eco giving 19mpg

[darksobsession]

lately my gas consumption has got down to 19mpg, much of this was freeway.

i never calculated the mpg before, but now i'm filling it up more often, so i took notice and started keeping track.

mods i have are pacesetter header, cai, larger wheels/tires

took it in to the dealership and they didn't find anything wrong.

got it back no charge and replaced the spark plugs and fuel filter myself. i have called the dealership trying to make certain they tested the iat sensor, but they ahven't got back to me yet.

any idea what else could be wrong w/it?

[AbHeLlRaZoR]

Yikes! I don't know what could be wrong with it, I get 38 mpg in higher elevations (yes that is MPG and not KMPL) I would suggest checking tire air pressure.

[colonel6632]

i get the same as abhelirazor (your name is too hard to type, nevermind. reread it, makes a little more sense now) and better yet at times.

check your normal things. tire psi, spark plugs, air filter. if those are all good. maybe try replacing your upstream o2 sensor. that has alot to do with mpg.

also try seafoaming your engine.

hopefully this helps you out

[AbHeLlRaZoR]

i get the same as abhelirazor (your name is too hard to type) and better yet at times.

check your normal things. tire psi, spark plugs, air filter. if those are all good. maybe try replacing your upstream o2 sensor. that has alot to do with mpg.

also try seafoaming your engine.

hopefully this helps you out

Yes do those for sure, maybe even get a compression check.

Colonel and anyone else on the site can just call me Evan.

[darksobsession]

tire pressure and air filter ok

[TheEdgeofSanity]

maybe a clogged fuel filter? also, how do you drive your car? keeping it below 3K when accelerating and using cruise control means all the difference between 20 mpg and 29 mpg for me with my car.

[darksobsession]

just changed the fuel filter when i got it back from dealership, along with my plugs.

driving the same way i've always been, but having to fill up a lot more, so def some kind of prob.

[colonel6632]

clogged fuel filter shouldn't really affect mpgs. might affect power more, and the way the car runs

[wrestlingandrunning]

clogged cat?

[HazMatt24]

mine did the same thing too after I put in the WAI and exhaust. I just thought it was cause I idle all the time

[darksobsession]

have had the CAI and other mods for a long time.

excessive gas consumption has only started recently.

have you fixed your prob yet or are you still getting bad mpg?

[HazMatt24]

I haven't done anything, I notice when I do drive on the freeway for long distances I get around 26 (the only trips I've done have included a lot of elevation change though so I wouldn't read too much into that). I only drive 4 miles to work and idle a lot in between and stop lights or dropping my daughter at school so I just credit it to that, but if you are having the same problem, I'd be interested in knowing what was causing it and I'd check mine out

[cherrington17]

even at idle... a wai should still improve mpg... more hot air + fuel = better than stock

so far, I have no advice other then whats been said, though.

[HazMatt24]

I'm sure I need to look into it, but I drive 18 miles....a day...and that includes going home for lunch so it hasn't been that pressing of an issue for me

[darksobsession]

so finally got in touch with dealership guy, he said mechanics didn't check iat sensor.

am taking car in on sat to have that tested.

anything else it could be?

[HazMatt24]

that makes sense, could be running rich if it's picking up the wrong temp

[cherrington17]

tires - check
air filter -check
fuel filter -check
spark plugs -check

hmm.. leaking fuel injectors? does it start rough at all?
clogged cat, possibly
maybe clean your TB/MAF (unlikely, but could be giving a wrong answer) If thats the problem, it might be caught by the IAT test though

[mbeals]

Did your gas station just start using ethanol blended gas?

You say larger wheels/tires. is the final diameter actually larger than stock? Was your speedo recalibrated?

[darksobsession]

no, hawaii's been e85 for awhile now

[mbeals]

How long have you had the headers on? Did you retorque the bolts? I wonder if you have a slight exhaust leak richening up the mixture. It was mentioned before, but how old is the O2 and did you do anything to it when you moved it for the new exhaust? They are supposed to throw a code when they get lazy, but sometimes they can be lazy, but not lazy "enough" for a cel. A live view of sensor output while driving in closed loop would help a lot.

Are you having any drivability issues at all? Even something minor? Slight hesitation? Surging? Popping? Does it happen when warm? Cold?

It would be interesting to reset the pcm to default the fuel trims and see what happens.

[darksobsession]

blah, gm was packed an won't be able to take the car til monday. in the meantime i'm still getting 17-19mpg.

[clutch1]

Would be best to get a live data scanner.

There are lots of things that could be wrong.

Does the fuel trim say it's running rich (abve regular, positive percents, however it's displayed on the alero)???
Or is fuel trim normal???

If it's fuel trim, the comp is getting a reading that it needs more gas for some reason..
is your coolant temp sensor working?
intake air temp sensor working?
If those read cold then it'll dump nasty rich in.

If you have an exhaust leak (pre sensor), your o2 sensor will pick up lots of extra o2 on it's reading and dump in fuel to compensate.

Get a scanner and look at live data... if any of the sensors read funny those are prolly your culprit.

If fuel trim is regular something is holding the car back...
Dragging brakes/ ebrake
Tires
wheel bearing making it hard to drive
etc.

Also, as they said, plugs and wires are always a good idea. I gained about 4mpg when I changed plugs in the Aurora.... Gotta see how much voltage each plug is pulling (gonna need a spark analyzer)... Should peak around 8-15kV. If it's more than that you need plugs and or wires.

[darksobsession]

no wires on the 2.2.

[billytheman1188]

How long have you had the headers on? Did you retorque the bolts? I wonder if you have a slight exhaust leak richening up the mixture. It was mentioned before, but how old is the O2 and did you do anything to it when you moved it for the new exhaust? They are supposed to throw a code when they get lazy, but sometimes they can be lazy, but not lazy "enough" for a cel. A live view of sensor output while driving in closed loop would help a lot.

Are you having any drivability issues at all? Even something minor? Slight hesitation? Surging? Popping? Does it happen when warm? Cold?

It would be interesting to reset the pcm to default the fuel trims and see what happens.

hmmmmm this could be on of my few problems w/my engine....header bolts loose...idk. but that was a good post.i have the 3400 though so its a little more PITA ;) Ruby is gettin fixed this week though....thank god. Then.....dare i say.....struts/springs :coolio:

[darksobsession]

i'll check the headers, but do'nt think thats thatr prob.

i'm hoping it's the air sensors, they didn'tc heck before.

no drivability issures.

pcm hasn't been messed with.

[darksobsession]

wasn't the IAT sensor.

there is no mass airflow sensor on the 2.2.

i did find a leak in the CAI piping, though, which was (99% sure) the cause of the prob.

also put in some new tubing to replace the stock accordion plastic part.

will test it out.

[clutch1]

A leak in the intake WONT cause problems if you don't have a MAF, as long as it's before the throttle plate... then it's just the same air you pull through the filter.

Keep lookin... did ya get to see any of those sensor numbers yet? esp O2..

[darksobsession]

ok after i changed the CAI around a little bit i'm still getting 19mpg freeway.

wtf?

[clutch1]

O2 sensor... what are it's readings...

[darksobsession]

how would i get teh o2 reading?

is this something the dealership would check? the car isn't throwing any codes.

thnx

[darksobsession]

what kind of mileage are other 2.2 ecos getting?

[cherrington17]

2.2 should get mid 20s in city, 30s highway.

O2 sensor can be read with a digital multimeter.. for voltages.

[HazMatt24]

just thought of something, would any of that stuff cause an emissions fail? Just asking cause I just went through emissions no problem, yet I'm getting poor gas mileage.

[clutch1]

O2 could be read with a multimeter on the signal wire, or even better with an oscilloscope to graph the pattern.

On that note.. even more helpful, get the short/long term fuel trim numbers. Find someone with a scanner and get the datastream pulled up.

Chances are you'll see o2 be OK.. probably, but fuel trim will be VERY high. That would indicate clogged injectors or carboned intake/valves. If o2 is reading lean and fuel trim is also reading rich you could have an exhaust leak before the o2 or weak spark. If you have ok o2, but rich fuel trim at idle, rev it up... if fuel trim goes normal you have a vacuum leak.

Start with those if you'd like.

Poor gas mileage could come from many things that won't mess up emissions. Unless the extra gas that's being added is coming out the tail pipe it won't fail. You could have a carboned up intake/valves absorbing all the injecter fuel, requiring it to add more, for example. And remember the cat eats up loooots of HC that would otherwise get let out and fail your emissions if it's running rich (causing poor gas mileage). Too many variables for an exact answer, but it's certainly possible.

Really I can't answer that question again, without the fuel trim numbers / o2 readings. Those are absolutely invaluable for that.

[darksobsession]

any pics, faqs, or diagrams on how to test/replace it? what does heated mean, and why the variance on # of wires?

wouldn't this be something the gm dealer would have tested for?

[clutch1]

For o2 sensors??

O2 sensors read the amount of oxygen in the exhaust. They do that w/ an chemical reation that produces electricity... that needs heat, o2, and zirconium IIRC.

One wires have a signal wire and are grounded to the exhaust w/ the housing
2 wires have a signal and dedicated sensor ground.
3 wires have a heater +/-, and one signal wire
4 wires have a heater +/-, a signal, and a sensor ground.

The heater is there to bring the sensor to temperature faster so it can accurately analyze the exhaust gasses and tell the PCM how to deliver fuel/ timing quicker.

To test it, backprobe the signal wire, and rev the engine for a while to make it hot. Pull up the pattern on an oscilloscope, it should look like this.
http://www.samarins.com/glossary/o2sensor_signal.gif

Should have about 10 peaks/valley per second. If it only have like 5 or less then it's getting lazy and doesn't read as well, which happens.

If its mostly high, you have a rich condition where too much o2 is being burned.
If it's mostly low, you have a lean condition, which may be from not enough fuel being delivered, incomplete burn, exhaust leak, vacuum leak, etc.

It may be broken and not able to see lean/rich. In your case, it may be stuck on lean.

Inject some propane into the intake, and look for the graph to spike up to rich. That proves it can see rich.
Pull a vac hose, look for the graph to hit the basement, that proves it can see lean.
If it passes those the O2 sensor is ok.

However, depending on the graph you see, we can help you furthe diagnose what's going on.

[HazMatt24]

so assuming I can't get a hold of anything to test the o2 sensor, start with spark plugs? Makes sense, I don't think they need to be changed but it couldn't hurt. I don't know exactly when my mileage went down, but it was ok before mods, low after intake, exhaust, wheels/tires

[heineck]

I'm gettin real shitty mpgs too like 220 miles on a full tank. Haven't checked anything out yet. Plus I think the 2.5" catback is partially to blame but it shouldn't kill my mileage that bad. Haven't changed my plugs since b4 last years ASS

[HazMatt24]

I'm gettin real shitty mpgs too like 220 miles on a full tank. Haven't checked anything out yet. Plus I think the 2.5" catback is partially to blame but it shouldn't kill my mileage that bad. Haven't changed my plugs since b4 last years ASS

I was thinking the 2.5 cat back was doing it too, only other engine mod was WAI, and thought too little back pressure might be causing it.

[darksobsession]

i'm taking the car back in next week to have injectors cleaned and o2 sensor checked. i hope that's it.

[clutch1]

I would think autozone would rent out oscilloscopes... it's such an integral tool I'd be a lil disappointed if they didn't.

But hey, I did indeed get like.. 4-5mpg better when I changed plugs. Went from just barely making 20 to just barely making 24.

Can't really comment on the catback/ low backpressure... but did ya mess with the manifold at all that would make it leak pre-o2?

[clutch1]

i'm taking the car back in next week to have injectors cleaned and o2 sensor checked. i hope that's it.

If it's a decent shop they should be able to give you a pretty good estimate of what's wrong after maybe.. 30 minutes of diagnosis. I would make sure they do that first off. Cleaning injectors is a good thing for sure, and won't hurt a bit, but if I were you I would make sure they find the exact, instead of just good guesses.

Also, does their injector clean include decarboning the intake? Good ones do, and it helps a lot!

[HazMatt24]

I would think autozone would rent out oscilloscopes... it's such an integral tool I'd be a lil disappointed if they didn't.

But hey, I did indeed get like.. 4-5mpg better when I changed plugs. Went from just barely making 20 to just barely making 24.

Can't really comment on the catback/ low backpressure... but did ya mess with the manifold at all that would make it leak pre-o2?

I never touched the manifold. I had a shop weld everything up, and I don't see why they would have gone that far up the exhaust.

[darksobsession]

i'm using the gm/gmgoodwrench dealer here, so they should know...

[darksobsession]

ok, o2 sensor checks out ok.

having the injectors flushed.

injectors been flushed, car seems smoother and accelerates faster. will keep track of miles and update.

window mounts broken, fixing would cost 700+, but they told me to take it to an auto glass place that could do it cheaper, am doing that tomorrow.

[darksobsession]

window was fixed for 150.

o2 sensor ok.

flushed injectors, now the car is accelerating faster, is smoother.

still getting only 18mpg.

what's up w/this?

[cherrington17]

you car is possessed.

your tires aren't completely flat? hmm... gotta get ion to check this out.

[darksobsession]

tire pressure is fine

[heineck]

u need a new carb

[clutch1]

Lolol.

Any fuel trim numbers for me yet?