Surging 70-80mph--AFR FUBAR

[LAStang1234]

Usually on my Boost/Vacuum gauge I use to idle at roughly 20 vacuum, driving usually around 15. Skip to this past week, my idle has been right at 8 and driving almost at the neutral part of the gauge. This is a vacuum leak right? I literally haven't done anything to the car, it's been barely driven the past 3 weeks.

Now onto AFR. Idle it's where it usually is 14.5-15.5. When I'm driving it's pretty normal also. Now when I get to 70-80mph my AFR starts jumping all over the place. I get above 90 or so AFR is back to normal for the most part. WOT is fishy at times too. I only stay there for a second because I'm a little worried. It'll jump to 11.5, then I let off and it jumps to SUPER LEAN like in the 18-20s in the AFR. Taking a little to get back to normal. I have no clue whats going on and am looking for some help fellas. Thanks

 

[muztangman93]

I would check all vacuum hoses. Also When you let off the gas it should go lean because its mostly air coming in on deceleration

 

[LAStang1234]

I would check all vacuum hoses. Also When you let off the gas it should go lean because its mostly air coming in on deceleration

I checked for leaks. I might go a little more in depth this weekend on it. Isn't there a trick for finding a leak, spraying brake cleaner or something?

 

[hamish]

muztangman93 is correct, when you let off the gas it should go crazy lean.

o2 sensors should swing above and below their true reading, it's how they work.

How much is it jumping?

I checked for leaks. I might go a little more in depth this weekend on it. Isn't there a trick for finding a leak, spraying brake cleaner or something?

I believe you can use a propane.
HERE

http://www.youtube.com/watch?v=YH6306zM-Ug

 

[BruceH]

It sounds like unmetered air. Vacuum lines are the usual suspects. Physically grasp each end to make sure they are connected. Sometimes they will look ok but not have a solid connection.

Suspect number two would be a loose intake manifold. Make sure it's still properly torqued. If you are running breathers make sure the pcv plugs are secure. Also check your bypass valve.

That's all I have for you.

 

[muztangman93]

I think its carb and choke cleaner. You can spray it on and if the engine stalls thats where its at but I doubt you would find it unless its the intake manifold that way.

 

[RLF9409]

Been sitting for 3 weeks? Might be something in the gas. If you haven't done anything to the car, usually something has to happen for something to change...did you wipe down the engine or anything out of the ordinary? Does sound like a vacuum leak or something allowing more air to come in.

We're abouts are you in Germany? Been to Racewars yet? I was in Vilseck for 3 years and then Heidelberg for 2 years. Had a blast with the Saleen there...

 

[skwerl]

Agree, it's unmetered air entering the intake. Look at every connection between the MAF and the intake manifold following each vacuum line all the way out, then check the manifold as well.

 

[Fullboogie]

Use brake cleaner, not carb cleaner.

 

[LAStang1234]

Appreciate the help fellas. I'll tear into everything this afternoon!

 

[LAStang1234]

Still no luck! Sprayed brake cleaner, no leaks were found. Still runs like shit at 70-80mph.

 

[LAStang1234]

Just wanted to update, turned out to be a vacuum leak in my intake manifold. All's normal. Now if I could just get some good weather to swap this kit!

 

[skwerl]

A vacuum leak, huh? You don't say.

 

[UltraKla$$ic]

A vacuum leak, huh? You don't say.

Yep, nobody suggest THAT. LOL!!!

 

[LAStang1234]

A vacuum leak, huh? You don't say.

Yep, nobody suggest THAT. LOL!!!

I figured it out all on my own!! Lol

 

[california gt]

so you removed it at one time and now the bolts had loosen?

 

[RLF9409]

I curious to know where the leak was from too.

 

[Paps]

Same. Was it leaking from temp sensor tapped into intake?

 

[LAStang1234]

so you removed it at one time and now the bolts had loosen?

I curious to know where the leak was from too.

Same. Was it leaking from temp sensor tapped into intake?

Took the entire manifold and aftercooler off. Reinstalled and it's back to 20ish in Vacuum on my gauge. Everything seemed pretty tight, I honestly have no idea what the pin point problem was. I sprayed brake cleaner on the sides, but it never showed a problem before.