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View Full Version : Gas Mileage sucks worse than usual



wigleym
05-23-2009, 03:18 AM
Setup: 03 Dak R/T with M1, K&N, Air Raid Throttle body, & Mopar Performance Headers.

Usually get 10 MPG but just installed new O2 sensors and sparkplugs (had too since two O2 sensers fouled out and right bank was running rich). Now getting 8 MPG.

Check engine light came on afterward since some moron did the exhaust with three O2 sensers all placed before catalytic converter (downstream O2 sensor wires were cut off before, when corrected, check engine light came on). Currently have one O2 sensor on each header and one on Y pipe after headers but before CAT. No O2 sensor after CAT. Believe stock had 4 O2 sensors.

Questions:
1. Does the 03 have 4 O2 sensors? Does it matter?
2. Will the downstream O2 sensor effect anything if its before the CAT? Not suposed too effect the PCM from what I've read.
3. Any recommedations for getting my gas mileage up?

bad360rt
05-23-2009, 04:47 AM
'03's do have four sensors, but it sounds like you have the configuration wrong. Two are supposed to be pre-cat and two are supposed to be post-cat. The one that you have in the y pipe is probably what's screwing you up. Try taking that one out and see if it improves. You have to leave the two front sensors in the exhaust. I've had my two rear sensors tied to the frame for years with no issues.

RTchas
05-23-2009, 12:48 PM
Funny I just had to do this on the 99. I was getting check engine for downstream o2 (punched cat) so I pulled it out zip tied it to the frame thru in a 16mm plug and no more code! Gota love it..:woot:

Warrior Poet
05-23-2009, 01:09 PM
Setup: 03 Dak R/T with M1, K&N, Air Raid Throttle body, & Mopar Performance Headers.

Usually get 10 MPG but just installed new O2 sensors and sparkplugs (had too since two O2 sensers fouled out and right bank was running rich). Now getting 8 MPG.

Check engine light came on afterward since some moron did the exhaust with three O2 sensers all placed before catalytic converter (downstream O2 sensor wires were cut off before, when corrected, check engine light came on). Currently have one O2 sensor on each header and one on Y pipe after headers but before CAT. No O2 sensor after CAT. Believe stock had 4 O2 sensors.

Questions:
1. Does the 03 have 4 O2 sensors? Does it matter?
2. Will the downstream O2 sensor effect anything if its before the CAT? Not suposed too effect the PCM from what I've read.
3. Any recommedations for getting my gas mileage up?
10 MPG.... Mine was getting something like 17 last time I was home and drove it

BryanRT360
05-23-2009, 02:15 PM
the front two measure your A/F the back two measure the Cats efficiency. Basically the rear sensors want to see a different reading than the front. You could have 02 bungs welded in after the cats or just hang them out in the air like dave mentioned. I also have mine hanging with no codes.

Warrior Poet
05-23-2009, 02:36 PM
No codes, but is there any gain from this "free" mod?

BlueCCRT
05-23-2009, 04:19 PM
Hell the best I get is 16 on the highway, and that is very few mods. My average is like 13.2 overall.

BryanRT360
05-23-2009, 04:47 PM
No codes, but is there any gain from this "free" mod?

yeah no codes:jester:

wigleym
05-23-2009, 07:21 PM
Started off with the Y pipe O2 sensor being clipped off and every once in a while I would get a low voltage code but no other problems. Then all of a sudden I got a Low voltage on two O2 sensors plus a misfire on cylinder 8. Had two O2 sensors replaced (right bank and one on my Y pipe) and then the Cat code came on (since the Y pipe was the downstream). Not sure why gas mileage went down so bad since downstream O2 sensor is not supposed to affect the PCM.

Like the idea of pulling the downstreams, anyone know where to get the plug. Autozone only had 14 and 18 mm plugs and person mentioned needing a 16 before.

wigleym
05-23-2009, 07:27 PM
Does the fact that my 4th O2 sensor (downstream) is missing have any effect either? Know where they plug in at? Maybe the person who did the exhaust just removed it.

bad360rt
05-24-2009, 01:43 AM
You need to have all of your sensors plugged in, but the rear two out of the exhaust. You'll need an 18mm plug for the bung, it's the same size as your oil drain plug. :biggthumpup:

G-Man
05-24-2009, 04:04 AM
Like the idea of pulling the downstreams, anyone know where to get the plug. Autozone only had 14 and 18 mm plugs and person mentioned needing a 16 before.[/QUOTE]

Its 18mm isn't it ?

wigleym
05-25-2009, 01:12 AM
Went to Autozone today and the O2 sensor is larger than the oil plug. Where else can I go to get this plug for the O2 sensor hole?

Any way to tell the difference between the downstream and upstream O2 sensors? Read previous post and you'll see my jacked-up exhaust. Was running rich on right side and think one of my downstream O2 sensors and upstream O2 sensors might be reversed. ALso cant find one of my downstream O2 sensor connections so if you know where they are located please reply. Thanx

wigleym
05-26-2009, 12:16 AM
O'Reilly's AutoParts stocks 18 mm plugs,

Anyone know how to tell the difference between the upstream and downstream O2 sensors?

BryanRT360
05-26-2009, 12:32 AM
O'Reilly's AutoParts stocks 18 mm plugs,

Anyone know how to tell the difference between the upstream and downstream O2 sensors?

the front ones should be further up on the harness than the back ones

Hugh Jassole
05-26-2009, 01:44 PM
'03's do have four sensors, but it sounds like you have the configuration wrong. Two are supposed to be pre-cat and two are supposed to be post-cat. The one that you have in the y pipe is probably what's screwing you up. Try taking that one out and see if it improves. You have to leave the two front sensors in the exhaust. I've had my two rear sensors tied to the frame for years with no issues.

me too, what Dave said

wigleym
05-30-2009, 09:17 PM
OK, I hung the two downstream O2 sensors and plugged the holes. Cleared the catalitic converter code and now the truck sounds like its trying to stall out when sitting still, also now has a code P0174. Any ideas?

wigleym
05-30-2009, 11:30 PM
Since I'm getting a lean code, thats supposed to mean too much oxygen in the exhaust. Since I pulled the two downstream sensors out I'm leaning toward thinking one of the downstream sensors is probably an upstream sensor. Two on the right bank are really close together. Think that might be it?

BryanRT360
05-30-2009, 11:48 PM
sounds hopeful to me. you could also disconnect that sensor and see what code it throws.

wigleym
05-30-2009, 11:54 PM
that sensor originally had its wires clipped off and I occasionally got a low voltage code

wigleym
05-30-2009, 11:56 PM
what code should I get if I disconnect it and it is the upstream sensor, any ideas?

BryanRT360
05-31-2009, 01:48 AM
the front sensor should be further up on the harness closest to the pcm

BryanRT360
05-31-2009, 01:50 AM
I would think one of these...

P0151 (M) 2/1 O2 Sensor Shorted To Ground Oxygen sensor input voltage maintained below normal operating range.
P0152 (M) 2/1 O2 Sensor Shorted To Voltage Oxygen sensor input voltage sustained above normal operating range.
P0153 (M) 2/1 O2 Sensor Slow Response Oxygen sensor response slower than minimum require switching frequency.
P0154 (M) 2/1 O2 Sensor Stays At Center Neither rich or lean condition is detected from the oxygen sensor.
P0155 (M) 2/1 O2 Sensor Heater Failure Oxygen sensor heater element malfunction.

wigleym
05-31-2009, 02:14 AM
Thanks for the help, all looks good so far. Got no codes for now. Pulled the upstream off and got a code 51 so knew it was upstream. Hanging one down stream (which connection is above the transmission which makes no sense because of how the original configuration was). And havent found the other downstream (maybe up under the tranny, but at least its not throwing a code).

wigleym
06-02-2009, 12:45 AM
took it for a drive today and the overhead console is saying I'm getting 5.5 MPG. Is this normal after you mess with the O2 sensors? Seems to drive alright. Actually better than alright and seem to idle better. Was a short trip under 35 MPH. Maybe I need to taker it out on highway? Know ya need to drive a few times when upgrade the Throttle body (which I'm about to do) but not sure on messing with the O2 sensors. Any thoughts?

Ryacuski
06-16-2009, 10:16 PM
I'm the opposite. I had my sensors hanging, and it was throwing a code. So they went back in the exaust system, and BAM..No more codes since.