Catalytic Converter Installation Help Please | Ford Explorer Forums - Serious Explorations

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Catalytic Converter Installation Help Please


New Member
April 4, 2011
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City, State
Amsterdam, NY
Year, Model & Trim Level
'99 XLT
I am getting ready to replace my catalytic converters. The core of my drivers side cat is broken apart and rattles terribly. While I'm at it I figure I would change both and be done with it. I know that the flange bolts from manifold to exhaust pipe flange are notoriously difficult and tough to access. I have been spraying down for several days with PB Blaster. Has anyone else tackled these? If so, do you have any tips, tricks or advise? I considered just cutting the bolts, however they appear to thread into the manifold flange and I am not sure how the heck I would get them out once cut. Again, access is a PITA. Thanks for any help.


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I've taken mine off a couple times when I replaced my transmission but I'm in CA and didn't have any trouble with the nuts. If you have trouble getting the nuts off you could always cut the studs off and the drill them out and replace them with new bolts.

I am a non-mechanic who needs need catalytic converters on my 1998 V8, and I understand it is wise to replace the O2 sensors at the same time. I was thinking of trying this myself, maybe with the help of a local community college class, and I wonder just how hard a job it is, too.

So, anyone out there, please let us have your experience. I have searched a fair amount and did not find anything approaching the great ball-joint information.

I am a non-mechanic who needs need catalytic converters on my 1998 V8, and I understand it is wise to replace the O2 sensors at the same time. I was thinking of trying this myself, maybe with the help of a local community college class, and I wonder just how hard a job it is, too.

So, anyone out there, please let us have your experience. I have searched a fair amount and did not find anything approaching the great ball-joint information.

Are you asking about how to replace the O2 or the cats?

Well, both I guess. Sorry for the confusion. I assumed it best to replace the O2 sensors when replacing the catalytic converters, sort of a "while you are at it might as well replace everything" notion.

I talked to a couple of shops and it looks like about $1300 to replace everything. I might go ahead and just do that, since I hope to keep this X a long time. Plus, I gather the job is more than I can handle.

You might want to call around some more on that. $1300 sounds high. Book is 1.4 hours labor for cat removal and replacement. The parts themselves vary a lot from $250 - $1500 for direct fit pieces depending if you have CA emissions or performance exhaust. You can also go with universals for under $100. Many muffler shops use them for an easy cut and weld job without messing with the manifold.

Its kind of a personal call based on your comfort and ability. It may work out much better just paying a shop. If you decide to replace yourself, I'd recommend you have air tools and a propane torch on hand. If the exhaust is rusty those cat bolts can be tough to turn.

The O2 sensors aren't horribly expensive ($50 each) but I'd test first and only change if needed. Honestly the sensors just don't fail all that often. Most sensor error codes indicate something other than a bad sensor.

They are a managable install for beginners using handtools with the truck up on jackstands. There is a very large special socket with a slot in the side sold for changing the sensors. Save yourself a lot of frustration and do not buy it. It doesn't work well because there isn't a lot of free room between the sensors and the body of the truck for swinging a ratchet. The best advice is get the $12 O2 tool from the helper section at you local autoparts store (it looks like a black figure 8 with openings in the ends in it). You use with a standard 3/8" ratchet wrench. It gives you extra torque and a low profile for removing the sensors. If you have small hands reaching around to the wiring plugs isn't hard. If you have big mits the front wires are easier to reach through the wheel wells instead of from under the truck.

Thanks Romeoville. That's a lot of good information that I hadn't found on the site before.

The codes I have gotten have been 420 and 430, indicating the need for catlytic converters on both sides, but the codes haven't come back after clearing them for several months. So, I was thinking the O2 sensors might be "weak".

The shop I was dealing with (Muffin, in Austin, TX) is well respected but not cheap. The lowest price converters they wanted to install were $400 each, plus $175 labor.

Muffin would also put in any O2 sensors I provided for $20 each. I priced them from about $50 each at Autozone to about $85 each at a dealership. Apparently the V8 I have has 4 sensors.

I have heard of a lower-end shop that will put in the lower end converters and that they have had pretty good luck with them. So, I may just forget about the sensors and have the $100 converters put in on both sides for a total of roughly $400 and hope that works.

I bought this Explorer hoping it would last a long time with the V8 and transmission seemingly strong and only 144,000 miles. I just need to decide how much money to spend on it.

Again, thanks.

If you need to replace the cats on the rear of the truck and not pay through the nose you will need to find a smaller shop that will install what you want... I have used the Muffin shop in the past but since they have moved from Burnet Rd. they have gotten super expensive and will not install most parts the customer brings in...

They have told me that the Explorer is too tough to install most aftermarket pats but they can get oem parts to install... Not happening...

I have used parts from and have used a shop off of Highway 29 west of Seward Junction and a shop in Galveston, Texas...

And the codes you are getting are the bank 1 and bank 2 Catalyst System Efficiency Below Threshold...I wouldn't think the o2 sensors are bad; it is probably the sensors are not seeing the change in the exhaust stream needed at that point in the exhaust...

I know the v8 configuration is different from the v6 convertor wise but the front o2 sensors are in front of the front cats and the rear sensor is behind the last convertor... I would look at the front cats being defective and see if the codes go away...

If you plan on replacing the o2 sensors yourself, I would drop the exhaust pipes from the exhaust header/manifold and then work the exhaust that way then put it back into the truck...

I changed the 3 o2 sensors when I changed the engine last year and I had no real issues removing them. I used a slotted socket and had a slotted black socket in case I needed it...

I've always removed my O2 sensors with a 22mm wrench.

you can also clean the 02 sensors by heating up the tip with a propane torch,gets rid of all the carbon/oil deposits.also always use a 22mm wrench to get them off,then put anti seize on the threads before reinstall.


Well...Those manifold to converter bolts sure are stubborn. I have saturated for almost a week with PB blaster then attemted to break free with 12mm impact socket and a manually 200 ft/lb mallet driven impact adapter. I also tried a breaker bar with a cheater and really felt like the bolt head was going to shear off so I stopped. All I did was start to round off one of the bolt heads....Took a step back, applied heat to threaded manifold "ears" with map gas torch. This heated the manifold but it would not develop that cherry red hot appearance. Bolts still would not budge. Saturated with more blaster, applied heat and due to the partially rounded bolt I used a serated "bolt-out" extractor with manual impact driver. Still no luck....I don't want to snap the bolt heads off. I am trying to stay patient and cool, I knew this would be difficult. Now I have booked some time at a friend's home garage who has oxy-acetylene. Fingers crossed these will come out after applying some serious heat to the manifold side. More to come, stay tuned!


How did you finally get the bolts out? I am thinking about trying to do this myself.


I had to drop the driver's side cat to remove my transmission, and you all are right, it is very difficult. I sprayed MPL on them repeatedly, from below and from the fender area (with splash guard removed). I used a 1/2" air impact wrench w/ a six-point deep impact socket. I recall having to hold the impact on there for several minutes, and it seemed as though they were not going to break loose. I kept spraying & impacting, and finally they came out. It took quite a while. So I thought I had better put new bolts in, and even those were difficult to get back in.
Best wishes.

I had the driverside pre-cat break apart, causing the main cat to break apart.

I have a '03 Sport Trac (same setup as Explorer) I shopped around, talked with Todd Z at Zabteck Technology and bought both Stainless Steel Y-pipe (pre-cat delete) and High Flow Stainless Steel Cat (one main cat instead of two) for less then it would've cost me for factory style Y-pipe and Main Cats. The best part is no more rust, no more Pre-Cats (no codes from doing this and past emissions testing in Pa. for the last two years), only one high flow Cat.

The sound is amazing too and I know I gained some HP and MPG's from the change over.

I already had the body lift on my Trac so it made it easier to access the bolts.

cat bolts

Hey David...sorry it took so long to reply.

I was unable to handle the cat to manifold bolts. I had to resort to a friends help and his oxy-acetalene (sp?). Even then the bolts ended up breaking.

However, once the bolt heads broke off, the bolt tension was released and the stud of the bolt threaded right out. Of course that was also after applying alot of heat to the manifold ear which I'm sure helped as well.

In retrospect, when I figure all the time and aggravation I had into this project, it would have been worth paying the exhaust shop the couple hundred dollars to install the cats.

Oh well...there is no such thing as free education. We pay for knowledge in green backs or red knuckles.


Old thread, but anyone know what size and thread pitch the bolts from the cat assembly to the manifold are? The ones that thread into the manifold.