Kenne21

Ok so I have an 89 Cherokee. Its 4WD, 4.0L l6, 245k on it. It runs and drives like it's new. Doesn't leak a drop of anything, starts right up every time, doesn't burn anything, etc. It will not pass emission testing. The CO levels are too high still. It has (all were done last week) a new intake/exhaust gasket, cat, map sensor, cleaned injectors, cap and rotor, plugs, wires, new oil castrol gtx 10w30, new filter, a few new o rings, fuel filter, brake booster, new air filter, and I've checked 20 million times for vacuum leaks. I am clueless on what to do next. I can't figure out what else could be causing it not to pass. Any ideas or advice would be great.

dukie564

first, any state that has emissions testing has a waiver you can apply for once you spend a certain amount of money trying to fix the issue. Apply for it.

I can't see how you're still failing after putting a brand new CAT on there. It pretty much guarantees a pass when brand new....

Did you replace the o2 sensor? That should have been your first stop

Aaron N.S.

did you get the cat up to temp, if the engine and exhaust system is cold the cat isn't doing anything

dukie564

true that also

5-90

High CO (and HC) emissions indicate incompleat combustion (HC and CO are partially-burned fuel, NOx is a product of elevated combustion temperatures.)

This indicates that the EGR should be working - but it would be easier to assess this with all of the numbers, even the ones that passed (emissions control and diagnosis is a holistic process, and it's difficult to get the full picture without all of the information.)

At first gloss, here's what I'd think:
- Operating temperature too low. Go for an extended (30-60 minutes) freeway cruise before testing, prefereably in fourth (manual) or with locked out overdrive (auto) before testing.
- Spark plugs may be one range "too cold" - meaning that they're bleeding heat out of the combustion chambers that needs to be left in there.
- You may be running a bit rich - which diagnosis would be confirmed or refuted by examining the remaining numbers. This could be caused by any of a few different sensors failed/failing, or by injectors requiring cleaning (something is keeping one from closing entirely.)

Repost with all numbers - either scan the report and attach the image (we don't need personal information, just "sniffer" results,) or type them in manually. Having only one number out of range, and no other information given, makes diagnosis difficult (NB: for anyone else with an emissions question, this applies. We need all numbers at both speed ranges to even begin to make an intelligent diagnosis!)

Gorillaxj

some good ideas.

but don't forget timing. if timing isn't correct the equation will never complete. If i were you I would check timing, then (if its off) retest, if its not try a new 02 sensor. the engine is reaching normal temps correct? no matter what the vehicle should be driven in 1-1 (not overdrive) and then thrown directly to the test without sitting, while its good and hot.

Kenne21

I'll get the numbers up tomorrow. I didn't mess with the o2 sensor because I know on most cars the check engine light comes on if those are bad, so I assumed mine was good. Today I drove it 70 miles before the test, and left it running while it was waiting to get pulled in and tested. So trust me it was good and hot. The sticker under the hood said the timing wasn't adjustable...so is it adjustable?

evilxj85

it might fail cause its to hot, maybe u need a new cat. o2 sensors my not turn on the check engine light.

adkodak

I'd check your O2 sensors, bout the only thing left. I see your in texas, are you going to a inspection station that is using odb2 emissions check? might try disconnecting the negative and clear any errors built up in the ecu. If not go out to a rural county bro, inspection is only 15$ here in gainesville and there is no emissions test, just tell them you just moved to the area, google map out an address if all else fails.

RenixHeep

It's a renix engine, its pre-obd and doesn't have a CEL. I'd say 02 sensor aswell

Kenne21

it has a new CAT on it haha

an o2 is only $50 so screw it why not

dukie564

for future reference - most common causes for emissions test failures are o2 sensors and bad/cold cat

Kenne21

well drove it for a little bit and went and got it tested with the new egr valve and still failed so i guess o2 sensor now...

The numbers were:
Idle at 919 rpm
HC 263 ppm (limit is 220)
CO2 14.1%
CO 1.40% (limit is 1.20%)
O2 0.1%

2467 rpm
HC 155ppm (limit is 220)
CO2 13.4%
CO 2.57% (limit is 1.20%)
O2 0.1%

5-90

A failed/failing EGR won't increase HC and CO - it will, in fact, reduce them!

My first thoughts are that you're running a bit rich, so check the:
- Intake Air Temperature sensor
- Manifold Absolute Pressure sensor
- Heated Exhaust Gas Oxygen sensor.

The first two are the basic inputs for fuel metering, while the latter provides the feedback for trim. Any or all of those three could be causing you the trouble - which is why I say to test them. If you don't know which one is bad, what are the odds you'll get it the first time?

Granted, the HEGO is the most likely culprit (they burn out due to elevated temperatures, and depend on porous ceramics that get clogged up with carbon,) followed by the IAT (which, due to that wretched EGR setup, gets the sensing tip coated with carbon and response falls off.)

But, you didn't have to replace the EGR to correct this one...

dogger15

Make a friend that lives where you don't need an e test ive had to do that a couple times here in Colorado and yes emissions do suck here