Shigun

iTrader: (2)

As stated in the title, I'm apparently running rich (as best I can tell). Long term fuel trim levels while at idle range from 8-12%, and I'm getting roughly 8mpg city. Front O2 sensors seem like they are bouncing back and forth properly.

Scanning the obd port, I get no codes. I have 4.10 gears in the rear, stock LS1 with an LS6 intake, stock tune, EGR blocked off, rear O2 sensors removed, emissions equipment removed from PCM. Car feels like it runs and drives great, nothing that I can really tell seems wrong except that my fuel gauge sinks like a rock.

Anything obvious I should look at or check into?

ULTIMATEORANGESS

iTrader: (4)

you might be in need of a tune. maybe some things you changed have effected your A/F ratio.

Shigun

iTrader: (2)

Nothing much has really changed. Everything is basically stock except for the LS6 intake and a simple cone filter. Even the exhaust manifolds are stock, though I have it going to true duals back with an HFC->Resonator->Muffler on each side, though I don't think that would have such an effect as I am seeing.

Shigun

iTrader: (2)

To add, got my wideband setup, and am getting roughly stoichiometric constantly, going a little bit lean at appropriate times (when sitting in an idle, coming to neutral), though generally even then it goes back up to stoich pretty quick. This is all read from the driver side exhaust pipe.

I did some driving around yesterday and, after filling up initially, filled up again and got roughly 18.5mpg, so....I'm confused as to what changed that caused the variance. I literally did nothing but get under the car, check out the fuel filter and lines to make sure they were fine, check out fuel pressure to ensure it was fine during revs, and took it to fill up.

redtan

iTrader: (5)

Regardless though, his o2 sensors are keeping it at 14.7 through the use of trims.

OP until you can verify with a separate wideband that the car is indeed running rich just looking at trims is not going to get you squat. Sounds like the car is running fine and you just have a heavy foot in town along with a less than ideal situation (eg. lots of idling at stop lights, lots of slow driving etc.)

Shigun

iTrader: (2)

It very well may be just the incredibly unideal driving scenarios here, as about 99.999999% of my driving thus far since I got the motor rebuilt and installed has been nothing but city driving (and this is my first V8 and LS, so I'm feeling out fuel economy). In a given example, my outing yesterday that should have taken probably 20 minutes wound up taking me about 1.5hr simply because of horrendous traffic.

As for the heavy foot, I am actually trying to be quite conscious about driving habits (for now ) to eliminating leadfoot-itus from the list of potential problems.

RockinWs6

Is the air filter a oiled type? If it is the maf is probably fouled with oil. Also check carefully for vacuum leaks and recheck the intake bolts.

Shigun

iTrader: (2)

It is. I'll get some maf cleaner and check over everything to be 100% sure there are no vac leaks.

redtan

iTrader: (5)

Yeah lots of idling and stop n' go driving will kill the fuel economy of any car short of an electric hybrid.

RevGTO

iTrader: (12)

Here is something that happened to me. My exhaust smelled pig rich although the car seemed to run normally. I checked my LTFT's and they were in a range like yours.

I looked under the hood because I recently had had the lid, MAF, and bellows off as one piece to do some cleaning. I saw that I didn't get the bellows properly seated on the bottom of the TB and it was pulling in unmetered air. Problem solved.

Shigun

iTrader: (2)

Mine actually might be similar, as just yesterday I noticed that the throttle body itself started making a weird noise....one bolt had come out, another was backing out. Got a replacement, took all 3, locktite'd them and torqued them all down to spec. I have noted that my intake temps are pretty high as well, though I haven't been able to drive enough to judge if that has had any effect either.

Shigun

iTrader: (2)

So, going to bump this back from the dead to give an update and see if I can get some more ideas.

City, roughly 16mpg. Highway, roughly 20mpg. This is with driving super conservative, shifting at 2k, never going over 2.5k in almost every scenario. Wideband (driver side) still reflects that I am pretty much stoich all the time. Car seems to run and drive great (though, just recently I have started to get a hesitation at ~2.5krpm, going to get some MAF cleaner since that seems to be the most common cause), but my gas mileage is still complete garbage.

Any other potential thoughts of something I could look into?

Shigun

iTrader: (2)

Back with another update.

Plugs changed, gapped to 0.055". Both O2 sensors changed, brand new Denso 234-4617 sensors. MAF cleaned. Still getting roughly 16/20 City/Hwy, 18 combined, when doing nothing but babying the throttle and shifting at 2k.

Checked the LTFT levels, they generally hang within 1-1.5% of each other, going anywhere from -3.9% to 9.4% on B1 and B2, staying right around the 4-5% on average. My wideband on the driver side hangs around the 14.5-15.5 range basically all day except when it's heating up. I've visually checked for vacuum leaks and all, have not seen anything which made me think there was a leak, though I can't really think of a definitive way to test it outside of perhaps spraying some MAF cleaner around general areas and see if the idle bumps up.

Variance from original post is that I'm now running 3.54 in the rear, the exhaust setup is changed to go stock manifolds -> high flow cats -> x-pipe -> mufflers, all on 2.5" piping, and I did a port/polish on the throttle body, but none of that should be causing what I am seeing, especially a scenario where I took the car on a drive from home to a shop, ~2 hours away, cruise control the whole way set at 70, no traffic or slowdowns, and just barely got 20mpg.

Help!?

85GPLEf41

iTrader: (4)

20mpg is good IMO lol!! i did the ls1 swap on my g body and the only thing i care about is it passing smog! lol

JimMueller

iTrader: (9)

IIRC, GM advertised the fuel economy as 17/29 on the 98-02 V8 F-bodies with a manual transmission, which trans do you have? With a manual transmission I'd be satisfied with 16 city, but not 20 highway. When I had the original motor with a manual transmission I never really cared about city MPG, but I know the best I got on the highway was 31MPG.

If you're using the original exhaust manifolds with the original O2 locations, that'll give you the best O2 switching and best fuel economy. Negative LTFT's will indicate O2's are hanging below the 450mv switchpoint too often, indicating too much fuel. But the stock PCM calibration can handle that as long as they aren't maxed out (above 25%). What model of spark plugs are installed, maybe they are the wrong heat range?

If you have a GPS, compare it's reported speed to what your car is telling you; preferably using a scanner instead of the dash gauge. If it's too far off it might be misreporting your trip mileage and skewing your math. If you happen to have an Android, try out the Torque app with an Elm OBD2 adapter and it will easily display GPS MPH vs PCM MPH. There might be something similar for Apple devices.

What method are you using to calculate MPG? The only way to find out your true MPG is to fill up the tank, reset the tripometer, drive it until it's near empty then divide miles driven by how many gallons it took to fill the tank again. And no topping it off by putting in a few extra ounces after the pump has shut off. You can't get an accurate fill each time that way.

You said you rebuilt the motor, what is no longer stock? Depending upon what was or wasn't done, maybe using some top-end cleaner (I prefer GM) and fuel system cleaner (I prefer Techron Concentrate Plus) will help.

Other ideas:
Check your tire pressure
What oil viscosity are you using?
Coolant sensor okay? What scanner temp is it reporting once the motor is warmed up?
Try replacing the thermostat, if it never closes tightly the engine may never warm up completely.
Change fuel filter
Change to paper air filter
New GM ignition wires
Gas... what octane, does it have any ethanol, have you tried other gas stations, etc.
fuel leak
misfires? Have the misfire tables in the PCM been desensitized?
exhaust restriction
slipping transmission
compression check

Shigun

iTrader: (2)

Yeah, the 16 city isn't that big a deal to me, I know I'm doing a lot of idling and everything which is killing fuel economy. The main part is the highway, when I'm barely getting 4 more MPG than in the city. It should be noted, as well, that the motor is in an S2000, so I've got about 7-800lbs less than a Camaro.

LTFTs are generally always in the positive. Spark plugs are the NGK TR55s, basically what everybody here says is the go to spark plugs.

I've used Torque on Android and DashCommand (and Waze) on iPhone, both are reporting roughly a 2mph difference from the speed on my dash.

That's the exact method. Every time I fill up, I will do the calculations, and the gas cutoff point is when the pump kicks itself off. I only tend to fill up when I'm right towards E

It it all stock still, it just had about 160k miles and an unknown history. Only thing I have changed, performance wise, afterwards was a port & polish of the throttle body. I also used IAT sensor TS10077, since the motor didn't come with one, but I read that should basically be a stock replacement. I'll give those two a try.

- Roughly 36psi all around

- Rotella T5, 10W30. Will swap to full synthetic T6 after a few more oil changes, just didn't want to use a synthetic with new piston rings.

- Scanner is reporting roughly 160-170* normal driving, 180-190* with idling. Fan controller turns fans on at approximately 170*.

- Definitely seems to warm up enough, and when I am letting the car idle from a fresh start I can feel the lower hose is cold and the upper is warm, until that ~190* point when the lower starts to warm up, presumably from the thermostat heating up.

- I can try this, but the fuel filter is less than 1 year old, and only has about 5k miles on it.

- I'll have to check for one that may work, but the problem is this is a motor swap, so finding a paper filter as a cone would be a must.

- I ohm'd out the wires that I have (MSD) and they all seemed fine, but I'm thinking this is probably the next step I will take

- 93 octane always, various gas stations but always 93. Up to 10% ethanol. Have not seen any signs of a fuel leak anywhere. When I was setting up the system I primed the fuel pump manually by jumping it with power and went all along the system to ensure it was nice and tight while priming, since that is when the pressure would have been highest.

- It's a stock tune, just with the AIR/EGR/Rear O2/Stock fan control deleted, so I doubt it.

- It's a potential, but from my understanding, my exhaust doesn't really seem to be any more restrictive than others, especially with a 95% stock engine setup. Stock manifolds -> High flow cats on each side -> x-pipe -> turbo style mufflers, all in 2.5"

- Transmission has felt pretty strong, just the occasional grind going in the 3rd or 4th if I do it quick, so probably the synchro. I am going to replace the clutch/pp/flywheel soon.

Thanks for the very thorough response, I greatly appreciate it.

Shigun

iTrader: (2)

20mpg highway on a car that is about 7-800lbs less than the car the motor originally came from, while being babied on the throttle, when other people are talking about getting close to 30mpg, is far from good. But, I did pass emissions, so there is that

JimMueller

iTrader: (9)

I'm inferring you purchased a used LS1 longblock which had 160K miles then completely tore it down and completely rebuilt it? Any non-stock clearances? How many miles on the rebuild? What type and age of injectors are you using? It could be that the engine is still tight and just needs to break in for 2-3K miles before you get the best economy.

Even though the fuel trims are inline, the fuel has to be going somewhere... how much the fuel economy can reasonably be estimated to briefly drop on a fresh motor I do not know. I'm now more concerned knowing that you have new piston rings, as too much fuel will wash down the cylinder walls and kill the ring seal. I'm hoping others will chime in with additional ideas.

Shigun

iTrader: (2)

All clearances were well within stock, all stock bearing sizes. Reused the stock pistons. Rebuild has around 4-5k at this point.

I've been keeping an eye/nose on the oil, it seems to be fine. I'm going to be sending a sample off to Blackstone at this next oil change, as it will be my first full 3k interval since the rebuild.

Shigun

iTrader: (2)

Interesting development, was driving around and doing some logging. Noticied that, at idle, my LTFT was around 5%. When I start driving it would jump up to around 8.6-10.2, with 10.2 being favored by bank 1 and 8.6 being favored by bank 2. There was a little fluctuations here and there, but it was pretty consistent as a whole.

That would generally mean that it's needing to add fuel, I believe, which makes me wonder more if I have a vacuum leak somewhere, though my wideband is still reading stoich.