NJ Emissions problem: 94 Jeep GC V8

It is really going to come back down to an oxygen sensor problem of some sort. I have to assume alot to arrive at this, such as the fact that your mechanic was thorough in checking the O2 sensor operation. The computer is commanding a fuel mixture based on what it sees as inputs, and if there are no DTC's, it is probably safe to assume that the computer is happy with what it sees as the final product: an O2 sensor that toggles from rich to lean nicely while staying within fuel trim parameters. It is possible, and not unusual, to get faulty O2 sensors off the shelf. I highly recommend buying one from the dealer and installing it, so that you know you have a quality part plugged in.

The catalytic converter is good, as evidenced by the healthy CO2 number. Winter fuel has it's problems, including a marked decrease in fuel economy, but it doesn't usually wreck emissions. If it did, all of your neighbors would be having the same problem.

Start with the air intake, make sure it isn't restricted anywhere (I have seen mice build nests in the air intake, and also well-intentioned shop towels that make their way into the air intake tube.). Replace the PCV valve if you can't remember the last time you did so. If you are equipped with a multimeter, check the ground side voltage drop from the engine to battery negative, should be less than .2V. If higher, you have a faulty ground, and a faulty ground will produce a faulty O2 sensor reading.

Don't spend any more money on ignition components, this is strictly a fuel mixture problem. Give us updates, so we know what works and what doesn't.

Jerry

Hi, thanks for the response.

I bought the O2 sensor from Napa. I'll have to see if I can test it. If I simply return it, there's no guarantee I'll get a good replacement. It's also not exactly convenient to go get the car reinspected for each alteration. For that reason alone I may have to just throw a load of $ at the local Jeep/Chrysler service centre.

What I do find puzzling is how the CO has slipped so much since the mechanic got it tested.

I'll look into a new PCV valve, though the mechanic said it was ok.

I do have a multimeter. Are you referr>It is really going to come back down to an oxygen sensor problem of some

There isn't any accurate way to field test an oxygen sensor. It will switch voltage like it is supposed to, I suppose, but you can't tell if the calibration is shifted, and that is what will tend to happen.

I didn't see that the CO number moved appreciably from the first test to the second test. .01% isn't anything to get excited about, you are looking for .5% drop. A few hundredths, or even a couple of tenths of a percent is normal variation, and is present if you just swing the car around and immediately test it again. You are looking for the magic bullet that will swing it down near zero, and near zero is absolutely attainable with a good catalytic converter, which you seem to have.

No, NAPA won't give you your money back on the sensor. You live and learn about things like oxygen sensors. I don't know how much NAPA charged for it, dealer is probably gonna nail you for $75-$100.

A voltage drop test measures the potential from one point in a circuit to another to determine the integrity of the circuit. What you want to do is set your DVOM to DC volts, put one lead on the intake manifold or other convenient engine part, and the other lead to the negative battery post. This will produce a small amount of voltage, because there is voltage drop across any circuit. The idea is to keep it under .2V or 200mV. (Same thing) This test needs to be performed with the circuit loaded i.e. engine running at normal operating temp. This same criteria applies to any circuit that you test this way, and is darned reliable.

An ohmeter will show a circuit to have less than 5 ohms resistance, even if there is only one strand of wire holding it together. A voltage drop test will tell you whether current can actually flow through a circuit. In the case of electronic fuel injection, the computer is relying on a good ground to provide accurate feedback information. It only knows what it sees, it doesn't know if the ground has deteriorated, and it cannot compensate for things like that. In cases like this, there is a saying: think like the box. If you were a computer, think about why you would be fattening up the mixture based on what the various inputs told you. That will lead you to probable causes of failure.

I understand that you can't run back to the testing station every time to make a change. You alluded to the most logical choice: take it to the dealer and let them tell you what's wrong. Look at how much you have spent already. For under a hundred bucks, they will tell you what it is, and you can stop throwing money at it. It may be something that you don't want to tackle anyway, then you can make a happy mechanic by giving him something to fix.

Let us know how you proceed, I am interested.

Jerry

Well, I put the Jeep into a local emissions repair centre, who charged me $85 for the privilege of telling me what they believe is wrong.

They reported back that a "worn engine" is the problem. They concluded this with a compression test. Their paperwork states "Smoke checked for vacuum leaks none found. New tune up parts and o2 sensor. All checked good. Verified failure results on dynometer. Compression check revealed low compression across all cylinders. Recommend repairing cylinder problems to get through inspection".

I asked for details of the test results, and was given the following:

RPM 198 DWELL DEG 22.9 SEC KV 10.2 COIL + 11.0 COIL - 0.94 VOLTS 11.3 AMPS -151 HC PPM 148 VAC "HG 1.9 TEMP F 204

Actual compression: Cylinder 1: 80 Cylinder 2: 85 Cylinder 3: 80 Cylinder 4: 85 Cylinder 5: 50 Cylinder 6: 75 Cylinder 7: 65 Cylinder 8: 80

I spoke to the original mechanic, who said if it's compression then I would be getting misfiring problems (which I'm not - the car runs excellently). It seems his theory is that the problem is not with the car at all but with the gasoline.

So I'm stumped.

Well considering I only bought the thing fairly recently, I had no ability to change the oil every 3000 miles. And even a mechanic with over 45 years' experience says the engine is running fine and strong. What I need to know is what I am supposed to do now, not what someone else didn't do before.

You have a carburator on a Fuel injected 5.2? Never heard of that.

With those compression numbers, your 5.2 would be running like complete crap.

Marc

First thing to do is 'verify' the compression values. Buy a cheap compression gauge and do it yourself. If the numbers are close, then in all probability the engine is shot. My reason for verification it is just possible that the mechanics gauge is shot or has drifted from the original calibration. Unless you use a recently calibrated gauge, take most 'numbers' with a grain of salt.

Go to the parts store and buy the emissions system pass in a can. It will enable a cleaner burn just follow the directions on the can. If you are burning oil your co2 will increase however, your cat converter should get hot enough to cook off minor oil burning. Your cat converter may be going bad also.