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Discussion Starter · #21 ·
I'm no expert in this area but the way I understand it the upper O2 sensor is there to analyze the exhaust gases before they enter the catalytic converter. By measuring the level of oxygen present in the exhaust the PCM can sense if the air/fuel mixture sent to the engine is either too rich or too lean and subsequently make corrections by adjusting the pulse width sent to the fuel injectors. The converter is most efficient when the air/fuel ratio is 14.7:1 which is the stoichiometric air/fuel ratio for gasoline. The lower O2 sensor has no effect on engine performance. It's output signal should be essentially a straight line. As the catalytic converter degrades, the signal from the lower O2 sensor starts to look more like the upper sensor signal. When the the signals look too much alike the PCM (on my car) will set DTC's P0420 and/or P0430 (Catalyst System Efficiency Below Threshold (bank 1 and/or bank 2)).
My understanding that on these older motors the lower sensor that is after the cat has no influence on engine tune but will trigger a check engine light
I had previously gutted the cats and to stop the check engine light I simply put some O2extenders on those lower ones to put them further away from the exhaust and it worked
Will ask the Aussies what they do with these headers to deal with that
 

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In order to avoid throwing a code, some people have installed MIL eliminators on the rear O2 sensors. I have never done this nor do I know if these devices are even available for a Suzuki engine. Here's a link to a short video.
 

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So if mtbowhunter orders these headers (or "extractors"), how does he avoid the P0420 / P0430 codes? How does he pass emissions testing?

Just curious.

Edit: I'm too slow! Thanks.
 

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Azure Handwriting Font Rectangle Gadget

The upstream O2 sensor (sensor 1 in the graph above) bounces between 0.1 volts and 0.9 volts in normal operation. I think that signal still continues to correct the air/fuel rartio even if the cats are gutted. The downstream sensor (sensor 2) is basically a constant 0.62 DC voltage if the cats are in good condition. I believe the MIL eliminator just sends a 0.62 volt signal to the PCM telling it the cats are in good shape even though they are no longer functioning. Another thing to consider is that only pre-cats are monitored by the PCM. even if the exhaust manifolds are gutted, the main catalytic converter under the car is still going to function normally once it reaches operating temperature. The pre-cats (or PUPs) heat up quickly and are only there to clean up emissons while the main converter is still cold.
 

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My Chevy service manual doesn't call for threadlocker on the manifold bolts / studs. I chose not to, but if I were doing it again, I'd reconsider.

Recently I found several loose ones, after replacing my manifolds about 3-4 months ago.

So I would say at minimum, re torquing them after a few heat cycles would be a good idea.
 

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Mine were either cold or just barely warm. Came off with a ratchet.
 

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I don't really know. They were loose, but I couldn't see them below the manifold. So I just cranked them down.

Interestingly, only my lower fasteners were loose. It's possible I never torqued them down to begin with.
 

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Discussion Starter · #31 ·
so, my guy in Australia that i ordered the wildcat headers from said that downunder the 2.5L suzukis only had the upstream 02 sensors as they did not use the exhaust manifolds with the built in cats, only when the 2.7L came out.
so the ECM in those rigs did not use the downstream 02 sensors, different exhaust manifolds
may have to weld some bungs in the wildcat Y pipe so i can put my 02 sensors in them with the extenders on them like i have now so they dont kick they service engine light!!
 

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Discussion Starter · #32 ·
Wow, only 5 daysfor mu exhaust headers from australia to arrive here,fast!!!!
i have a muffler/pipe assy comminf thru amazon and they have had the order for 5 days and still have not shipped!!
unfortunately, kinda sorta, i am away in my rv so will not see them for another 2 or 3 weeks when i go to install them, lots of time to put nut loosner repeatedly on the stud nuts!
 

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Discussion Starter · #33 ·
HELP!
CAN one of our members PLEASE measure the overall LENGTH and WIDTH of the 2.5L V6 engines exhaust port on the cyl head or on the exhaust manifolds for me
just got a look at the AUS headers and the exhaust ports are considerably smaller than my manifold gaskets openings and i want to check before i remove my manifolds!!
 

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Discussion Starter · #34 ·
Thanks guys for the PMs with the info
so it looks like i screwed up ordering those headers
it seems the australian GV 2.5L V6 has smaller exhaust ports than ours over here
their specs called for it to fit 2.5 but NOT the 2.7
their 2.7L engine has larger exhaust ports, probably the same as our 2.5/2.7 !!!
i may be able to mill the ports out on the headers to match but what a pain to get done
too much to remove to use grinding wheels
to bad as the headers look great and well made
live and learn!!!
 

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I took a look at the parts catalogs and the later production (04~05 model years) Australian market & US market 2.5 V6 engines use the same part number cylinder heads, so the ports should be identical - the part numbers for the earlier years are different for both markets, so the difference in port sizes is not market specific but year specific - I'd suggest you pull the manifolds on your 2000 and check them, it'll cost you your time and the gaskets, and who knows, you might get lucky.
 

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Discussion Starter · #36 ·
my GV is a 2000 Canadian model which i believe is identical to the USA model
if you lay the gasket on the manifolds they are not even close and part numbers for the ex gasket for the 2.5 and 2.7 are the same
wildcat lists the headers as being for 2.5 only and NOT the 2.7
should have checked the gasket part numbers first
the PMs sent by 2 members with port measurments on 2.5l confirm this
 

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Just so you understand, I have no horse in this race - you asked about the exhaust ports, but you're looking at exhaust gaskets - what I'm telling you is that depending on the year of production the heads are the same or may be the same.

You've already spent the money to acquire & import the headers, if you want to walk away at this point, it's your choice, but if I were in your place, I would be looking at the ports and not the gaskets.
 

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Discussion Starter · #38 ·
yes, i understand
2 of our members were kind enough to take the time and effort to measure a 2.5l exhaust port and a 2.5l ex manifold for me and that verified the big difference in the port size versus my headers port size
the info for the headers says years 1998 to 2005 for the SQ625 engine???
 
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