I have a problem that I'm hoping you can help me with. I installed a new air intake when I installed my new tune from MPT (91 Oct Performance Street), and I've been throwing lean codes off both banks pretty consistently ever since. I know that K&N intakes are a "no tune required" system, but mine is a custom-built 4" intake with a K&N filter and air dam. I also have a functional hoodscoop that dumps into the air dam.

I've looked everywhere for vacuum leaks and anything else that might trigger the lean codes and found nothing, and my MAF and O2 sensors are functioning and reporting properly. My longterm fuel trims are constantly positive, so the lean condition is genuine. so my question is; if my air intake is bringing in more air than an off-the-shelf K&N intake, could it be that the tune has reached its allowable limit of enriching the air/fuel ratio, still not being able to add enough fuel, and this is triggering the lean codes? Been going on for about a month now. I sent an e-mail off to MPT too, but you guys have helped me out a lot in the past. Any input would be greatly appreciated.

Thanks.

 

Oh, and my signature picture and mods list is out of date. I'll update soon.

 

Last night, I took apart the air intake, RTVed any possible leaks, checked the PCV valve to see if it was stuck open, removed and inspected the PCV to intake hose, removed the throttlebody, cleaned it and inspected the gasket, and there was a vacuum line running from the back of the TB that has a plug from the factory - the plug wasn't all the way in, so pushed that back in. Couldn't find any obvious issues anywhere. Cleared my DTCs after that. I'll post back to let you know if the CEL comes back on.

 

Yeah, CEL's back on. Any ideas? I'm leaning (hah!) towards it being the tune. It's just too much of a coincidence for it to be anything unrelated to the air intake, seeing as how it first started throwing lean codes 2 days after installing the new CAI. Thoughts?

 

I'd talk to MPT. I need to talk to them about my tune myself as I'm having an issue with the same tune (89-91 Perf) but it's a different issue than running lean. You may need to swap injectors if it's pulling substantially too much air, but I can't imagine it's pulling enough to where the stock fuel system can't keep up. Maybe your pump is going out or your fuel filter isn't flowing freely anymore?

 

So does it throw a lean code with the factory intake on it? Please dont tell me you got rid of the factory intake......

 

All right. I'm still waiting to hear back from MPT. Hopefully tomorrow. Yeah, I doubt it too that it's pulling so much air in that the fuel system can't send enough fuel to re-balance the ratio. I really think it's the tune. Fuel filter's brand new as of last week too.

 

Haven't tried swapping the factory one on. Actually hadn't thought of that. But I can tell you that it never reported running lean with the factory air intake (and Gotts mod). It started 2 days after installing the new air intake and the new tune from MPT, about a month ago. And when I initially contacted MPT, they said it couldn't be the air intake or the tune - so I've been looking at everything else, and not finding anything.

 

Try swapping the factory intake back on then with the tune. Then let MPT know of your findings.

 

Good idea. Thanks.