Thread: Running lean on bank 1

So I have tried to find a cure for this and right now I feel like I am just throwing parts at the car. I am getting a P0171 Fuel Trim System Lean Bank 1 code on and off again.

So far I have replaced the stock injectors with rebuilt flowmatched ones from ZZP. I have changed the fuel filter. I have changed the fuel regulator. I have changed the two fuel pump relays. I have bent the one pin on the outer relay out to make the pump stay in "high" mode. I have changed the MAF. I have changed the MAP. I have replaced all of the vacuum line with new rubber line. I have tested the fuel pressure. It is 41-42 normal and with the vacuum line from the fuel pressure regulator pulled it goes up to a steady 50.

The code is intermittent and usually only comes on when the car is coasting, at idle or bearly above idle. When I'm pressing on the gas more than a little bit, then it doesn't come on. Yeah, I know. Just keep it to the floor, but seriously I need help fixing this. I have a new AC Delco pump coming to me and a high flow fuel filter on the way also, just in case.

Any knowledge, thoughts, or enlightenments would be greatly appreciated.

For the sake of getting help, I have a 99 GTP 3.8 Supercharged stock.
Thanks again in advance.

Originally Posted by Fivefingerdeathpunch

At this point I would be doing a smoke test.

Could be a crack in the EGR tube, could be a leak between the TB and supercharger. Hard to say when we are just guessing and you are tossing parts at it.

I would be watching fuel trims on a scanner and either spraying carb cleaner or brake cleaner around anywhere that can suck in extra air past the MAF sensor. Watching for a change in the numbers, only nice data logging scanners will pick up the minor changes as they have fast refresh rates.

If things go over my head, then I apologize for my ignorance as I am not a mechanic, but I am trying to pour my love of my car into fixing it. I am not sure what a smoke test is. I assume it has to do with trying to find a vacuum leak? While replacing the vacuum lines I did a recommended check of spraying WD40 and seeing if the car changes how it runs. This is the check that lead me to find a bunch of cracked lines. I replaced them and now the test doesn't reveal any more leaks. How does this smoke test work?

I replaced the paper gasket between the throttle body and the super charger with the rubber one from ZZP performance. I retightened it after you said it. It is very tight still.

As for scanners, what type of scanner are you talking about and where can I get one. Right now I just have a code scanner that tells me the code and resets the CES light. I am more than happy to get good tools to trouble shoot. I just need to know exactly what is needed so I get the right one.

Thanks again for the quick replies.

Oh, and where is the EGR tube so I can check it?

The egr tube goes into lower intake just below the throttle body. Its a metal flex tube that's known to crack. Check out torque pro app for Android if you want something cheap to scan with. You need a Bluetooth obd II adapter. There is a ton of info around about it and which BT adapter to buy. This will allow you to monitor fuel trims and can help find a vac leak. Helped me find one on my sienna and netted me 4mpg after I fixed the leak

If your code is coming on shortly after you reset it, I'd say you have a decent sized vac leak. It took me about 4 cans of carb cleaner before I found my leak. I had to spray it in just the right spot/angle to make it register. Could be something you overlooked like o-ring on dipstick or oil filler neck.

Originally Posted by BillBoost37

For a lot of great info...without me having to repost it. Please search on P0171 and my username.

Bill, I did what you said, but it only returned 19 results with most stating you were a great help when they read what you posted, but I couldn't see the older posts for some reason. I did see that I should clean off the battery terminals and check the EGR tube. Is the EGR tube easy to replace or even get?

Thanks, brother, I will check those. Are those tubes an item that can be picked up at a parts store, or do I have to junk yard hunt?