Hey guys and gals, I'm now at a roadblock in my diagnosis. There's countless threads on these 4.9L engines on this site, yet it seems that only a very few have been successfully completed (of the multiple I've read anyway) with a solution to the original poster's problem.

The sick child is my '91 F-250, and what I'm fighting is the computer I believe, as I only have automatic transmission codes and my truck is factory manual. It idles great, most of the time, but it actually feels like the trans "slips" and the truck stutters/jerks under acceleration intermittently but becoming more frequent every time I drive. Clutch is brand new, less than 1,000 miles, and upgraded to the heavier duty 11" diameter from the original 10". No vacuum leaks have been found, all sensors have been tested and are working appropriately, fuel pressure stays over 50psi constant, no CEL and no other codes than the 7 for the transmission. ICM on side of distributor is new, as well as the O2 and ECT (engine coolant temp) sensors. Now, I do not have a working coolant temp gauge, but the sensor does perform properly and is communicating to the computer.

KOEO Fast Codes are:

637- TOT Sensor high/Open
654- Trans Selector not in PARK
​​​​​621- Shift sol 1 circuit failure
622- Shift sol 2 circuit failure
629- Torque converter clutch fault
626- Trans coast clutch fault
624- Electronic pressure control current high


Oh and my fuel mileage is absolutely horrendous, about 7mpg. With an empty truck and just myself at 140lbs I'm going about 140 miles, or less, for every 19 gallons of gas. I know this is almost definitely a repeat thread, however maybe someone can still provide some advice. Thank you all in advance!

 

Welcome to FTE.

If it is still there, post the calibration code on the door frame as a first step of getting the correct computer.

That will get you closer to a better running truck.

 

It was still there, here is the information on the door jamb stickers.

 

Just for sheets & grins, I plugged that calibration number into the super-dooper, World Renowned FTE search engine & came up with this post:

Post # 19 & 2 others following in this thread (source is absolute):

https://www.ford-trucks.com/forums/1...c-iv-part.html

Currently there is an AEA box at rock auto if you drill down a 91-4.9-F-250 .

But I figure either the ABA manual box or the ADA manual would work too if you found one elsewhere.

I did not see the ATB listed in stock, they had quite a few numbers for that year computer, might have missed it...

 

+1- start with the right engine computer.

Also, once you have it, check your MAP sensor. I have had MAP failures on the 4.9, and
your symptoms sound familiar. I never got MAP codes, but when I looked at the MAP output,
it was not responding in any way that made sense.

hth
t
​​​​​​​

 

So I finally got the computer and installed it into the truck, no improvement. It actually seems like it made the engine run worse. I reckon I'm going to have to go back to square one and recheck all of my sensors again. This thing is driving me crazy. I always stated that she was my "old faithful" and she hasn't let me down yet, but I'm getting nervous now haha...

**By the way, I ordered the computer from a local parts store. Maybe that has something to do with the problem? Also, new symptom has developed, even before replacing the computer. Now the engine will intermittently skip, especially when idling, then go back to all 6 cylinders (although still rough under throttle) firing again after driving for a couple minutes. ICM on side of distributor is brand new, about 300 miles on it, but I know that doesn't necessarily mean anything with almost everything being "made in China" now.

 

So, you can/can't say what computer you put in?

The only ICM you should use is Motorcraft. It may be made in China too, but more likely be correct internally.

 

Quick question, is the color gray on the ICM? I had a similar problem with mine, unfortunately I found multiple items that was bad throughout the process (fuel pump, incorrect fuel press reg, incorrect color ICM, bad p.u. coil, etc) The one item that had me banging my head to find was the signal wire going to the coil from the dist had work hardened over time, the wires internally broke in the insulation right behind the spade terminal at the ignition coil and was making an intermittent connection. At times it would run fine, hit a bump and misfire, or the engine would stop running until I go to diag things, then I would accidentally move the wire bundle enough to make connection, then the truck would run just fine without me find any 'smoking gun' issue, and rinse/repeat.

Moral of the story, our trucks are getting enough age, that when you do your testing on sensors and are not finding anything definitive, don't be afraid to move the wire bundle around to attempt to get a hard fault to chase down instead of an intermittent fault.

 

I ordered the F1TF-AEA series computer. The check engine light has now decided to grace me with it's presence so I will be reading the codes later today and can update you afterwards with the results. Also, I will make sure to examine my connectors a lot more closely and the ICM is gray in color, but the truck was running perfect with a gray one previously installed (at least 9 years, I bought it in Feb 2014 and it's always had the gray one as far as I can remember)all of this.

 

CEL went back off, no codes active by the time I could read them. I do have the part number for the original computer I pulled out of the truck, will attach with post. Did I order the wrong replacement? New computer part number is the F1TF-12A650-AEA.

 

No, that is not the correct computer for your truck with a build date of 8/90.

F3TF is for at least a 1993 truck.