Cat Converter needed on 90 K5 blazer?

[7387chevynut]

Hi guys,

I had new dual exhaust put on my 90 blazer, and forgot about the O2 sensor, and now found out that without the O2 sensor that the motor will run ****ty once its warmed over and stall on me in gear.

Somebody told me that even if I install the o2 sensor on the exhuast.........that I will still need a Cat converter for the whole system to run correctly.

But if so, then how does that work with DUAL exhaust? will I need 2 converters or just one installed on O2 sensor side pipe.

Just curious if anybody else runs 87-91 K5s with out Cat Converters (and I'm sure theres a few) and what you guys do.

 

[82355]

You don't need one unless you have inspections.

Martin

 

[4xcrazy]

O2 sensors have never cause my engines to stall when not hooked up, heck on the drive from Phoenix to Indiana last year, I accidentally unplugged mine while messing with the wiring, check engine light came on, but nothing else major happened, still ran fine, maybe a bit more fuel used.

Everything will run fine without the Cat on that year of truck, it's the years when they installed two 02 sensors, one before and one after the cat, the second was only there to make sure the cat was working properly. Went through this whole crap with my dads car last year when the Cat innards blew out, CEL came on and could not get any temporary or cheat fixes to work, it needed a new cat, after that, everything was fine, but even still his car ran fine. Just would not pass an emission inspection with the CEL on.

 

[smier]

Do you need a Cat? Depends on your local emissions regulations. Feds say you need it regardless of your local regs. Do you need an O2 sensor? Yes, its necessary for the computer to make adjustments to the fuel injection system etc. Where you locate it is dependent upon if you are running stock manifolds or headers, some guys have solved the header issue by installing a heated O2 sensor. This system is an antique and only requires one O2 sensor before the catalytic converter, some newer cars run 2 or more (my inlaws old V8 Ford explorer had 4 O2 sensors).

Now, some of these systems will run without a sensor hooked up like 4xcrazy mentioned. When I was into 3rd gen Camaro's guys used to call it "Limp Home Mode". Basically in the event of a sensor failure, the computer would use a preset program to make the engine run so you could drive the car or truck to get it repaired. It seemed like for some it worked, and others it didn't. Typically the computer will run a very rich program, when I had it happen the car would run amazing, but would burn a ton of extra fuel. We used to get guys that had driven around like this for months wondering why their fuel mileage had plummeted. Their check engine light had been on for months, but they claimed their cars ran better than ever... For others, the car would start fine, but once it gets warmed up would just die like yours. It needs an O2 sensor to run properly.

 

[plyr2k]

Find a good place to burn you a chip? Eliminate it. That can take the O2 sensor out of the program

 

[smier]

Find a good place to burn you a chip? Eliminate it. That can take the O2 sensor out of the program

Probably cost more than fixing the mistake, and has the potential to cost him more long term. Why reinvent the wheel, any muffler shop should be able to weld in a bung in no time. Problem solved.

 

[longbedder]

You don't need a cat to run well. You can typically run better without one as it frees up the exhaust flow. Disclaimer: it is illegal (Federal EPA) to remove a working catalytic converter from a vehicle that came originally equipped with one.

You can run without an O2 sensor on a TBI vehicle like yours - it will revert to open loop operation (it has no idea what your mixture is based on feedback so it falls back to lookup tables based on RPM and throttle setting). Having the O2 sensor hooked up and working will give you better performance and fuel economy - it lets the computer know what the engine is really doing.

 

[Littlun68]

Back to the first post, if you do install one sensor on one side, will it get true data to make the right ajustments for correct fuel-air mix ratios....because if you run true duals you will have half the exhaust mixture to sample from....I plan on running true dual exhaust with headers and have that same question.....

 

[y5mgisi]

It does not need a cat to run properly. It does need ab o2 sensor to run properly. Seems that people have had them work fine installing it into just one header.

 

[AJMBLAZER]

Even in the factory setup it only reads one side anyway. The O2 sensor is before the Y and the cat in the driver's side pipe.

 

[K5Jimmy]

Back to the first post, if you do install one sensor on one side, will it get true data to make the right ajustments for correct fuel-air mix ratios....because if you run true duals you will have half the exhaust mixture to sample from....I plan on running true dual exhaust with headers and have that same question.....

FWIW, I have an 89 and had to pass the sniffer in Dallas. I run true duals, headers, no crossover and have the O2 bung on the collector drivers side. I use hiflow cats into magnaflows. The stock engine was never an issue. After I replaced it with a slightly modded crate roller motor, cfm tech kit, injectors, etc. I had issues. Luckily, I had a neighbor that raced 2nd Gen camaros (had some Really sweet toys) and he tweaked everything to work with the chip he burned (a couple of times). It's good to have a computer engineer/gearhead for a neighbor.

 

[Littlun68]

Thanks for the replys !!!!!! and you are right....it does only sample one side!!!!!I am trying to dig too deep...lol....

 

[jekquistk5]

adding a heated o2 sensor will help as well.