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Old 07-08-2014, 04:13 PM   #1
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1995 4.0 Emissions fail, high CO. Ideas?

I just changed the oil and took it in for the first time. Engine is completely stock. Here are the results - any ideas?:



Thanks!

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Old 07-08-2014, 07:49 PM   #2
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CO (carbon monoxide) is partially burned fuel. You must first understand the state of tune. Plugs, clean air filter, distributor cap not tracking, distributor shaft steady, timing chain steady, valves sealing properly. It is not likely that the converter is bad as that would have led to high HC (hydrocarbon) as well, which is completely unburned fuel. The EGR system is functioning well or else the NOx (nitrous oxides) would be too high. You are very close to passing, so it will be something minor.

I suppose we can assume that the engine is running smoothly?

You will not need to worry about leaking injectors because that would give you high HC, which you do not have.

First off, check or change the plugs and air filter. Examine the distributor cap for any signs of cracking or carbon tracks running from one port to the next. Check ignition timing carefully. At idle it should be steady and at higher revs it should advance and then remain steady. If it is not steady then you may have either a bent or worn distributor shaft or loose (worn) timing chain. If no joy yet then connect a vacuum gauge to the engine. At operating temperature check to see if it is steady at idle; if not you may have an exhaust restriction.

Beyond this point you'd be looking for a leaking valve which you could find by checking compression. Read any manual for detailed information on how to do that.

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Old 07-08-2014, 10:10 PM   #3
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Thank you, Paul! It's running smoothly. I'll change the plugs and air filter, and check out the distributor cap too. I hope that does it, but I'll follow through if not. Great advice - thanks.
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Old 07-09-2014, 01:33 PM   #4
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Quote:
Originally Posted by old paul View Post
CO (carbon monoxide) is partially burned fuel. You must first understand the state of tune. Plugs, clean air filter, distributor cap not tracking, distributor shaft steady, timing chain steady, valves sealing properly. It is not likely that the converter is bad as that would have led to high HC (hydrocarbon) as well, which is completely unburned fuel. The EGR system is functioning well or else the NOx (nitrous oxides) would be too high. You are very close to passing, so it will be something minor.

I suppose we can assume that the engine is running smoothly?

You will not need to worry about leaking injectors because that would give you high HC, which you do not have.

First off, check or change the plugs and air filter. Examine the distributor cap for any signs of cracking or carbon tracks running from one port to the next. Check ignition timing carefully. At idle it should be steady and at higher revs it should advance and then remain steady. If it is not steady then you may have either a bent or worn distributor shaft or loose (worn) timing chain. If no joy yet then connect a vacuum gauge to the engine. At operating temperature check to see if it is steady at idle; if not you may have an exhaust restriction.

Beyond this point you'd be looking for a leaking valve which you could find by checking compression. Read any manual for detailed information on how to do that.
1) its a 4.0L, he has no EGR
2) a leaking injector will/can cause high CO, not HC, HC is the result on ignition issues, the cylinder not firing, CO is a partial fire, resulting from too much fuel for the available air...
3) Ignition timing is not adjustable, again, its a 4.0L

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Originally Posted by VividBlack View Post
I just changed the oil and took it in for the first time. Engine is completely stock. Here are the results - any ideas?:



Thanks!
What causes CO:
O2 sensor giving a LEAN reading causes the computer to add fuel
Leaking injector/s
Dirty air filter
Excessive fuel pressure
MAP sensor error
Coolant temp sensor error
Lean misfire (normally goes with high NOx)

Your HC, though elevated (13221 i believe) a bit, is not an issue, and will drop with the CO repair (CO is your target gas).
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Old 07-09-2014, 05:32 PM   #5
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Fine, it does not have an EGR, but if it did, it would be functioning. That is the point - not that I pretend to have memorized every variation of possible emission controls.
A leaking injector indeed will cause higher CO but it will produce high HC as that is completely unburned fuel which can occur. Of course ignition failure results in HC, but that is not the only thing.
Ignition timing is not adjustable; no argument. But if the shaft is bent, or the shaft bushings (or bearings, or whatever it has) are loose, or the cap is tracked, the timing will jump around. That is the purpose of the check.
I stopped at this point as it seemed best to do a few simpler steps to start.

Sorry I jumped into a private club in error. I'll take my Master's certification along with the L1 certification and the many years of teaching this stuff at the corporate level, back under the rock from whence I came.

(In other words, while I'm happy to read an expansion of my notes, there was no need to be condescending. Ah, it's the scourge of most internet forums though.) Bye y'all.

Quote:
Originally Posted by 2xs View Post
1) its a 4.0L, he has no EGR
2) a leaking injector will/can cause high CO, not HC, HC is the result on ignition issues, the cylinder not firing, CO is a partial fire, resulting from too much fuel for the available air...
3) Ignition timing is not adjustable, again, its a 4.0L



What causes CO:
O2 sensor giving a LEAN reading causes the computer to add fuel
Leaking injector/s
Dirty air filter
Excessive fuel pressure
MAP sensor error
Coolant temp sensor error
Lean misfire (normally goes with high NOx)

Your HC, though elevated (13221 i believe) a bit, is not an issue, and will drop with the CO repair (CO is your target gas).
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Old 07-09-2014, 06:58 PM   #6
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You did not jump into any private club, we are all friendly here, and if I gave you the wrong impression, I apologize.

PLEASE dont let one experience spoil the Wranglerforum.com experience for you.
And if you really want a bad forum experience, try posting at Pirate4x4, those bastards criticize EVERYTHING to DEATH!

Im just trying to clarify/specify for the OP.
We work/live/play Jeeps, here, this is the YJ section, and alot of us know our Jeeps VERY well. Its all we talk about here!

However CO is the target gas, the only reason HC is elevated is because of the excessive CO, ALWAYS follow the target gas!

Timing might jump around, but remember, these Jeeps pick up their timing signal off the crank rotation at the bellhousing.

And since you wanna play the "look at my credentials" game:
Dont worry, Ill hold onto my A1-A9 and L1 re-certified since 92 (except for A9, which is the new light diesel), And add my Cali Emissions repair and test licence, 8 years of GM, and 2 years of Diamler Chrysler dealership working as a diagnostic tech, and continue on.....
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Old 07-15-2014, 11:35 PM   #7
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OldPaul and 2xs, I appreciate both of your replies!

Here's what I've done since my last post: new plugs, g2p (guaranteed to pass) fuel system cleaner, new air filter, new plugs. It still failed. I took it to a local Jeep specialty shop to see what they said. He looked at cat temps at the inlet and outlet, and said it was about 250 degrees going in and over 400 going out. He said that it's an indication that it's working. He said it was a universal type replacement cat of mid quality. He also said the o2 sensor had been replaced. I told him that I might still have some of the fuel system cleaner left in the fuel. He suggested to put a tank of premium gas in and run it through. He also looked at the exhaust manifold for cracks and found none.

Any other ideas? Again, thanks for your help!
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Old 07-16-2014, 12:26 AM   #8
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Mid quality ey?
Could

Just because the O2 has been replaced, does not mean its good.
I would think about injectors / Fuel Pressure Regulator, but you have to verify that O2 is working correctly.

Do you have a way to measure voltage? the O2 voltage varies between 0-1 volt.
Measure the voltage with it hooked up, with that much CO, you should have a high voltage reading (.8 to 1Volt), anything else means it s bad (would be nice to see the actual O2 reading in that report you posted).

Remember, dumping that much CO through a cat can quickly kill it, so you might fix the problem, but still need a cat.
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Old 07-22-2014, 12:42 AM   #9
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I did a fuel pressure test tonight. 70 psi at the rail. I have good vacuum at the regulator, so I'm guessing I need a new regulator.
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Old 07-22-2014, 11:22 AM   #10
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Originally Posted by VividBlack View Post
I did a fuel pressure test tonight. 70 psi at the rail. I have good vacuum at the regulator, so I'm guessing I need a new regulator.
Yes, 70 is WAY HIGH, almost to the point where you could easily burst a fuel line.

Definitely replace the regulator, and re check your pressures.
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Old Jeep that was totaled (and SOLD!):
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Old 08-01-2014, 06:45 PM   #11
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Fixed!!

Turned out to be the return line on the fuel pump assembly. It was touching the bottom of the tank and blocking the return line.

I took the tank out and couldn't see any visible dents in the tank or the skid plate. So I cut 1/2" off the bottom of the return line and rubber cork that holds the return line in place.

I put it all back together and re-tested the fuel pressure. It tested right at 30 instead of 70 psi.

Back to the emissions testing place. It passed with flying colors!

Whew...
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Old 08-01-2014, 10:06 PM   #12
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Good, a plugged return line will sure act like a bad regulator!

Nice repair!
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'04 SV1000s:
http://www.svrider.com/forum/showthread.php?t=280873
Old Jeep that was totaled (and SOLD!):
http://www.wranglerforum.com/f330/2x...ad-101879.html
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Old 08-02-2014, 01:23 AM   #13
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Good, a plugged return line will sure act like a bad regulator!

Nice repair!
Thanks for your help!

I learned something valuable throughout this project: I'm too old to be doing this stuff!

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