hey guys, quick question for ya. I have a 00 ram with a 5.9 magnum v8 w/ 104,000 miles and have replaced cap, rotor, plugs, wires, two of the three sensors on the throttle body (cant remember the names) the only one that I didnt replace is the map sensor. also thermostat, o2 sensor (sensor 2) and coil pack. have added a cold air intake and aftermarket exhaust. Heres my question, it is running lean when it is cold but when warms up it runs like a top? so to be more descriptive is that I can start it in the mourning and let it run for two or three min. then it starts to idle rough for about three min or so then cleans right up and doesnt act up again till I shut it off and leave it off for a hour or two. but if i start it in the mourning and take right off it is fine for about 5 min. then it dogs out when I hit the throttle and wont go over 2500 rpm so I pump the throttle and after about 2 or 3 min it is fine. does anyone have or had this problem and can u help by tell me what the problem is? Thanks

 

could be a bad temp sensor .this only happens cold ?it takes more than 5 minutes to warm up so i doubt it would be #1 o2 sensor but you never know .id go with the temp sensor .test your fuel pressure 1st just to rule that out .

 

could be a bad injector or an injector not firing, or the ignition.

You will not know if you are running lean unless you hook up an air fuel gauge

 

usually only happens when cold. and prolly stupid question but how do u check fuel pressure, and where is the temp sensor? thanks for the help.

 

get a fuel pressure gauge, and there is a small valve on the top right side (Drivers side) that has a plastic cap. unscrew the plastic cap and put the gauge on. Then turn the key 3/4 of the way (Do not start it) you will hear the fuel pump priming the system. Read the fuel pressure. Then, after that, turn the engine on and check the fuel pressure.

It should read 49 with the motor running (the gauge will be moving).

 

thanks for the help will check today and let u guys know.

 

forgot to elaborate on the prime test (Leakdown test). When you do the prime, you check the gauge when the key is in the prime position, then turn it off and look at the gauge. there should not be any leakdown (Drop in pressure). if there is, then you are leaking pressure somewhere.

WHen the motor is running you should see the needle "around" 49 psi.

 

That's the pre-cat oxygen sensor failing. Every darn time so far that this symptom has been described, that's the fix.

 

checked the fuel pressure and it was normal. It couldnt hurt to change the other oxygen sensor, so I will try that first hopefully it works if not guess on to the injectors. will keep updated.

 

ok so I havent replaced the pre-cat o2 sensor yet will do it this weekend but this is why I am replying, the last two mournings it has been about 20-30 degrees out and hasnt acted up at all. so im puzzled, should I still replace the sensor?