*Semi Urgent* Need an assist from someone with a Temp gun

[Cree]

Can someone do me a favor? I need somebody to measure exhaust pipe temp fore and aft of the rear converter, with the truck at operating temp. I'm 90% sure my rear cat is clogged, but no CEL or pending codes. Doesn't rattle either. I'm only seeing about 20 degrees difference on either side of that cat. Any help is appreciated. Thanks!

 

[YFZsandrider]

I had a p0420 code a while back, and after changing the o2 sensor, I was convinced it was the cats. I found a video online where a mechanic explained that that the temp reading from an infrared temp gun should show the temperature before the cats to be lower than the temp just behind the cats, as the converters burn emissions inside.

With my clogged cats the reult was the oposite. After the vehicle was up to normal operating temp, and while the throttle held at a cruising speed(roughly 2000-2500rpm)the reading in front of the cats was significantly higher(I want to say it was somewhere around 100 degees) than just behind the cat. They were building heat and pressure in front of the cat. After replacing them, the code hasnt come back in the last 2 years and the temp readings I took just after replacement showed them to be higher just after the cat. i cant remeber the temps exactly, but it was significant- somewhere around 100 degrees.

 

[Cree]

I had a p0420 code a while back, and after changing the o2 sensor, I was convinced it was the cats. I found a video online where a mechanic explained that that the temp reading from an infrared temp gun should show the temperature before the cats to be lower than the temp just behind the cats, as the converters burn emissions inside.

With my clogged cats the reult was the oposite. After the vehicle was up to normal operating temp, and while the throttle held at a cruising speed(roughly 2000-2500rpm)the reading in front of the cats was significantly higher(I want to say it was somewhere around 100 degees) than just behind the cat. They were building heat and pressure in front of the cat. After replacing them, the code hasnt come back in the last 2 years and the temp readings I took just after replacement showed them to be higher just after the cat. i cant remeber the temps exactly, but it was significant- somewhere around 100 degrees.

The front cat is about 120 degrees between the front reading in the rear. The rear cat I'm only seeing about 20, but I don't have anything to compare it to. I don't know if that's normal or if there's supposed to be a huge temperature difference on both.

 

[YFZsandrider]

The front cat is about 120 degrees between the front reading in the rear. The rear cat I'm only seeing about 20, but I don't have anything to compare it to. I don't know if that's normal or if there's supposed to be a huge temperature difference on both.

ya know I honestly cant be sure. I dont have a temp gun right now to go out and check, but Im about 80 percent sure after replacing cats, that the difference is 100+ degrees for both cats.

Wish I could help more.

 

[YFZsandrider]

On another note, if you do end up replacing your cat, its probably a good idea to do both. I dont know that you want a fresh downstream cat with a 20 year old one just in front of it, for obvious reasons.

I went with walker cats on my 00 Limited(cali emissions) and it was something around 360 bucks in total. Walker has a 90 day satisfaction return policy, no questions asked, and a 5 year warranty beyond that. Couldn't be happier with mine.

 

[Cree]

ya know I honestly cant be sure. I dont have a temp gun right now to go out and check, but Im about 80 percent sure after replacing cats, that the difference is 100+ degrees for both cats.

Wish I could help more.

I'm betting you're right, and it would explain some things. Hopefully someone else will chime in, help a dude out.

 

[wcjeep]

I've seen ir temp guns on sale for $20. I use mine for many things mechanical.

 

[YFZsandrider]

I'm betting you're right, and it would explain some things. Hopefully someone else will chime in, help a dude out.

You said it's not throwing a code... what's the problem then?

 

[Cree]

You said it's not throwing a code... what's the problem then?

Odd noise over half throttle and down on power. Classic symptoms right? Except I'm also just recovering from a pink milkshake. So I'm trying to narrow it down before I commit to pulling a trans.

 

[jgue467]

Odd noise over half throttle and down on power. Classic symptoms right? Except I'm also just recovering from a pink milkshake. So I'm trying to narrow it down before I commit to pulling a trans.

Many other things cause those symptoms. Where does the odd noise come from, engine, exhaust or both?

Down on power, hmmm. Meaning it surges then power drops after half throttle? :cowboy:

 

[Cree]

Many other things cause those symptoms. Where does the odd noise come from, engine, exhaust or both?

Down on power, hmmm. Meaning it surges then power drops after half throttle? :cowboy:

Noise is under the truck, seemingly exhaust. Yes, drives fine until over half throttle. No surge, just doesn't accelerate like it should.

 

[LittleCaesar]

I measured pre and post non CA 4Runner years ago (2010 or so) and if memory serves me correctly there was about a 120f difference. Make sure to measure as close to the cat as possible on both sides. I think my exhaust manifold temps hovered around 300f. If it is original, the kitty has seen better days.

 

[96RedRunner]

measure exhaust pipe temp fore and aft of the rear converter,

Your post got me curious, my numbers are after 7 mi 75 mph run on interstate 2.5 mi to my house at 45 mph.
372 in 426 out. shut off 5 min restart 250 in 278 out, exhaust system has 12k mi on it. Fed twin cat sys.
Have my base line now.

 

[octanejunkie]

Your post got me curious, my numbers are after 7 mi 75 mph run on interstate 2.5 mi to my house at 45 mph.
372 in 426 out. shut off 5 min restart 250 in 278 out, exhaust system has 12k mi on it. Fed twin cat sys.
Have my base line now.

If it weren't raining here I'd post mine too

For grins and giggles, I'd get the temp while running, and above the first cat

 

[96RedRunner]

If it weren't raining here I'd post mine too

For grins and giggles, I'd get the temp while running, and above the first cat

wud up Mike Happy New Year.
Couldn't get good angle with I/R gun my bi-metalic wire thermometer was dead.
Be good to have both.

 

[YFZsandrider]

For the sake of consistency, how are these temps being taken? At idle? with the throttle held at a cruising speed?

 

[Cree]

For the sake of consistency, how are these temps being taken? At idle? with the throttle held at a cruising speed?

At idle after a drive.

I'm confused now, got two different readings. First one was identical fore and aft, second was about 90 degrees difference. I may just pull the exhaust this weekend and take a peek inside.

 

[96RedRunner]

At idle after a drive.

I'm confused now, got two different readings. First one was identical fore and aft, second was about 90 degrees difference..

Interesting, indentical readings seem to indicate free flowing, 90* diff seems as it's higher than it should be indicating blocked.
Look at my numbers post 13 and compare.

 

[Cree]

Interesting, indentical readings seem to indicate free flowing, 90* diff seems as it's higher than it should be indicating blocked.
Look at my numbers post 13 and compare.

Flip that. It should be higher due to the catalyst process. The only difference was I managed to get to it immediately on the same read, it had idled four a second when I got the difference. I'm putting money on it being partially blocked. Find out this weekend.

 

[96RedRunner]

Flip that. It should be higher due to the catalyst process. The only difference was I managed to get to it immediately on the same read, it had idled four a second when I got the difference. I'm putting money on it being partially blocked. Find out this weekend.

Yes I agree blocked because my diff maxed at 54* at it's hottest with 12k mi cats, Your almost twice that, chokes engine.
Your case with no temp diff core broke apart no back pressure, ECU detunes.
Either end can cause issues with ECU/engine.
Something's up, good luck.