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Checks to make before installing a reman PCM

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Hi Everyone, I've been visiting this site for a year or two now.  I had what I think was a multiple failure with my Bronco (1993, 5.8L, E4OD, VIN 1FMEU1543PLA48028, PCM F2TF-12A650-CC).  One day, leaving work, it wouldn't start.  There was no spark, traced it to the hall effect sensor in the dizzy; replaced the dizzy...  installed a new coil and TFI module while I was at it.  Got spark, still no start, then I found on this site that the fuel pump running with the key on is bad.  Had it towed home.  Sure enough, the PCM capacitors were shot.  I had them replaced at the local TV repair shop  :)   It then started and ran, but would go into limp home mode when it finally warmed up (open loop to closed loop, I think?!). After a week or so of driving it, having it regularly fail into limp home mode, replacing what I though were associated sensors (ACT, ECT), cleaned all the grounds I could find... finally I got a code scanner, which passed with no faults (???), still the problem ensued.  Finally, the PCM quit with the fuel pump running key on again.  I got a breakout box, have been checking for other issues (I replaced the Idle Air Control Valve this morning...), running through the Haynes manual checks...  (A friend thinks it could be the HEGO, which is only a few months old).  I'm about to install the new PCM, but want to be sure I check all the circuits so that it doesn't fry too.  I'm thinking I should disconnect the old PCM from the harness and look for grounds.  Any suggestions?  Thanks in advance!

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Yo Whipsaw,



PCM capacitors leak mainly due to age.

First here is the EEC IV PIN LEGEND @



CONNECTOR PIN DIAGRAM & How the EEC-IV Computer Connector Comes Apart in case a pin is damaged, badly corroded, or what Ford describes as terminal back-out or missing due to a previous owner or shops big hands @




Before removing current PCM and installing the replacement PCM, disconnect the battery. After installing new PCM, ensure battery is fully charged; its post, clamps, cables strands (especially under first 1/2 " or so under insulation) are clean, tight. Including all grounds from battery to engine block to firewall and to frame.



If the engine control system is not going into closed loop, chances are the coolant sensor or oxygen sensor are not working properly. If spark timing seems to be over advanced or retarded, the problem may be a faulty MAP sensor, misadjusted throttle position sensor or overly sensitive knock sensor. And if nothing seems to work right, low charging voltage due to a weak alternator or poor battery connections may be the fault.



An example of how a high ground or connection resistance can have very serious effects is as follows. This particular case applies to a 2005 Mustang GT, but can easily be extended to any electronically controlled Ford vehicle: consider the case where a PCM is reading a MAF sensor signal of 4.1 V (due to a high ground or connection resistance) when it should really be reading 4.3 V. This equates to a difference in measured air mass of 13%. That is, the MAF will be telling the PCM that there is 13% less air entering the engine than there really is. Let’s say this happens at WOT, where air/fuel ratio is critical not only to performance, but also to engine durability. The result is that the actual air/fuel ratio can go from a safe 12.5:1 to a potentially damaging 14.1:1, just from a 0.2 V change in the MAF return signal!

All PCM sensors, not just the MAF, are affected in a similar fashion, so it is absolutely critical that all electrical connections are solid and that the grounds are reliable. The potential penalty for a bad ground can range from strange drivability issues that are difficult to diagnose all the way to a damaged engine, as in the above example.


All resistance tests should be done with the ignition key in the off position. Having voltage going through the system can return a false reading of excessive resistance. Additionally, it is possible to have a ground that tests OK when the engine is cold, but not when the engine is hot. Heat increases resistance, so these tests should be performed on a warm engine when possible.

To test for an adequate ground circuit in the EFI system for a 1986 to 1995, use a Volt/Ohm meter to check the resistance of the following circuits: DISCONNECT PCM CONNECTOR;

• To verify a proper ground to the PCM, check the resistance from PCM CONNECTOR pins 20, 40 and pin 60 DIRECTLY to the negative side of the battery. Resistance should be no greater than 0.2 ohms.


A weak ground connection can also cause the PCM’s internal reference voltage regulator to function incorrectly. This can be checked at the TPS by checking voltage between the black ground wire and the orange reference voltage wire.


With the key on, this voltage signal should be somewhere between 4.7 V and 5.3 V.


The EEC (computer) ground comes from two main sources, one is the body/frame ground (G104) and the other is the small black wire that goes directly to the negative terminal of the battery (G101/102). G104 goes to EEC Pin #20 and the TFI ICM. G101/102 goes to EEC Pin #40 & 60. This a direct ground to the battery(-) post and the connection on the radiator support is frequently the cause of problems. It can also corrode developing a poor connection at the negative battery cable connection at the battery post.

Location Diagram @


Slow to load

It is on driver side fender liner near hood hinge



TPS Overview & Testing @


TPS Wiring Diagram @



See other diagrams there @ http://www.revbase.com/BBBMotor/Wd

Includes technical service bulletins.



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This is awesome,thanks! I'll go through this. I've gotten the engine compartment grounds, and the one on the rt side frame rail. I have a new MAP, will likely return the O2 sensor tomorrow as the problems somewhat correlate to its install.


You talked about not going into closed loop, would the same cause it to go into 'limp home mode'? Of what I've been able to find, its caused by the pcm getting an out of spec value from a sensor. Unable to determine what senors might be the likely culprits.

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What's your name?


Limp Mode aka "Failure mode effects management (FMEM) is an alternate system strategy in the powertrain control module (PCM) designed to maintain vehicle operation if one or more sensor inputs fail. .


"...Vehicles Equipped with EEC IV

The CHECK ENGINE LIGHT (CEL) will come on while engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on as long as the fault causing it is present. In FMEM mode, the computer is receiving a sensor signal that is outside the limits set by the calibration strategy. In this mode, the computer uses an alternate strategy to maintain reasonable vehicle operation in spite of the fault. The following chart lists the system faults which will turn on the CEL in this mode. The error code associated with this system fault is stored in Keep Alive Memory (KAM). If the fault is no longer present, the light will turn off and vehicle will return to normal vehicle strategy. The error code stored when the light was on was not erased. This code is one of the continuous error codes and can be accessed by running the KOEO self-test. HLOS mode is used when the system fault(s) is too extreme for the FMEM mode to handle. In HLOS mode, all software operations have stopped and the computer is running on hardware control only. The default strategy for this mode has a minimal calibration just to allow the vehicle to operate until it can be serviced.



The engine temperature must be greater than 50° F for the Key On Engine Off (KOEO) Self-Test and greater than 180° F for the Key On Engine Running (KOER) Self-Test. Run it around to heat the engine up and shift thru all gears incl Reverse. Then turn off all accessories/lights, etc. Make sure A/C is off and transmission is in Park (automatic) or in Neutral for a Manual & release clutch. Do Key On Engine Off (KOEO) portion first..."

by me


OK, why no code?

This is by Ryan M.

"...Failure mode is a stand in strategy in the EEC designed to maintain vehicle operation should one or more sensor inputs fail. When a sensor input is perceived to be out-of-limits by the EEC, memorized data from the computers KAM memory will be initiated. EEC continually checks the sensors against its records of normal readings during operating conditions similar to its current state. Hold on that sounds hard! Not really, randomly EEC looks at the past to see if the engine is somewhat where it usually is. If for some unknown reason a sensor is off the charts, it can’t be trusted. So instead of tuning the engine to a possible faulty sensor reading and harming the engine and drive-ability; EEC replaces the sensor reading with a best guess from a past memory.

***This is why unplugging the battery to fix something works against you. Unplug the battery causes EEC to memorize all the sensor data as base line and normal. If it memorizes a bad sensor it will take it longer to call it a liar. Ford did however give EEC a very broad idea of what the sensor should be reading in its permanent ROM memory, so it will catch on to failed equipment sooner..."***

@ http://www.fuelinjectedford.com/page64.html


Also by Ryan;

"...There are main strategies that EEC uses to run the engine; and back up strategies for emissions and diagnostics. In each strategy the master Look-Up table must use the sensors PIP, TPS, ECT, MAF or MAP. Those sensors run the show and which part of the flow chart EEC is directed down. The set values that dictate which Strategy to use and when to use them are different for each vehicle application. This table quickly explanes the strategies control of fuel, timing, and emissions..."

See the Open & Closed Loop Table @ http://www.fuelinjectedford.com/page3.html

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I'm back, I go by Ray...  Yesterday I checked the resistances on as many of the sensors that I could (ECT, ACT, EVP; the Idle Air Control Valve was full of gunk, so I replaced that; checked for grounds using the break out box (I guess shop manuals are needed to get them most out of it, next on my list)).  I decided to exchange the HEGO this morning, extracted that (threads stripped bad) and it was covered with soot.  I exchanged that, and picked up an O2 Sensor thread chaser to re-tap the mounting hole.  After chasing the threads, the new HEGO screwed right in.  I had the old battery out so I pulled the battery tray, painted it with a galvanize type paint and replaced the body clips that held it in (they rusted through).  Installed a new 850 CCA battery.  Then I pulled all the break out box cables out, tried the old PCM once more (still with the CEL and the fuel pump on constant).  Disconnected the battery, pulled the old PCM and replaced it with the Blue Streak reman (interesting... Canadian company, the PCM came from Mexico).  Buttoned it up, connected the battery... crossed my fingers...  and it fired right up!  :D   I let it warm up and the CEL light didn't come on.  Drove it, runs smooth, shifts nice; pulled in the driveway, shut it down, restarted it.  Shut it down again and let it cool off, then drove it again later. I think its a full up round.  Need to run the code scanner in the next few days to see if anything shady is going on behind the scenes. 


Thanks for all the excellent gouge, I found myself thinking through the operating modes as I was driving... 


Still some other projects to hit:

- When I pulled the ACT sensor, it was covered in black gunk, so the intake manifold needs cleaning (any suggestions?  Thinking Gumout spray or SeaFoam, would rather not pull it if I can help it).  Assuming that is from the PCV, is that abnormal?

- The 4WD won't engage, press the button on the dash and nothing happens.

- Need to treat and paint pretty much the entire underside, its rusting.

- The rear defogger only has only one line that heats up, need to get the paint kit and fix that.

- Spark plugs are due.

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Yo Ray,


Here we go...

Intake Air Temp (IAT); (Air Charge Temperature [ACT] prior to 1992)

The intake air temperature sensor (IAT sensor) (12A697) changes resistance in response to changing intake air temperature. The IAT sensor resistance decreases as the air temperature increases, providing a signal to the powertrain control module (PCM) (12A650) indicating temperature of the incoming intake air. On a diesel and MFI engine, the IAT sensor is installed in the lower intake manifold and in the air cleaner tube on SFI engines. by Ford

Could be age, blow-by, etc. There will always be some oil getting through the PCV valve in the form of condensates.

Testing by Ryan M @ http://www.fuelinjectedford.com/page29.html

Pull the EGR Valve and clean it and as much of the Intake Manifold passage.

Removal in 92-96; "...If you plan on replacing yours go buy a 1 1/16 wrench you'll need it to get the egr pipe off the egr itself..."

Source: by Bobby (blue)


Source: by Waltman

carbon between EGR pintle valve and seat holding the valve off its seat. Remove the EGR valve and clean it with carbon remover.



Intake Manifold; I think that you need to enjoy driving your Bronco this winter and clean the manifold in spring. Whaddaya think Ray?



Now the 4x4

This is by Ford;

Four Wheel Drive (4X4) General Information, Operation & Troubleshooting TSB 92-1-8 ... Bronco, F Series & Ranger (partial); Includes Electric Shift On The Fly (ESOF) Troubleshooting; same for 87-96; exc for that in 87; power from Fuse 6 (15 amp) to "ELECT SHIFT CONTROL MOD" WHT-PPL and CB 12 (30amp) to "ELECT SHIFT CONTROL MOD" BLK-WHT; SEE A7 and A8 in the 4x4 diagram, it shows those two wires BLK-WHT as BK/W from SHIFT MODULE to P1 BATTY and and WHT-PPL as W/P to P2




See page 19 for the testshaft, that are for;

Nothing happens (dead system).

2. No range shift.

3. Attempt to shift into 4H from 2H or 4L results in the module clicking and chattering and the system stops in 2H.

4. At start up, the vehicle shifts on its own.

5. Indicator lights don't register the correct information.

6. Shifting on the fly isn't smooth and may require stopping in order to complete the shift.


I guess your issue is #1.

One significant excerpt is "...unbolt the motor and have someone activate a shift again. If the motor doesn't actually turn, it is malfunctioning and must be replaced..."



The 1356 Electric Shift Speed Sensor is in the tailhousing.

Some confuse this with rear axle mounted VEHICLE SPEED SENSOR (VSS).



1356 Electric Shift Motor Typical Failures & Prevention; "...Most units fail because of water or mud intrusion. Carefully inspect motor boot or protective coverings. Be sure connector seals can keep water and debris out. Check wiring harness and connector. Replace or repair wiring as necessary. After installation, periodically select 4-wheel drive mode to ensure operation when needed..."

Source: by CARDONE®



Some brave soul rap the motor with a rubber mallet, while someone presses the button.



1356 Electric Shift Motor Troubleshooting & Repair (travel stops)

Source: by Richard C (Bigric, Money Pit) @


To view narrative, under Richard's name in upper left, click Select Alternate View; clicK Thumbnails + Captions



Electric Shift Motor Replacement by autopartsdirect2you via Alex M @



1356 Electric Shift Motor Connector, Missing Pins, Bronco & Ford; "...Carefully record wire pin positions. Using a suitable tool, release each sensor wire pin. NOTE: Some harnesses may have a center pin as shown in the sample graphic. If there is a center pin, it must also be transferred. Install wire pins in the replacement motor connector in the same position as in the original motor connector until they snap in place. Note that the sensor and harness wire colors must match. Verify pin placement, then replace red locking tab. This completes wire pin transfer. The white pins are the ones for the speed sensor that need to be transferred..."

Source: by CARDONE®




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Just a quick update, the Bronco is running like a champ!  It has been interesting to note the performance improvements as I drove it after the new computer was installed.  I replaced all the stock speakers (at least one was blown) with a new set, sounds great.  I ran the code scanner, the only code it threw was the 'you forgot to hit the gas for the dynamic test' code.  Not too shabby!   :D  No other progress due to weather and time constraints, though I do have new spark plugs on hand for when the opportunity presents itself.  :)

Edited by Whipsaw

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Yo Ray,

Great! You saved boo-koo $$$$ by diy.

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