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Exhaust shop claims running rich

IslanderOffRoad

IslanderOffRoad

NAXJA Forum User
NAXJA Member
Location
Houston, Tx
My muffler shop just called, they just finished installing a flowmaster for me and the guy asked if he could put a heat shield over the muffler. I said sure but why.

He said my exhaust quickly got to over 300 degrees, and he thinks the Jeep has a rich condition. I replaced the cat about a year and a half ago due to it being clogged shut, possibly from the same thing.

Plugs/wires cap and rotor were done July 2006
O2 Sensor was done August 2006
Jeep has had less than 20k put on it since then.

I have noticed an occasional fuel smell on startup, I was thinking injector leak but maybe its running rich?

Let me know what you guys think may be causing the rich condition and I'll start there, I dont want to replace unnecessary components chasing this.
 
Exhaust gas analysis would confirm whether or not you're truly running rich. Does the exhaust shop your vehicle is at have this capability? Assuming no check engine light? Pulling the plugs and inspecting them is another thing you could do as that tells a lot about how the engine is running.
 
No check engine light, he said nothing about the ability to do an analysis, the shop is fairly old school.
 
and the heat shield is supposed to lean out the jeep? or protect your floor from the heat? really not until you have a check engine light i wouldnt worry about it. i'm not sure how jeep does their emissions but the cars i work on has a purge to let out vapors left in the canister. thats maybe why you smell gas on start up.
 
EFR98XJ said:
and the heat shield is supposed to lean out the jeep? or protect your floor from the heat? really not until you have a check engine light i wouldnt worry about it. i'm not sure how jeep does their emissions but the cars i work on has a purge to let out vapors left in the canister. thats maybe why you smell gas on start up.
Click to expand...

Protect the floor until I get it figured out.
 
Hallo Jeeper. CTS and MAT sensors can give a rich running when bad.
Watch out with the buildingyear, because the sensors do have a different resistance scale! The O2 sensor gives a rich mixture, when the engine is still in the warm-up mode. If you are travelling only short drives, you keep smelling gas. :wave:
 
wim hoppenbrouwers said:
Hallo Jeeper. CTS and MAT sensors can give a rich running when bad.
Watch out with the buildingyear, because the sensors do have a different resistance scale! The O2 sensor gives a rich mixture, when the engine is still in the warm-up mode. If you are travelling only short drives, you keep smelling gas. :wave:
Click to expand...

CTS... as in coolant temp?

If the Jeep is running cold, it should be running rich right? I have a 3 core rad and a Grand Cherokee fan clutch, my temps tend to stay around 180-190... could this be it?
 
You want to be 210. A common "high performance" mod to some vehicles is to make the computer think it's cold to run on the richer mixture. Change your thermostat to a 210 degree one and you'll improve your gas mileage and probably stop your hot muffler problem. Rich mixture can also wear out rings and cylinder walls more quickly.
 
winterbeater said:
You want to be 210. A common "high performance" mod to some vehicles is to make the computer think it's cold to run on the richer mixture. Change your thermostat to a 210 degree one and you'll improve your gas mileage and probably stop your hot muffler problem. Rich mixture can also wear out rings and cylinder walls more quickly.
Click to expand...

I have an oem t-stat in, plus the t-stat does not impact the running temp, only the temp that the t-stat opens at. So I think if I were to change back to a "stock" fan clutch I would probably do better. I'll likely keep this one for the summer months.
 
When was your last smog check? If its running rich wouldn’t it show on the report?
Just a thought.

BTW: How do you like your flowmaster?
 
surf2snow said:
When was your last smog check? If its running rich wouldn’t it show on the report?
Just a thought.

BTW: How do you like your flowmaster?
Click to expand...

Last smog check was mid 2007, right before I had the new cat put on. I didn't have to do one in 08. The cat was working when replaced but the catalyst had broken apart and was clogging up the exhaust leading to an overheating condition, so we replaced it. I've seen at least one other XJ with the same problem.

I'll be due for a smog this year.
 
If you can get a hold of the installation instructions for the Flowmaster it will help explain why the Flowmaster will be "hotter" than the stock muffler. I can't remember the details, but I do remember reading about it in the instructions from Flowmaster.
 
4LowandGo said:
If you can get a hold of the installation instructions for the Flowmaster it will help explain why the Flowmaster will be "hotter" than the stock muffler. I can't remember the details, but I do remember reading about it in the instructions from Flowmaster.
Click to expand...

He mentioned it had something to do with a single wall vs double wall casing.

I do like the sound of the Flowmaster Delta 40, great burble at idle, but damn the zj fan clutch is so loud that thats often all I hear.
 
i would go back to the xj fan clutch. i know my xj ran super rich because the temp was so low. thats probably what it is. because it thinks its in open loop so its basically dumping fuel into the motor.
 
Also my stock and any XJ I've owned has never read a perfect 210. I know the gauge isn't accurate but checking under the hood I'm always below 210.

Our exhausts will also always be hotter then most so heat shields are okay. I agree with the above loop statement.
 
Thanks guys.
 
IslanderOffRoad said:
I have an oem t-stat in, plus the t-stat does not impact the running temp, only the temp that the t-stat opens at. So I think if I were to change back to a "stock" fan clutch I would probably do better. I'll likely keep this one for the summer months.
Click to expand...

Sorry, can't agree. Tstat opens at rated temp and closes back up when it cools down from the cooler coolant coming from the radiator. It is always opening and closing once it gets warm. Only if the radiator is too small, or the fan inadequate, then coolant never cools down enough and the tstat stays open. A Jeep should run 210 both in the winter and in the summer.
 
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