70Bee

I'm putting the fabspeed cat bypass pipes on am car and am wondering what level of confusion this is going to cause for my ecu. Will the ecu try to compensate for the missing cat ? SHould I just disconnect the o2 sensors? I emailed fabspeed but they blew me off. Thanks!

Kevin

It is a crap shoot.. It will vary from one car to the next.. If you have them, put them on and see.. You will most likely get a CEL within the first 20 miles.. You will have to clear it.. If it keep on coming on, you have a ECU that doesn't like them..

70Bee

I have already disabled the CEL light. I'm concerned that without the proper input from the fore and aft o2 sensors the ecu is going to think that the exhaust is too rich and or too dorty or too something and make an inappropriate adjustment. Or perhaps, I do not have a good understanding of what the o2 sensors/ecu do and am over/underreacting.

ScottMellor

Does your bypass have a port to screw the sensors into?
(FVD ones do and I never had a CEL.)

70Bee

yes. both fore and aft of the cat.

tlark

I too have considered doing this as well and was worried about the same issue. Was sent a PM by another owner that said to simply "pull the sensors post cat and simply tie them off so they read ambient air" no problems.

Other ? I have are what is the weight savings and HP increases. Also, I assume the increase in noise is pretty substantial. Muffler & CAT bypass on the street, too much ???

ScottMellor

Muffler and cat bypasses on the street drone at freeway speeds. I usually just run that way at the track. By the time I get home, I'm ready to stick ice picks in my ears to make the noise stop.

70Bee

I ran both bypasses for about 30 seconds. My inner brain then reached harmonic sympathy with the exhaust note and started to ooze out my ears. Needless to say I went back to mufflers.

Tom, thanks for the info. Pulling the aft sensors and letting them read air seems like it would work but then would the ecu think combustion is too complete and enrich the air/fuel?

Red rooster

The second lamda is there to measure cat efficiency. I would be suprised if the fresh air" solution " didnt give CELs as the second lamda expects to see some kind of credible signal .
Diasabling the CEL light doesnt stop the Motronic recognising an emmissions fault and taking action !
You could try screwing the second lamda into the exhaust boss but with a spacer so the second lamda doesnt "see" as much exhaust . This can fix 100 cell cat problems !!

Good luck

Geoff

K24madness

70bee,

The FABSPEED cat bypasses are a excellant choice. Much better than ANY 100 cell cat options. You will see much quicker spoolup and the reduced underhood temps. The primary O2's are responsable for AF ratios. Secondary O2's measure cat efficenty. It will not affect anything. It may give you a light. Reset it 2-3 times and it should not come back. Combine the catbypasses with the FABSPEED maxflow mufflers and you will have the ultimate combination. IMHO that combo has the best sound/performance/cost of any system on the market.

PM me if you like I am local. You can hear it on my car.

Kevin

As you start increasing the output of these engines, and stay with factory Motronic's. These engines just do not perform at there peak level with Catless systems. With options that are available with high quality large diameter 100 and 200 cell options that meet emissions why risk constant CEL's that one has to reset for short term cures..

CP

Hi Henry,

I am thinking about the CAT issue as well. But with you bypass set-up, you need to remove that when you need to pass smog to register the car, right? So it is something that needs to be revisited every 2 years or so?

Thanks.

CP

tlark

So....you are of the opinion that one could be waisting time by doing this b/c the minimal gain is outweighed by the potential problems and lack of better performance?

That is unless one is willing to set-up an entire engine with other modifications used in combination with a by-pass system.


If I were going to a 100 to 200 cell option what are the measured gains in you opinion ?

Kevin

Tom, removing a stock 400 cell cat and replacing it with a large diameter 100 cell unit (European made) allows the engine to breath (less backpressure) and thus free's up the turbine wheel. This also can be done with a quality cat bypass system.. However, the Motronics react differently from car to car when the cats aren't in place.. Most cars have issues when the cats are not in place..

70Bee

CP
I have a house in no-smog Wyoming so the car will be plated in Teton County, not California, through the miracle of snail mail registration.