[Mohawk_1SS]

All,

I am getting a code on my car associated with the fuel trims being too lean and I'm looking for a little guidance.

The car was modified in 2021 with ARH headers (catted) , MSD intake, soler performance, ported 95mm throttle body, and a rotofab intake. I never had any issues with a CEL until maybe a year or two ago. I would occasionally get this code if I let the car sit for a while (on the order of a month or more), but the light would clear the next time i filled up on gas within minutes. This lead me to believe that perhaps I had bad gas and just needed to refresh the tank, though I'm now doubting that is the case.

Today, the light came back, but I have been driving the car regularly for the past few weeks, and filled up last week. I was at a quarter tank of gas, so decided to fill up and the light did not clear. I then manually cleared the code, but it returned after about 30 miles of regular driving (mix of city and highway).

Given that I now think I may have a more serious underlying issue (probably should not have ignored the warning signs), I was looking for some tips on what I should investigate and simple things to look for before taking it to a shop.

This is a learning experience for me, so I appreciate any and all help!

I've uploaded a log with a few minutes of driving for any experts to review, but it only shows a few sensors because i'm not sure what is useful. Link below. If there is anything else i should include in the log which would be helpful, please let me know.

https://drive.google.com/file/d/16Sm...usp=drive_link

[Mohawk_1SS]

Figured I'd upload some plots with examples of the fuel trims for anyone weary of clicking on links.

[SWFLZL1]

Check for exhaust leaks first.

[vince3]

I’m going to say check the Msd intake too. Sometimes the bolts can become loose and I’ve seen the gaskets have issues.

[Mohawk_1SS]

Thanks for the reply, It makes sense that Intake or exhaust leaks might be the culprit. Fuel trim I see that both bank 1 and bank 2 have high long term trims (even though I'm only getting the bank 2 code). Would this tend to rule out an exhaust leak? I will definitely be going over the bolts and connections for the MSD.

Regards

[GreyGhost702]

Originally Posted by Mohawk_1SS

Would this tend to rule out an exhaust leak?

Regards

No. It's asking for more fuel on both banks. If anything, it says the sensors are likely not the issue. Since the trims are pegged asking for more fuel, the place to start is unmetered air.

The usual places a sensor would detect unmetered air is either IM or Exhaust connection. Even an exhaust connection shortly after the sensors will sometimes wash enough fresh air to be picked up. Which is why we tell folks who delete secondary cats from the OE setup to make extra sure there are no exhaust leaks there, as it will throw a code. Also why I prefer V-Band's or welds only on the exhaust. Typical factory flanges at the manifolds are prone to leak after disconnecting/reinstalling.

Like most have pointed out already, another common leak point is the intake manifold. I can't say I've ever had intake bolts back out, but you should always re-check your bolt torque after the first couple heat cycles to make sure they are still to spec. Same with your exhaust bolts/studs. Parts expand and contract at different rates when heated/cooled.

And of course, check all vacuum connections to the manifold as well.

[KingLT1]

Vacuum and/or exhaust leaks between the closed loop sensors (Maf/O2) and the engine. MSD manifold is 2 pieces with a rope gasket... Check the bolts.

[bishopts]

Dont forget to check the o ring on the dipstick too.
Low rail pressure will cause the same readings too.
I would lean toward intake manifold leak. Gaskets or hoses that go to it.
What i would do is set it up to see live data on stft and spray small controlled squirts of starting fluid along the seal areas of the intake manifold. If you get a leak there you will see the fuel trim flip really quick to negative numbers. Then you will have an idea of approximate leaks. Then switch to a spray bottle of water. Spray in that general area and if you get water on the leak it will make a slurp sound.
With both sides doing the same its really unlikely to say it is exhaust related (not impossible). Look at parts that are common between the two banks. Intake gaskets are specific per side but they share a central plenum, throttle body gasket, brake booster, map sensor and o ring, purge solenoid (very common with gm), intake tube hole or not attached correctly, catch can hoses.
Usually you should see +5/-5 fuel trim at idle. So just check what you can until you narrow it down.

[ctrlz]

Originally Posted by GreyGhost702

No. It's asking for more fuel on both banks. If anything, it says the sensors are likely not the issue. Since the trims are pegged asking for more fuel, the place to start is unmetered air.

Agree, trims are rich to compensate for a lean condition.
Since both banks are affected, I would favor intake over exhaust as source of vacuum leak.
Try a search here for "msd intake vacuum leak." pretty sure every intake has had some posts here with leak problems.

[Mohawk_1SS]

All, thanks for the suggestions. I'm going to go over all the bolts and connections for the MSD tonight and I'll report back either way.

[Mohawk_1SS]

Update: I'm made contact earlier in the day with the shop that did the work and the owner provided similar thoughts as you all. I ended up tightening the bolts on the MSD and confirming connections were tight. Long term fuel trims now look much better (just under 5% at idle on both banks). Still waiting for the light to go away, but the tuner has been very responsive and I've sent logs to him to have a look. I do wonder if the spikes in short term fuel trim are something to be concerned about. They seem to occur when i roll onto the throttle. I will let everybody know if anything more comes of this.

Thanks