cats or no cats

[sperold]

High HC is the result of incomplete combustion.
The plugs and wires and the tune-up was the correct thing to do.
You have it in both situations, so it is not likely a vacuum leak.

Pulling the spout will help your situation, that, and getting the car nice and hot after a long drive in 3rd or 4th.

I bought my 89 when the owner could not pass the emission test, and therefore could not resell it.
At idle, the HC limit was 200 and he tested at 51.
At 40 km/hr, the HC limit was 71 and his tested at 89.
Other bad news was, the NO ppm limit was 805 and he tested at 1261.

With a tune up and pulling the spout (and not changing the cats) I was able to get a HC test number of 17 at idle;
and at 40 km/hr, a test number of 43.

And the NO pmm tested at 464.

People claim it is better to have high test gasoline and even some gas-line antifreeze mixed in, as the claim is, it burns cleaner.

 

[rubydist]

you have a very good chance of passing if you pull the spout. my experience is that the hc and nox will drop almost in half with the spout pulled.

did you replace the oxy sensors in your tune up? because high hc is generally due to rich mixture.

fwiw, I would also take it on a 3-4 hour drive within the week before I got it tested again.

 

[cali+Mocasho+]

you have a very good chance of passing if you pull the spout. my experience is that the hc and nox will drop almost in half with the spout pulled.

did you replace the oxy sensors in your tune up? because high hc is generally due to rich mixture.

fwiw, I would also take it on a 3-4 hour drive within the week before I got it tested again.

lol only replaced 1 mise well replace the rear. ill try to smog later today or tomorrow,. wish me luck

 

[cali+Mocasho+]

Pulled spout and barely passed.
Much appreciated for the help.

 

[rubydist]

first, double check your plug wire routing (using the wiring diagram found on this site) to make sure you have the plug wires on the right plugs. I say that because a 3x jump in hc is due to a misfire - bad plug or bad wire or wrong order - that sort of thing. If the plug wire routing is correct, then I would run the koer test to see if you have a consistent miss on one cylinder.
let us know what you find.

 

[cali+Mocasho+]

first, double check your plug wire routing (using the wiring diagram found on this site) to make sure you have the plug wires on the right plugs. I say that because a 3x jump in hc is due to a misfire - bad plug or bad wire or wrong order - that sort of thing. If the plug wire routing is correct, then I would run the koer test to see if you have a consistent miss on one cylinder.
let us know what you find.

Pretty sure there on right but I'll double check. She has a very steady idle. I'll get back to you guys tomorrow.

 

[NOTAURIUS]

The problem with cats and SHO's is that they don't play well together. When I purchased my 90 in April of 2000, it was on its second engine due to ingesting the cats. When I got my 91 in 2004, it had pieces of cats in the mufflers. Then, in 2014, my 90 shot pieces of the cats out of the exhaust and I still have not determined if it caused engine damage. That time was a SHO shop high performance y-pipe.

 

[AREA 91]

I have never heard of a broken up cat causing damage until I discovered the SHO.
It is absolutely 100% possible to happen.
I can confirm the above, it can and does happen.

 

[Nuke]

Pulled spout and barely passed.
Much appreciated for the help.

Believe me when I say, in Ca, passing by an inch is as good as a mile. Congrats. I know it can be a struggle.

The problem with cats and SHO's is that they don't play well together. When I purchased my 90 in April of 2000, it was on its second engine due to ingesting the cats. When I got my 91 in 2004, it had pieces of cats in the mufflers. Then, in 2014, my 90 shot pieces of the cats out of the exhaust and I still have not determined if it caused engine damage. That time was a SHO shop high performance y-pipe.

I have never heard of a broken up cat causing damage until I discovered the SHO.
It is absolutely 100% possible to happen.
I can confirm the above, it can and does happen.

How? I have had several cars (not SHO) blow cats, and have not had any issues. What happens to a SHO that blowing a cat out the tailpipe ruins them?

 

[luigisho]

The scavenging or the EGR or something can move some of that stuff the other direction and makes it's way into the cylinders. Haven't noted that in any other car but i have owned mostly SHO's last 15ish years

 

[Nuke]

Yeah, I suppose if the EGR sucked it back in that would be bad. Makes sense.

 

[AREA 91]

It can happen during a high rpm shift/deceleration when the throttle is closed. There is a nice article in one of the old SHO Registry magazines.
Basically what happens is exhaust reversion when the throttle is shut at high rpm. It pulls the broken cat pieces back into the cylinders. Not good!

 

[NOTAURIUS]

Brian is right, I had a professor in college in 2001 who said I was wrong and this was not possible. This professor also said Mitsubishi made the SHO engine the first year.

 

[cali+Mocasho+]

My ignition wires are routed right. it just feels like i dont have as much power as i should. I know the car was running rich before i got the car. Had a stuck open thermostat,stock plugs in the back with stock wires with 1 misfiring. stock o2 sensors. stock egr, bad evap lines all replaced. Got to be cats. thinking of taking the cheap rout and buying the cat less y pipe. Thoughts anyone?

 

[sperold]

For the time-being, don't do anything. You did pass, by the way. Keep driving the car on a regular basis and include some long hauls, and things should improve by themselves; particulairly as you improve and change things that you find flawed.

There is the probability that the dyno test will be replaced by a stationary test with sniffers on the OBDI cars. This test is easier to pass for some reason. That is what happened in my jurisdiction. Cars that got only a conditional pass with the dyno, stated to outright pass with the stationary test.

In my jurisdiction the OBD2 cars get the OBD port analysis which proves to be trickier, with redyness issues, cancelled codes and whatnot.

 

[rubydist]

How? I have had several cars (not SHO) blow cats, and have not had any issues. What happens to a SHO that blowing a cat out the tailpipe ruins them?

Blowing it out the tailpipe would not be a problem. However, due to the close location of the cats to the exhaust ports, when the cat is in little pieces, and one snaps the throttle closed with the engine at high rpms, the pieces of cat tend to get pulled into the cylinders where they cause all kinds of havoc.

 

[Nuke]

OK, in that case, now that the Wagon has passed smog, and retesting isn't required for me, should I get a catless y-pipe and install it?

 

[cali+Mocasho+]

OK, in that case, now that the Wagon has passed smog, and retesting isn't required for me, should I get a catless y-pipe and install it?

im in the same boat,. except ill buy a catted y pipe when needed before my next test in two years.
i need to know what you (SHOHEADS) think,should i go cat-less?
Also could i nullify the sound with quality mufflers?

 

[rubydist]

I have owned over a dozen of these cars and have never had a problem with a broken cat, so I have no worries there.

I do not like the sound of this engine without the cats, and I do not think that you can "fix" it with mufflers, but I have never tried.

 

[luigisho]

If you have no smog or no further smog tests to pass then catless is an option. The sound issue then is another factor to deal with (or not). If it was me and I had to deal with annual smog test, I would replace both cats and be done with it. Some people have had both y-pipes and they swap back in every year for emissions, but I'm not that motivated for extra work anymore