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Vacuum leak

T

TUFTOUR

Hard-core CEG'er
Joined
Dec 6, 2002
Messages
2,908
Location
Harrisburg, PA
2.5L with NPG kit...vacuum/boost gauge is reading about 17psi (I thought it should be around 22?) at idle. Wide-band sensor reads about 17.3 or so, but the car seems to be running pretty rich by the smell. This was a problem that's been developing for awhile that only very recently became worse...at idle, the car used to be 14.8 to 15.1, but then started idling at 15.6 and now hovers around 17 and 18. I checked for leaks around couplings, etc. but nothing obvious came up...can the Xcal check for codes with NPG tune despite no CEL? Also, any ideas on where to trouble-shoot?
 
Joey said the vacuum/boost gauge should be reading between 15 and 17 idle, which is exactly where mine is at...any ideas why the wide-band would be reading over 17 at idle? The idle is midly rough and smells rich...no smoke out of the tail pipes or anything else obviously wrong. Any ideas?
 
Just datalogged this afternoon...car ran fine on boost and at steady cruise...only issue is the lean reading at idle from the wide-band. Sent the datalogs to Joey for review, but suspecting that the wide-band might be going bad and needs replaced.
 
AFR at idle isn't particularly important.

I wouldn't focus so much on that gauge at idle, but more the rough/rich conditions. Are you running colder plugs? That cause me a rough/rich idle.
 
NGK TR6 plugs...Joey gets back into town on Wednesday and should be looking at the datalogs I sent him this week....I'll post his feedback.
 
if you are concerned about a vacuum leak then do a pressure test. if it leaks vacuum it leaks pressure, and pressure is much easier to find with some soapy water. simply pull the MAF and insert the pressure tester into the coupler, tighten the clamp down, and then hook up an air compressor (with the pressure regulator turned all the way down). then slowly bring up the pressure to about 15-20PSI and listen for leaks. if you hear any then break out the soapy water to pin point the leak.

you can make a pressure tester from a PVC end cap (one of the round glue on ones) and a pneumatic fitting, whatever size fits your air hose. will cost about $5 total and is an invaluable diagnostic tool for finding boost/vacuum leaks.
 
Vacuum should be between 15 & 17. Thats where mine stays @ idle. I imagine u're running 24lbs or larger fuel injectors. Very possible u'd be getting wiffs of fuel at startup. I do. I'm running 45lb Cobras'.
 
Based upon the wideband readings, I thought there was a vacuum leak. My vacuum gauge is where it needs to be, so now I'm thinking the wideband is bad...I saw that when the wideband fails, it might not get hot enough and then will read all the way lean...^ and yes, I am running the 24lb injectors. I'll know for sure once Joey gets back to me about the datalogs I sent him.
 
From Joey's email tonight regarding the datalogs, "Short trim are perfect the long terms are less then 5% your tune is spot on you have a good setup." It appears that the wideband is bad...a new one should fix things. If anything, this thread provides some info. on what happens when it fails.
 
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