jmettee

Let me start by saying I know it’s a Trans Am with the LS1 & I don’t expect high fuel mileage. But I have also searched quite a few threads & think I should be getting better fuel mileage & am wondering what might be affecting my mileage. Everything seems to be running right, but I am seeing that it’s not uncommon for people to be getting in the 24-27 MPG range for mostly highway & long trips, even with the V8 & auto tranny.

My setup: 2000 Trans Am, 5.7L V8 (LS1), Auto 4-speed. Mods that I am aware of: K&N FIPK, Magnaflow muffler, & TSW Wheels (P245/40R18). I’m only using 93-octane. Pretty sure the rear end is stock 3.23 from my calculation….I run exactly 1500 RPM @ 60-61 MPH. I have no idea if the PCM has been changed/tuned from stock. The MAF & throttle body looked clean when I had the K&N off for cleaning/re-oiling.

Since I got the car about 2 months ago, I’ve put about 2000 miles on it. I’ve calculated each tank of fuel & the range has been 19.7 to 21.3 MPG. I babied 1 whole tank & ran another one hard & it didn’t make any measurable difference. I live in a rural area, so I hardly see any stop signs & run surface streets around 45-55 MPH & interstate around 65-70 MPG. The spark plugs are iridium & look good, exhaust tips look good (not carboned up), & the car doesn’t smell rich at all.

So I am wondering what people with similar setups are getting with the auto. Is this normal or are others seeing better mileage? Again, not looking for miracles on a performance car, but I think I should be seeing about 3-5 MPG more than I am based on what I've read & how it's normally driven. On all our other cars, we see the listed highway mileage or better.

Justin

murphinator

iTrader: (2)

I would say fill the car up , note the mileage , run down the interstate at a constant speed in the 65-70 range for an hour , pull over and fill up again , note mileage and calculate , if its above 25 its normal , if its down near 20 you have something causing you to burn excessive fuel , your convertors not locking up or something... if you are running along those rural roads in 4th , downshift to 3rd then back up to 4th keeping the gas pedal constant do you see the tach drop at the upshift to 4th and again upon lockup?

FirstYrLS1Z

iTrader: (4)

My 3.23s' are 1800rpm(read off a ScanGaugeII) at 60mph(read off GPS).
Your 1500rpm at 60mph looks like 2.73s' and convertor lock-up clutch is locking as it should.
My 3.23s' give me 24.5mpg at freeway legal speed,my 4.56s' gave me 21.5.
Check your option code,GU5=3.23,GU2=2.73.

jmettee

I left my Excel file at work, but somehow I made an error & still convinced myself I had 3.23 gears. Just redid them from scratch & got 2.73. So it looks like I have the lowest gear & shouldn't have to worry about having a high gear & lowered fuel economy.

My drivers door was replaced in the past, and it doesn't have any factory stickers or codes....so I'm forced to compare with others or calculate.

Mercier

iTrader: (15)

Have you cleaned your mass air meter? K&N-type air filters that you must oil do put a little of that oil into the intake tract. This can collect in/on the mass air meter. It wouldn't look "dirty" as the film oil wasn't really visible. This used to make my Mustangs run a bit funny but not actually throw a code. A shot of "QD Electronics Cleaner" (car off and preferably meter off car but not critical) and let dry for 5 mins and it usually cleared up. Doubt you will find 4MPG there but I noticed you mentioning oiling your filter..the most oil likely comes off of it when the oil is fresh.

Also maybe try resetting the computer (remove battery cable for a while)? Shot in the dark but sometimes things like to be rebooted.

Are you sure your cat(s) are in good shape? PCV? Check for vacuum leaks? Clean the IAC valve port in the TB?

jmettee

Haven't done anything with the TB...yet. I did just re-oil the K&N & figured I would need to clean out the oil fouled intake after a week or 2. The car didn't get driven much for about 4 years, so the PCV, IAC, & any other TB related items probably need a good cleaning. The CAT doesn't rattle & the car doesn't seem restricted at all, so I wouldn't really suspect it as a problem but I guess it's possible.

Is there any easy way to scan the PCM to see if it's been reprogrammed or not?

Mercier

iTrader: (15)

Sounds like you know you should give a few things a basic cleaning/check. You might find your 10% there. You might be down more than that compared with some of the best examples out there, but I am guessing that if you were 10% better than what you are now you likely wouldn't be as concerned. Usually if you have something bad wrong you're going to be off more like 30% or more. I'd cover all the easy stuff and not worry about finding a smoking gun until you know everything else is "right." While I'm shooting in the dark:

Have you checked your transmission fluid level and color/smell? Tire inflation? Heck, you can run a little closer to max tire pressure and reduce your rolling resistance and pick up a few % right there. Have you calculated the diameter of your drive wheels/tires compared with stock? If that's off any at all, your MPH/RPM assumptions could be off also. Basic math would tell you that highway gears plus larger diameter would reduce gearing even further and turn less RPM and give better MPG but there's a tipping point where you can actually lose too.

Good luck. I would clean everything and establish a _real_ baseline and go from there.

jmettee

OK, checking back in with an update. I cleaned the MAF with Electronics Cleaner spray. I've gone through 2 tanks since the last message. I got 22.5 MPG & 20.0 MPG, with the better mileage including a traffic free interstate drive about 35 miles each direction. The 22.5 was promising, but I'm still checking some things out before just settling with that.

I put my ODB2 reader on the car & using the Torque app, I monitored some things. I got a few concerns that I'm checking into. First, I'm studying up on Fuel Trim & O2 sensor readings. I think the trim is looking OK, but think the downstream sensors are reading rich for some reason. I have no codes at the current time.

The update period is 1 second in these plots, but they show the normal oscillation of the 1st sensor in each bank, but the downstream sensors are reading a bit high (images attached). The X-axis is about 10 seconds & this was taken while driving steady at around 65 MPH.

I also have some reports of a failed sensor value as well as some misfire in the Mode $06 report....but again, not throwing a code. The car runs fine & I haven't felt any misfire. I am still researching & going to re-test tonight, but this is from the report:

O2 Sensor, Bank 1 Sensor 2
TID:$02 CID:$31
- Lean to Rich sensor threshold voltage(constant)
Max: 120
Test result value: 65,518
FAIL

TID:$07 CID:$0c
- Minimum sensor Voltage for test cycle(calculated)
Max: 0
Test result value: 65,491
FAIL
----
TID:$07 CID:$0d
- Minimum sensor Voltage for test cycle(calculated)
Max: 1
Test result value: 65,535
FAIL
----
TID:$0c CID:$20
- Misfire counts for last/current driving cycles(calculated)
Max: 407
Test result value: 63,686
FAIL
----
TID:$0c CID:$30
- Misfire counts for last/current driving cycles(calculated)
Max: 302
Test result value: 58,748
FAIL

Latch

iTrader: (8)

That fuel economy is not low at all, it's actually right on the money. These cars were rated 16 city/23 highway. If you're averaging right around 20 mpg you're doing good.

Chris25

iTrader: (1)

Thats pretty good MPG for an A4 to be honest with you.

DANOZ28

iTrader: (1)

your milage is pretty normal. when i first got my car bone stock with A4 trans i was getting 21 city & 24 hwy. best was 25.5 hwy. now i get 18-20 city & 22-24 hwy. i really dont believe the people that say they get 30mpg. i've asked them to prove but no takers! imagine that.

thunderstruck507

iTrader: (18)

You are doing fine.

Someone might see mid 20s on a long interstate drive but that would be strictly that and not include normal stop and go driving.

My truck can get 20-21mpg on those types of drives, but usually does ~19mpg. But in town it does around 14.5mpg average and around 16-17mpg mixed driving.

Firebrian

I ran my A4 '98 Z28 for 92,000 miles from 2000 to 2009. My overall overage was in the 18-22 mpg range. For longer trips maybe I got 22-24 mpg. But 20 mpg sounds about right. I did routine fluid and filter changes. Car was 100% stock.

Latch

iTrader: (8)

On the way to LS Fest I got 29 mpg on one fill up, but that was entirely highway other than stopping to get gas... and I was drafting my buddy's enclosed car trailer the whole way.

FirstYrLS1Z

iTrader: (4)

TRUE freeway/interstate MPG needs to be calculated from LONG trips.
For 7 trips from Cleveland Ohio to Spring Hill Florida(1100 miles on I77/I26/I95) and starting with a full tank and then filling the tank at destination(5 fill ups along the way and not filling up from empty),adding up all the gallons added and calculating,gave me 24.5mpg with the 3.23s'. Same 4 trips with 4.56s' gave 21.5mpg.
2.73s' should give 26-27mpg on extended freeway driving.
City mpg is of no concern as it is right foot dependent.

1 FMF

iTrader: (1)

if you want to throw some money at yours, the most likely things to help are two new front O2 sensors and an oem delphi MAF sensor, and ditch the K&N and go back to stock setup with paper filter. any contamination/oil from the K&N onto the MAF can cause problems and a K&N filter or any cold air intake will not increase your fuel mileage. have 35 psi or higher in your tires, and being an automatic transmission verify the torque converter clutch is locking up on the highway, you should be able to tell that based on rpm and speed.

RPM WS6

iTrader: (3)

You're likely looking for a problem where there isn't one.

You didn't mention the current mileage on the front O2 sensors, but assuming they are not fresh you could probably pick up a small improvement by replacing those, even though you are not getting a DTC for it. They aren't as accurate as they age.

You've already cleaned the MAF and that's an important thing to do, especially with a K&N filter.

You mentioned that the plugs looked clean, but that they have unknown mileage. Replacing them wouldn't hurt, but you probably won't see much there if they look good.

A bottle of good fuel injector detergent might also have a small but positive effect.

All of these things together might result in a small overall improvement. Your MPG isn't really low though, so no matter what you aren't going to see a huge gain at this point. Factory MPG rating for an A4, 2.73 car was 17/25, as per my window sticker. I recall getting between 24-25 on long expressway-only trips with my stock 2.73/A4 car and never any better than that. That same car would get between 16-19 around town depending on traffic and time of year.

Keep in mind that some members have had access to gasoline that does not contain ethanol, and as such they will always report better MPG than those of us who have only E10 fuels to choose from.

jmettee

Thanks for all the replies - all the info is good. I realize nothing is really broken as I have no codes, so that says a lot. I don't know the history of the car, but it had 88.5k on the clock when I got it 2 months ago. I'm only thinking I should be in the 21-23 range when driving it easy & the 18-19 range when I drive it hard...but I'm seeing no difference really. I don't do ANY city driving & the commute has hardly any stop lights. I keep tires at 32-34 psi, so all good there. The plugs are Iridium & I read they are good for 100k or so, but again, I have no idea how long they've been in there.

Don't get me wrong, I'm enjoying the car & so is the wife. I very may well be looking for a problem where there isn't one, but I am just checking to see that the car is running as expected. I'm not going to throw money at it to replace parts that aren't broken. My next steps are to pull the EGR & TB to thoroughly clean them. Beyond that, I *may* consider O2 sensors, but they seem to be working decently.

Fry_

This is very true, I've noticed a 2-4 mpg gas mileage difference on every vehicle I've tried this on. Unfortunately now that the price difference between 87 with and 87 without ethanol is $0.30 it's a wash, so I just run the cheap stuff in the DD beaters. I still only run ethanol free top tier rated premium in the TA because although it barely breaks even $$$ wise the car still runs better and it's worth at least a few hp. I've also started started filling up with top tier rated E10 in my DD because my new commute goes buy several BP's and a Phillips 66 and after 2 tanks the SES light on my Malibu turned off after being on for 4 months and I gained 2.5mpg. So I guess my long winded point is always buy the best gas you can and it will pay off in the end.

smokiechicago1988

iTrader: (4)

My 02 z28 a4 3.23 with 3200 stall and catback/intake managed 28 mpg on a long trip from Chicago to middle of nowhere WI. I was going 55mph though....