Question about 1999 Mercury Grand Marquis

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How do i replace the catalytic converter on my 1999 mercury without breaking a stud?

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Cut it out with a saws all

Posted on Aug 26, 2010

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It may be impossible to not break the stud. You can try cleaning them well with a wire brush, penetrating oil, and heat. Those are the best ways to avoid breakage. I really wish you the best on this one; hope it turn out how you would like it to.

Posted on Aug 26, 2010


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How di I replace a catalytic convertor

Replacing a catalytic converter ranges from easy to moderate for most DIY mechanics. It is best to take off the entire exhaust system (not the exhaust manifold or headers) for a through inspection when doing this job as a bad catalytic converter is a sign that other parts of the exhaust system may be requiring replacement as well including the muffler(s) and tail pipe(s). Tenneco's Walker Muffler site has detailed schematics for both domestic and foreign cars. TRW Aftermarket may carry them too. (If you own a very expensive car; you plan on keeping for a long time , see about a stainless steel exhaust system... Borla, Remus, Supersprint, Bosal, and ANSA make many for foreign cars.) The other thing(s) to check and remove before taking the exhaust pipes off are the 1 or 2 Oxygen sensors... they will affect your gas mileage significantly. Unplug the wires to them and unscrew the front one and look at it. If it's filthy fouled replace it and the lower (if there are 2) one too... the information from both of them influences the car's ECM/ECU computer to adjust the air/fuel mixture.. (NGK, Beru, and Bosch make oxygen sensors for most cars.) Ensure you buy new exhaust pipe hangers and mounting bolts, if your hangers don't include them. Use Penetrating oil on a COLD exhaust system to help free up the bolts that join the lower part of the exhaust manifold to the first part of the exhaust system. Letting it sit overnight seems to work best. You may need a new gasket there so prepare and buy a new one to replace it. (When replacing, tight is good, too tight is bad as you may break off the stud or bolt.) IMPORTANT!!! Old catalytic converters need to be disposed of as hazardous waste as they contain several gridded wafers of electroplated platinum base metal. (Contact the new catalytic converter seller to see if they will take your old one or contact your city or county disposal office to see how to properly dispose of a used one.) Exhaust pipes typically fail where there are bends as the metal is stretched and thinner there... look for holes and rust. Typically, a ratchet set, rubber mallet and hacksaw may be required to cut a catalytic converter out and then crush the round inner sleeve remaining inside the exhaust pipes ends with a thin flat chisel, pulling it out of the "good" exhaust pipes using locking pliers (a.k.a. Vise Grips tm). (Alternatively, a rubber mallet may be used to strike the catalytic converter to break it loose from the exhaust pipe ends... DO NOT DO THIS if the catalytic converter is in the disintegration stage. Do Not use the mallet on the exhaust pipes as they will bend!) Use crocus cloth or sand paper to smooth the inside of the exhaust pipe connections and ensure by trial off the car that the new catalytic converter goes in the pipe ends easily before mounting the separate pieces on the car... terrible to learn it won't go in, due to carbon soot or rust when you're on your back underneath!

Oct 13, 2014 | 1999 Dodge Grand Caravan

1 Answer

Mechanic says I need catalytic converter do I need to replace all three at once

Only replace the one that is not functioning. These are expensive, and should last years without needing replacement.

Jan 15, 2014 | 1999 Mercury Cougar

1 Answer

Mild brief gas smell and sluggish starts

Possible Catalytic Converter Heat Shield They Are Only Spot Welded And Break And Rattle. Could Also Be Broken Converter Bed If So Have Converters And 02 Sensors Checked.

May 16, 2013 | Mercury Sable Cars & Trucks

1 Answer

1999 mercury villager won't pass 1 sensor on smog 02 replaced and ran it for ever after replacing battery. Please help

There can be more than one sensor in the system. But here is what happens when your old sensor goes bad. The fuel mix can go rich and this results in a buildup of soot in the catalytic converter.

Sometimes the catalytic converter can recover over time. There are cheater additives which go in the gas and may help you pass the test.

You need a better diagnosis of your potential problem. The onboard computer in your van will not Code every problem and has to be showing a "check engine" light to display any problem.

However, better Scanners (Some costing thousands) can probe the system and reveal many defects.

New sparkplugs, clean fuel injectors, can help lower emissions. Just remember that an additive which dissolves debris on fuel injectors can also send that debris to your Catalytic converter.

Now as far as running it "forever", you want highway speeds, which in terms of RPM is about 2000 RPM on many vehicles. You can shift out of "overdrive" and this will keep the RPM higher at a slower speed, but it needs to be above 45mph to be effective. Your overdrive does not always kick in below 45, so to make a difference using my tip would require driving above 45.

Feb 20, 2013 | 1999 Mercury Villager

2 Answers

How hard is it to replace the y pipe and catalytic converter.

not to bad as long as you have a set of oxygen and acetalyne torches, a sawsall with metal blade. Heat one nut at a time on the manifold and remove then go to next ! you do not want those to break or strip cause then you will have a world of pain.

Jan 12, 2011 | 1994 Chevrolet K1500

1 Answer


couple hundred call around bargain with them tell them hey such such says he can do it for this price they sometimes will drop there price the way the times are right now

Dec 10, 2010 | 1999 Mercury Cougar

1 Answer

Replacing my bank 2 catalytic converter - 2000 mercury cougar

what does code P0430 cat bank 2 mean? how many cat. converters does my car have? which one do i need? on my 2000 Mercury Cougar 2.5 liter auto trans.

Sep 01, 2009 | 2000 Mercury Cougar

1 Answer

Does my 1999 Mercury Mystique have 4 O2 Sensors or am I wrong?

the sensors before the catalytic converters are the upstream sensors, the ones after the after the catalytic converters are the down stream sensors, Ford calls them the Catalyst efficiency monitors.

Apr 26, 2009 | 1999 Mercury Mystique

2 Answers

1999 cougar diagnostic code p0430 and p0420

Failed or faulty oxygen sensor, or faulty catalytic converter. It's actually the oxygen sensor reading that the catalytic converter is not functioning properly & needs relacement. That's provided the oxygen sensor is not faulty, which personally, I'd go for that first.
Both would explain excessive fuel usage.

Jan 21, 2009 | 1999 Mercury Cougar

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