Ok, so teach me about O2 sims. My buddy wants to replace his O2's and his cat with a straight pipe and 2 O2 sims. Besides the fact that it's illegal my question is this, will these sims just simulate one specific set of running parameters with a fixed resistance? If so, won't this allow the engine to run rich when it should be lean, or vice-versa? What are the detrimental effects of these sims?
Most likely. The 02 sensors tells the ECU if the mixture is correct. The second one is redundant if the cat. is removed. Best thing is to put a bung in the down pipe and install the # 1 sensor. He still will get the MIL for the missing #2 sensor.
Most likely. The 02 sensors tells the ECU if the mixture is correct. The second one is redundant if the cat. is removed. Best thing is to put a bung in the down pipe and install the # 1 sensor. He still will get the MIL for the missing #2 sensor.
He'll need the one before the cat to give the ECU a helping hand when it comes to sorting out the mixture, at least on those areas on the map where it's running in closed loop mode.
As iceracer says, the second one is there to check if the cat is working so that would be redundant...
Apart from the kudos of driving around like an outlaw, is there any specific reason for this undertaking?
There's absolutely no benefit in removing the first O2 sensor. The fuel injection system depends on it.
The second is there to monitor the health of the cat, although newer EFI systems are remarkably sophisticated in how they check the function of the sensors. I have heard of people using spark plug anti-foulers to mimic the behavior of a cat by pulling the rear O2 sensor out of the main airstream, that might be worth checking out.
The plug anti-fouler trick works very well on most cars and are MUCH cheaper than 02 sims. I did it on my P5 when I gutted the mid-pipe and never had any trouble.
Also, a good 02 sim needs to change resistance with time to simulate the light off of the cat. Most ECUs will know somethings up if it just gives a fixed resistance back.
Here's a thread with pics showing how the non fouler trick works.
VFR guys use 330 ohm resisters in place of the O2 sensor (this is in an electrical sense). This is all the commercially available O2 sensor simulators are so Radio Shack and some electrical tape later, $5 and you'd be set.
Keep the front one, simulate the rear.
Hmmmm. A narrowband O2 sensor is actually a chemical cell that generates voltage (about 0.7V) in the presence of excess Oxygen in the exhaust gas when at operating temperature. Using resistors and whatnot can often fool the sensing circuitry into thinking the sensor is present, and that's enough for some ECU's. But what happens in closed loop is that the ECU slowly (in this case a fraction of a second is slow) leans the mixture until the O2 sensor detects Oxygen and generates a voltage, which causes the ECU to slowly enrich the mixture, until the O2 sensor stops generating voltage, which causes the ECU to repeat the cycle, over and over. This result of this is that the sensor voltage is continuously cycling. You can uses an oscilloscope to see the waveform, it's the classic method for finding a dead or contaminated sensor. So a simple resistor just can't reproduce this behavior for ECU's that look for a cycling waveform. It's easy to build a circuit that will create a similar waveform, and that will fool some ECU's.
But some later model ECU's are more sophisticated (like the ones with pre and post sensors). They will lean (or enrich) the mixture, and then wait for the sensor to switch. No sensor switch = MIL light.
So bottom line, there is no one single answer, depends on what ya got.
Carter
Thus my suggestion for the spark plug fouler trick. You've still got a live O2 sensor in the rear, so it still responds like one when the ECU does a test like firing off a rich cylinder.
You don't want to remove the front one, regardless of the chemistry :) It's part of how the EFI works. The only question is how to handle the rear, assuming you have some reason to pull the cat.
Why pull the cat in the first place?
Pull the cat, the O2 sensors and the entire EFI system and put a carb on it and call it a day. If he is running some sort of EFI one functioning O2 sensor is important isn't it?
If he wants to do it to be an outlaw, tell him to leave things as they are and drive 5 over or roll through a stop sign or two.
He's being cheap. He got a code that says "O2's or bad cat" and wants to pull it all. I'm trying to help him see that he needs the front O2, and the rear will make his life easier. Here in MI there's no inspection or anything so only he'll know if he has a cat. I'll look into the spark plug fouler trick.
So, the non fouler just get's the O2 out of the direct exhaust stream? Can you 'splain this to me a bit?
The non fouler is a tube that you can thread into the exhaust and the 02 sensor goes in the other end. It moves the sensor an inch or so out of the exhaust flow so it sees very little of the exhaust gas. Pulling the sensor out of the exhaust gas makes it read about what it would if it were installed correctly behind the converter. This is ONLY for the rear 02 that verifies the function of the cat. Putting one on the front 02 would just make a car run like crap.
You need the front 02 for basic functionality of the EFI system, the rear is ONLY to verify the presence and correct function of the cat.
I'll add that removing all the cats from my protege made it smell like an old lawnmower and was torture if I had to sit in traffic for a long time. But it was a lot cheaper than replacing the cats.
There are a bunch of different codes related to O2 sensors (front and rear) as well as cat efficiency. Find out what code it is, that'll help you narrow down just what's happening.
Keith wrote: There are a bunch of different codes related to O2 sensors (front and rear) as well as cat efficiency. Find out what code it is, that'll help you narrow down just what's happening.
That's what I'm trying to get out of him now. He took it to autozone and the guy said "oh, you need new O2 sensors and a new cat." I asked him to get me the actual code so I can see what we are dealing with here. This is all heppening via IM So this defouler is like, uh, some people would do back in the emissions testing days. We'd, uh, they'd hold the sniffer about 6" behind the tail pipe to help it pass.
A generic catalytic converter is $50, another oxygen sensor is darn near free at a U-Pull. It really isn't hard to fix this problem the right way if one of those are indeed the problem. Heck, sometimes you'll get codes for crummy wiring; I just fixed an oxygen sensor code the other day that was caused by a wire that was pulled out of the connector by a hamfisted mechanic. He said he thought it needed the $100+ sensor.
Relying on Autozone "technician" advice is like asking the guy at the pawn shop about engagement rings.
Bryce
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