88 XJ 4.0 Wont Pass CA Emissions

I have a 88 XJ 4.0. New oxygen sensor, new MAP sensor, new TPSensor, new plugs coil and wires, clean k&n air filter, less than 1500 miles on the cat. By the way, the cat was replaced last smog test and it barely passed then. The hydrocarbons and carbon monoxide levels are too high. The smog tech said it is probably running rich. Is there a way to adjust the fuel/air mixture on a Renix? Are all cats created equal, can I get a super efficient model cat ???? The ole Jeep runs good too.

Sounds like the EGR might be stuck open - how's your idle?

I ran into this a couple of whiles ago on my 87...

Also, check for vacuum/exhaust leaks - especially any manifold leaks upstream of the HEGO sensor (false RICH.)

If the EGR is failing closed, it will drop HC and CO at the expense of NOx. If the EGR is failing open, you will see HC and CO rise due to incompleat combustion.

If you post the numbers, it will give more useful information...

As far as cats go, I'm running BBC converters on mine with no ill effects - mainly because they'll support higher outflow. Also, the idle speed, base timing, and FAR on RENIX are not (technically) user adjustable - at least, not without system modifications that would probably fail visual smog checks...

Givvus the numbers, and I can probably give you some more ideas.

5-90

Idle was low 300 rpm, i had to adjust it to 750 rpm. Hydrocarbons and CO high , i dont have the numbers with me. I think hydrocarbons were 175 fails at 138. O2 was 1.8%. Cant find any leaks. Is the HEGO the manifold temp sensor?

I pass/failed CA SMOG last week on my '89. The failure was only NOX at 15mph but everything was elevated and near failing. A new CAT promptly solved. I just stuck a white-box CAT on and the sniffer test went way, way down below average on everything. Mine has over 265k miles and the head has never been off.

They checked timing as N/A on the test form. 'Sorry I can't lay my hands on the paperwork to share sniffer numbers but the CAT was dramatic.

A tech would also monitor 02 output voltage for good switching if the system is even reaching closed-loop operation. For the latter, all temp sensors must be good and your thermostat functioning properly. Get it good and HOT. Check the temps sensors with a DVM per FSM. PM if you need FSM in PDF format.

As far as Renix in general, TPS adjustment can have a dramatic affect on emission output and it's easy to get that wrong. As well as proper vacuum plumbing for the MAP. Qualify everything MPI and it should pass with little trouble.

jcnoble said:

Idle was low 300 rpm, i had to adjust it to 750 rpm. Hydrocarbons and CO high , i dont have the numbers with me. I think hydrocarbons were 175 fails at 138. O2 was 1.8%. Cant find any leaks. Is the HEGO the manifold temp sensor?

Click to expand...

How did you adjust idle? With the TB stop screw? If so, that's where people screw-up TPS adjustment because they don't realize they're also changing TPS position with the throttle plate.

Also, is your IAC (idle air control) motor working? Does it rev-up at start and drop down to idle? Is the TB/IAC port clean? Bad 02 with Renix will cause HOT suck idle too as long as the IAC is funtional.

Best to adjust HOT idle via throttle plate with IAC fully closed and electrically disconnected. Then adjust TPS per FSM for your transmission type.

I got ahold of FSM. I will check my sensors and verify they are operating properly. If they are then I guess I'll replace the Cat. and pray. Thanks for you folk's input, I appreciate it.

Before you buy a cat check the coolant temp sensor on the block just below the intake/exhaust manifolds... If the sensor fails, it will cause the injection to run full rich all the time, regardless of what the O2 does... I had to replace mine the last time I smog tested... Oh yeah, do the pretest..saves headaches and Gross poluter that way..

HEGO = Heated Exhaust Gas Oxygen sensor. You've already changed it, but if there's an exhaust leak that's managing to pull air INTO the header, it will also cause false readings. Take an hour to retorque all the bolts, it's time well spent.

5-90

cant an adjustable map sensor be used to treat a rich/lean condition?

drive to the worst part of any surrounding city and im sure $50 will get you passed.

Gee that might be hard to find in L.A. Yuk Yuk Unfortunately I am stuck with a test only station, I know I could find someone to pass me somewhere but if I truly am running rich I would like to correct that problem.

Add a bottle of Lucas injector cleaner, make sure the sensors are reading right, (MAP sensor hose gets a pinhole and numbers go waaaay up!)
Most important is that right before you go for a test, get an oil change and DON'T fill your gas tank up! If you fill the gas, then keep topping off till you can't get anymore in, it floods the charcoal cannister, which sends your numbers through the roof, even though the motor runs fine. Make sure you have the correct spark plugs for your engine. Autolite non-platinums are what I run and I passed the WA state test (regs are same as CA now) without a working cat! (guts went into the old muffler I had)
Only thing I came close to failing on was NOx (I didn't clean out my EGR before going in) and I made sure the throttle body was super clean. It also improved my gas mileage from 15 hwy to 19 hwy ('88 Comanche with 4.0L, 5 speed, 6" front lift and SOA rear with 33" tires) and 10 to 13 mpg in town.

Does the injector cleaner affect the readings? I cleaned out the throttle body with a gas soaked rag. Thats impressive passing with no cat, the last time I tried with a bad cat I got gross polluter status. I looked into having the injectors cleaned professionally but new injectors are cheaper. $48 from Autozone.

The cleaner not only affects the readings in a good way, it also helps bump up the octane level a bit by helping the fuel break down to vapor more readily. Another NAPA shop near where I work at here in Seattle charges @$35 an injector to clean AND circuit test the injectors. (NAPA on Lakecity Way, near Northgate neighborhood)
They found up to 3 duds in sets that other shops had "cleaned" but still didn't work right in the car. (and that was after paying the other places up to $300 for the previous work! Often the story they got from the others was "you have something else wrong with your motor")

You defintely need to spray the throttle body cleaner into yours and let it sit for a bit. Especially around the IAC inlet port on top and the throttle plate in the bottom.

I measured the manifold temp sensor and coolant sensor, both seem to follow the table in the FSM. How is the EGR supposed to function? It appears to open under acceleration then close when the RPMs are constant.

Ok, Im thinking about pulling the head and cleaning off the carbon deposits and the intake/exhuast (140,000 miles) unless there is an easier way , has anyone done this?? What results did you see?

Since you replaced/checked pretty much everything (sensors, exhaust/vacuum leaks), I would suggest you give it one more try.

Call up your station and set up an appointment. make sure they won't make you wait. (No drop off in the morning, p'up in the afternoon! )
Now. On your way to the test station, take it out on the freeway and drive it for at least 15 minutes @ highway speed.
The longer the better.

If you drive it just on city streets, you will not get it hot enough.
Once you get to the station, Do Not Turn The Engine OFF! Let'er idle.(take somebody with you who can sit in the car while you go inside and do the talk)
The flow of hot exh. gases keeps the cat @ op. temp.

Good Luck

jcnoble said:

Ok, Im thinking about pulling the head and cleaning off the carbon deposits and the intake/exhuast (140,000 miles) unless there is an easier way , has anyone done this?? What results did you see?

Click to expand...

I'm not BS'ing that my '89 has over 265k miles and the head's never been off. At least since I've owned the thing with 83k miles showing. After the CAT last week, it passed so much below the average of similar XJ's that I know Renix can get it right.

Before you start tearing into the engine there's plenty of ways to qualify it's condition with a compression gauge and other methods. I don't believe this is your problem though .

You've never explained IAC function/non-functioning or how you adjusted idle speed and TPS or if you've checked the 02 with a DVM to see if it's switching strongly? Something ain't right but if it's poor engine condition, I'd be highly surprised. Stranger things have happened since we don't know the vehicle history but an engine in bad enough shape to blow SMOG should be easy to identify without pulling it apart.

I suppose it's possible you could have a bad ECU too? Driver circuit blown in the IAC output section? 'Never heard of a bad Renix ECU but it sure sounds like it's staying in default/open-loop mode for some reason. Have you tried resetting the ECU? Disconnect power for a few seconds with key on. Renix FSM mentions KAM (keep alive memory) so if something has crashed, perhaps that could use a reset?

The best way I've found for cleaning carbon from the chambers is easy - but unbolt the converter flange and run an open pipe while you do it.

Once you have the converter inlet clear, get a spray bottle and fill it with clean water. Detach one end or the other of the air inlet tube (whichever is easiest), hold the idle up around 1500 or so, and spray bursts of water into the intake in a fine mist - about once each 10-15 seconds. Make sure it's a FINE mist.

How it works - the water gets into the chamber with the fuel, and begins to soak into any carbon deposits. The flash temperature of combustion is sufficient to flash the water into vapour, which has the effect of blasting the carbon right off the surface. The carbon is then blown out the exhaust - which is why you pulled the cat (you don't want to clog it with carbon.)

Usually, you just do this until you don't see any carbon coming out the pipe.

A couple other things -
I just took my 88 in for that "Test Only" rubbish - and I told them it had been converted to AWD. Test results are usually lower if you have all four wheels on the ground...
You might also try pouring 4oz of acetone in the fillup before you get smogged again. The aceton encourages vapourisation of gasoline and helps keep HC and CO down.

I can't find my last test at the moment, but the numbers were agreeably low - especially for an 88 with 242kmiles and no internal work - just biennial tuneups (I use the smog interval for a tuneup key.)

If HC and CO remain high, it may not be a bad idea to pull the EGR, clean it, and reinstall. It picks up a lot of carbon, and can get crapped up enough to stay partially open (I've seen this before.)

If you can lay hands on the numbers, it would really help - diagnosis of failed smog is easier with not only "what" but "how much?"

5-90

I cleaned the throttle body again, found more grime. Afterwards the idle went up, so I adjusted it down to spec with the threaded throttle stop thingy (technical term). And yes I measured the Ox sensor with a meter it was switching like the nice post I read said it was supposed to (the post had nice waveforms and everything, Thanks by the way) I didnt get onto the TPS yet, I set it in the middle of the adjustment. Anyway the nimbers were a bit high on CO and hydrocarbons, 175 and 153 I think. Which is about 40 points over for hydrocarbons. I finally gave up and took it in for a diagnostic check, talked with the mech. about all I had done, now I am waiting for him to call back with an answer. (My checkbook is stocked and ready) postdate please.

There is a little known sensor that can cause a run rich condition. It is the air charge temp sensor. It is mounted on the intake manifold just rear of the throttle body. Now you can tweak the mixture with a MAP sensor adjuster. I built mine, but you can buy them for less than $50. It will let you dial in the mixture.

Here is a pix of its location

Both temp sensors can be checked with an ohmeter Here is the table
Temperature Sensor Table
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temp F temp C Ohms
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212 100 185
160 70 450
100 38 1600
70 20 3400
40 4 7500
20 -7 13,500
0 -18 25,000
-40 -40 100,700
==================================