For a 1990 F150, I6/300/4.9 liter, 4x4, standard transmission:
After a second visit to the garage, my truck still runs like crap....this is getting expensive!

Here is what is going on:
When driving the truck at low speeds, (25/30 mph), the motor sounds like it is missing when I lightly accelerate. When the missing occurs the truck feels "jumpy" and jerks a lot...to the point that you would think the truck is going to fall apart! It runs great when first starting it, (cold or hot and at idle and when giving it gas in neutral.)

I am stumped after the following maintenance has been completed:

New spark plugs (with proper gaps set), new spark plug wires, new fuel filter, new distributor cap and rotor, new water pump, belts, and thermostat. The EGR valve was checked and it seems to work fine.

The mechanic told me that the battery died on him during testing and that I should replace it since it only had 300 cranking amps left. Prior to installing a new battery, the mechanic read codes #556 (fuel pump relay primary circuit failure) and #527 (KAM failure.) He advised me that the old (dying battery) might have a caused the ECU (electronic control unit) to affect the mix of fuel and air, thus causing the issue I have. I was told to install a new battery and drive it both in town and on the highway during the weekend so that the ECU could reset itself and hold onto the proper settings, (which couldn't be maintained by the old/dying battery.)
I was advised that if this didn't fix the problem, that I would likely need to replace the the ECU (electronic control unit), also known as a PCM (power control module)....does any of this make sense / has anyone had the same problem?!

Thanks for your advice!

Nabor J

 

have you checked the trans at all?

and the ecu/pcm if you dissconect the battery it will go back to factory settings in my experience.

 

Regarding the transmission, what could it be?

I had the truck "gone over" by a mechanic and they said that it looked solid, along with the transfer case, etc. After the work done so far, I'm guessing that the ECU has gone bad, but time will tell. What's most frustrating is that the truck is running WORSE since doing all the work!

FYI: The truck has only 61,000 original miles and isn't a "beater". It was driven only 1,000 miles each year since 2005 and originally was a phone company's truck for service calls.

 

Ok well if the ecu is bad the check engine light would be on and would not be able to pull codes at all i know because my ecu was in fail safe mode.

the clutch can cause the jerking you described. you can always get a second opinion after you do what the mechanic said to do.

 

Do you have an area where you can go downhill in neutral, will help eliminate drive shaft, diff. and u-joints.
Or just put in nut. after getting up to speed.

 

Rookie-
What should I look / listen for when going downhill as you described? BTW: I replaced the u-joints as well and the drive shaft, etc are in great shape.

TheCollector-
How would the clutch cause my issue?

In addition to how I described the issue.....when getting on the gas really hard, the truck jumps / sputters and then takes off and runs smooth....all of this is at low RPM's and especially bad in gears 2 and 3 and going 25-30 m.p.h., but it sputters a bit in 1st and 4th as well. Again, it's really odd how the problem got worse after doing all of the recent work!

*This forum is great, thanks for everyone taking the time to post!

 

Did he bother to check the fuel pressure?

 

No fuel pressure check yet.....would this really cause these issues?

 

yes it would most mechanics know to check the fuel filter and pressure if its the old efi systems if that's off or low it can cause hesitation and so on.

as for the clutch I was thinking about the jerking you described.

 

Do a compression check. A bad valve can cause it to run like that too. Fresh gas ? maybe water in the gas?