will exhaust manifold leak cause lean idle and rich under boost

[spools420a]

i have a lean idle/rich under boost,idle is 17afr and under full boost im seeing 10.0 afr.
boost leak tested the induction system at turbo inlet and only had minor leaks at 15 psi which i fixed,i then pressurised the exhaust and found a leak between the turbo and manifold which is now my suspect.

i understand how this will creat lean under idle as venturi effect from pulses draw air in but i dont understand how this could create a rich mix under wot because the manifold becomes pressurised how would this create a rich mix?

any thoughts?

[jedi03]

my initial though is that an injector is sticking or not operating correctly...that could definitely cause a lean condition, but i doubt it would cause a rich condition...

[Kingtal0n]

exhaust leak makes a lean wideband reading.

Tuning and maf issues cause rich reading. Or bad parts as suggested such as a bad injector of course.

[spools420a]

i never like to leave dead end threads for those who have the same issue the fix was fixing the exhaust leak pre o2.
what happens is your engine creates pulses at idle these pulses suck in and blow out air and exhaust gasses,so when these pulses accure your getting fresh air drawn into the leak which the o2 then sees a lean condition,

if you have a lean idle that goes away when you increase rpm suspect either exhaust leak like i had or vacuum leak/boost leak,a vacuum leak will cause identical condition because you are at most vacuum during idle and the more rpm the less vacuum which means less vacuum leak of unmetered air drawn in bwith increased rpm.


best method for finding both type of leaks is building a homemade boost leak tester thats basically a coupler with pvc cap and tire shrader valve installed in it so you can pump air into the system and find leaks,beause there are countless videos and threads on this topic just youtube "diy boost leak tester" and you can use this to also find exhaust leaks by installing it on exhaust tip.

[slider2828]

Originally Posted by spools420a

i never like to leave dead end threads for those who have the same issue the fix was fixing the exhaust leak pre o2.
what happens is your engine creates pulses at idle these pulses suck in and blow out air and exhaust gasses,so when these pulses accure your getting fresh air drawn into the leak which the o2 then sees a lean condition,

if you have a lean idle that goes away when you increase rpm suspect either exhaust leak like i had or vacuum leak/boost leak,a vacuum leak will cause identical condition because you are at most vacuum during idle and the more rpm the less vacuum which means less vacuum leak of unmetered air drawn in bwith increased rpm.


best method for finding both type of leaks is building a homemade boost leak tester thats basically a coupler with pvc cap and tire shrader valve installed in it so you can pump air into the system and find leaks,beause there are countless videos and threads on this topic just youtube "diy boost leak tester" and you can use this to also find exhaust leaks by installing it on exhaust tip.

Actually I should post my vacuum leak tester DIY part numbers... I know there are a lot of DIYs, but it never gets too specific enough.

Question for you, when I did my leak testing, from what I can tell, it actually doesn't hold air, you just have to listen for leaks or spray soap right? I had to cap off my electronic boost solenoid....

[spools420a]

Originally Posted by slider2828

Actually I should post my vacuum leak tester DIY part numbers... I know there are a lot of DIYs, but it never gets too specific enough.

Question for you, when I did my leak testing, from what I can tell, it actually doesn't hold air, you just have to listen for leaks or spray soap right? I had to cap off my electronic boost solenoid....

the more pressure you add the more acceptable you allow presure to bleed of,the rule of thumb i heard was it should bleed down to 0 in no LESS than 30-45 seconds.i read this on a dsm forum awhile back,the decay in presure leaks pat the ring and the more psi the more we allow decay be sure you remove oil cap before adding pressure.

what i do for starters is i blow as much into the system with my mouth then i plug the line and wait about 15 seconds,after 15 second you should hear the air rushing out your tester,if not you have massive leak.of course we recommend you always pump the system to the same psi your running from the turbo,i found a leak at injector o ring that only leaked at above 4 psi so now its beome the rule.but i like to start by simply blowing in the system first before i add psi just to see if its major or minor leak.

[240boosted]

what about a smoke machine test do that also to see if you have leaks i know there some autozone that had it that lent them out