Hi all . Not to post another redundant problem but here goes. 97 4.2l code P0174 only. Have checked all vacuum lines PCV valve & tubes are great. LTFT BANK2 is +25 @ idle and of course drops to normal range while driving. O2 sensor on bank2 is fluctuating normally. Have tried LP to find leak while watching SRTFT and cannot locate . Upper & lower intake manifold gaskets have been replaced. Exhaust manifold is nice and tight to head. Inspected exhaust manifold from top & underneath truck did not see any black areas to indicate exhaust leak. I really am stumped . Any help would be greatly appreciated!

 

No issues with the brake booster hose, check valve, or booster it's self?

Any issues with the HVAC control, that is vac operated too and wouldn't show up on your propane test.

Good luck.

 

Checked all vacuum lines . Brake booster /check valve good. Manifold @ idle is steady 20 inch vacuum measuring directly from intake manifold . Compression test on all cy in bank2 are 175 psi. Still showing LTFT ON. BSNK2 is +25 . Ugh!!!!!!

 

the metal plenum 4.2's has a vac hose under the plenum that is an issue and is easy to overlook when testing, maybe????? I'm shooting in the dark just a little.

Two other odd ball you can get a vac leak is the rocker cover gasket on the PCV side or maybe the IMRC, I believe that is also vac related.

I'm not trying to question your testing abilities, just throwing out some of the more rare causes. The reason I asked about the HVAC control is because some have had issues with the vac lines breaking close to where they go through the firewall and testing under the hood won't show a leak inside the cab.

I hope you find it soon, good luck. If any other stupid stuff pops into my mind I will pass those along also.

 

No problem. I appreciate any and all suggestions. After thoroughly checking and rechecking yesterday I took the truck out for hard drive back/ forth on the freeway. Pulled into a drive through and while I was in line there was a tick, tick, tick coming from engine. Maybe I have an exhaust leak. I'm gonna pull the manifold on bank2 and inspect because I could not see anything while it was still connected. Hopefully that's my problem. That or a fueling issue to that bank.

 

It's not just the head to manifold leak that will cause the lean code from exhaust leaks. If the exhaust is leaking close to the o2 sensor that can trip it also.

 

I'm gonna shove a smoke machine up her tailpipe !😳😄 see if I can find it that way🤞🏼. Thx

 

Found where my un meter air was coming through causing p0174 code lean bank 2 . Hope this helps anybody else battling this code

 

Sorry . Should of posted this with pics. The way I found holes in exhaust was, I put air hose in tailpipe & sealed it . Pushed 7-10 psi. After about 10 min the black soot appeared revealing the pinholes in exhaust manifold.