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2 Lean codes 0171/0174 after MSD manifold install **FIXED**
So my 18 Grandsport is nearly done with bolt ons. Its had 1 7/8 long tube headers, afe intake, catless x pipe, tune for a few months. 2 months ago i tied in the flex fuel sensor and got an updated tune for the E, cars been running great. To help monitor condtions, i also have an AEM wideband and banks idash gauge installed. Fast forward to last week, me and my son installed a soler 95mm tb along with the msd atomic manifold at the same time. I made sure to get the correct adapter piece's from soler to fit the 95mm tb onto the msd opening along with the silicone tube that goes from the afe intake to match up to the tb correctly. We followed the instruction booklet to the T along with the proper torque specs for the bolts and the proper sequence of tightening. After a few heat cycles we rechecked the bolts and did another tighening to the correct specs.
This brings me to yesterday, i had already reached out to my tuner and he had prepared an updated HPtuner tune for me to take account for the new manifold and tb. After getting some logs i sent those in and got a further revision adding a little bit more fuel. Later in the day the CEL came on for p0171 & p0174 system too lean bank 1 and bank 2. Tuner wanted me to double check header bolts and we did and they seemed perfectly tight. Next my son hooked up his automotive smoke machine and we attached it to the pcv inlet port on the front of the msd manifold to see if it leaked any smoke out and thus showing us where the air was coming in at. After running that for 10 minutes, there wasnt a single hint of smoke anywhere showing any kind of air leak. Im at a loss what and where to check next to try and find out where this vacuum leak can be coming from causing the lean codes.
Anyone with an msd manifold ran into similar issues?
Thanks
Last edited by geeteedan; Apr 13, 2026 at 03:24 PM.
Run the engine at idle and look at your long and short term fuel trims...now run the engine at 3000 rpm's for a few minutes...if fuel trims DECREASE you have a vacuum leak...if not you have something like a fuel delivery or possibly a MAF issue...this is engine diagnostics 101...BTW, if you used the PCV to introduce the smoke the TB should have been blocked off...it is not fully closed with the car shut off.
Run the engine at idle and look at your long and short term fuel trims...now run the engine at 3000 rpm's for a few minutes...if fuel trims DECREASE you have a vacuum leak...if not you have something like a fuel delivery or possibly a MAF issue...this is engine diagnostics 101...BTW, if you used the PCV to introduce the smoke the TB should have been blocked off...it is not fully closed with the car shut off.
I had this problem with mine in cold weather. I never found a leak but wound up pulling it back off and putting a bead of black RTV in all of the channels where the gaskets sit and retorquing the thing back together then reinstalled it on the car the next day after everything cured. So far so good. In the instructions they recommend retorquing the bolts on the manifold after 500 miles (can't remeber the exact number). There is also at least one YT video where a guy shows a similar problem and starts to check the bolts and several are loose, like really loose. Just be careful retorquing the manifold to head bolts. I snapped one during that 500 mile re-torque and it was a bear to get out but I managed to do so. But yeah lots of people run into this with this very expensive manifold.
Did you remove the foam under the stock intake? I know i had to, that was the only way the MSD would sit flush. Also replaced all the seals on the manifold and put rtv on them just to be safe for this very problem. I would also check the vacuum tube in the rear, I know it was a pain to push it all the way in.
Did you remove the foam under the stock intake? I know i had to, that was the only way the MSD would sit flush. Also replaced all the seals on the manifold and put rtv on them just to be safe for this very problem. I would also check the vacuum tube in the rear, I know it was a pain to push it all the way in.
we did not remove the foam underneath but plan to take it back off and do the rtv sealant. When we do, ill remove the foam. I did purchase 8 new intake seals and installed those when we originally installed the manifold
The foam was removed along with the stock intake when I did mine and didn't go back. The MSD has more volume than the stock intake and some of that takes of space previously occupied by the foam.
That was it, car is running so much better with 0 codes. Was able to get some data logging done for the tuner finally. My full bolt on c7 is complete. Maybe next year I'll look into a cam and head work. Hoping I'm close to that 500rwhp # now
I'm glad everything worked out. I wish MSD said to remove the foam to begin with. After I dry fitted the manifold I realized there was no way it would sit all the way down flush with the foam still there.
I'm glad everything worked out. I wish MSD said to remove the foam to begin with. After I dry fitted the manifold I realized there was no way it would sit all the way down flush with the foam still there.
absolutely agree that it should be in the instruction to remove the foam, would save a lot of people the extra headaches
2 Lean codes 0171/0174 after MSD manifold install **FIXED**
