Help with smog test

Bluesman123 · April 24, 2004

I have a set of DTCs that I'm wondering if they will eventually correct themselves. << did that make sense??

1997 L31 5.7 Vortec

I just had the VCM reflashed yesterday by the dealer, and I am putting some miles on it when I get P0172 and P0175, fuel/air mixture rich on both banks.

Fuel Trim: ST = -1% LT = -18% in both banks

02 Sensors check OK

Catalyst Check Incomplete

I have not looked at the plugs yet

It looks to me like the injectors are "dialing back" on both banks, so I am hoping this condition will self-correct. Am I wrong in this?

I have to get it refereed and smogged next Friday. Would it help if I yanked out the air cleaner until the check is over?

Thanks for your thoughts,

Dave

Jeremy WI · April 25, 2004

You are probably going to have to get in the upper intake manifold to fix this one. Either the fuel pressure regulator is leaking in there or an injector is, check for falling fuel pressure after the pump quits with the return line pinched(on hose section under vehicle). Do you know what the cam retard is? It could possibly be relative to your problem

Bluesman123 · April 25, 2004

Thanks Jeremy, I did have that problem before. I installed the updated MFI injector set and that solved the leakage problem.

By the way...for anyone else reading this post...if you have a 96-98 (I believe these are the years) 5.0 or 5.7 MFI, there is a service bulletin update on your system. If you have less than 100K miles, GM will do it for free! Otherwise, it is $315 and a busy afternoon to install it yourself.

I think I've narrowed the problem to a restrictive air filter. I think it is making it too rich at highway speeds, but too lean at idle (hence the high HC). Tomorrow I'm going to install a K&N and see if that helps.

I'll keep you posted...thanks again for your suggestion.

Dave

Jeremy WI · April 25, 2004

Check the cam retard with the scantool, my truck set the same codes after intake manifold replacement, I found the trucks cam retard was -11 degrees- not quite enough to set the P1345 but enough to cause some slight misfiring. I don't think the problem will solve itself, as long as the long term fuel trim average is low enough the code will remain