I've found out that one of my catalytic converters is clogged (mine has two, for California emissions). I figure this since gas mileage has started to suffer, it runs a little warmer than normal, and power is also lacking a little. I've been keeping a close eye on the oil, no chocolate milk, no foam, and no milky residue on the oil cap. Plus, I kept out about a quart of used oil from my last change to check for water separation which was a few weeks ago, and nothing.

Anyway, I was planning on taking out the cat in the y pipe since Virginia only requires one cat. This would free up a little power from reduced back pressure. But Virginia (at least in the county where I get it inspected) only does visual inspection of exhaust/emissions. I could gut the big cat and put it back, and it would still look like I had one. My question is this. If I remove one (splice in straight pipe) and gut the other, would that make my service engine light come on?

Also, with tax time here, I'm going to replace the lifters, pushrods and rocker arms. Obviously, I'll need to replace the lim gasket in the process. What is the best lim gasket set to use?

Thanks for your time.

1999 Olds Bravada, California emissions

 

Both converters work together and are both necessary. If you remove the upstream converter, the downstream converter will overheat and meltdown, and the check engine light will come on when the catalyst monitor runs. If you remove the downstream converter, the check engine light will come on when the catalyst monitor runs.


So what about one of those gadgets that "fool" the PCM to make it "think" the converter is good? Wrong, not gonna keep the light off, here's why. When the PCM runs the catalyst monitor, it checks the fuel mixture via the upstream oxygen sensors. If the exhaust is lean, the PCM momentarily richens the mixture more than normal, then immediately leans the mixture. Then it "watches" how long it takes for the mixture "spike" to reach the downstream oxygen sensor. If it arrives on time, or late, or not at all, the converter is fine. If it arrives too early, the converter is not doing it's job, hollowed out, or missing. Just to make it more interesting, if the exhaust is rich, the PCM momentarily leans, then richens the mixture more than normal, then immediately leans it. The time frame for the rich mixture "spike" to arrive at the downstream oxygen sensor will be different, but the PCM "knows" when it should arrive. Bottom line: the "gadget" has no idea what signal to send to the PCM, and no idea when to send it. If it ain't right, the check engine light is coming on. The PCM programmers had their stuff in a pile when they wrote the program All in an effort to make things difficult for guys like us to bypass or eliminate stuff.

 

The federal emissions y pipe doesn't have a cat in it. And I really do not want to spend that much for two converters.

Wouldn't the PCM be able to account for the change? And why would the federal pipe not have a cat?

 

Unfortunately the PCM knows it has California Emissions, so it doesn't want to. Second question... because California emissions used different hardware to meet different emissions requirements (but you knew this already ;-).

The Felpro LIM gasket set with rubber coated metal gaskets is the one to use.

Are you sure you really want to replace all the lifter/pushrods/rockers??? They are really pricey. Hope you have a good reason.

Good luck

 

The peoples republik of kalifornia is in its own little world, (called the Left coast). The PCM is programmed to pacify that little world. Unfortunately, if you tamper with your emission system, the PCM is programmed to detect the tampering. The 49 State, (Federal) "Y" pipe doesn't have a cat because the engine meets emission requirements for the rest of the world, without it.

 

I've got lifter tick. I looked it up on Rockauto and it really isn't that expensive for me to replace the lifters, pushrods and rocker arms. I'll have the extra money with my taxes here soon anyway.

So I couldn't just put the federal pipe on it, and not have any issues at all?

Crap. I guess I could just get a universal for the both of them, cut the one out of the y pipe and weld the new one in, and do the same for the second.

I was really hoping there was a way around it.

 

Nope. When the catalyst monitor runs, it will fail. The PCM will detect that the upstream converter is not working, turn the check engine light on, and set a DTC in memory. You won't notice any driveability issues, but the idiot light will always be on. If your State requires emission inspections, the vehicle will fail. Depends how tough they are, but they might be required to report the tampering to the EPA, and you REALLY don't want that. If your State does require testing, you might want to have a friendly little chat with them before you do anything.

 

Virginia only does visual inspection of emissions components, except in Northern Va, where they actual put a sniffer behind it.

Any suggestions for a high flow cat? That way, I can still have it able to pass with less restriction.

 

As long as the converter is not restricted, (poisoned or substrate meltdown) back pressure is not an issue. Normal back pressure is one half psi at idle, virtually nothing. The factory exhaust system on these trucks is fine. Very easy to check back pressure, then you know if it's a problem.

 

I checked it out, and one of them is clogged. Next question. I can use a universal cat instead of a direct fit, right? I figure that as long as there are still two of them, they should still do what they need to do and keep the service engine light off.

Because I'd rather only spend $50-$60 each instead of $130+ for each.