would an exhaust leak cause lean or rich sensor reading?

Okay I know my old exhaust manifold is leaking, and is at it's worst when cold so I'm wondering if a leaking manifold could fool the O2 sensor and cause the Cater stepper motor to go too rich, until the engine gets a little warm (at which point the manifold has expanded from the heat and sealed things up a little better) and then leans out.

Would an exhaust leak before the O2 sensor cause rich or lean? In other words would the sensor detect MORE O2 (lean) causing the computer to go too rich?

I'm about to get out and check the stepper metering pins to make sure I've actually got a rich condition (pins all the way forward) and watch it to see if it's backing down as the engine warms up.

Reply to
Simon Juncal
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Reply to
L.W.(ßill)

Simon, I just had this problem. I had a bad leak before the o2 sensor and my engine ran increadibly rich. It was mis-firing and failed emissions badly. I just had the leak fixed and my Jeep now runs great as a direct result. Nick

Reply to
Nick N

The O2 sensor is ignored until the engine is warmed up, junior.

Reply to
bllsht

HMMMM AFAIK the 02 sensors are heated so they come online sooner (closed loop happens faster) and possibly before the engine warms up. I am not 100% sure with the Jeeps though and have not timed mine....yet! :-)

I believe that if you do have an exhaust leak before the 02 sensor, you system will run richer. I gotta fix my XJ's exhaust manifold one of these days. lol BTW it is probably best to watch how your system is performing with a scanner/reader/tester for your system!

Reply to
Dave

The O2 sensor is new and the stepper motor initilizes indicating that the O2 sensor (and computer and stepper) are working. The Cat is also new.

Reply to
Simon Juncal

No heated O2 sensor on his Jeep, but even if it had one, when to attempt to go into closed loop is determined by a coolant temp switch.

Reply to
bllsht

I've got a minor leak (or leaks), once it's warmed it runs like a clock so I'm thinking the leaks are worse when it's really cold; causing or contributing to it running really rich at startup.

Reply to
Simon Juncal

Took me a sec to get what you were getting at until I saw what you quoted. I've got Mr. bullshit filtered. One of the symptoms was that it idles fine for bit and then gets rough, like possibly when the computer starts using the O2 input. Anyone know how long roughly it takes for the ECU to go to closed loop?

Bullshit are you locked up in your parents garage with your computer? You don't seem comfortable or familiar with interacting with real people. You strike me as one of those geeks who uses the anonymity of the internet as an opportunity to act like an ass. If you're an actual mechanic I feel sorry for anyone who brings their vehicles to you, but of course you don't act like this to them, you need the anonymity to make you bold.

Reply to
Simon Juncal

You could take the O2 out and throw it away and the steeper will still initialize. You shouldn't make such assumptions, junior.

Reply to
bllsht

What a shame to miss out on good info, simpy because you don't like who delivers it. Oh well...

My customers don't have to come here and ask the same question fifteen different ways. If they can't fix it, they bring it in and get it handled right.

Filter away, junior! LOL

Reply to
bllsht

Which Jeep do you have? I have only worked on FSJs and XJs. Most of the FSJs do not have 02s, but most of the XJs do. It could be that bllsht has good information to share and he is talking sense! And hey I am locked up in my parents' garage with a computer too! lol

The ECU will see that an engine is going to "normal" operating temperature and after checking sensors will go into closed loop. The engine may not be in the "normal" operating temperature at the time the 02 sensor comes online in closed loop. At least that was my understanding of most FI systems and it may only apply to the newer style FI with more stringent emission standards. I am still learning though. ;-)

from

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"Recalling that an oxygen sensor will influence the air fuel mixturepreparation only when it has reached proper operating temperature (at least350oC), it is essential to first ensure that the engine and sensor are warmenough to allow operation in a "closed loop" condition. It may take as longas 2 1/2 minutes after cold start for proper exhaust temperature to bereached (somewhat shorter for heated-type oxygen sensors)" Is this the information that you wanted to hear?

I reindexed my XJ 4.0 engine's distributor and got a smoother idle. So many factors could make the engine run rough and one could be just some bad injectors. It is good to fix what you see is wrong first though and hope that is the problem. later, dave

Reply to
Dave

There are plenty of people here being helpful, and sharing what they know (such as yourself). All he does is contradict people without actually adding information. Instead of saying "no that's not how it works; it works like this" he just says "no you're wrong". He's also answered a number of people's questions with assholian "take it too a mechanic" answers. Frankly being a mechanic is nothing worthy of getting all arrogant about.

Notice that he hasn't offered an opinion on what my problem might be? Just contradiction, and his little "junior" insult attempt, sad really.

So am I obviously.

Reply to
Simon Juncal

If you can get any carb with a timer choke to start and come up to operating temperature without needing input on the gas pedal you are a wizard.

That just don't happen unless you are at the 'exact' temperature and humidity as the jerk that designed that piss poor excuse for a choke was at when he figured it was an OK thing to use.

Probably the same turkey that designed the CJ 'heater' if I can use the term 'heat' so loosely....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

Sim>

Reply to
Mike Romain

Reply to
Jeepster

I do like that sol vac trick. I have a manual choke and need to monitor it for the first 30 seconds or so depending on how cold it is.

Mike

Jeepster wrote:

Reply to
Mike Romain

LOL, okay maybe I'll just live with it and do a manual choke mod when next winter rolls around. Thing is it runs perfectly smooth for 7 or 8 seconds and then takes a nose dive to stumbling before slowly getting to the fast idle setting.

I think I've got the same "heater" in my YJ, crack the window for a smoke and and icicles form on the output ducts. Fortunately the winters been pretty tame in VA this year, though they're never anything like up in the great white north.

Reply to
Simon Juncal

Mine used to work like that in the fall and summer. It was plain crap in the real cold.

Yup, you have the same heater.

You can fix it's case easy! A blower motor from a full sized 73 Blazer

4x4, 350, auto with AC fits right in. The hole under the battery needs to be cut bigger, but the squirrel cage fits right on.

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Some place in the US sells two versions of the motor for some reason. Labeled wrong is my thought. One is longer shafted. You want the short one if they have 2 choices.

It is a wicked upgrade! Literally low is better than the stock high was for volume. You can defrost all the windows, even in the real cold.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's
Reply to
Mike Romain

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