Glowing red hot Cat.

[platoribs]

I need a little help from the wise SHO wrenchers here.

I removed the snakes and valve covers on my low mile 95 mtx this past Saturday,
see: http://www.shoforum.com/showthread.php?p=387151#post387151

It wasn't running well before this weekend's work, (I'm a little fuzzy about specifics but...) seems like it wasn't idling smooth, getting poor milage (22mpg highway), 80 mm MAF throwing CEL on decel after getting on it (typical, so I thought), but it was not too bad.

Everything looked pretty good inside this SHO's engine (53K miles). Get everything buttoned up with new wires & plugs & gaskets and start it and it's idling poorly, chuffing, and the occasional backfire. So we warms it up to do the KOER test and one of the guys notices the rear bank catalytic converter is glowing red hot!

Please offer potential explanations and diagnostic proceedures to pinpoint and resolve. Thank you all in advance for your advice.

 

[Havok]

Mine had the rear converter do that when I first bought it. It melted the pass inner cv boot and started the car on fire. The cause of mine was either the water in the plug wells or the two bad plug wires I found. Either way it was caused by unburnt air/fuel entering the converter and igniting.

I did a complete 60k while it was in my shop being repaired. I removed the y-pipe and cut a small rectangular hole in each converter, gutted them and capped the holes.

Have the plug wires recently been off? Double check posts 5 and 6 at the coil pack. They are opposite what you think they would be. Makes them pop at idle but seems to run ok otherwise.

 

[platoribs]

Mine had the rear converter do that when I first bought it. It melted the pass inner cv boot and started the car on fire. The cause of mine was either the water in the plug wells or the two bad plug wires I found. Either way it was caused by unburnt air/fuel entering the converter and igniting.

I did a complete 60k while it was in my shop being repaired. I removed the y-pipe and cut a small rectangular hole in each converter, gutted them and capped the holes.

Have the plug wires recently been off? Double check posts 5 and 6 at the coil pack. They are opposite what you think they would be. Makes them pop at idle but seems to run ok otherwise.

Seems like if the 5/6 wires were switched the raw fuel would be hitting the front bank converter? yes?

So if your right about the raw fuel then it might indicate a switched 1/2/or 3 wire switch.

 

[Yamaha V6]

Catalytic Convertor may be on the way out, which could be the cause of your pre-weekend issues. If you have access to a known-good Y-Pipe, swap it out & see how it runs.

 

[platoribs]

Any more advice/recomendations appreciated

I'm heading home now and have no access to the web untill work tomorrow, if anybody knows the various things I can check, how to check them, and you know a map to find my...uh tools, yeah, that's the ticket!

I'll be much obliged!

Plat0

 

[projectSHO89]

Check your plug wires as already mentioned.

Miswired plugs will cause all your symptoms.

Notice that you didn't have this problem before replacing the plug wires.

Don't ask me how I learned this, but be assured it was the hard way.

Steve

 

[Havok]

You are correct, 5/6 would cause a problem with the front converter. Wasnt thinking when I posted that. I switched 5/6 on my 60k thinking the wires should run numerically sequential from the top to bottom post on the coil pack.

Double and tripple check your wiring. As stated above, check anything you unplugged or moved before this problem started. Also make sure you feel a good positive lock between the plug wire and the plug. Sometimes the wire can be a bit recessed in the boot and not even touch.

Its still possible the converter is on its way out, usually when they start glowing the core has already started to melt down and it just perpetuates from there.

Im not sure how strict emissions are in illinois but a cheap option for now is to remove the cores like I did. Coupled with a dynomax cat back it sounds mad when you stomp the gas. Ads a bit more rasp though.

 

[platoribs]

I'm planning on getting the leak or switched wires fixed first, then check out the Y-Pipe to see if it's cashed, I'll buy a new one from Mikey if necessary, then Stainless Steel Cat-Back, ala Chris Gates group buy, and voila new SHO!

Thanks for the feedback.

#1 and #2 wires crossed. Running smooth now. Thanks for the help/advice.

I can't believe I didn't check those more carefully. Valuable lesson learned, take your time!