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Hey guys. I have a 1990 Buick Century Custom with the 3.3L V6. I have an exhaust leak directly after the O2 sensor at the flange and I was wondering if it could be causing the rough idle that the car has. I found a picture on another site from the same car so that you can get a visual of where I’m talking about. It’s leaking around the gasket at #2.
I was always told that if there is an exhaust leak after an O2 sensor that it wouldn’t usually contribute to a problem but given the proximity of this O2 sensor to the leak could it be the reason for my idle issues? There is no downstream O2 sensor on this car. Any input would be appreciated!
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The oxygen sensor compares the amount of oxygen in the exhaust to the amount in the ambient air outside the exhaust. If you have a massive exhaust leak at the flange, the outside ambient air would consist partially of exhaust and give a bad reading. That said, I used to have a 1992 Plymouth with a single O2 sensor and when the oxygen sensor failed the car ran better but probably got worse mileage (I never checked).
Anyway, back in the early 90’s oxygen sensors weren’t expected to last much past 50,000 miles and so I think the engine computer was more than happy to ignore it and never go into closed loop. No code was set.
Thanks for the quick reply! This leak is definitely noticeable both inside and outside of the car and when I’m working around the engine I often get a whiff of a strong exhaust smell so I’m assuming that it’s coming from that flange gasket. It looks like it’s gonna be a royal pain to replace so I think I’ll wait until it’s a little warmer out to do it lol.
Yeah, my wife’s car decided it needed a radiator right in the middle of this cold weather. I managed to get it swapped out between polar vortexes. I’m ready for spring.
Yes, exhaust leaks close to O2 sensors can cause issues and upset the O2 sensor readings. Here’s a video on how O2 sensors work that can give you a better idea as to why.
Also an article on solving idle problems.
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
Good luck and keep us posted on what you find.
I looked over the engine today to see if there was anything else contributing to the misfire condition and noticed that 4 of the ignition wires were reversed on the coils so I switched them around and made sure that they were hooked up correctly.
The ignition wires that were backwards were on the middle and lower coil packs i.e. cylinder 5 was connected to the coil tower for cylinder 2 and cylinder 2 was connected to the coil tower for cylinder 5 and it was the same at the lower coil pack too.
I started the car and immediately noticed that the idle inside of the car was much smoother in regards to interior shaking. When I walked around to the exhaust to see if the misfire had vanished I noticed that it actually got worse and seemed to have more consistency to it, and as if it were misfiring on more cylinders now. I am absolutely positive that the plug wires are properly connected to the correct coil pack tower and to the proper cylinder. The spark plugs, coil packs, plug wires, and ICM are all new and all are OEM AC Delco parts.
What has me confused is that when I sit in the car it’s MUCH smoother at idle as compared to what it was before I corrected the mismatched ignition wires. I haven’t fixed the gasket at the flange yet but I’m gonna make an attempt to do it within the next few days to see if that has any effect. Any ideas?
It is wasted spark system so both spark plugs of same coil fire at once. So putting wires of same coil backwards shouldn’t matter. But since it did maybe there is problem with wires or coils.
It doesn’t matter if the plug wires are switched as pointed out in the above post. The way those coils work is they fire both plugs at the same time so the order that the wires are connected means nothing. The smoother idle may only be your perception. As stated, exhaust leaks near O2 sensors can offset their readings and therefore upset the fuel mixture. You might address the exhaust leak and recheck for the problem.
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