could a minor exh and int leak cause HUGE failing #'s during smog test?

Ok well I took the 90 in for smog check and it did smell very rich out the pipe. But literally everything that is normally wearing or even close to it is new under the hood. It drives great and has good power.

Well it failed Miserably! Like 2 to 3 to even 4 times the allowed amount of exh crap. Its even a remanuf. long block. Total on all the replaced parts is like 6 hours of run time.

So I figure screw it and left it with them, they offered a 69$ diag. fee to find the reason. Well they just called and told me that the tech said that theres a Exhaust leak as a ink leak at the TB base and those are going to allow the O2 to think its lean and richen it up.

Well I can barely if at all hear a Exh leak. I welded the manifold up Very well when I replaced the motor. And the TB has been off like 3 times since the eng due to cleaning it and replacing the IAC, and the base gasket looked fine. It idle's a little rough but at like 600-700 rpm's.

So is even poss that those leaks, minimal at best could cause this major failing of outputs in a smog test?

Thanks

How old is the CAT? Mine was smogged right before I bought it, and it's got a cracked header. Passed with flying colors. Everytime I've had one fail, it's been the Cat. Same thing, new wires, plugs, rotor, cap, airfilter, o2.

I think they are feeding you a line of baloney. The 02 sensor is reading the same gas that goes out the tail pipe and the ECU will use the 02 sensor readings to make that gas right. Is the MAP sensor properly connected and is the 02 sensor good? Also, it may not be in closed loop if the ECU doesn't think the engine is up to temp either because it isn't or because there's a bad temp sensor. Sounds like you need to test some sensors.

Exhaust leaks allow air into the exhaust which will tell the O2 sensor the mix is lean thus richening it up. This in turn will make the Cat overheat and fail eventually from an overly rich condition.
Thats why Im told Cherokees smoke cats so often.

I was told the cat was relitivly newer when I bought it so I am expluding that For the time being..

The only sensor that is not new is the temp for the ECU. the other temp and all others are new. I couldnt find a New ECU sensor (its the lower near the mount side of block one right?)

They rationalized the leaks as saying that If it was a exh leak that the extra air coming in before the O2 is making it think its running lean and richen it up. And the the int thier saying is the same but that doesnt sound right.

I did install a 180T-stat when I put the motor in so maybe the temp sensor and the t-stat are causing a open loop at all times? The gause reads before mid down to about the first 1/4 of the temp gauge when running. The hottest its shown on the gauge is just before mid. Where does a stocker run normally?

What about your EGR? It has a seperate selenoid and a gasket that could be the source of your leak.

well never touched the elct sol. on the drivers inner fender well. But I did replace the EGR assembly on the manifold..

I've been running an 180* thermostat in all my XJ's save one (my 88 doesn't seem to like ANY thermostat. Don't know why...) without any ill effects on smog...

It would help to post your numbers but here goes...

An exhaust leak upstream of the HEGO sensor would cause a "false lean" due to the extra oxygen in the exhaust gas - causing a fuel enrichment and high CO and HC.

A vacuum leak anywhere in the intake will cause a "wandering idle" as it "opens and closes" - but should not effect emissions significantly (the system reads the air pressure and temperature in the intake manifold to determine fuel metering.)

A leaking EGR gasket will cause a vacuum leak - watch out, those bolts are the dreaded external Torx. I don't recall the size offhand, but they're an UNC thread and can be readily replaced with hex head capscrews (fine for most) or with socket heads (which I did - but I'm cranky. I can find my hex big sockets quite easily.)

A non-functional EGR will manifest as REDUCED CO and HC, but INCREASED NOx (EGR decreases NOx at the slight expense if increased CO and HC - makes me wonder why they still use the thing anymore.) Check the EGR by running the engine at idle and opening the valve - if the engine stumbles, the valve is not blocked. It's best to do this with a vacuum pump, so you can check the valve diaphragm for leakage as well. The solenoid should "trip" with a 9V batter and a pair of crocodile clips - you can test that way. The solenoid is not electrically polarised.

I'd have to find my emissions test reports (they're in the office somewhere...) but my emissions run down to zero, or pretty close to it.

It should be noted that "open loop" operation has NOTHING to do with engine temperature - it has to do with the HEGO sensor reaching operating temperature (which is why they're now heated - they've got to get to about 800-900*F in order to work properly,) and the HEGO should be able to reach operating temperature independently of the engine coolant.

Granted, I don't trust any smog shops around here (and as far as I'm concerned, they're ALL "Test Only" stations.) I'll usually take the report and translate it myself. Besides, I also know my vehicle's history - they don't.

Post your numbers, and be ready for some questions.

5-90

well I dont go pick it up till after work, so I dont have the paper work. I did just call though and was trying to ask them what the numbers were where it failed. The guy said he didnt have my paper work at hand and that why did I need them. I told him basically that I had resources to help me figure out why and such they were so high and he told me well ya know theres all kinda of problems with the motor and thats whats wrong and theres no way of telling anything with out fixing those issues first.

I asked him, ok what are all the problems. He said well there are int leaks all over. I dont think there were, but this is a new creature to me so I could be wrong. And then he said theres exh leaks also, at the head he thinks but he went on to say "as I walked up to it I could hear them". Well when I had the manifold off and the engine on a stand I welded up the manifold very well at the collector. It had a crack but I decided to over do it. So if its leaking It must be at the head/man area.

Is it the exh or what I thought, when I heard the clicking type sound that is faint and goes away with throttle I figured it was the injectors?

Anyways I stop on the way home tonight and pick up a man gasket, temp sensor, TB gasket, and will replace all those tonight and may stretch to fri. Either way they are retesting it for free to make sure thats what it is. Seeing as now I have to go to a test only station to get a cert...

I will post numbers tonight though.

Thanks for all your help so far.

In my experience, the only thing that will make a car fail at 3-4 times the legal limit is a misfire. Of course this only will fail you on the HC's...due to unburned fuel going out the exhaust.

I'd think a leaking intake would make a real mess of the emissions since some cyls would be running lean, others rich. Its hard to think it would idle ok with an intake leak though.

" 6 hours of run time"

It could be a matter of the computer not having enough time to learn
after making the changes. If possable try to run through a couple tanks of gas after fixing it up.

well the readings are
Max HC Max CO Max NO
15mph 123 252 .73 5.68 1015 225
25mph 103 236 .93 5.64 875 188

We disco'd the IAC adn no change in running at all at idle.. Is that right?

Looks like your EGR is working - note the low NOx numbers

The high HC and CO numbers are making me think a fuel mix problem - the higher CO numbers tell me that the fuel is getting burned (the HC numbers are only 2x allowable,) but that it's not getting burned fully (the CO numbers are at least 5-6x allowable.)

Why do I think this? HC is remaining fuel - not burned. CO is incompletly-burned fuel - with compleat combustion, a pure hydrocarbon (which gasoline ain't - and I think that contributes to the emissions problem more than anything else...) will yield water vapour (H2O) and carbon dioxide (CO2). If it doesn't burn all the way (due to reduced oxygen or reduced temperature,) you'll get H2O and CO - with some free oxygen, if it's due to reduced temperatures.

I think it would be instructive to measure free oxygen in the exhuast as well - it would be a great disgnostic tool - but they don't.

Incompleat combustion products (CO and HC) are further oxidised in the catalytic converter to yield H2O and CO2 - have you replaced your converter recently? Is it original? If it's original, I'd be inclined to think the catalyst has "worn out" or become coated with carbon (another byproduct of the EGR system - I really wish I could do away with the damn thing...)

Go find a "universal-fit" catalytic converter and some pipe, cut the flange off your old converter (that bolted joint is USEFUL!) and replace the thing. With a little luck, it should run you less than $100. I went through this a couple years ago with my 88 - I replaced the cat with a "universal-fit" specified to go behind a BBChevvy - and it's worked fine ever since.

5-90

well let me ask. Is the diagnostic DRB a specific tool and not many shops have? And what aout a nice snap on unit, do they have adaptors that fit on them to allow it to ready the DRB on these XJ's?

Do you honestly think that just a Cat would fix this? I mean it runs rough and you can Smell fuel out the exh. I have to believe that its running really rich?

Just a side questions though, If I remove the IAC plug should it continue to idle the same as it was just before unpluging it?

once warmed up and idleing normaly the IAC isn't really doing anything, so yes thats normal. It will be hard to start and idle low when cold with the IAC unplugged.
In any case your bad numbers are at speed on a dynamometer, so the idle doesn't enter into it.
Of course if when you say "the same" you mean its still ideling badly, thats a whole other question..

Put in the correct t'stat and fix the intake leaks if there are any. It'll probably pass then unless the Cat is worn out. The funny smell of your exhaust is partially burned money.

Move to a locale that doesn't have emissions testing. It's none of the government's business anyway. Better performance and fuel economy is plenty of incentive for a person to desire the correct tailpipe output.

Interesting thing up here in BC, Canada... they test for 7 gases..
HC CO CO2 O2 NOx SOx and particulate

but will only tell you HC, CO, and NOx

HC, CO, and NOx are the usual "greenhouse gasses," with SOx usually being important for Diesels.

CO2 is a product of compleat combustion, and (theoretically) O2 should be right around ZERO - it should be fully consumed due to combustion.

Particulates are exactly what they sound like - ashes. Again, a bigger problem for Diesels than for gasoline engines.

The only thing they didn't test for that I would see as a product of combustion is H2O - water vapour. Burning a hydrocarbon in the presense of oxygen will yield H2O and CO2 - water vapour and carbon dioxide. Elevating CO2 and H2O indicates combustion efficiency - elevated HC and CO mean the fuel isn't burning all the way. Elevated NOx is an indication of high combustion chamber temperatures (usually running with a lean mixture,) and SOx would be a sign of fuel contamination in gasoline engines (not so much for Diesels.)

The three they're telling you about are the ones that will "fail" you on your test.

5-90

I recently had my '88 4.0l smog tested here in CA and failed. My HC were 4x's the limit. Since it was a Test Only Center, I didn't get hit with the sales job. After a quick online search, I figured my best bet was the O2 sensor. When I crawled underneath to change it, I saw one of the connector wires had slipped out and was dangling from the harness.

So effectively I had no O2 sensor. Since I had already bought a new one I swapped it out anyway. Took it back for the retest and passed.

NOx are right but it's rare to fail this test unless timing is way to fast or your are way to lean. By the COs and HC numbers lean is not one of your problems.
It depends were the leak in the exhaust is if it will make a difference, Find it fix it. Same with intake. Do you get free retest if so save the money on the cat unless she fails again. Once again many cars will pass without a cat if everything else is right. Most of the test are set up to make it as easy to pass as posable. If you fail bad you got a REAL problem.
If the dude at the testing station has been there for some time take his/her word of it. In many states they can tell you how to get it pasted (NOT NECESSARILY RUNNING RIGHT) as cheep as posable. In others they MUST hand you your paper and keep there mouth shut. If they want to keep there job. LUCK