I have a 2000 F-150 with a 4.6L and around 101,000 miles on it. About 4 months ago the problems started, Intermittently Bucking at low and fast speeds and stalling out at idle (changing gears/ making turns) p0320 diagnostic code. Thinking it was an automatic transmission issue not an engine issue, I took it to a transmission shop and had all the solenoids replaced. Found out quickly that that wasn’t the issue. Next I:<o></o>

-Replace Crankshaft sensor(CSS) with an Autozone part<o></o>

-Problem subsides for several days reappears and take it to the ford garage instead of just throwing parts at the truck.

-Ford garage replaces DPFE sensor and they say the CSS signal “Looks Weak”<o>:</o>

-Now Low EGR flow code from OBD<o></o>

-Ford garage cleans EGR system<o></o>

-Works fine for several day then same thing again.<o></o>

-I replace the Idle Air Control<o></o>

-Ford garage replaces CSS plug and makes a new harness all the way up to the computer

- Solves the problem for a little while, I take it back to the ford garage.

-They keep the truck for a week and replace the CSS.

-That solved the problem for about a month and now the p0320 code again. Tonight I decided to disconnect the alternator and aftermarket sound to see if RF was the culpruit. RF is not the problem. They only resort I can think of is to replace the computer. Is there any other ideas out there? Thanks in advance.<o></o>

-Ben<o></o>

 

First the tonge lashing.
Why do you guess and throw parts at it before you find out what the 320 code is.
It has nothing to do with the transmission.
Nothing to do with the EGR.
The delay you see after any service is just the drive cycles it takes for the code to be reset.
Shame on the dealer service for acting as they have on your problem.
The 320 code is a detected erratic input to the PCM from the crank sensor.
What could be causing it is a poor connector contact, wiring and it's shielding, interference source, interference suppression caps on the injector lines could be faulty, bad coil with intermittant shorted turns sending trash back thru it's harness etc. Anything that faults a solid signal to the PCM. After all, everything that goes on with the motor is referenced from the crank sensor.
Look at the fault from that point. May be hard to run down but that's what your looking for.
Once you clear the code, it often take more than one drive cycle to reset the code if the problem is still present. It's designed to be this way or you would see the CEL flash a lot for intermittant conditions that take place.

 

I love people like this. I've replaced everything and it still doens't fix it!! Then they bring it to us and we actually perform DIAGNOSTICS on the truck and figure out whats wrong. Thats the difference between techs and parts replacers.....

 

Thanks for the input bluegrass. I will get the o'scope and the multimeter out tomorrow and see if I can hunt down some interferance. I don't know if this helps but the only time it throws the 320 is when it is bucking in drive going over 5mph. When it dies idleing in drive, no pending codes are thrown. Also what is the normal Idle RPM when the engine is warm. Mine is around 550-600RPM's.
-Ben

 

Normal idle on a fully warmed motor is closer to 650+/-.
You could have more than one issue at the same time.
The idle is a set value in program that is added to for various other input conditions
such as cold start, A/C use, added electrical power demands etc.
The crank position sensor signal tells the PCM what the crank speed is then the PCM attempts to correct by pulsing the IAC opening, to bring the crank signal within the program value tolerence.