I've posted a few times about this issue. I have an 09 Cobalt SS TC with GMS1 and I've recently bought an Injen CAI. I heard you can install them as SRIs so I did that to avoid hydrolock and have noticed some loss in low end torque. Most people said I need a tune but I backed out because of the warranty and installed it on the GMS1 tune. I've just bought a scanner and looked at my fuel trims. STFT is good - almost always 0% and occasionally jumping up to +/- 3%. The LTFT is hanging at -22% to -23% though. I have no experience tuning and modifying so any help would be appreciated.

Firstly, how can the trims be skewed to negative? I would think an Injen intake would have less restriction and bring in more air so it would need to burn more fuel and trims would be skewed to positive.

Secondly, is there anything I can do to bring the LTFT down? I really want to take advantage of a less restrictive intake but I don't want a tune because of the warranty. A member recommended that I go back to the stock box and cut the restriction out of it but I'm sure there's more to be had out of an intake even with no tune.. but I could be way off since I have no experience modding.

 

wow those ltfts are bad! you need to get that tuned. Nothing you can do about it other then getting tuned honestly.

 

Even tuned the injen is the worst intake for fuel trims.
I reccomend selling it and getting a k&n Sri or do the airbox mod with ZZP intake pipe and k&n drop in.
Aside from getting a tune not many options. Injen and stock or gms1 tune is a bad idea.

With fuel trims like that I doubt the intake is beneficial power wise over the air box.

 

-22% to -23% sounds like a boost leak, lol. Might explain loss of torque!

You should have thrown a code by now so that could also be your loss of torque. Scan for DTCs.

Basically your LTFTs is telling you your car is running 22% to 23% richer than what it should be and the STFTs are like "Yeah dude, your good after we trimmed away 20% of the fuel we were suppose to be adding...lol. you either A.) have a dirty MAF that thinks its seeing more airflow than it actually is, B.) have faulty GMS1 MAP sensors, or C.) Boost leak.


Idea. Reset your ECU by disconnecting the battery and waiting 5 minutes and reconnecting it. Then monitor your trims. See if it jumps immediately or takes a long time to get there with some mixed driving styles (a few pulls + coasting).

Also do this with the stock intake on the car. If you still have LTFT issues with the stock airbox on the car then you actually have a problem. Before doing any of this though, first scan the car to see if you have hidden DTCs which could tell you if there really is an issue.

 

yea, I was surprised when I saw the trims. I thought they would be between 10%-15% (and positive) but not over 20%. I can't get a tune, especially because I have extended warranty so I would be losing a lot of value if something happens and my warranty is voided. Otherwise, I would have got a tune right away..

I saw in your signature that you have GMS1 with K&N SRI. Did you tune after the GMS1 or you're running on that tune? Any problems/high trims?

 

lol yea I figured.. I thought of boost/air leak but I popped the hood, started the car and tried to listen for any unusual noises but couldn't hear any. What should I be looking for if that's it?

CEL came on.. I scanned and found a couple of DTCs but both are the same code - "P2178 System too rich off idle". The DTC that triggered the CEL has some data saved with it (RPM, temperatures, fuel trims, pressure, etc.)

 

Its not a boost leak, the Injen and AEM intakes throw it off that much at times. You are on the borderline for throwing a MAF code. I was honestly remove it until you get a tune and if you don't plan on getting one, get a K&N and sell the Injen. This has been discussed a LOT, read before you buy! My .02.

 

Trims are good. Run between -4+5 most of the time. Often better than my air box.
Just gms1 no custom tune.

Trims can be mildly adjusted by turning the filter on the k&n due to it not being round it effects the way the maf sees air. I love it.

 

My boost leak caused my LTFT to drop to -29 with no DTC's

OP i would def take that off so you don't mess anything up and you probably caused it to have less power than a stock airbox. At least its not +22 though.. Put it back the way it was to see if it fixes the problem if it doesn't check for leaks, loose maf sensor etc.

 

sorry to thread jack....

but i am curious to know what is different between the k&n and the injen or any other intake that causes the fuel trims to be skewed?? design, pipe diameter????

 

Some due to the maf location receive allot of turbulence. Too close to the filter... On a bend...angle of filter to Ibrushing air all play a factor. Basically if the sensor is not located do that is getting an accurate depiction of the air coming in it will skew the trims one way or another.

 

I feel its pipe diameter that poses the biggest issue. If the point where the MAF is mounted to the intake does not have the same circumference as the factory tubing then the amount of air flowing in is not being properly measured.

if the aftermarket intake tube is bigger than the factory tube at that point, the MAF is only reading what it thinks is the volume of air moving through a factory intake tube and cant account for that extra volume of air flow.

Its strange that most companys that make intakes didnt take that into account... they only care about the money those greedy bastards, lol.

They probably figured people would get tuned if they get an intake.

K&N intake has a proper sized MAF location circumference.

 

If it were a boost leak, you would have the same terrible fuel trims with the stock airbox. You would also not be hitting full boost and might experience the turbo overspooling trying to get there which could throw a code as well.

Reset the ECU and monitor the fuel trim and see what it does at idle and then at cruising without engaging the turbo, and then at WOT.

BYT is more than likely right though, I didnt research the injen intake but I do remember people getting terrible trims with them. It just feels like 22% is a huge number.

Like everyone else said though, put the stock airbox back on for now and see if that removes the terrible trimmage.

 

Thanks. Have you ever got it dyno'ed?

 

Why is +22 worse than -22? And I'm sorry if this is dumb but I'm still not sure why my trims would be skewed to negative and not positive. Shouldn't the intake bring more air than engine used to get with the stock and more fuel is required?

I reset the ECU and started the car (in cold weather) and it stayed at 0 LTFT and STFT (about 20-30 seconds) until I started moving and then STFT jumped to -15 to -20 and LTFT followed shortly after. After a day of driving (mostly stop and go traffic though and boost rarely hitting above atmospheric) the LTFT were back at -22 to -23 and STFT is back to normal +/- 3%. I think I'll put the stock back on and see what happens.

If it's a boost leak, what should I be looking for?

 

I haven't dynoed.
It should bring in more air but that doesn't necessarily get seen by the sensor 2which is where the problem lays. Turbulence could cause both a lack of air being seen and Too much air being seen. This would make it fluctuate.
Pipe diameter wouldn't assist anything in regards to this.

 

With a small boost leak, you will see negative fuel trims immediately. The reason is measured air is leaving the system when your under boost and the car over fuels. The measurement to determine if the AFR is off is done after the combustion occurs and the exhaust leaves the cylinder/ header/ turbo (turbine side). An O_2 sensor takes a reading and sees the % off from targeted AFR (command AFR) and tell the car computer to make an adjustment. In this case, it says to trim away fuel therefore -% fuel trim is used.

When not under boost or if you have a faulty MAF sensor, unmeasured air could be entering the system and the car see's and underfueling issue occurring. A triming in the positive directing (a.k.a - adding more fuel) is accomplished to get a good AFR when this occurs. that would be the +% fuel trims.

Fuel trim skews could also be caused by improper intake tubing size. and what I mean by that is the MAF needs to be tuned for since the MAF is measuring for a circumference of what the factory intake tube size is. Imagine a 5 inch intake tube and the MAF inserted into that. You'd probably be seeing a CEL for sure and the airflow going in is going to be greater that what the MAF reads. The diameter is a constant in the computation of the volume of air flow to the engine and the rate limiting change is the velocity of the air. If the velocity is the same rate but the circumference has changed to something greater then the car is underfueling and will result in + fuel trims. The same is reverse for a smaller diameter intake pipe.

Hopefully Im not blowing smoke up everyones ass but this is how I imagine it works. lol. Im sure a real tuner will come in here to tell me im 70% correct

 

The size of the piping and location of the MAF will determine how far the trims are thrown off.

 

Thanks for the explanation.
Got my stock intake back on today but haven't had a chance to scan fuel trims yet.

 

hell yea dude... my injen was horrible....

once i popped the turbo xs intake on, it took a few times for vince over at trifecta to tune it... the injen, took him weeks to tune it right....

 

Yea, it definitely was the intake lol.. scanned my trims today and LTFT was -1.5.. with the Injen, it used to jump to at least -19 after 1 day of driving.

 

welp there it is. lol. You'll either need a tune for that intake or sell it and buy one thats not that bad.

 

lol yea I put it on sale and going to try a K&N SRI.