3.0 liter sidi poor fuel mileage

[redonetoo]

Anybody have any suggestions on trying to get the fuel mileage up on a 2010 Terrain with 3.0 liter sidi. You would think with all the tech. in this engine it should be able to get more than 20 mpgs. I have the v2 flash and tune. I am new to this whole tuning thing so I apologize for my ignorance.

[swingtan]

There is no tuning support for the V6 yet, so it's going to come down to...


How the car is used.
The fuel being used.
Driving style


You may be able to adjust the auto settings though and that can help with mileage.

Simon.

[GMPX]

Actually Simon, we do support the 3.0L and 2.4L SIDI as used in the Terrain, it uses an E39 ECM.
Redonetoo, I think the problem comes down to the weight of the vehicle, getting all that mass moving with a small engine takes a lot of effort. If the Terrain has an instant MPG readout take a look when you take off from the lights. I've only just started playing around with the 3.0L V6, but so far the fuel economy is about on par with what I thought it would be (11.5 L/100), which is about 20MPG. I would expect about 26-27 MPG on the highway.

[redonetoo]

I am looking at the short term fuel trims and they seem to always stay in they negative. Also the o2 sensors seem to run constantly around .750 volts. Which makes me think it is rich. I have changed the gear ratio in the transmission to 3.39 to help with the weight factor. Just in my mind it makes no sense that an engine of this size gets close to the same mileage as a v-8. I had a 2000 5.3 in a full size truck that got 18.

[redonetoo]

It does have the instant mpg feature. And you are right it does seem to drop quickly. But even at light acceleration on the highway it drops hard. I thought the advantage of the sidi was to more accuratlely control fuel timing. They have the injection timing at 300 degrees or so before tdc. So how is this better than MFI? I was told I could play with the MAF settings to help with the running rich. Like I said I am new to this.

[redonetoo]

This car has never seen 26 mpg. I went to Greenville NC from raleigh the other day all interstate 19.5 mpg. After I reset the trip.

[GMPX]

Again, it's how hard the 3.0L needs to work to get the vehicle moving, a 6.0L GenIV will move a 2 tonne vehicle away from the lights with ease, maybe shift at 2,200RPM at moderate throttle. Your 3.0L has to work twice as hard as the 6.0L, rev a little harder etc, if it's working hard it's got to use more fuel. At speed the 3.0L should do pretty good though.

SIDI allows them to have far higher compression, the LF1 is up at 11.7:1 from memory, that's race gas levels from days gone by. Injection timing is probably not something you want to 'experiment' with, GM would have spent a long time getting that timing right.

[redonetoo]

Even at idle the o2 sensors are running close to.750 is this normal? I live in Eastern North Carolina flat land. And most of her driving is interstate 75 to 80 mph. We had a Mariner it got 26 mpgs average with a 3.0 liter. The Terrain is much heavier. I just don't see the advantage of the sidi.

[redonetoo]

Another thing this Short term trim thing. It seems to stay in the negative numbers. Is that normal?

[redonetoo]

I work on Diesel truck engines. We can advance and retard injection timing at different rpms to get better performance. But if not careful you can melt a piston. I was just amazed at the time at which they were injecting fuel. The are injecting on the intake stroke instead of on compression stroke. I guess with gasoline that would be impossible.

[GMPX]

Running close to 0.75V does seem high, but with the funky exhaust port these engines have maybe it's how it is on them, I'm not sure.
Ah yeah, this ain't Diesel direct injection.

[redonetoo]

I found a service bulletin on gm site about MAF causing fuel trims to be out of wack. Where they cast the plastic housing it was casuing a disturbance in the air flow. I cleaned up the casting flaw and thought I would try that but I doubt that did it. These engines run pretty low vacuum too. I put a vacuum gauge on it and it is running somewhere around 15 inchs. I had a local tune shop owner drive it this week and he said the computer was constantly taking fuel out. He said the MAF could be adjusted to compensate. He didn't have the software to mess with it. I bought EFI from a diesel shop who was too intimidated by the whole thing a gave it up. I am starting to understand his frustrations.

[redonetoo]

There really isn't a whole lot you can do with these ecms without adding boost is there? Nice to have that capability but not on a daily driver for wife.

[swingtan]

Actually Simon, we do support the 3.0L and 2.4L SIDI as used in the Terrain, it uses an E39 ECM.

Ahh, yes... I missed the E39 bit there :doh:

Some logs of the car would help, it would help shown the longer term details of what the fueling is doing, if it included wide-band O2 data it would be even better. Also, a copy of the tune file to see what may be possible.

The MAF its self does not make any "adjustments" to any thing. The MAF is just a sensor, it measures air flow / density and reports that back to the ECM. If it's faulty (broken or even just dirty) it will report the wrong values and the ECM will try and correct when in Closed Loop (CL) mode. If the ECM can't correct, it should throw and error code.

STFT's should not remain negative, they should oscillate +ve and -Ve. LTFT's can remain either +ve or -ve though. If the NB O2's are stuck at 750mV and do not oscillate at all, then I'd say the closed loop function is just not working, and the car is always running rich. So it's probably worth doing the following...


checking for any error codes before trying anything else.
Log the car ensuring STFT's, LTFT's and O2 mV are being logged. Also the Fuel Mode (OL vs CL) should be logged as well as ECT.
Clean the MAF, use a "carby cleaner" to rinse off the sensor elements inside the MAF.


It sounds like it's stuck in OL mode and simply running too rich. This might be due to a faulty O2 sensor or even a stuck thermostat not letting the car warm up correctly.

Simon

[redonetoo]

The o2 are oscillating along with the stft"s the Ltft are staying pretty much in positive. It is going into closed loop. I cleaned the casting flaws from the MAF sensor and watched the trims and it seemed to help . I went back to a custom tune I purchased from another vendor also. He was able to play with the throttle response and a few more things I can't or don't know how to do in EFI.
I wish I could read his file with EFI so I could see what he has done but it won't read his cal. He didn't change the Final drive ratio in the ECM. I don't know what that will effect. The transmission controller seems to work the speedometer. I have it calibrated to the 3.39 and the engine is programmed to the 2.77. His files are trt files instead of tun or bin files.

[kangsta]

you wont be able to open the file directly in EFILive but you might be able to flash the trt into your ECM then read it out with EFILive

[redonetoo]

I think i tried but it says the ecm isn't supported I may try again

[redonetoo]

Gives an error code and says file not formatted

[kangsta]

I take it you can read it out with a stock tune? Try EFILive v8 Pass thru (Use the software interface) instead of BBR

[redonetoo]

I have to read it with V8 with the stock tune. I tried with the pass thru that doesn't work either. What does the ecm use the final drive calculation for if the speedo doesn't need it?

[swingtan]

OK then....

It's going into CL, that's good.

LTFT's are positive, but STFT's are -ve, this is why we need some log data. It may be nothing, but who knows.....

It might just be the final ratio change that's causing issues though. If you have gone from 2.77:1 to 3.39:1 and not updated the transmission calibration to suit, then it'll be shifting at the wrong places. It may be locking the TCC too early and making the car labor a lot more, causing it use more fuel.

Simon

[redonetoo]

I flashed the TCM to an SRX file which is the only 2wd version that runs that gearing. That made a world of difference. The transmission cal fixed the speedo.

[redonetoo]

But does the ecm need to know the final drive ratio to calculate load?

[redonetoo]

With the e39 controller it won't let me read AFR wil it?

[redonetoo]

One more question. On my 2009 silverado if I use e-85 it gets 13 mpg, If I use e-10 I get 15 mpg, If I use regular gas no ethanol I can get 18 mpg. On this Terrain it makes no difference with e-10 or regular gas. It isn't flex fuel so I haven't tried e-85. How can it tell the difference?