Running Lean And Dying.. Throwing Codes P0171 0174

All right.. I'm going to describe what happened and make it as short as possible. And I do appreciate any info and feedback..i recent purchased a 1997 cobra.. I used to own it .. I sold it . And recently bought is back.. when I bought it back it was throwing codes p0174 p0171 lean ... causing it to die out at idle after about 5-10 seconds..i rev the engine to keep it from dying .when I drive and it's moving .. it's fine... also another code for the exhaust ..the car does have a off road xpipe.. no cats.. So that is why I got the one code..as far as the other codes I'm trying to figure out where to start.. I hear people say it's the MAF.. vacuum leak.. etc.. I want to try and narrow it down before I start replacing a bunch of things . I one thing I noticed was that the car is a little more louder .. I think I might hear a exhaust leak.. would that cause the codes? And cause it to die at idle ? Or is it a MAF? I still have the stock one... I did spray carb cleaner around the engine for leaks . Really didn't find anything. Only performance things done to engine is CAI... and msd coils...am I missing to check anything? Any help would be appreciated .. Please help.. thank you

wmburns said:

An exhaust leak can CAUSE a lean DTC. Note that it will be a false lean condition. The exhaust leak will allow air to enter into the exhaust. This will make the PCM "think" that it's running lean. However in actually the motor will be rich due to the extra fuel that the PCM will add.

Have you checked the battery and battery cables?

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U know what.. funny u say that .. I think I hear a exhaust leak and the codes say its running lean.. but I smell the exhaust and it smells rich.. do you think it could be a exhaust leak causing me all these problems...? And why would I check the battery? What would i be looking for ..? I know before I bought it back he put in a new battery .. any info would help

wmburns said:

Yes. That is way I gave the information along with the reason behind it. This goes double now that you also mentioned the exhaust actually smells rich. Bottom line. The O2 sensors can't tell the difference between O2 left over from the combustion process or pulled in from outside air.

At the very least it seems silly not to attack an obvious/reasonable issue before moving onto more difficult (and expensive) "possible" causes.


IMO every trouble shooting session should start with a review of the charging system. Making sure that the battery and alternator are working as they should. Rest assured that there are alternator and battery issues that can CAUSE apparently unrelated symptoms.

Besides wouldn't it just feel wrong to do a bunch of work and replace a bunch of parts only to find out it was a bad alternator all along?

Here's some more information to review.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

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Ok thanks. I'll take a look. And let you know what i found .. I'm going to take it to a exhaust shop and have them take a look

So I went to a exhaust shop. Have a leak in one of the flanges from h pipe to muffler.. and exhaust leak on both sides from exhaust manifold to h pipe... I was thinking I'm going to have the stock h pipe with cats put back in.. u think that is what causing my lean codes ? Also have my 02 sensor hooked up witch is also throwing a code..? Thinking with install of stick pipe and new gaskets will fix my problem? Any comments