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Older Ls400 Owners: Have You Had To Replace The Cats?


harjp
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My '90 LS400 won't pass emissions this year, after 3 tries. NOx just misses the standard. The standard is 2.50 g/mile. My car produced 2.53 and 2.58 last two tries.

EGR is not the problem (so I'm told). Tried Seafoaming a couple of times to make sure the valves are free.

Only thing left to do, it seems, is replace the catalytic converters. Cats are not plugged, but possibly used up? Would like to hear from others who found themselves in this situation. I'd hate to replace the cats and still fail emissions.

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My '90 LS400 won't pass emissions this year, after 3 tries. NOx just misses the standard. The standard is 2.50 g/mile. My car produced 2.53 and 2.58 last two tries.

EGR is not the problem (so I'm told). Tried Seafoaming a couple of times to make sure the valves are free.

Only thing left to do, it seems, is replace the catalytic converters. Cats are not plugged, but possibly used up? Would like to hear from others who found themselves in this situation. I'd hate to replace the cats and still fail emissions.

I replaced them on my 94 LS400 for another reason and they were very expensive. Like 1k each at dealer for OEM. I got them off Ebay for like $400.00 total.

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Sounds like the cats are at fault, but seeing how close they are to producing the right numbers, the shop should have passed you simply because their equipment probably has a variation of at least the amount you failed by.

Most manufacturers use a very rich setting when the throttle is wide open - the ECM switches to open loop from closed loop as the throttle switch reaches wide open. The reason is to briefly overheat the cats with a bit more fuel to burn them out and clean them. It's like a regenerative phase. If you rarely use full throttle, or never, it is worth a try. With the engine fully warm and topped up on oil, plant your foot in it and let the engine breathe deep for a few minutes.

When I first purchased my LS it used to stink in the exhaust whenever I used full throttle - a sure sign the cats were not working up to snuff. Now I can use full throttle and the exhaust remains quite clean.

You won't hurt the engine, and it's fun too! Then run the test again.

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Sounds like the cats are at fault, but seeing how close they are to producing the right numbers, the shop should have passed you simply because their equipment probably has a variation of at least the amount you failed by.
The shop is run by a state agency. They do a few runs to try and pass you, but it's setup to eliminate any discretion: pass or fail is determined by the computer.
With the engine fully warm and topped up on oil, plant your foot in it and let the engine breathe deep for a few minutes.

When I first purchased my LS it used to stink in the exhaust whenever I used full throttle - a sure sign the cats were not working up to snuff. Now I can use full throttle and the exhaust remains quite clean.

You won't hurt the engine, and it's fun too! Then run the test again.

I'd love to give that a try. I use full throttle for seconds at a time whenever I can. Yes -- because it's fun. I sometimes run with the overdrive off, or even run the car in 2nd gear, because that's the only way to get the RPMs up for any length of time and the throttle response is great.

But full throttle for a "few minutes"? I can't think of anywhere I could go that fast around here. And even if I could, I have to admit I don't have the balls to run at 100+ mph on public highways.

I don't mind getting the cats replaced if that means I'm definitely going to pass emissions. My only concern is to spend the $$$ only to find that the cats weren't the problem!

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I wasn't clear in my last post - sorry. What I meant by a few minutes was several full throttle accelerations from a standstill, like merging onto the highway. Three or four of those should do it. What is important is that full throttle (WOT) is reached, because that's when the fuel mixture goes rich. Anything less and the ECM stays in closed loop, and that's not going to make enough heat in the cats to clean them.

You might also try a high octane fuel, perhaps an ethanol blend- that too can help.

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Oh, OK. Thanks. I'll try that.

I checked the emissions results from 2 years ago. The NOx reading was 1/2 of what it is now.

What I didn't mention above was that on the first try, the NOx reading was over 8.0. It looked like the EGR vacuum modulator was not working right, so I by-passed it, running a hose from one of the intake manifold vacuum ports straight to the EGR valve. That brought the reading down to just above the standard.

I just picked up a new EGR VM. Maybe that will make the difference. I find it difficult to believe my cats are spent.

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Oh, OK. Thanks. I'll try that.

I checked the emissions results from 2 years ago. The NOx reading was 1/2 of what it is now.

What I didn't mention above was that on the first try, the NOx reading was over 8.0. It looked like the EGR vacuum modulator was not working right, so I by-passed it, running a hose from one of the intake manifold vacuum ports straight to the EGR valve. That brought the reading down to just above the standard.

I just picked up a new EGR VM. Maybe that will make the difference. I find it difficult to believe my cats are spent.

Newer cars have a federal warranty on Emissions (cats) good to 80k/8yr. I have read since 96, most will last 100k on a properly tune car. Things that cause them to fail are: oil blowby (rings, valve seals, etc) bad O2's (unburned gas) Bad EGR's, Coils or any ignition related problems...the older cats on carbureted cars didnt last long becasue of the imprecise metering of a carburetor as opposed to the FI monitoring. Rust or ehaust leaks that let in O@ into the cat can casaue them to overheat and melt the substrate, causing a clog. A backpressure guage can diagnose a cat gone bad (clogged) or a downstream O2 sensor compared to an upstream O2 sensor. Dont pay for an OEM cat, they are here in So. Cal for 95 bucks a piece installed. Imagine what you can get for more? Long time ago i heard someone say that you could cut 'em out after 7 years as that is all they were worth, probably a wives tale.

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One of the things I was looking for in this thread was whether LS400 owners with 100K+ on their cars have had to replace their cats. If they don't last for 200K miles, then I'd expect to hear from others who have had to replace them by now.

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run the fuel down as low as you possibly can and dump 2 bottles of isopropyl (rubbing) alchohol in the tank and got ot the emissions station ,I'll be you pass and no damage to the car. It's an old trick that worked for me a few years back with a different car...

post-53431-1193448375_thumb.jpgMy 91 LS400 has 119K miles and seems to be doing fine--passed inspection in June. Of course, I will be watching now. May try a few more full throttle accelerations just to keep things clean. Good info in this thread!
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Well, it was the cats after all. New cats dropped the NOx emissions from just above 2.50 g/mile to 0.77.

Not sure why mine got "used up" with less than 120K on the car. Oh well.

I know there are ways around it, but I wanted the car to be in good working order and emissions complaint.

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I'd like to hear as well. My '93 has 206K on it and barely passed the last test.

Luckily, it is the 'last' emissions test, as Missouri has decided not to test anything

without the OBDII interface ('95 and older). However, the borderline pass is

probably an indication of something going, my guess is the cats...

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  • 8 months later...
Well, it was the cats after all. New cats dropped the NOx emissions from just above 2.50 g/mile to 0.77.

Not sure why mine got "used up" with less than 120K on the car. Oh well.

I know there are ways around it, but I wanted the car to be in good working order and emissions complaint.

Did you get OEM CATs?

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