4.0 OHV, bad ECU/PCM?

[Bobby'sFFRanger]

Hey everyone;

So after all my bluster and questions about dropping a 302 into my ‘94, I let the nay-sayers in my world convince me to just put a new 4L in it.

I picked full reman from S&J in WA, and had a local shop swap it. It’s been nothing but trouble. After the time and money spent, the new motor had an apparent lifter tick. After swapping a few lifters, the shop sent it back to S&J who swore there was nothing wrong with it, but redid the top end anyhow.
New motor: version 2 came back, no tick. But immediately, there are ignition issues.

At first, it would start fine but idle rough and low. Kinda wiggle around at 550. Assuming stuff got bumped and mangled during the work, I replaced the IAC, MAF, EGR.
From there, it ran smoother, but idled high. Hung out at around 1100, but every other start, especially when it was warm, it would struggle like before at idle. After about 15 seconds it would smooth out, but like I say, would land at 1100rpm.

So I go back to the shop, they search around for vacuum leaks, rebalance the throttle body and idle screw, patch a few small vacuum leaks (in the intake-to-throttle body boot, which is impossible to replace, it seems).
Idie was returned to around 750-800, but with a slight shimmy at idle. And still, it will occasionally start, sputter, fight to idie at around 500, and I can hear a minor miss every few seconds.

At this point, I’ve spent many months and many thousands of dollars making everything in my engine bay new. The old 392,000 motor ran smoother.

I’ve tried searching for a fresh PCM (manual, 4.0, 2WD, EGR) but no luck so far. Is this a bad computer? Is it possible my firing order is wrong? I can’t help this feeling that the shop that does the work may not be doing a great job, they see “OBD1” and an old truck, kinda blow my issues off as “runs pretty good for its age”. Which pisses me off.

My code reader shows good codes (111, 10) when I use it, CEL comes on at startup, and this isn’t even the original PCM (was replaced in 2021). Would all that still happen if computer was bad?
If it’s the firing order, why would the truck run well under power? These are pretty much idle & startup issues.
Any help greatly appreciated.

 

[gaz]

@Bobby'sFFRanger ,
The last rebuilt OHV 4.0l I got ahold of, turned out the "builder" installed the head gaskets upside down and installed used heads without addressing the valves, valve seats, valve guides, valve seals, pushrods or rockers???

I feel for you having to deal with a warranty and those who do not desire to back it; keep on them with no love before it's gone.

If all you need is your PCM updated, that is awesome . You mentioned the firing order, in case you don't have a manual to reference.

 

[DRanger024]

Mine has done the same thing since I put a 4.0 in it. I always chalked it up to having the wrong injectors in it but every once in a while, it will start and run like normal. I’ve just gotten used to it to the point it’s normal.
I do have another engine going in spring and plan to re-loom the engine harness at that time for inspection as well as make new ground straps. I think I’m missing the strap from the drivers side head to the firewall.

 

[Bobby'sFFRanger]

@Bobby'sFFRanger ,
The last rebuilt OHV 4.0l I got ahold of, turned out the "builder" installed the head gaskets upside down and installed used heads without addressing the valves, valve seats, valve guides, valve seals, pushrods or rockers???

I feel for you having to deal with a warranty and those who do not desire to back it; keep on them with no love before it's gone.

If all you need is your PCM updated, that is awesome . You mentioned the firing order, in case you don't have a manual to reference.

Thanks for your reply.

I already raised hell the first go-round on this new motor with S&J Engines; they transported it back to Spokane (from Seattle) and, according to them, replaced the top end part by part. I'd like to think that after the yelling and threats and money spent on transport and time, they would've simply decided to do everything right and be done with me.

Assuming the motor is good to go, this is an engine control issue. I've gone down the line of emissions control hardware, all seems to be functioning and fresh and sending/receiving power.

 

[Bobby'sFFRanger]

Mine has done the same thing since I put a 4.0 in it. I always chalked it up to having the wrong injectors in it but every once in a while, it will start and run like normal. I’ve just gotten used to it to the point it’s normal.
I do have another engine going in spring and plan to re-loom the engine harness at that time for inspection as well as make new ground straps. I think I’m missing the strap from the drivers side head to the firewall.

Thanks for the reply;

I too have had my harness nightmares. After 30 years, the original harness, in near-all areas, was exposed and eaten through. Many months and moneys spent hand wiring new harness sections, as finding a good new harness for my exact truck was also near-impossible.
Apparently when my dad bought this 4.0 2WD 5-speed, he didnt know he'd be buying a fairly rare combo. Finding ECU-specific anything for this truck is really hard.

That said, my two theories over it's current runability may prove the same thing, yeah? Can a bad ECU/PCM create an incorrect firing sequence? And would either a bad computer or a bad electronic firing order allow it to run at 85% most of the time? Or would it simply die/never start?

 

[Bobby'sFFRanger]

Also, if anyone has ECU/PCM experience:

I know the code for a Ranger ECU breaks down by vehicle. 1994 = F4, 7F = Ranger, 12A650 = ECU/PCM (part), <last three> = software version (denoting 4wd or 2wd, motor size, transmission, etc).

Ford dealer locally says my ECM number is: F47Z-12A650-CJA
But everything online says a 1994 Ranger is F47F. Is there a compatible conversion here I'm unaware of? I have found ECM's stating both 7F & 7Z, but nothing acknowledging why the two codes exist and if they differ or not.
Is it possible they're different parts manufacturer designations for Ranger?

 

[DRanger024]

The only thing ECM related that’s made a difference with my truck was the level of degradation in the electrolytic capacitors on the board. I have two ECM’s that I’ve repaired and the one that had burned traces (that I fixed with a jumper) runs better than the one that didn’t

 

[RonD]

1994 ECU needs new capacitors, regardless

No, they wouldn't effect spark, but do effect fuel pump running and air/fuel mix, so.....................

4.0l OHV is a simple engine, so unless it has bad valve train or bad valves after a rebuild it should run just fine
Do a compression test to be sure

1994 ECU uses Batch fire fuel injection, not sequential, so ECU only has 2 wires for injector control
Each wire opens 3 injectors at the same time, so every rotation of crank shaft 3 injectors open, then the other 3 on the next rotation
Common pattern for V6 Batch Fire wiring is ODD and EVEN
i.e. 1, 3, 5 open then 2, 4, 6 open
So both sides of the intake have air/fuel mix that can be sucked into the next intake valve that opens on that side

1994 ECU doesn't care about 2WD or 4x4, or regular cab or super cab
So in this case it just needs to be for a 4.0l with manual trans

In 1994 there were ECUs for Calif sold only Rangers, these 4.0l will have an EGR system and a Cam sensor, so if you do not have those then its a regular Federal 1994 4.0l ECU that you need, and they are common
1993 or 1994 ECU will work the same in either year
So F37F or F47F starting numbers

Its good to Match the last 3 or 4 digits but as long as its from/for a 4.0l with Manual trans it will work, plug and play(with new capacitors!!!)

 

[Bobby'sFFRanger]

1994 ECU needs new capacitors, regardless

No, they wouldn't effect spark, but do effect fuel pump running and air/fuel mix, so.....................

4.0l OHV is a simple engine, so unless it has bad valve train or bad valves after a rebuild it should run just fine
Do a compression test to be sure

1994 ECU uses Batch fire fuel injection, not sequential, so ECU only has 2 wires for injector control
Each wire opens 3 injectors at the same time, so every rotation of crank shaft 3 injectors open, then the other 3 on the next rotation
Common pattern for V6 Batch Fire wiring is ODD and EVEN
i.e. 1, 3, 5 open then 2, 4, 6 open
So both sides of the intake have air/fuel mix that can be sucked into the next intake valve that opens on that side

1994 ECU doesn't care about 2WD or 4x4, or regular cab or super cab
So in this case it just needs to be for a 4.0l with manual trans

In 1994 there were ECUs for Calif sold only Rangers, these 4.0l will have an EGR system and a Cam sensor, so if you do not have those then its a regular Federal 1994 4.0l ECU that you need, and they are common
1993 or 1994 ECU will work the same in either year
So F37F or F47F starting numbers

Its good to Match the last 3 or 4 digits but as long as its from/for a 4.0l with Manual trans it will work, plug and play(with new capacitors!!!)

Thanks for this;

Helpful to know the ECU doesn’t control firing sequence much.

But, as I say, the Ford dealer clearly said my first-four code was F47Z, rather than F47F. Online, there are units for Rangers with the Z designator as well as with the F designator. Do you know what this inconsistency is?

And finally, my truck was bought brand new from Sunland Ford in Victorville CA = EGR. So that makes my ECU hunt a lot harder. Most ECUs offered for sale don’t say if they’re Federal or CA emissions units, so I gotta use the full code.
Which brings me back to the Z or F question, as I’m finding F units that match my truck, but Z units with different EGR/no EGR possibilities.

Like everything on this truck, it’s harder than most would expect.

 

[RonD]

F or Z is the Department at Ford that designs and/or takes care of that year's part, in this case the Ford Electronics departments, and there were two designations, but same thing
Good read here on Ford part number prefixes: https://www.fordification.com/tech/partnumbers_overview.htm

E9 = 1989
F0 = 1990
F3 = 1993
F4 = 1994
F8 = 1998

It can also be F3TF, or F4TF, or Z
7 = Ranger(or Mazda B-series starting on 1994)
T = Truck
interchangeable in earlier year Rangers but usually 7 in 1993 and up

Actual ECU part number is 12A650 but used for EVERY engine computer in every model Ford and still used for a 2023 ECU, so it basically meaningless to match, lol

 

[Bobby'sFFRanger]

Oh wow, this is great info!

I cant tell you how valuable this information is. Thanks so much Ron! Lastly, if I wanted to verify the software version of ECU my truck calls for (the parts guys seemed a bit lazy, at first told me he couldn't find that info then threw the CJA number at me), is there a place I can input my VIN and get that number?

I wish people selling these would more clearly outline 1994, Ranger, M/T, 4.0, CA emissions (EGR), but alas...
And would you suggest a used unit or a reman one? I know the components on a reman are newer, but I'm finding more and more that the workmanship on remanufactured parts is spotty at best. Humans = Errors. OEM = Best.

AND! What does "HUD0" mean in these codes? It seems to be shown on some for sale...

 

[RonD]

Ford never publish the suffix codes meaning or a cross reference and they don't mean the same thing every year
Like CJA in 1993 might or might not mean the same thing in 1994

No, the VIN would only tell you engine size not ECM used
Ford would have had that but hard to get that info from them if they even have it after 15 years

Best cross reference I have found is at https://www.car-part.com/

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