To Catalytic Converter or Not (1 Viewer)

[1979 FJ40ish]

I have a 1979 FJ40 that I recently acquired. At some point during the last 30+ years it misplaced its catalytic converter (CC). Knowing that I needed to replace the exhaust system I ordered an aftermarket CC and muffler from SOR.

When the CC arrived I discovered it has an “extra” 6 inch long x ½ ID tube on the inlet end of the CC. More research revealed the tube is for a Thermo Sensor. If my cruiser ever had a thermo sensor it apparently was taken off along with the CC. The thermos sensor is no longer available. I’m spent hours searching the web for one. Anybody got one they aren’t using?

I’m not subject to emission testing but the next owner might be. So what do I do now?

1. Install the converter and plug the thermo sensor tube. If I do this does the converter provide any benefit? Is there any risk to the engine or other components?

2. Try to find a converter without the thermo sensor tube. Not sure this option is really any different than just plugging the tube on the CC I have.

3. Send the CC back to SOR and don’t bother installing one.

Looking forward to getting your thoughts.

 

[Downey]

Back in the day we thought removing the Cat might give better performance, it didn't, just made the rig louder (Cat is also a muffler). I'd run without a Cat, then let the next owner worry about getting the rig smog legal if he has to (or you have to for him). Note, nothing says the Cat has to be a genuine factory part, or SOR. I you looked a Cat supplier's websites (such as Allied Exhaust Systems), their Cat listings also tell what engines/years the cat is registered as legal on, and their Cat cost a small fraction of a factory part.

 

[1911]

The best thing about getting rid of the cat converter is losing all the heat they radiate.

I wouldn't worry about the next owner; you shouldn't sell a good 40 anyway.

 

[Output Shaft]

The thermosensor's purpose is to tell the smog pump to stop pumping air into the exhaust when the CAT reaches about 1200° or so. To prevent overheating it.
Overheating a CAT can damage it, and it's not like the rest of the exhaust system enjoys being bolted up to it at that temp.

 

[reddingcruiser]

Skip the cat if your smog laws don't require it. Spend the money somewhere else.

 

[1979 FJ40ish]

I was cruising the net and came across this picture of a EGR Temperature Sensor which I assume is what the manual was referring to as a thermo sensor.
Can someone tell me WHAT and WHERE the green connector plugs into on a 79 FJ40?

 

[gcrump01]

Pretty sure that plugs under the drivers seat to the wiring harness that includes the rear heater, seat belt light, etc. Hole under the driver's seat about 1 inch in diameter should fit that rubber plug.

 

[1911]

Can someone tell me WHAT and WHERE the green connector plugs into on a 79 FJ40?

There is (or was) a matching green plug under the driver's side floorboard that it plugs into. Mine is just zipped-tied out of the way now; maybe whoever took the cat off of yours just cut it off?

 

[1979 FJ40ish]

I guess that explains the grommet I found in the floor under the driver's seat with a golf tee stuck in it to plug the hole.

Looks like I still have the mating connection under the seat.

Thanks for the education.

 

[catslug1]

Hi. I came across this old thread when researching wiring for the cat on my 40. I have the cat, thermostat sensor and all wiring and mating clips in tact. However, I think the seat belt and cat wirning inside the cab are switched/connected to the incorrect mate. Could you please confirm what color wires the cat sensor attaches to inside the cab: black and white or double green with white and red stripe? Thank you.

 

[1979 FJ40ish]

On my 79 the leads to the driver's seat belt are solid black and white with a black stripe.

 

[residualboulders]

This is maybe a dumb question - any reason this cat sensor has to be plugged in? I guess what I mean is does having that plugged in complete a circuit or whatever that the truck needs to run properly.

I've had my 40 for 20 years and it has never had a Cat converter but the sensor was plugged in and zip tied up underneath all these years. Now I am working on restoring the truck and wondering if there was a reason the PO left that sensor plugged in even though the cat was removed. Could easily just be lazyiness by the exhaust shop that cut the cat coverter out, but I wondered if the wiring harness is set up in a way it needs to be plugged in.

 

[1911]

This is maybe a dumb question - any reason this cat sensor has to be plugged in? I guess what I mean is does having that plugged in complete a circuit or whatever that the truck needs to run properly.

I've had my 40 for 20 years and it has never had a Cat converter but the sensor was plugged in and zip tied up underneath all these years. Now I am working on restoring the truck and wondering if there was a reason the PO left that sensor plugged in even though the cat was removed. Could easily just be lazyiness by the exhaust shop that cut the cat coverter out, but I wondered if the wiring harness is set up in a way it needs to be plugged in.

The oxygen sensor provides an input for the emissions "computer" (circuit board under the dash), which in turn controls the fuel cut (idle) solenoid and some vacuum switches for the charcoal canister, EGR system, and etc. Without being connected to a cat converter, it's not going to supply any useful data. I just unplugged the sensor from the harness and left the connector on mine when I de-smogged it and ditched the cat converter. the 2F has been running happy that way for at least 12 years now.

 

[residualboulders]

The oxygen sensor provides an input for the emissions "computer" (circuit board under the dash), which in turn controls the fuel cut (idle) solenoid and some vacuum switches for the charcoal canister, EGR system, and etc. Without being connected to a cat converter, it's not going to supply any useful data. I just unplugged the sensor from the harness and left the connector on mine when I de-smogged it and ditched the cat converter. the 2F has been running happy that way for at least 12 years now.

OK, so I have been trying to get mine started for several weeks without success. We ruled out any issues with the holley sniper which would suggest it has to be a timing issue. I'm pretty sure we have the timing correct. I was just wondering this morning if that sensor has to be plugged into the harness for the system be 'complete' and allow the truck to start and run. From what I understand from your reply, it does not need to be connected and will run without.

Sorry, I would just go test it but my 40 is at the exhaust shop and the sensor is at home. Just reading up on other possibilities that might be keeping it from running.

 

[kerplunk]

OK, so I have been trying to get mine started for several weeks without success. We ruled out any issues with the holley sniper which would suggest it has to be a timing issue, even though I'm pretty sure we have it correct. So, theoreticaly (from what I understand from your post) not having that plugged in could be preventing my 40 from starting and running.

My understanding was that the sniper used an oxygen sensor, when reviewing what I needed to install one I saw that in the instructions... No idea what it does when it doesn't have one, can't imagine it would be good...

If you've got a sniper installed, all the rest of this is pretty much a mute point, it replaced the carburetor so there is no longer an idle solenoid.

There's some value in maintaining some of the remaining vacuum lines for the charcoal canister and PCV system in my view, if only to control smells vented from the gas tank and engine... But the rest of that, air pump, EGR, cat converter and any kinda stock emissions computer is probably not going to play along well with a sniper, didn't see any mentions of them in the instructions for the sniper I was reviewing, don't think they'd all just work together.

 

[residualboulders]

My understanding was that the sniper used an oxygen sensor, when reviewing what I needed to install one I saw that in the instructions... No idea what it does when it doesn't have one, can't imagine it would be good...

If you've got a sniper installed, all the rest of this is pretty much a mute point, it replaced the carburetor so there is no longer an idle solenoid.

There's some value in maintaining some of the remaining vacuum lines for the charcoal canister and PCV system in my view, if only to control smells vented from the gas tank and engine... But the rest of that, air pump, EGR, cat converter and any kinda stock emissions computer is probably not going to play along well with a sniper, didn't see any mentions of them in the instructions for the sniper I was reviewing, don't think they'd all just work together.

Yes, those were my thoughts so I left it unplugged. Just wondered if there was some kind of failsafe that would prevent it from running if not plugged in. Likely not, being as old as it is; but figured I'd ask the community so i can rule that out.

 

[1911]

From what I understand from your reply, it does not need to be connected and will run without.

It does not need to be connected for it to run with the stock carburetor, but as @kerplunk says, I'm pretty sure the Holley Sniper needs an oxygen sensor, to adjust the fuel/air ratio. In the factory 2F Emission Control manual, it calls it a "thermo sensor", so the one in late 40's may not even be an oxygen sensor.

 

[residualboulders]

It does not need to be connected for it to run with the stock carburetor, but as @kerplunk says, I'm pretty sure the Holley Sniper needs one, for it to adjust the fuel/air ratio.

thank you all for the feedback. I think I can just leave it off. Yes, the Holley sniper has a sensor on the exhaust and the motor. I have it in the shop now getting exhaust work done including the bung for the exhaust sensor.

 

[MOTOV8R]

The CC will burn up remaining combustable materials in your exhaust which translates to less stinky exhaust. That said on my 79 I removed it a few years back because it was cooking my feet. The exhaust smells worse and it’s noticeable since my exhaust is routed out the back (which seems to draw it inside) and not the side. If i can find an effective heat shield I may install it again or route the exhaust out the side. Maybe both.

 

[residualboulders]

The CC will burn up remaining combustable materials in your exhaust which translates to less stinky exhaust. That said on my 79 I removed it a few years back because it was cooking my feet. The exhaust smells worse and it’s noticeable since my exhaust is routed out the back (which seems to draw it inside) and not the side. If i can find an effective heat shield I may install it again or route the exhaust out the side. Maybe both.

I noticed this too, redoing the exhaust now and plan to run it out the side.