Finally, I would like to say that the information on this site has been invaluable. The informative and entertaining dialogue from those experienced and knowledgeable is exceptional. I hope that I can return the favor to someone else. :thumbup