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Cats failing, info on carb tune and affects on combustion?


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9 replies to this topic

#1 SnatchedHatch

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Posted 12 February 2014 - 08:17 PM

I'm splitting my last post about the CEL's and O2 sensors to focus on this:

-are there tell-tale signs of an improperly tuned carburetor?

-wouldn't it technically reak havoc on the catalytic converters over time?

 

~I'm going to scour the forum for information on the topic, however at the moment my home internet is down.

~I'm limited to my phone, unless I hit some FREE wifi (yeah Dunkin.. haha),

but reading the posts and pms is doable.

 

What do y'all think?
 

My front cat is overheating, possibly due to a failed O2 sensor. The rear cat either has a rattling guard, or from what I could tell a crumbling infrastructure. Engine seems weak on power.

 

:headbang: Any ideas, thought, info, comments would be greaat!

-Sam



#2 suprjohn

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Posted 12 February 2014 - 08:54 PM

I'm no expert, but if your rear cat is plugged or partially plugged, perhaps heat is being trapped in the first cat. 

 

As for an out of tune carb, there could be a few different symptoms, depending on whether it's running lean or rich. Reading the color and condition of the spark plugs can be a good indicator. Black and wet can mean rich, white or gray can be lean. 

 

Of course that's just the tip of the ice berg. Others with more knowledge and experience will weigh in. Don't be discouraged; you'll get it goin'!

 

John



#3 El Presidente

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Posted 13 February 2014 - 12:39 AM

Sounds like your front cat is plugged or your running lean, overheating is a sure sign of both. I've never heard of an out of tune carb killing a cat, but what usually does is things like carb cleaner or shooting brakeleen down the intake.

 

Have you used carbcleaner on it?

Are you running it lean right now?

Do you have any running issues like an idle that stumbles?

What do your spark plugs look like?

--What does your exhaust smell like? --

a metalic, burning, rotten egg smell is typical of a dead cat

 

Do you need to pass emmisions?

 

Try taking the rear cat off and take it for a drive, its probably fine and has a loose heat shield, but this would rule it out. It won't hurt anything, it will just be loud, so watch out for cops. If you do notice a big increase in power you might have found your problem.

 

Let us know what you find.

 

Josh


Edited by El Presidente, 13 February 2014 - 12:44 AM.


#4 SnatchedHatch

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Posted 13 February 2014 - 09:40 PM

Sounds like your front cat is plugged or your running lean, overheating is a sure sign of both. I've never heard of an out of tune carb killing a cat, but what usually does is things like carb cleaner or shooting brakeleen down the intake.

 

Have you used carbcleaner on it?

Are you running it lean right now?

Do you have any running issues like an idle that stumbles?

What do your spark plugs look like?

--What does your exhaust smell like? --

a metalic, burning, rotten egg smell is typical of a dead cat

 

Do you need to pass emmisions?

 

Try taking the rear cat off and take it for a drive, its probably fine and has a loose heat shield, but this would rule it out. It won't hurt anything, it will just be loud, so watch out for cops. If you do notice a big increase in power you might have found your problem.

 

Let us know what you find.

 

Josh

 

Wow, I'm sorry I forgot to mention another "symptom" of off-tune besides weak/low power.

Everyday, on my first start, I have to pump the gas two or three times for an effective start.

Once she is warmed up, it starts normally.

But if not, even a second start needs some gas.

 

I have a muffler, so no cats isn't too big of a deal for me. Cops are cool around me, had a 2.5L Sentra with a 3.5" catback exhaust and was never bothered with.

 

My plan is to either replace the O2 sensor, or if the cats are failed I will straight up cut them out for now.

I passed emissions in Dec. 13' with FLYING colors, better than my '02 car.

 

I have had a rattly guard *before on a different car*, but as I was working on the CV shaft with my car on a lift, my mechanic buddy knocked about the rear cat and in his opinion it was failing/crumbling. I can imagine he would notice if it was the guard instead.

 

That said,

let's say the rear cat is toast, then the front could just be suffocating. It almost sounds like gas is trying to escape from that area on hard acceleration.

 

 

 

 

I will check the plugs,

the only thing I sprayed through the carb was a good amount of starter fluid (note, it didn't need it. I have a faulty gas level gauge :/ That was embarassing lol). This was in November/early December.

I made sure I bought the starter fluid with lubricant.

 

I'll check the exhaust smell.

 

Besides the rough cold start, it idles well but I have instances of putting down the gas (pedal) and I will get *rev+accelerating* more gas pedal *rev and stagnant acceleration, just more revs and more noise*. My clutch is good, and this is what I mean by weak power.

 

At other times, oh man it powers through just fine and I even manage to overtake someone. The boxer growl reminds me of our 3.6L Outback at full throttle B) . I have to note, that I don't believe in coincidences and I took my car to the car wash recently. As I left I made a flawless getaway. The water cooled Something down


Edited by SnatchedHatch, 13 February 2014 - 09:46 PM.


#5 czny

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Posted 14 February 2014 - 10:53 AM

Here's a simple test(c/p) for clogged exhaust system courtesy of(& to) Shawn:



 

ShawnW


 

Posted 10 September 2005 - 11:50 AM



You can put a vac gauge on the
engine to verify clogged exhaust.



1. Put the gauge on an intake manifold vac source.

2. Allow engine to reach full operating temp. (fans cycle on/off)

3. From idle (700-850 RPM) rev up engine to 2000 RPM.

(Vac level on gauge should remain the same)

4. Quickly release throttle and watch gauge. Reading should slowly rise then
smoothly return to normal reading you were getting at idle. If it rises or does
not quickly return to normal the exhaust is likely restricted. This can be the
cat or the muffler even if the muffler is clogged with cat material from a
previous cat failure.

5. Disconnect exhaust and test if car fails test.



  •  

 



 


Edited by czny, 14 February 2014 - 10:54 AM.


#6 silverback

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Posted 14 February 2014 - 10:16 PM

Starting fluid is the absolute worst substance.

 

How old are your timing belts?  Has your gas mileage been slowly getting worse? 



#7 SnatchedHatch

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Posted 27 February 2014 - 10:59 AM

I'll double check the timing belts but I believe they have been replaced, there was a lot of maintenance done by the previous owner.

 

I have only had the car for half a year now, and only a few months ago measured the mileage, it was decent. Now these problems have arouse, or gotten worse, in the last month or so. I haven't check the exact mpg, but I didn't have to tank up about once a week and I certainly got more miles per tank.

 

I'll check with my mechanic buddy and see if he would even consider doing the vac test, based on if he can tell if the muffler is clogged with cat substrate. What equipment is needed for a vac test?

 

He (mech.bud) already said the cat is failing, and

~today I took the car into a shop I frequent and they said the cat is dead,

~and that the piping behind the cat is double walled, prone to rattling.

 

~They wouldn't do what I wanted as I suspected, but said I can most definitely replace the cat with some pipe and secure it in place (flex-joint clamps) without welding.

That is my plan at the moment, but I will get a confirming opinion on the state of the cat. This will work out even cheaper than I imagined.

 

Even the shop owner, who I know from the past, said if I'm on a budget that I can just run the car as is. But if mileage is down and I'm prepared for DIY, to go for it.



#8 SnatchedHatch

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Posted 27 February 2014 - 11:02 AM

By the way, the cat doesn;t overheat as horribly as before. After a week from the smokey incident, it only gets bad after long drives, albeit the power and mileage issues.

 

This leads me to believe the cat substrate crumbled significantly, and I've heard of the chance of it getting caught up in the muffler. What say you suprjohn? Is there any way to tell? I realize one way is to disconnect the muffler and see how she runs, but I wouldn't be able to peer inside as at most I'll be cutting up at the rear cat. Don't want to make more cuts than needed.



#9 silverback

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Posted 27 February 2014 - 03:22 PM

Typical early warning signs of timing belt problems (failure) are: hard starting, decreased gas mileage.

 

Failing/clogging cat risks burning exhaust vaives.



#10 SnatchedHatch

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Posted 12 March 2014 - 01:06 PM

Man, I really wish cash wasn't so tight! I'd love to slap on a sport exhaust and hear that burble!

 

Talked to a bud of mine, I'll be going with the easy route, disconnect the cat, BANGARANG for a bit, check for particle in the muffler and bolt it back up.

 

If I still have issues, I'll swap the o2 sensor up front that probably fried.

 

Thanks for all the help guys/gals, and I'll have a look at the t-belt and do an oil and coolant change when I get her on the lift.

 

 

Anyone know if the EA81 has non-interference valves? Purely out of wonder, no crazy ideas there :mellow:


Edited by SnatchedHatch, 12 March 2014 - 01:06 PM.





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