I have 03 5.7 4x4, I just changed the o2 sensor to a cheap 02 sensor, everything worked great my MPGs shot back up to 16 or so on the high way and i avg. 12 in town oppsed to the old o2 at 9 in town 12 on the high way, well after my second start up with the new o2 it was running kinda rough again.( Bad idle and when im driving i could let off the gas and it would drop the RPMs down below 500 and sometimes die) So i switched back to the old o2 the next day. I made 6 miles out of the 12 mile trip and my truck acted like it was out of gas, stumbling no power, couldnt stay running so i pulled over and shut it off, it barley started back up only to do the same thing so a buddy pulled me home.

Now thats its home it wont even start, it will try but its like it either dosent have enough gas or its putting way to much gas in.

I have another OEM o2 sensor coming in the mail this time the one that made the orginal o2 sensor ( Ive read the cheap ones will not work now i found out with experince) but im afraid since the new o2 sensor started acting the same way the old o2 sensor did that this isnt the problem.

Does anyone have any idea of where to start? Am i on the right track?

 

when you replace o2 sensors you MUST and I mean MUST reset the PCM... Kill power to the truck for 1minute and reconnect, then start the truck and drive it around town.

It probably did not like what it saw for readings and went into Limp mode, which the PCM will do to prevent serious damage to the truck.

It likely did this because you did not reset the PCM which would reset the Fuel Trim Learning, the cheap O2 sensor probably failed too which would cause this.

I would also check the 2nd O2 (usually called UP-Stream or Pre-Cat) O2 sensor and make sure it is reading correctly.

 

I forgot to mention i reset the PCM both times i changed them, sorry.
And as for the First o2 (Upstream) I prolly need to change that as well.
Thanks for the reply maybe since you know now that i reset the PCM youll have another good hunch?

 

the upstream is the most important O2 sensor, as it generally reads the Air Fuel Ratio, the Downstream sensor is generally just a pass/fail sensor to check that the Cat is working correctly.....

I would try replacing both with new ones and resetting the PCM.

Don't forget to work with the Engine 100% cold!

 

I wish i could get a code this sure would help me out alot. But have you ever heard of an o2 keeping a truck from starting?
Cause its weird how good it was running??

 

You've tried the key trick to pull the trouble code?

Starting in Off Position - Turn Key On Then Off (Doors Closed and all Accessories Off)
Repeat that 3 times and turn the key to the on position one last time right after the 3rd repeat

You should then see the trouble codes on the dash.

(someone correct me if I am wrong on the procedure)

 

You have the procedure right, and i have
no codes....

 

Have you tried using the SC 3815 to read the codes?

To be honest if you don't have any codes then I would start checking fuses and trying to get live DTC (Diagnostic Trouble Codes) when you attempt to start the truck.

Next steps would be to check for spark and fuel.

 

I sold the tunner kept the tune lol.
Still no codes today.
And tomorrow is to see if im getting fuel. Is there a easy way to see? besides fuel rail pressure

 

We have had the same issues with our 02 1500 360. The truck died and would only run a short time, We were told to replace the main computer and we did. The truck starts and runs great most of the time but still stalls out. So far we have replaced the exhaust system,o2 censors, main computer, plugs and rotor. It has been put on a computer many times but will not give a code. Where to go next?