2004 dodge ram 1500 suddenly getting only 5mpg

[shelby5041]

hi
i have a stock 2004 dodge ram 1500 with 5.7l engine 190k miles...have owned it for 8yrs.

i have always have about 1000lbs in it including bed cap tools etc and typically i get about 12-15mpg in city driving

recently that changed drastically for unknown reason.

the previous 2 tanks gas ive been getting ridiculous 5mpg...26 gallon tank got me about 140miles.

ive done nothing to the truck to cause this...truck runs fine and i dont notice anything diff in how it runs or sounds other than the high use of gas...tires psi are all ok.

what could be the cause of this substantial reduction in gas mileage ?

i have a stock digital avg mileage fuel economy gauge and typically if im driving 30mph on a straight away it will show about 17mpg...but now its showing 5mpg.

update
i used scan tool and showing 2 codes

p0171 new code never had before.

p0137 have had for over 5yrs...i ignored it since i did not notice any performance or mpg issues.

 

[Dean2]

Hole in tank, leaking intake gasket are the first two things I would check. I had an intake gasket go on one of mine, still ran fine but the computer was dumping a huge amount more gas into the mix to offset all the extra air coming in.

 

[shelby5041]

hi

ive got a obd2 scanner that shows data...would any info it provides help find cause?...

 

[Dean2]

If you are throwing any codes that would be a big help. Pull them and look them up along with the diagnostic tree. To be honest, when I answered I assumed you would have already chased down any warning lights and codes.

 

[shelby5041]

no..ive done no troubleshooting...i just decided to investigate this today.

 

[shelby5041]

note..for the past 6yrs ive had a bad o2 sensor code that i just left alone as it wasnt causing any noticable issues...for some reason the faulty o2 sensor code didnt come up today and now have a diff code uve never had prior.

ok..some preliminary info

code read

p0171 code
system too lean bank 1

real data at idle
stft b1 33%
stft b2 13
stft b3 -57
stft b4 -27

ltft b1 33%
ltft b2 -4
ltft b3 -4
ltft b4 -12

stft b1s1 33%
stft b1s2 99
stft b2s1 0
stft b2s2 99

intake manifold absolute pressure 34.0 kpa

 

[Dean2]

34 KPA is about 5 PSI. Should be 18-20 at idle. Error code says Lean condition bank 1, tells you it is sucking more air than it has gas to accommodate. Likely cause, like I said the first time, Intake Manifold Gasket failure.

 

[shelby5041]

.

 

[shelby5041]

Hi dean...update
i do have another code in addition to p0171

p0137
o2 sensor circuit low voltage B1 S2

actual o2 sensor real voltages at idle per scan tool

B1S1 0v
B1S2 0v to .015v

B2S1 fluctuates crazily from .1v to .7v
B2S1 .78v

Is it possible at all the O2 sensor is reason for excessive fuel consumption,?...or do u think an intake leak as u mentioned is the only logical reason?

 

[NCRaineman]

P0171 is a big indicator of a bad O2 sensor. That going along with the other code, good possibility both O2 sensors on bank 1 are bad... pre and post cat. That alone isn't going to kill your fuel mileage... something else going on.

 

[shelby5041]

ok thanks...other than possible intake leak what else could cause this sudden drastic drop in mpg?...i dont see anything disconnected or loose inside engine..air filter looks ok...it does seem this could be an excessive air issue....looking at my scan tool data there are several values way out of tolerance....do any of them pinpoint root cause?

 

[Dean2]

ok thanks...other than possible intake leak what else could cause this sudden drastic drop in mpg?...i dont see anything disconnected or loose inside engine..air filter looks ok...it does seem this could be an excessive air issue....looking at my scan tool data there are several values way out of tolerance....do any of them pinpoint root cause?

Change thee 02 sensor with OEM replacements. It is the easiest part to fix and givem the error codes you have and voltages they need doing. Might also have to fix the connectors. Once you do that clear the codes and see what you get. I am still betting root cause is the intake gasket but no point in digging into that till you have fixed the easier stuff that is also wrong.

 

[shelby5041]

.

 

[NCRaineman]

Sensor one would be pre-cat, sensor two is post-cat. If it were me working on a twenty year old truck I'd go ahead and pull all of them for inspection. Check the wiring and connectors too.

If you're not sure check YT, there will be tons of videos of people changing theirs.

 

[shelby5041]

its possible all the o2 sensors could be orig and truck has 189k...i was thinking same thing...to just replace all since the sensors do a have a limited life..i just wish the cheap aftermarket ones for 60$ for all 4 would work but it does seem the risk may not be worth it...i can get 4 walker o2 fir about 120$...as with all rust belt vehicles removing any parts can be a b i t c h.

 

[Dean2]

If you go the non-OEM O2 sensore route, make sure you can take them back, even after being installed. The 2004s are old enough to not be quite as intolerant of non-OEM sensors but using aftermarket sensors from Napa etc is often the source of problems. The number of 02 sensors will depend on which exhaust system you have. Locate your Catalytic converter and you will quickly find them. Penetrating oil over a few days and heat from a propane torch are likely going to be needed to get them out.

 

[shelby5041]

yes it seems that many unbranded ebay amazon o2 sensors can create problems..and are risky even if returnable because of labor invloved ...i will prob spend little more on walker or ntk or denso...saving 60$ total for 4 o2 sensors using unbranded and then create more headache and time in future is not what i want to do.....i typically always buy cheap aftermarket parts on mechanicals and have never had issues...but from research it seems cheap aftermarket no brand electrical parts are more susceptible to causing issues....my truck has 4 o2 sensors...and as you said the o2 sensors are probably not causing the sudden 75% drop in gas mileage but i need to take 1 step at a time and deal with known problems first.

 

[shelby5041]

hi dean..i was about to order new ntk o2 sensors but the guy on the phone is familiar with cars and when i told him my mileage suddenly dropped to 5mpg he said i may have skmething more serious going on with the dumping of fuel..and changing o2 sensors is not good idea because they could get damaged by the excessive fuel...he doesnt think the bad o2 sensor could affect gas mileage that much....so now im not sure what to do...he was mentioning intake leak (like u said) map sensor maf sensor....im not an auto mechanic.or enthisiast...but.i can certainly troubleshoot if guided but i dont want to spend days on this..should i bite bullet and pay 100$ take to a shop to see if they can find reason ?..im not going to drive truck anymore since it could cause more serious issues with this excessive fuel use condition.

 

[Dean2]

hi dean..i was about to order new ntk o2 sensors but the guy on the phone is familiar with cars and when i told him my mileage suddenly dropped to 5mpg he said i may have skmething more serious going on with the dumping of fuel..and changing o2 sensors is not good idea because they could get damaged by the excessive fuel...he doesnt think the bad o2 sensor could affect gas mileage that much....so now im mot sure what to do

He is correct. Bad 02 sensors cause issues but they are not what is causing the massive fuel consumption. The fact you have zero or low voltage could be the seensor or the connector but you havent even set about checking the existing sensors to see if they are working correctly need coonections cleaned etc.

I have said consistently there is more wrong than sensors and so have others. I still think the most likely cause is too much air caused by a gasket failure. I don't know what else to tell you. Either take it to a shop or start looking for the problem but I can't help you any more than I already have without you starting to do some basic diagnostic and elimintion of potential causes. The fact you initially posted without even checking for codes tells me you may not have a good handle on how to fix stuff. Maybe find someone local to help coach you are take it to a good independant shop.

 

[shelby5041]

hi dean..today i did some reviewing of livestream data...with engine off and key on..all 4 o2 sensors show 1.27v snd manifold absolute pressure is 101kpa...when i start truck from a cold status the manifold absolute pressure immediately shows 133kpa and then drops to 33kpa within few seconds and the b1s1 b1s2 o2 sensors voltages gradually go from 1.27 v down to 0v within a few seconds of starting truck.