Resident Sicko

I recently picked up some goodies and was told by what I would consider to be a reputable source to info that makes me consider selling the parts I just bought.

1. Fabspeed Cat Bypass pipes. These were lightly used, got them for a decent price, polished them up and was told since my '98 C2S is an OBDII car, the check engine light will illuminate since there are four O2 sensors and only 2 bungs in the pipes. Bypassing the secondary (After cat) O2 sensors will not work. Inserting an extra bung into each pipe wil not work. I live in SC where we have no DEQ, but do not want the car to run lean or rich with trying to trick the O2. Stupid purschase? Any way to make these bypass pipes work without custom welding 200 cell cats? (More $$)

2. Lower Valve covers. I bought a lightly used pair of Eagle Day Billet Valve Covers. My OE covers were fine and dry, just like the look of the finned covers. Bought the plug wire clips and new gaskets only to be told it is a 5 1/2 hour job to install them as the heat exchangers need to be dropped in order to swap the lower valve covers. True? I wanted to have it done with a complete oil change but not about to pay $550 in labor for something I can do myself.

Thanks in advance for any insight.

lopro

I changed the lower valve cover gaskets without removing the heat exchangers, It was not 5 hours work. remove the rubber tube and do not drop the bolts in the heat exchanger - or else mirror and magnet tool fishing

I don't know about your first q as I have the obd1 version.

Sounds like a nice set of v covers but maybe another member has more input that ive overlooked

AOW162435

Sicko,
The bypass pipes seem like more headache than they're worth - just my opinion.

The lower valve covers can be removed/installed without touching the heat exchangers. Whoever told you otherwise is FOS.



Andreas

Resident Sicko

Thank you. I suspected what you have said from looking at the car and reading tutorial on rocker/lifter service.
Thank you.

Quadcammer

with respect to the cat bypass.

The front 02 sensors are what provides feedback for the computer to make fueling changes (i.e. rich/lean). The rear 02 sensors are for catalyst efficiency and will pop check engine lights without cats as they read too much fuel. By free airing these (just sticking them in the engine compartment), you can get around this. They will not cause any fueling concerns from my experience. That said, back in the mustang world, you could buy these 02 sensor Mil eliminators that would alter the signal to make the computer think all was well.

All that said, I think you should run cats. Minimal power reduction but big reduction in fumes and headaches, as well as, imho, a nicer sound.

Bill Verburg

To use cat bypass pipes on an OBD2 engine you need to fool the DME

This is what it is looking for


It wants the averaged load and rpm dependent ratio of the pre and post cat signals to be less than a predetermined value. w/ the post cat signals in the cat-less pipe the ratio will approach unity, which is too high and will throw a code, to reduce the ratio don't install the post cat O sendors in the pipes, let then see fresh air. This cause the post cat signal to be reduced , thus reducing the ratio below the threshold value, or you can apply a fixed voltage to the circuit that mimics the appropriate value

pp000830

When upgrading 993 stuff the old adage holds:
“Accept the things I should not upgrade, have courage to upgrade the things I must and have the wisdom to know the difference”
Sounds like you are on your way to making a wise choice to not change anything!

Resident Sicko

Great comments from all!
The main reason I wanted to install the pipes was mostly for experimentation with the internal muffler work completed some time ago. Bill, I doubt this was your intention but I think you have offered the right amount of science and math to the dilemma to scare me right out of the water. I design (style) things for a living and math makes my head hurt. WHile I want to posess your knowledge as well as your car, I am not willing to do so if it means opening a book. : ) However what you and other shared makes sense and knowing there is probably little chance I will be able to sell these things for what I have into them, I may just decide to plop them on using your guidance to see just how snarly the exhaust sounds, how much toxic fumes I can smell in the cabin and just how much of a performace advantage I may be able to detect.
As far as the valve covers, they will be going on this weekend when I change the oil to evaluate Brad Penn's offering and the impact on engine clacking. -Since they are sitting on the workbench collecting dust anyway..but yes pp000830, I will keep the OE parts on close hand to go back on, no doubt.
Many thanks to you all!

phoneyman

I agree with the above opinions. Coming from the Audi world with ODBII, its a pain in the *** to trick the computer into accepting the readings from the rear O2 sensor. There are options out there, like long runners to vent off emissions before the reading or letting them hang in the bay, but unless you have a specific purpose in mind, I would skip the bypass pipe, unless your emissions control in your state dont look for that sort of thing. As for the valve covers, what I've read makes it seem like a reasonable job for someone who knows what they are doing. Those are on the list for my winter time projects, along with a lot of other 60k mile service items.

hkspwrsche

Another easy trick is to thread the rear /downstream o2 sensors into a couple sparkplug non foulers. Pretty popular as an alternative to the simulator and just spaces the o2 away from the direct exhuast gas to trick the computer.

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