torqls1

02 ws6
m6
lid
cutout
catback
315's on the rear

I consistantly shift at 2k rpm and somehow only manage to pull 200miles out of a tank with 1-2 WOT pulls.... Ive changed my fuel filter, cleaned my air filter, cleaned my throttle body+sensors, seafoamed my injectors and also changed my plugs. Im assuming the last step would be to change wires.. with that being said it seems like my car has a missfire while idleing itll idle fine then idle kinda rough then idle fine then idle kinda rough, however im throwing no codes. any ideas?

RPM WS6

iTrader: (3)

1) What exactly do you mean by "200 miles per tank"? More specifically, how many gallons do you refill with after going 200 miles? A "full tank" would be 16+ gallons, but rarely does anyone run the tank that low. The only way to tell your real MPG is by knowing exactly how much gas you're buying between fill-ups. Additionally, is this 200 mile range on the expressway or in the city?

2) You mentioned cleaning the air filter, which suggests you're using a K&N-style filter. I don't like these filters for engines that use an MAF, because the filter oil tends to build up on the MAF wires over time, causing less-than-ideal readings. I know you also mentioned that you "cleaned throttle body + sensors", and I'm assuming by sensors you mean the MAF, but if you oiled the air filter after cleaning the MAF you might already have some deposits on the wires (especially if you accidently over-oiled the filter).

3) How old are the O2 sensors (miles)?

4) Personally, I always notice a decrease of about 2-3mpg in the winter months, due to the change in fuel blends for my region and longer engine warm-up times.

5) Inconsistancies in engine behavior at idle can be a result of many different conditions. Even though you are not throwing a code, you may learn something by hooking up a full range OBD scanner and checking several parameters. However, this only applies if you have access to this type of tool and understand what the data values indicate.

bad_408_vert

iTrader: (6)

I like to add that those 315s are alot for city driving, if you are in alot of stop and go traffic.

Fuel blends plus dense air in winter does change mpgs for the negative.

If you are following the gas gauge, its very inaccurate.
Every time I get a full tank of gas Its great until I 'm at half a tank of gas and then the needle drops much quickly than it did for the first half of tank being used.

If you already didn't test it by filling it up til you can't anymore, drive until you are almost empty . That will be your true mpgs.

Ryan0620

It has been about 20F here and I'm getting roughly 15-16 mpg in city only driving with a 6 speed. I generally shift anywhere from 2000-2500 RPMs. That's likely due to fuel and cold weather. Check your O2 sensors if you're that worried about fuel mileage. I usually end up getting around 18 mpg when it is warmer outside (60+).

608kZ28

if you want to tell your mpg then do what i do.
fill your car all the way up. reset your trip meter soon as you get in your car. drive around for a few days then go fill up again. look at how many gallons you use and look at your mileage. then just do the math

japsw20

I get about the same per tank and same m6 same mods but with 295's

Jays_SSZ28

iTrader: (2)

If you haven't recalibrated the speedometer for taller tires you're going to be reading less miles than you actually traveled.

torqls1

Alrite id like to start by saying i always appreciate your input on here rpm you always give great advice.
Anyways, when i stated 200miles to a tank i meant 200miles to a fill my check guages light popped up today at 176 miles and i had to go fill up when i filled up i used 93 octane like i always do and it only took 13.5 gallons, as far as the filter and maf, i cleaned my air filter awhile back and it still looks fresh , so i spiffed up the maf sensors with cleaner+q-tips. As far as the 02 sensors go ive not replaced them and the full range obd scanner i dont have ive always had this problem with my car ever since i took it off the lot, another thing id like to throw out there involving my gas is the fact that i could be driving around and when i turn my car off my gas gauge needle will o lets say a half a tank of fuel left, well when i restart my car the next morning or whenever the gas guage needle will then be alot lower then what it read when i shut the car off... it makes no sense to me (sounds like a leak i know but my car i can let sit in my garage and it has no spills underneath)

sandsk8erz400

iTrader: (1)

Can't help at all with the missfire, but I'm curious how "stop and go" is your city driving? I always see people saying they get 16-18mpg in the city, but some cities are quite a bit different then others. With all the stop signs and stop lights, the best I've ever managed in the city was 13mpg (shifting 1.5-2K no WOT.) I know my car's maintenance is up to par too, and I can pull 28-30mpg straight freeway, so I just chalk it up to worse city driving than most. But with the miss you have, I'm sure once it's straightened out you'll gain some mpg's back

And the gas gauge doesn't sound like it's an issue, I may be wrong here, so please someone correct me if I am. But I've always though that sometimes the tank just hasn't de-pressurized (for lack of a better word) from the gas it used prior to shut off. But once shut off, and given some time, "de-pressurizes" and is at the lower position you notice.

Hope at least something I said was useful haha

RPM WS6

iTrader: (3)

Assuming his "315s" are 315/35/17, then there would be no reason to recalibrate. The overall diameter of those tires is only marginally taller than the stock size, and it would not make any noticeable difference (25.66" stock vs. 25.68" with the 315s).

Well, if you had filled the tank full before driving those 176 miles, and then refilled with 13.5 gallons, that equals 13mpg. This is a bit lower than what I would expect, given the information you have provided about the car's specs/mod level and your driving habits. I normally see about 14-15mpg (city) during the winter (and that's Chicago style city driving, which means excessive stop-and-go), but that's with an A4 car.

One thing that's not being taken into account is other habits you might have that would reduce MPGs, like extended warm-up/idling intervals or many short trips/several engine restarts. These are significant MPG killers.

At this point, having already done all the maintenance you've listed, there isn't too much else you can do, other than possibily chasing that intermittent rough idle. If you had access to a scanner, there would be things I would suggest looking at. You could also check certain sensors for proper operating parameters using a volt meter, but this requires a certain amount of knowledge to understand what the values indicate (not sure how familiar you would be with these readings). Additionally, this will only show you a portion of the picture, as there are several important values that can't be seen with a simple volt meter.

You could pull and inspect the new plugs, maybe one has a hairline crack causing the idle condition. Replacing the wires might be a good idea as well (or at least double check them for any deterioration or poor fitment), since you mentioned this hasn't been done yet. Double check all connection points that could introduce unmetered air into the mix, like the air bellow/MAF/throtte body connections; and if you want to go a step further, check any/all points that could introduce a vacuum leak (basically anything that connects to the intake, and the intake itself).

Front O2 sensors provide critical feedback for proper fuel mixture, and this is one thing you haven't replaced yet. They may not be working at optimum, even though you don't have a MIL/SES (yet).

Considering the amount of eletronics that are involved in the operation of a modern fuel injected engine, I would suggest investing in a scanner/software if you plan to diagnose driveability issues. You don't need anything super fancy, I'm using an AutoTap program from about 9-10 years ago that still works great for my personal and basic needs. Idle issues can be some of the hardest to track down (I've done my share), and without a scanner the only other option you have (once the basic checks are exhausted) is to start throwing parts at the car and hope for the best. This can get costly and frustrating real quick.

As for your gas gage, I too have seen that same condition (needle drops right after a cold start). I would not be alarmed by that, nor do I believe it has anything to do with your current issues.

Jays_SSZ28

iTrader: (2)

Actually stock calibration is 24.91 and thats real close.

I did a rollout test on my stock 275/40/17's with 4500 miles on them.
One revolution is 78"

So thats 78/3.14159265 = 24.8"

RPM WS6

iTrader: (3)

To reach a 24.8" overall diameter, you'd have to be using a tire with specs roughly matching a 245/40/17 or 225/50/16, neither of which are stock sizes.

Stock sizes/heights are as follows:

SS/WS6/Firehawk: 275/40/17 = 25.66" tall, 80.62" circumference

Z28/Formula/Trans Am: 245/50/16 = 25.65" tall, 80.57" circumference

These are the correct factory specs.

Assuming the OP's tire is a 315/35/17, that would be 25.68" tall with an 80.68" circumference. As you can see, this is super close to factory spec'ed diameter.

Jays_SSZ28

iTrader: (2)

The factory specs are based on an unloaded tire.
When you do a rollout measurement you take into account the reduced ground to centerline distance caused by vehicle weight and inflation PSI.

Don't you find it odd that the stock VCM calibration for 275/40/17's is 24.91?
And the actual rollout calculation comes out to 24.8.

Thats one hell of a coincidence.

torqls1

i let my car warm up for 10min every morning and 10 min after i get off work to drive home so 20min total every day

Chronicle

iTrader: (7)

This.

RPM WS6

iTrader: (3)

It's been a while since I've retuned a PCM, but I just checked my old printed data from LS1 Edit, and the stock calibration for my '00 WS6 shows 25.66". Perhaps there is a correction factor somewhere in the PCM to take into account proper inflation and load.

Either way though, it wouldn't make any difference for the purpose of this comparasion, here's why:

A 275/40/17 tire has a sidewall height of 4.33". A 315/35/17 tire has a sidewall height of 4.34". As the sidewall height is nearly identicle, each tire should compress close to equally under the same inflation PSI and weight load. In other words, your "rollout" measurement should be nearly the same for a 275/40/17 or a 315/35/17 on the same car. So again, there would be no need to recalibrate the speedo from stock, regardless of whether you're using loaded or unloaded diameter specs.

RPM WS6

iTrader: (3)

I think you have just found the source of some missing MPG.

torqls1

alrite thanks bud, and another thing i know these cars pcv system isnt the best however i thought the 02 setup was better,anyways i noticed my pcv gromet was rotted out so i made my own with the write up on how to make a pcv gromet on this site and ever since ive been noticeing a strong oil smell inside my cab from time to time now

RPM WS6

iTrader: (3)

Well, best bet would be to inspect the entire PCV system then, make sure there aren't any other leaks (also check the fresh air line from the top of the TB to the passenger side valve cover).

If the PCV system is still leaking somewhere (more rotting, or maybe you knocked something loose during the repair), this could cause some idle weirdness.

torqls1

could u post a pic of the fresh air line? and when doing the repair all i did was cut the gromet off and attach a hose i was gentle and all to make sure i didnt break the plastic hose that connects to the pcv and runs behind the intake mani, thanks