Can exhaust leak from Exhaust Manifold not be noticed

[zedjr10]

Can a small exhaust leak before O2 not be easily noticed. I am trying to track down why my car runs so rich and someone mentioned on another thread i could have an exhaust leak. I thought exhaust leaks are easily noticed so i just assumed i don't have one. I hear,smell or see nothing noticeable in exhaust manifold or pipes. My car doesn't run hot but it runs rich and gets horrible city gas mpg. Can a exhaust leak be there and not be noticed. I do hear a very slight ticking sound. It is very slight and doesn't sound like a valve slapping or i'd have knocking on acceleration i thought. I can't imagine it was in pipe as i would notice that i thought easily. Any useful help is appreciated.

[Fleetw00d]

I suppose you could have one, but with the exhaust pressure likely being always higher than ambient pressure around it, it shouldn't be pulling in fresh air to affect the O2 sensor. I didn't peruse all your other threads for answers - what have you done so far to troubleshoot the problem? The O2 sensor itself is one likely candidate; how old is it? What brand?

[zedjr10]

I suppose you could have one, but with the exhaust pressure likely being always higher than ambient pressure around it, it shouldn't be pulling in fresh air to affect the O2 sensor. I didn't peruse all your other threads for answers - what have you done so far to troubleshoot the problem? The O2 sensor itself is one likely candidate; how old is it? What brand?

Thats alot let me try to list what is relevant to city and idle mpg issue.
1.O2 sensor(replaced with ngk)
2.Cat(flow is good). Though it seems be operating below operating temps. WHich makes sense as it is running rich. It was 370 F at cat entry totally warmed up. I thought minimum is 410 f.
3 Map sensor
4 EGR system cleaned, ported and checked thoroughly.
5 Vacuum leaks. Checked all vacuum hoses as best as i could. Maybe somewhere i missed.
6. Fuel Filter
7 Spark plugs(old ones looked fine)
8 Valve Adjustment(am rechecking that soon)
9 Full tune up(rotor,cap,wires,pcv valve, etc)
10 FITV & EACV valves
11 Fuel pressure regulator(replaced with JY one and o-ring replaced also)
12 compression test(140 dry/160 wet across all 4 cylinders)
13. ECT sensor.
14 Air charge sensor.
15 Shocks(not that this would effect it much)
16 coolant system purge
17 ICM on dizzy
18 butterfly plate gaskets on Plenum replaced.

Here are a few things i haven't done or i think are possibilities.
1. Clogged air intake manifold. I used a few cans of seafoam on it and intake still seemed clogged.
2. Exhaust leak before o2 sensor(likely on exhaust manifold at head). The only way i know to check for exhaust leak is look and smell around. I can put hand of tailpipe and car still runs fine but what does this test really say anyways.
3. O2 sensor possibly. It is new ngk but mpg might of gotten worse after replacing.
4. Worn valve seals or something else in head. I only have some white smoke on acceleration.
5. Dizzy. No really reason except it is old and maybe it don't function right. I think this is unlikely though.

Here are some other symptoms
1. Raw egg smell sometimes leaving exhaust. It is definitely running rich when cold.
2. Slight white smoke on acceleration(no knocking). It's not really that bad and car accelerates pretty good. I've had other cars that smoke worse.
3. Intake manifold pressure read low at 17 in hg vac(minimum healthy my book sais). So leads me to believe intake is clogged but not totally clogged. I just replaced with K & N air filter today so maybe i check again soon.
4. Car takes forever to warm up. 12 or more minutes idling and still not warmed up in cold. Which makes sense if running really rich.

Sorry this is long but i figured to be detailed since u asked. Thanks for any help.