TPS and OBD II question

[john112deere]

Long story short, I've had a long-standing, minor intermittent problem with my truck ('97 Ranger, 2.3, 5-speed) that I kinda think is the TPS but I can't get the thing to test out bad and am not ready to start throwing parts at it. Anyway, weather conditions were right for it to have acted up yesterday, so I had my friend help me check the TPS again.

Forgot to hook the TPS connector back on (Don't drink and wrench, guys!) which I remembered when it started bucking about 1/2 a mile out of my driveway this morning. Drove maybe another half mile before I could stop to hook it back up.

I would have expected this to throw a CEL. Is that a bad assumption? Also- since there is obviously some redundancy built into the system (I got out of my driveway no problem, never stalled it out, etc.) why would it buck driving at constant speed on flat ground with the TPS disconnected? I'd expect issues when changing throttle position, but not so much at as close to a "steady" position as I can manage.

Thanks!

 

[Skandocious]

Yes it should have thrown a code. You might have gotten as far as you did because the computer wasn't taking inputs yet because the engine was cold (open loop).

As for the bucking-- I did something similar where I accidentally disable the TPS and it did all SORTS of crazy things, shifting erratically, holding gears for too long (or not long enough), etc. I wouldn't put it past the computer to make it buck on flat ground at constant speed.

 

[CowboyBilly9Mile]

It should have tripped a CEL, any chance the bulb is burnt out or someone disabled it (paint, etc)? As for bucking with the TPS unplugged, it's most likely a consequence of the algorithm used when the system is in limp mode, no biggie in your case. Said another way, since the ECM isn't able to receive data from the TPS it's making throttle position assumptions based on things it can measure, like like vehicle speed and engine speed. There is no redundancy on this one.

 

[john112deere]

I'm gonna have to check that bulb...I KNOW it worked over the summer, because it was throwing the light for an issue with the EVAP canister. And I'm positive no one has intentionally disabled the thing.

(I wasn't real concerned about the bucking; I just thought it was odd. Would have expected the computer to have more trouble compensating when I was accellerating, changing gears, etc. than driving on a level surface is all.)

 

[john112deere]

Verified that the CEL bulb is functional when I drove home today. Came on with the ignition switch on but hadn't yet started the engine...