Hi everyone,

Newly rebuilt motor on 2002 Dodge Ram Quad Cab 4x4, 5.9 magnum. Mostly Hughes parts. All new sensors on the throttle body and a tune built for the larger cam and better flowing intake. Replaced the stock injectors with orange bosch 3 hole.

First start up: turned motor over by hand a few times just to get oil moving. Had already drained the old gas from the tank (jumped the relay to the fuel pump) and put in a quarter tank of 91 octane so know fuel pump works and fuel is correct for tune.
Turned key to on and let fuel pressure build, cranked a couple of times and it ran about 5 seconds and then died.
Every attempt to start it since does the same. It will run as long as I keep the starter engaged and then it dies. Pressing the gas doesn't seem to improve the situation.

Testing the wires on the TPS with the key turned to ON: I get 5.16 on the right, 5.11 in the middle and zero on the left (looking at the throttle body from the driver's side). One of these should be 5v, one should be .4 to .9 right? Whenever I test the leads the computer throws the code P0123, but if I clear the code, plug the connector in and turn the key to ON, I don't get a code.
Still, won't run but before I spend more time cranking over a newly built motor I want to be sure I don't have a wiring issue.

Thoughts?

Also, it doesn't have exhaust on it right now, just the headers so no o2 sensors. Would that keep it from running? Was hoping to start it up and drive it to the muffler shop.


Get this code after testing TPS leads

Middle wire

back/right wire

 

If you are seeing 5 volts on two wires with the sensor disconnected, you have a wiring issue somewhere.

 

That's what I'm thinking but can't think where it would be. Don't these wire just run straight to the ECM?

 

you fault code would indicate this also, circuit high would mean the wire is shorted to high voltage, in this case it appears shorted to the 5v supply. Supply current is not genreally spot on, you're within a few tenths so that's acceptable.

Check areas where wire run around corners or look subject to excessive chaffing. Check the connectors themselves. try disconnecting the bulkhead connector and measuring between the wires to isolate which end of the harness to be checking. Id imagine this failure could happen internal of the PCM even.

 

Follow up on this. (Had pneumonia from too much cold air, had to wait until we had some 60+ degree weather to go out and look again. The downtime gave me time to think on things. The catalytic converter was stolen while the truck sat at the mechanic for two years. Whole ordeal but they never finished the job and I'm trying to put it back together myself now.
Anyway,
There was no upstream o2 sensor but there was a downstream sensor that would have been reading good air since there's no exhaust going to it. Wondering if that might be an issue I installed a replacement upstream sensor and the 5v from both lines disappeared. Still no cat or actual flow past the sensors but no error now.
Truck still won't stay running, isn't behaving any differently but the trouble code is gone and the 5 volts constant at the signal wire is gone.
After doing this the system seems to respond to the throttle a little bit when trying to start. manually working the throttle at the TB seemed to more successful than at the peddle but in the end it still won't stay running.
Thought maybe my 8an rails on the 6an system could be starving it for fuel but its holding between 45-50 lbs of pressure the whole time, no drop when trying to start.
Throwing a youtube link I just posted. If you have any ideas please throw them at me. I'll start a new thread with that video if I don't have any luck here.