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#1
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02 sensor and gutted precats
Ok the question is that if I gut the pre cats will the O2 sensors still work properly or will the system need to be modified.....Long story short I bottomed out and mangled the main cat a little and am now looking to redo the exhaust either header back or at least precat back.
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86 GMC Jimmy Blue and Silver- R.I.P. 87 Integra RS ~228k miles R.I.P. 92 SVX LS-L Perly ~186k R.I.P. 89 240sx se red ~165k miles Gone and unknown 89 240sx se Black~185k R.I.P. 85 Toyota pickup ~205k R.I.P. 85 BMW 325e ~ Gone and unknown 85 Ford Mustang getting engine swap now! 05 Colorado ~108k Daily Driver |
#2
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I had read on here before some speculation that without the precats the 02 sensors do not get hot enough to read correctly.
I have been running with no precats for a few years now and have been getting 25-26 highway mpg and I don't have any CEL problems. So I don't think it will be a problem based on my experience.
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Matt Locker Link 2015 BRZ Limited 6MT 92 Ebony LS-L ECUtune Stage2av1, Z32 MAF, 370cc injectors, TomsSVX intake, BontragerWorks 22mm RSB #003, HID Hi and Lo beams, OT endlink and bushing mods, PWR Aluminum radiator, Harvey's QC shift kit, 2.5" flowmaster 80 exhaust, 17" Michelin Pilot Sport A/S, Poly sway bar bushings, Slotted Bradi rotors, AFBeefcake powdercoated calipers, 97 grill, and a huge set of air horns. 300,000 miles and counting 92 Ebony LS-L. ecutune stage1v4, motorsport 1pc pulley. Garage Queen - sold to Dad in upstate NY 155,000 miles 19 Subaru Ascent Premium - -Hers !. 89 DL 4x4 little red wagon - a.k.a. The immortal suby. 275k R.I.P. |
#3
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As is I'm only getting 23ish at best So thats good to hear, also right about when its up to temp if I stay low in the revs I can get a check engine light for the driver side O2 sensor, do I need to go with the Subaru $100 Oem one or can I just use a $40 universal and be just fine?
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86 GMC Jimmy Blue and Silver- R.I.P. 87 Integra RS ~228k miles R.I.P. 92 SVX LS-L Perly ~186k R.I.P. 89 240sx se red ~165k miles Gone and unknown 89 240sx se Black~185k R.I.P. 85 Toyota pickup ~205k R.I.P. 85 BMW 325e ~ Gone and unknown 85 Ford Mustang getting engine swap now! 05 Colorado ~108k Daily Driver |
#4
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Alot of people will tell you to only use OEM sensors and they are probably right.
But - last time I changed mine I went with the splice in sensors and I haven't had any mileage decrease or CEL's since. Only been about 6 months with them so time will tell if they do not last as long. They seem to be working fine so far.
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Matt Locker Link 2015 BRZ Limited 6MT 92 Ebony LS-L ECUtune Stage2av1, Z32 MAF, 370cc injectors, TomsSVX intake, BontragerWorks 22mm RSB #003, HID Hi and Lo beams, OT endlink and bushing mods, PWR Aluminum radiator, Harvey's QC shift kit, 2.5" flowmaster 80 exhaust, 17" Michelin Pilot Sport A/S, Poly sway bar bushings, Slotted Bradi rotors, AFBeefcake powdercoated calipers, 97 grill, and a huge set of air horns. 300,000 miles and counting 92 Ebony LS-L. ecutune stage1v4, motorsport 1pc pulley. Garage Queen - sold to Dad in upstate NY 155,000 miles 19 Subaru Ascent Premium - -Hers !. 89 DL 4x4 little red wagon - a.k.a. The immortal suby. 275k R.I.P. |
#5
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i have the exact same problem with my pass. side sensor. just had them replaced last oct. at the dealership too. |
#6
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After you replaced them or did that fix it?
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86 GMC Jimmy Blue and Silver- R.I.P. 87 Integra RS ~228k miles R.I.P. 92 SVX LS-L Perly ~186k R.I.P. 89 240sx se red ~165k miles Gone and unknown 89 240sx se Black~185k R.I.P. 85 Toyota pickup ~205k R.I.P. 85 BMW 325e ~ Gone and unknown 85 Ford Mustang getting engine swap now! 05 Colorado ~108k Daily Driver |
#7
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#8
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No matter how many times I tell people they still don't get it. Codes don't necessarily mean that the identified sensor is the actual problem. Changing (or just changing) a sensor because of a code is the Autozone approach. They'll read the code for free and even sell you a sensor but that usually isn't the root cause of the problem. It ends up costing you money, to their profit as most people just buy more parts in attempt to correct the problem - called the shotgun approach. Consumers get mad as hell when their dumbass mechanic ("but he's cheap, he has to be good") takes this approach but they seem to be willing to accept it when they are the uh.. underinformed party.
In particular O2 sensors are pretty reliable devices, especially considering the environment they operate in. By far and large they will survive the vehicle they reside in. What causes those that fail are bad gas, excessive fueling caused by other engine or engine management malfunctions, chemical pollution - such as silicone sealers or antifreeze contamination and physical damage. Then, of course, some just fail due to age and/or manufacturing inconsistencies but these probably comprise the smallest percentage of failures. That being said, when an O2 sensor fails there is almost always something else to blame and that root cause needs to be addressed in order to prevent subsequent failures. In answer to the original question, gutting the pre-cats will not affect the O2 sensors ability to reliably perform their intended function. Reduction of back-pressure in the exhaust can promote sluggish response or extended warm-up periods but just gutting the pre-cats, and leaving the main cat in place, should have little to no effect on that.
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ASE Certified Master Automotive Technician w/L1. ASE Certified Master Medium/Heavy Truck Technician. Certified EVT (Emergency Vehicle Technician) |
#9
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Ok then what about the accompanying Driver side knock sensor CEL? Also did the O2 sensor and I think fuel milage has already gone up.... 280 with 1/4 tank left and I usually get about 275.
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86 GMC Jimmy Blue and Silver- R.I.P. 87 Integra RS ~228k miles R.I.P. 92 SVX LS-L Perly ~186k R.I.P. 89 240sx se red ~165k miles Gone and unknown 89 240sx se Black~185k R.I.P. 85 Toyota pickup ~205k R.I.P. 85 BMW 325e ~ Gone and unknown 85 Ford Mustang getting engine swap now! 05 Colorado ~108k Daily Driver |
#10
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i've been throwing a code 32 for awhile now. i had new o2 sensors put in in oct and i immediately got another code 32. took it back and got another sensor put in and it was fine till the day i adjusted my brake band and then it started lighting up the code 32 again. i figured my cam timing might be off so i checked it and sure enough it was. i fixed that and now i'm still throwing a code 32 and threw a 37 once too. i was thinking my pcv valve being clogged and filling my intake with oil or the cam timing may be what screwed up the sensors and the cats which are now semi clogged and need fixed. what do you think beav?
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#11
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I do know that my PCV needs replacing and have had one for some time now guess I'm gonna hafta go to sears. (for a tool or two.) BTW that makes sense to me.
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86 GMC Jimmy Blue and Silver- R.I.P. 87 Integra RS ~228k miles R.I.P. 92 SVX LS-L Perly ~186k R.I.P. 89 240sx se red ~165k miles Gone and unknown 89 240sx se Black~185k R.I.P. 85 Toyota pickup ~205k R.I.P. 85 BMW 325e ~ Gone and unknown 85 Ford Mustang getting engine swap now! 05 Colorado ~108k Daily Driver |
#12
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#13
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I've not seen an O2 sensor go bad from oil contamination that wasn't also putting out an easily noticeable cloud from the exhaust. It also takes a LOT of oil burning to clog a cat, even partially. Until someone does a backpressure test and/or actually removes the cat and looks inside there is little reason to suspect clogging. Cats generally only go bad from design (usually the 'guts' work loose and rattle) or from gross negligence/abuse. Generally a car would be running fairly poorly for quite a while to have a cat to go down as a result. I would be inclined to think you may have a wiring issue since the problem recently returned after you were in the vicinity, adjusting the band.
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ASE Certified Master Automotive Technician w/L1. ASE Certified Master Medium/Heavy Truck Technician. Certified EVT (Emergency Vehicle Technician) |
#14
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#15
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The only way I know to check an O2 sensor is with a graphing multi meter or o'scope. Warmed-up sensor, engine @ 2000 rpm, voltage should rise and fall between ~.2vdc & ~.9vdc at least once every five seconds, the more the merrier.
Hissing could simply be leaking gaskets. Rotten egg smell comes from excessive fueling/poor combustion (which are the same thing as far as the cat is concerned.)
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ASE Certified Master Automotive Technician w/L1. ASE Certified Master Medium/Heavy Truck Technician. Certified EVT (Emergency Vehicle Technician) Last edited by Beav; 09-18-2005 at 02:46 PM. |
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