01 XJ Header/precat replacement

[dieselenthusiast]

I'm looking to replace my precats because they are 11 years old, probably pretty clogged and they produce enough heat in the summer that they cause vapor lock and cylinder miss-fires. Which is apparently a common problem even on stock 4.0s.

If the pre-cats flow as well as people say they do, then how could it cause vapor lock and cylinder miss-fires? I’m not calling into question your judgment; however, I’m just trying to figure out the 4.0L a little better. I understand how a diesel works much better than I know how a gasoline engine works. With a diesel, it’s all about reducing the EGT’s. A better flowing exhaust means lowering EGT’s and engine temps.

 

[dieselenthusiast]

That stupid stock version is so restrictive, it's producing enough heat to cause vapor lock and throw cylinder miss-fire codes in the summer with my 4.9L stroker... course I'm sure it doesn't help that it's 11 years old, probably pretty clogged up.

If possible, take pics of your cats when you take them off. It will be interesting to see if they are clogged and if so, how much. I’ve often wondering the same thing. Due to soot and unburned diesel fuel, a diesel engine can most certainly clog a cat. I didn’t know how susceptible a gasoline engine was to clogging a cat.

 

[Redsnake]

If the pre-cats flow as well as people say they do, then how could it cause vapor lock and cylinder miss-fires? I’m not calling into question your judgment; however, I’m just trying to figure out the 4.0L a little better. I understand how a diesel works much better than I know how a gasoline engine works. With a diesel, it’s all about reducing the EGT’s. A better flowing exhaust means lowering EGT’s and engine temps.

They can cause vapor lock because they get HOT and are sitting directly below the intake, and fuel injectors... That heat goes somewhere and can cause vapor lock and extremely hot intake temps.

I'm not necessarily looking to gain any additional horsepower on my '01, but I AM looking to fix that d@mn Check-Engine light (P0432) code I've had for going on a year now. All symptoms point to a clogged and malfunctioning pre-cat. Also could've been caused f/running a cracked cylinder head on my rig for a while and burning a lot of coolant thru the exhaust which can toast a catalytic converter. Since I've replaced the head, now on to the next fix on my rig. I'm thinking if I have to replace the Pre-Cat then why not replace the OE Cast-Iron manifold as well... it's only money right!! :|

 

[dieselenthusiast]

They can cause vapor lock because they get HOT and are sitting directly below the intake, and fuel injectors... That heat goes somewhere and can cause vapor lock and extremely hot intake temps.

I'm not necessarily looking to gain any additional horsepower on my '01, but I AM looking to fix that d@mn Check-Engine light (P0432) code I've had for going on a year now. All symptoms point to a clogged and malfunctioning pre-cat. Also could've been caused f/running a cracked cylinder head on my rig for a while and burning a lot of coolant thru the exhaust which can toast a catalytic converter. Since I've replaced the head, now on to the next fix on my rig. I'm thinking if I have to replace the Pre-Cat then why not replace the OE Cast-Iron manifold as well... it's only money right!! :|

That makes sense. Exhaust temperatures are hazardous, that’s for sure. I’ve already bought the headers, catback, and the third cat, so all I have left is the pre-cats and the pipe that connects them to the third cat. Than I’ll have an entire new exhaust system.

 

[Darky]

I'm looking to replace my precats because they are 11 years old, probably pretty clogged and they produce enough heat in the summer that they cause vapor lock and cylinder miss-fires. Which is apparently a common problem even on stock 4.0s.

Like I said, if yours are causing issues, by all means. But for the people with perfectly functioning cats, the money could be better spent elsewhere.

 

[DrMoab]

Like I said, if yours are causing issues, by all means. But for the people with perfectly functioning cats, the money could be better spent elsewhere.

Old thread I know but I'm doing a lot of research on overheat and heat soak issues. This thread came up and it's realivent.

I have no way to prove this. It's a total gut hunch on my part but my gut hunches are usually pretty sound.

I think these pre cats are the #1 cause of heat soak issues. I think, as the jeeps with them get older and older they plug up worse and worse causing them to get hotter and hotter which causes more and more issues with heat soak. They may not plug up bad enough to cause performance issues but I think it's the reason 00's and 01's with heat soak issues get worse and worse the older they get. I'm replacing mine. I have no idea if they are plugged up enough to cause a degradation in performance but if it will help the damn thing quit running crappy when I let it sit longer than ten min, it's worth the $200 or so to find out. Like others have said, I'm not looking for a performance upgrade I just want it to run like it should.

On a side note. If you think talking about removing part of a federally mandated system is going to cause naxja to get in trouble with the Feds, you need a tighter fitting tinfoil hat. With maybe the exception of making threats to the president, the Feds could care less. On that same line of reasoning. I read, watch and keep track of several very hard core environmental groups websites and blogs. I've seen them post some of the most outrageous and creative claims about how horrible off roaders are. Not once EVER have I seen a single one of them call us out over removing a cat. Never!

Those of you who think like that seriously need a reality check.

 

[dieselenthusiast]

The Catco aftermarket cats are also a high flowing cat, which should flow much better than stock in it's best form. Also, replacing the cast iron manifold for a better flowing stainless Borla header would make a measureable difference.

 

[Root Moose]

DrMoab, I believe you are on the right track. That is my hunch also.

Additionally, I believe that either the residual valve and/or the fuel cleaner "valve" may be related as well (non-optimal cat + minor presue bleed may be involved). I'm not certain if both things need to be "off" to make the issue prevalent.

In my case all three components could be replaced with PM so not a biggie.

 

[ScienceguyXJ]

Earlier this summer got the new header installed with the high flow Catco precat and a 2.5" magnaflow cat with 2.5" stainless exhaust. Sounds great with the 4.9L. There was definitely a noticeable difference between the Catco precat and the stock one in the size of the screen openings. It would be hard to tell how clogged the stock one is without cutting it open but I haven't seen any miss-fires or vapor lock this summer so I assume the stock one was ready to go.

 

[DrMoab]

Finally installed mine this weekend but I haven't started it yet. The belly pan and front axle are out of it right now. Cant wait to try it out.

 

[lazyxj]

It would be helpful if someone had access to a flow bench to measure the actual pressure drop across a few mini-cats, both stock and aftermarket.
Having actual measured data would help end some of the speculation.

Installing a second set of ports, on a set of mini-cats, and then measuring the pressure drop, at various RPMs and engine loads, would provide similar information.
You can't trust the performance information provided by most manufacturers, they too much of an incentive to twist the data.

 

[Redsnake]

Earlier this summer got the new header installed with the high flow Catco precat and a 2.5" magnaflow cat with 2.5" stainless exhaust. Sounds great with the 4.9L. There was definitely a noticeable difference between the Catco precat and the stock one in the size of the screen openings. It would be hard to tell how clogged the stock one is without cutting it open but I haven't seen any miss-fires or vapor lock this summer so I assume the stock one was ready to go.

Can you, or anyone lease who swapped on a pair of headers share what manufacturer & where you got them (for the 00-01 XJs) as I'm planning on swapping the Catco precast onto my 01 here in the very near future & think I'll swap in a set of headers (if affordable) when doing the swap. Thx

 

[DrMoab]

I wish I could have found some headers for mine. I looked everywhere.

 

[dieselenthusiast]

The Borla Headers fit the 2000 and 2001 models.

 

[Talyn]

AFE, JBA, Borla, Pacesetter, OBX and Banks all make headers for 00+ XJs.

 

[ScienceguyXJ]

It would be helpful if someone had access to a flow bench to measure the actual pressure drop across a few mini-cats, both stock and aftermarket.
Having actual measured data would help end some of the speculation.

Installing a second set of ports, on a set of mini-cats, and then measuring the pressure drop, at various RPMs and engine loads, would provide similar information.
You can't trust the performance information provided by most manufacturers, they too much of an incentive to twist the data.

This was from Catco,
From Catco:

Dear Sir,

The 2200 is a converter that would flow better then the OEM unit installed on the vehicle now. The reason is because the 2200 series uses a metallic substrate as opposed to the ceramic type used in the OEM on your vehicle. The wall thickness is thinner on the metallic 2200 converter then on the OEM converter. This thickness affects how the exhaust gas flows through the converter. Also the 2200 uses a 200 cells per square inch substrate as opposed to the 400 cell used in the OEM cat. Again this would cause the exhaust gas to flow faster through the 2200 cat.


Bill Kaminski

I agree manufactures are a little bias, however what they told me seems pretty sound.

 

[ScienceguyXJ]

Can you, or anyone lease who swapped on a pair of headers share what manufacturer & where you got them (for the 00-01 XJs) as I'm planning on swapping the Catco precast onto my 01 here in the very near future & think I'll swap in a set of headers (if affordable) when doing the swap. Thx

Here you go, these are the ones I ordered. I was impressed with the quality and look for the price.

http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&vxp=mtr&item=300666206077

 

[Talyn]

Looks like a Banks knock off.

 

[dieselenthusiast]

This was from Catco,

The 2200 is a converter that would flow better then the OEM unit installed on the vehicle now. The reason is because the 2200 series uses a metallic substrate as opposed to the ceramic type used in the OEM on your vehicle. The wall thickness is thinner on the metallic 2200 converter then on the OEM converter. This thickness affects how the exhaust gas flows through the converter. Also the 2200 uses a 200 cells per square inch substrate as opposed to the 400 cell used in the OEM cat. Again this would cause the exhaust gas to flow faster through the 2200 cat.

That's good info ScienceguyXJ, thanks for posting. :thumbup:

 

[lazyxj]

The 2200 is a converter that would flow better then the OEM unit installed on the vehicle now. The reason is because the 2200 series uses a metallic substrate as opposed to the ceramic type used in the OEM on your vehicle. The wall thickness is thinner on the metallic 2200 converter then on the OEM converter. This thickness affects how the exhaust gas flows through the converter. Also the 2200 uses a 200 cells per square inch substrate as opposed to the 400 cell used in the OEM cat. Again this would cause the exhaust gas to flow faster through the 2200 cat.

I agree manufactures are a little bias, however what they told me seems pretty sound.

All manufacturers are bias and claims mean little without verifiable testing and I'm a fan of the scientific method.
Cells per inch indicate only how many holes there are, not how large each opening is. 200 cells per square could have less available opening than the 400, depending on how thick the cross-hatching is. There are several factors that contribute to the amount of flow.
The new converter may flow better than OEM or not, we have no reliable data to indicate either.