'81 308 GTSi. Symptoms: Very low exhaust flow from one tailpipe as compared to opposite tailpipe. Exhaust temp much higher on low flow side. One cat significantly hotter than other. Bad cat??
Sounds like its is clogged. Get it replaced or put some straight pipes on her All joking aside, you pretty much nailed that problem Best, PerryC
Thanks Perry. If I replace with straight pipes, I'm assuming that I should have fittings installed to accept the O2 sensors ... ??
No, don't replace with straight pipes. Just get a new cat. Straight pipes are a bit vulgar, and also can have effects on your cars running ability. Go back with a worthwhile cat. Best, PerryC
As I've said on this board before, I highly recommend Hyper-Flows. Almost as little restriction as straight pipes. Far less chance of catching fire than OEM. Far less chance of overheating than OEM. Boost your injected car's performance back up into the hp range of the carbureted models. Legal and low maintenance - better than straights! NO, I don't work for Hyper Flow or have any stake in the company. Just a satisfied customer. If you've finally burned up your original cats, it's past time; surprised they lasted this long.
Ok, let me start by saying I know virtually nothing about 308's. But I do have a pretty good mechanical background. If you have decided that the cat is bad, and you've decided that you want to go with test (straight) pipes, you can simply gut the existing cats. Theyre junk anyway. The way (one of) a 355 cat fails is the core comes loose and breaks up restricting the flow through the cat and then the resulting problems that follow. Assuming the 308 cats are the same (or at least similar) you can pull them off and check inside to see what's up. If they are coming apart you are that much closer to gutting them as the ceramic core will be falling apart. A little help with a big screw driver or pipe should help remove the rest of the material. If there is significant material missing from the core, it may be inside the muffler restricting flow so you may need to pull the muffler and shake out any material that has worked its way in there. I like the idea of using gutted cats instead of test pipes as they have the stock appearance and they fit (the biggest plus). Now, Im not looking for a debate on whether you should or shouldnt remove the cats (so all you hyperflows guys can just take a deep breath) Im just giving you a little insight if you were to elect to go the test pipe route.
Perry, Can you elaberate please? "... are a bit vulger,..?" Huh? "... can have effects on your car's runing ability." Ok, how so? I am asking honest questions here. Please explain. V/r, Mark
I see you're in California. You will have to replace the CATs if you EVER want to pass a smog. Gutting them is nice for a temporary fix, but sometime in the next two years you're going to have to replace them.
1. Vulgar - The sound is not pleasant and usually can become bothersome. It increases the dB of the exhaust, and the pitch/tone. If I have a Ferrari, I want it to sound like a Ferrari. Not an 87 Chevy with glasspacks. 2. Due to the fact that cats disperse or contain emissions, if there is not cat in place the 02 sensor usually gets under used, and usually sends incorrect values to your ECM. It also can make it throw codes. Best, PerryC
Andrew, It doesnt matter where it is in line, I provides a certain ammount of back pressure that allows the sensor to properly meter the levels. Best, PerryC
Perry, It's Michael, not Andrew. But I will answer to it. Would you care to elaberate a little on the back pressure needed to monitor properly statement. I guess in the past 25 years or so I missed that. And I'm always willing to learn. Michael
Michael, I apologize about the mix up. I should have looked a bit closer. To answer your questions (or the best of my ability) O2 sensors are pretty much useless until they get up to Normal operating temperature. Once this 'ideal' temperature is reached the 02 sensor can begin to truely send exact signals to the PCM. If you use straight pipes, it increase the flow of exhaust. Anytime you speed anything heated up, it tends to not generate as much heat. The catalytic converter provides back pressure while it is burning all of the unused pollutants. Also, this is why people get 'performance' cats becuase they usually have a great balanace of flow to provide low end torque, and high end power. If the 02 sensor is slow to react, most cars have codes that will display 'slow response' of the 02. This can either be true slow response or, slow response due to the ammount of time it takes to heat the 02 sensors properly. This in itself can begin to make sensor go bad and codes begin to get thrown, which in itself can be expensive to diagnose. Maybe my wording was not concise enough, but that is my understanding. BTW, Im sure I can expound on this point with more relevant info, but that would take some time. Best, PerryC
Micheal, One more thing, there should be a minimum of 2 on all vehicles. Some have 4 dependent on the fact if it has 2 cats or not. There is one prior to the cat, which is the TRUE 02 sensor. If it was after the cat then it would be metering altered gas, which would not show what the motor is actually outputting. There is also one after the cat that is dubbed a 'cat monitor' which deems if the cat is operating properly. Otherwise we could have bad cats and not know it. Best, PerryC
An 81 GTSi would not have any oxygen sensors. It's a mechanical fuel injection system, remember? What the original poster asked about is almost certainly the pair of thermocouple "slow down" sensors, one of which was fitted to each cat of that era for this model. If you elect to use an aftermarket convertor / test pipe / whatever which does not have a "hole" for these sensors, simply forget about them and tuck them up and out of the way. Cheers - DM
If I correctly remember a posting on another site from years ago, and from personal experience, the exhaust flow on a 308, I have a 1981, is not even side to side. I have never had the temps checked to compare the cats, but I would not go spending a lot of money unless the cats are actually bad. Uneven flow from one exhaust side to the other by itself is not unusal.
Low flow is on the left [drivers side]. That would be normal on an 81. The heat is another issue but could be caused by less air running thru that side of the system at idle [just a guess].
As previously posted, I don't believe any of this is relevant to the car in question. There is no O2 sensor (lambda sensor in Ferrari speak for a 308) on this GTSi. They were first used on the 1983 308's.
