So the old truck has been acting up for the last few months. I've got it to run real good up until a few days ago. Now it shifts extremely hard on the 1-2, and has a horrible hesitation/stumble issue.


Its hard to explain, but it feels like your driving a stick, where if you accelerated from a stop in first then went directly to fifth. It bogs way down and sounds like its pinging or detonating. If you give it some gas so it'll downshift if picks itself right up but will return to bogging again.


I'm also having issues where the truck either wont stay running with the MAP plugged in, or it wont idle steady. I had run the truck with the sensor unplugged and it ran fine but now I'm back to having issues. The previous owner wasn't kind to this truck so its hard tracking down whats wrong.


I haven't had the chance to look at it (its been freezing) but I'll dig into it tomorrow. Any ideas on where to look? I'll pull the codes but I know theres going to be one for a map sensor.


Thanks guys.

 

Are you on Transamcountry? Same avatar?

 

You know it! Its funny seeing another T/A guy here


Any ideas?

 

I should also mention that it started this after going down an extremely rough road. I don't know if that played into it?

 

Might want to list engine, drivetrain, etc., etc. Kind of hard to diagnose otherwise because (just to use one example) diesel troubleshooting isn't going to be terribly useful if you have a gas truck.

 

Ah yes. I was tired when I wrote that and knew I left something out!


Its a 94 351 Auto. I've recently done intake gaskets, new TPS and IAC, and replaced the MAP with another used one I had laying around. The truck doesn't want to stay running with the MAP plugged in, so would this indicate a vacuum leak?

 

No, not at all. Check for codes before going any further. Without the MAP sensor the computer is defaulting to base parameters, it also is running the transmission in limp mode that's why you have hard erratic shifts.

 

Ok. I'll pull the codes tomorrow and report back. I've had the MAP unplugged for a while now and it shifted fine before.


I have a feeling I'll be writing down a lot of codes

 

List the codes by number and during which tests they were displayed ( KOEO or CM ).

 

What do you mean by CM?


I know KOEO.

 

Continuous Memory aka Historical Memory (stored codes).

In many cases the definitions change depending on when they are displayed.

 

So I pulled the KOEO codes:
114
116
122
126
332
636


I plugged the MAP back in after I started the truck and it actually ran good. I also shut it off and restarted it and it seemed fine. The CEL shut off also.


I don't know if this is the case with Ford products, but I know with some GM's if the coolant sensor doesn't read it can cause funky idle issues and stumbling. Im sure you guys would know if that is causing any issues or not.

 

114 KOEO: ACT out of self test range 0.3 to 3.7 volts
116 KOEO: ECT out of self test range 0.3 to 3.7 volts
122 KOEO: TPS circuit below minimum 0.6 volts CM: TPS circuit has intermittently failed below minimum 0.6 volts
126 KOEO: MAP/BP sensor out of self test range 1.4 to 1.6 volts CM: MAP/BP sensor out of self test range 1.4 to 1.6 volts
332 CM: EGR valve opening not detected
636 KOEO: TOT sensor voltage out of self test range CM: TOT sensor voltage out of self test range

Codes 114, 114 and 636 are typically caused by not warming up the engine and transmission before running the KOEO tests. Code 332 is a CM or KOER code.

I assume you had the MAP sensor disconnected when you ran this set of tests? If it was plugged in then you may have a bad MAP or connection to the PCM.

The code to investigate is the 122 TPS code. Measure the closed throttle TPS output with a meter, Key On. It should be between 0.6 to 1.0 VDC. Slowly open the throttle, watch the output for dips/peaks as it rises to Wide Open Throttle (~4.5 VDC). If that is good then you need to trace the wiring back to the computer PCM.

Warm up the truck then re-run the KOEO tests and CM display. The temperature related sensor codes should go away. If not you have more investigating to do.

For reference: Fuel Injection Technical Library

 

I did do the test with the MAP unplugged and the truck cold. I'll test the TPS and report back. I replaced it about two months ago, so I would imagine if something is wrong there it'll probably be in the harness itself.


Thanks for the help so far!

 

I ended up taking the truck around the block and it ran 100x better with the MAP plugged in. It shifts smoother and idles at 600rpm in gear. Whats weird is its not doing the idle surge when in park after its warmed up now. It also seems to stay smooth off of take off.


What would cause it to do it one day, then be fine the next?


I pulled the codes again now that the MAP is hooked up and it still throws 113 114 332.


I tested the volts going to the TPS and its 5v. I cant get a reading out of the sensor itself. How do you usually go about getting the reading? Just pierce the wires with the meter?