[Sixshooter]

Hey All!
I've got an 89 Jeep Cherokee with a 4.0 six, efi, header, MSD 6A box and an MSD Blaster coil. Just ran through MD emissions and failed the treadmill 3 times. First was pass HC 1.1089/2.4 gpm, pass CO 7.0978/80.000gpm fail NOX 4.73/3.00gpm. First number is the reading, second is the state standard.
I fixed a stuck EGR valve and brought her back for round 2 at state expense. This time I fail HC 4.14/2.4 pass CO 17.21/80.00 and pass NOX 1.51/3.00.
OK, says I, so I replace all the filters, install a new O2 sensor, plugs, cap rotor and test the wires. Bring it back for a re-test at my expense. Fail HC 4.37/2.4 pass CO 14.9/80. and pass NOX 1.48/3.0.
The truck runs like a scalded cat. No misses, great power. Timing, base and otherwise is controlled by the ecm. No vacuum leaks. Oil is relatively clean synthetic. Why is it that the HC (unburned fuel) numbers go up as the others keep improving? I haven't replaced the cat converter yet, because I want another opinion before I part with another $100 clams just to find out that it's not the problem.
Thanks.

[ap72]

We've done a lot of emissions work down at the shop. A cat will help your HC because it'll convert it to CO. You may be able to get by with just advancing the ititial timing about 2 or 3 degrees. It will raise your NOx though. If you get a free retest I would recomend running premium gas and advancing the timing. It should be enough to get you through.

[KULTULZ]

-EXHAUST EMISSIONS ANAYLSIS-

It sounds as if the fuel system is too rich after repairing the EGR system which was causing a too lean condition. Maybe a bad or leaking injector? Can you perform a leakdown test? Have you had the ECM scanned?

[Sixshooter]

Believe it or not, you can't advance the timing on these things. You can loosen the dist and turn it back and forth, and the timing never changes. I know, I've tried it. The ecm takes it's base tiiming signal off a flywheel trigger and then compensates. Strange, but true. Drove me crazy for a while after I grazed the crank trigger reinstalling the motor and had a hard time getting it running.
Leaking injector is a possibility. I haven't pulled them, and to be frank I don't know how to test for one. They're too spendy to just start replacing them at random. Other than smelling for gas, how can you test? By leakdown, you mean charging the cylinder at tdc like you would to check for leaking valves and rings? I don't see why that shouldn't work.
I don't have a scanner, and there's no manual way to do one with a blinking engine light, like you can with Fords.
Thanks for the tips.

[KULTULZ]

Other than smelling for gas, how can you test?

You need a fuel pressure gauge and a few other tools. Pressurize the fuel rail and see if the pressure drops. The manual way is to pull the rail upwards, freeing the injectors, pressurizing the rail and see if one dribbles. It is also possible that an injector drive is sticking (or bad regulator). Without out these special tools and a scanner, you are kind of out in the cold.

Have you tried to find any JEEP specific boards that may have tech sections?

[35chev/302gmc]

You can pull off the crank sensor and longate the mounting holes and advance the timing that way

[Sixshooter]

Looked at the old plugs today. All of them showed healthy burn, none looked like it was firing a rich cylinder, but I'll try the manual version of the injector test. Most of the jeep boards I've found are for serious off roading. Ask an emissions question, and they ask why your on pavement,anyway. Besides, I like hot rods

305, that'd do it, but I think I'll leave that as a last resort.
Here's another good link for emissions diagnostics I found this morning.
www.babcox.com/editorial/us/us30232.htm

[SmallBlock_guy]

If you HC is up you are too rich. I would look at a leaky injector or air leak at or near the manifold. Also, remove the map sensor and look for debris in the little hose that connects it.

Have you reset the controller and re-learned the fuel adaptives?
Are you at a warm condition when you test??

You HC can go up and nox and co stay the same due to the catalyst effiency curves. As AFR goes up HC goes down and nox goes up (to a point then they both fall off)

I will call the original emissions calibrator for that package tomorrow and get his input. I have not talked to him in awhile I don't know how responsive he will be.

[SmallBlock_guy]

Spoke with the Jeep calibrator I know. His thought: Get a new CAT. He has seen this in the past as the converter ages it loses reaction sites due to oil poisoning and such. The only cure is a new one.
That was his two cents. He has other ideas but they are very time and labor intensive.

[Sixshooter]

Did some detective work today. Injectors appear ok, no leaks when rail is pressurized. Nobody in my neck of the woods can bench test them, so that's going to have to do. Changed the seals when I reinstalled. Heard a small whistle near the number two intake runner when I listened through a hose, so I changed the intake/header gasket. Also found a tiny hairline crack in the MAP sensor vacuum hose. Hopefully the sum total of all this will whip it. I'm going to take one more run at the treadmill before I cave to a new cat.
Thanks for the info.