well the truck (1995 f250 4wd auto w 460cid ) starts, reluctantly, stumbles a little and catches its breath. Seems to Idle a bit high and has substantial power loss...still gettin us from a to b though, but needs help. I've replaced the tp and ect sensors. Now when i do a koeo test 23 comes up, and koer test code 23 and 998 which i understand is "limp mode" Crap! All the wires going to the tp sensor seem ok and the sensors resistance test shows fine, voltage on the other hand seems a bit messed up.
12v constant is there and the 5v reference power is there from the signal return wire. I must be doing something wrong cuz when I test to see if the sensors voltage is changing while opening the throttle , nothing. and the 12 constant voltage drops to around 7..I'm sure it's me (not the best mechanic in the world :/ ), so any input is greatly appreciated. Very frustrated...thanks for taking the time to read all this

Oh and the check Engine Light is on...thanks

Tim

 

Try again...............

Your truck should have three digit codes. You will never have a mix of two AND three digit codes....ever.

Could you explain "I must be doing something wrong cuz when I test to see if the sensors voltage is changing while opening the throttle , nothing. and the 12 constant voltage drops to around 7" in more detail and complete sentences?

 

Sorry, after reading that again it does sound a bit strange. Ok, before i go any further i am going to go check the codes again.
Thanks for the reply

 

I apologize, a little, for jumping on your post but you are not making much sense here. Some sensors are supplied with 12VDC others, such as the TPS, are supplied with +5 VDC (nominal) also known as VREF. I read into your first post the 12V supply is dropping to ~7 VDC when opening the throttle. This is practically impossible because the TPS is not supplied with 12 VDC.

 

You were right, its showing code 123(tp sensor higher than maximum voltage) and 998 (limp mode). To clarify, the tp sensor test i did was to jump the signal return wire to the ground wire by " back probing". This is where I got 5v's reference voltage . Also checked ground wire to the12 v source and that checked out good as well. The problem was checking the tp sensor signal voltage to the ecm..According to the book it should read between .5v's (closed throttle) and 4.84 volts (wide open throttle)..This is where I didn't get any reading at all while slowly opening and closing the throttle. The second time I checked the 12v power supply at the tps connector it read 7 volts and the battery was still 12v's and the reference voltage was2.85 v's not 5..

I appreciate your help and hope this shed some light on things.

Thanks

Tim

 

No problem, I don"t mind good criticism, I'm a big guy. i can take it hahaha..Well after reading your answer about tps not having 12v supplied to them the error code 123 seems to make sense.. I was definitely getting 12.5 volts at supply voltage and ground. the wires seem to have been hacked into as well. Who knows what the previous owner or owners) did...

 

The TPS is NOT supplied with 12 VDC. Take a look here for reference: Fuel Injection Technical Library » Throttle Position Sensor (TPS)

Code 123 does indicate the TPS output voltage is above 4.5VDC, assuming it was displayed in the Key On Engine Off tests. If you truly have 12VDC going to the TPS then someone has really hacked that truck.

Code 998 indicates a Hard Fault is present. That can be a devil to track down.

Going on the theory someone has wired +12VDC to the TPS instead of the +5VDC VREF signal I suppose it could trigger a hard fault. Start there, then work you way out of this hole.

Did this truck ever work correctly? When did the problem(s) start?

 

It seemed to work fine when I bought it 1.5 years ago. But then again I'm new to Fords, especially the 460. And it didn't seem to have a whole lot of power and the check engine light just recently came on. And yes the code 123 showed up in both KOEO and KOER. The problems started about 3 weeks ago, it runs rough, erratic idle and stalls sometimes shifting from drive to park and park to drive.

 

Take a look at the info in the link I posted. You really need to verify what voltage is being sent to the TPS as VREF. I cannot believe the truck has ran well for that long if someone had rigged the circuit that way. I think your measurement methodology is leading us astray.