Failed Emissions

Hey guys.

So, I'm new at this whole working on cars thing (other than oil, fluid, and spark plugs), which is one reason I'm really glad I have my XJ :laugh3:

But I'm having issues getting it to pass MARTA to tag it. The first time, the radiator reservoir cap busted, leaving me with an over-heated car and fluid everywhere. Irby fixed that, but taking it back, it failed: epically.

The HC reading was 1005, and the limit is 225 (I think). And the CO level was 2.28, over a limit of 1.something.

What would be the cause of this? And what do we need to do to fix it?

It has new cap, plugs, wires, and rotor, BTW

Year? Other vehicle info?

Edit: regardless of year, check the MAP sensor (and vacuum lines to it), O2 sensor, maybe Cat if all else fails.

O2 sensors? Exhaust manifold? Thermostat? Temp sensor? It sounds like it's running far too rich from that HC number. How's your gas mileage? If it's below about 15 this indicates you probably are in open loop at all times. If the temp gauge never gets above 170 or so (it should sit at 210 when fully warmed up) the engine controller will never enter closed loop mode and you'll be spitting a ton of gas out the tailpipe. It also won't warm the cat up enough to really make it effective. What I'd do:

* check temp. If it's running below about 200 degrees, replace thermostat with a dealer unit (195 degree) or a Stant Premium 195 degree.
* if it's running at 200-210 now but still sucking gas and you can still smell gas on the exhaust, check if the temp sensor for the ECU is faulty. Replace as needed.
* if it's still screwed up, check for leaks in the exhaust manifold upstream of the O2 sensor that could be tricking the ECU into thinking it's running too lean.
* if you fix any issues with that and it's still causing problems, replace the upstream O2 sensor. Penetrating lube and a good quality 7/8" box wrench or flare/line wrench will help you a lot here.

Curious - what year is it? If it's a 99 or earlier, you have one upstream O2 sensor probably. If it's a 00 or 01, I believe you have two, one for each bank of cylinders. If you end up replacing O2 sensors, get good quality ones (I'm personally a fan of Bosch since they invented them and are good quality) not the cheap fits-all types.

It's an '87 (sorry)
It runs at 210, as long as I'm moving. When I idle, it climbs to about 220, but I believe that's fine (?). And it is running rich- you can def smell it!
Just ran a fuel pressure test, and it's sitting right between 29 to 34, so that checks fine.
We can't check the mileage, the speedometer doesn't work (bad cable).
As soon as the key is turned off, the fuel pressure gauge drops... Could this be a faulty injector?

It is an 87 based on the profile which has one O2 on the exhaust manifold.

If the injectors are original, they may be a contributing factor. Mine failed on my 90 @ 147K.

Posted when you did! There are check valves in the fuel line intended to keep the PSI up when turned off. That is part of the reason these year XJ's take longer to start. I always wait for the pump to stop before turning the key for the starter.

I'd bet more on an O2 sensor with that info (running at 220 at idle is fine IMO, no airflow will do that), but that sounds like a bad fuel check valve or maybe bad injectors, not sure. Won't cost you much to replace them so I'd go for it and consider it part of the routine maintenance budget.

Good injectors is nearly a requisite for that age XJ. Replacing the O2 eliminates one more variable.

Everything you need to know about the sensors on your Renix XJ: http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

Lots of good advice posted here.

Still don't know which engine you have.

You can replace the 4.0 injectors with Ford Mustang injectors, orange or yellow top 19 lb injectors work, have a 4-hole disc nozzle instead of the single hole of of the originals.

its an 87 4.0 and no exhaust leak also tested map sensor it passed im thinking the o2 sensor

You should pull the injectors if they are original.

They would have two-piece bodies, plastic and metal, crimped together. They will eventually leak and probably start an engine fire, just so you know.

When they get old they start dribbling fuel even when there is no firing pulse--they can cause a rich condition.

it still has the stock injectors to my knowledge and i plan on replacing them at some point, but as of now they are ok. Ran a fuel pressure check yesterday and no drop in pressure so the arent leaking. Could the o2 sensor really cause it to throw both readings over double the limit???

Yup. If the O2 sensor is screwed up and the ECU thinks it's seeing a lot of oxygen in the exhaust, it assumes it's running lean because it hasn't put enough gas into the cylinders and will crank the injector pulse width up till it doesn't see a lean condition anymore.

ive got a smog test scheduled for late this afternoon for an 89 thats been sitting for a long time. i should have read up more about all this before i scheduled it, that way i could have tested all the sensors and such. the plan today is to change oil/filter, new spark plugs, new fuel filter, and run all the old gas out (1/4 tank). then fill the tank and run the piss out of it for atleast an hour before i go to the test. will probably put new battery cables aswell since they are quite old. the engine seems to run pretty good with 225k miles. atleast the exhaust doesnt "smell" like its burning rich. the injectors were replaced not too long ago. but since i have not been able to run this thing for the past year, i have no base line to go off of. i suppose a test to see were its at and go from there is my only way to know for sure without throwing parts at it that arent needed. i will keep reading up on these emissions threads to get more helpfull tips. thanks guys.

ya i had a yota that failed horribly due to a bad o2 sensor, id definately check that