4.0 carbon issues. any emission gurus out there?

alright guys im new here was referred by robz95xj. im assuming thats his name here to. but i just bought an 89 Jeep Comanche with the 4.0. only paid 1500 and its got a perfect body and interior. no rust since its down here in the south



went and got emissions done yesterday expecting it to fail and it did horribly.im moving this week so emissions wont be a problem as i wont need them but i still need to get these issues worked out. its getting less than 10mpg. truck runs awesome and smooth as a cadillac but its putting out alot of carbon and soot. i put new plugs in this past weekend and theyre already covered. and when i stomp on the gas i get so much out of the exhaust it looks like a freight train going down the road

i though it maybe oil at first but im pretty sure it isnt. also did a compression test on it a few minutes ago and it averaged between 145-150 on all 6 cylinders

so before i start messing with anything else what sensors should i look into replacing or cleaning on this thing? and how to clean correctly ive always been a ford guy so im new to these.

and to anybody who specializes in emissions heres some of the numbers it put out if this'll help with a diagnoses

HC ppm 479 out of 189 allowed
CO% 11.73 out of 2.36 allowed
NOx ppm 108 out of 1233 allowed
RPM 1590 / 2500
CO+C02 % 17.6 out of 6 allowed

so as the emissions guy said.... "your vehicle has... severe issues" :dunno: anyways this is my first post since i didnt see an introduction section when i joined

Check the O2 sensor first.

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=testing+oxygen+sensor

The test the CTS, MAT and MAP sensors.

Cap, rotor and wires condition?

Mileage?

cap rotor and wires seem fine, although its on my list of things im gonna replace, mileage is 150k

ill try to get ahold of a volt meter as soon as i can. which sensors would be quick and easy to clean. so i can go ahead and cross those off my list

Sensors don't need cleaning, they need testing. Clean the connector contacts only. Also, TEST, and clean, and replace as needed any of the three notorious jeep grounds on the beast, one near the oil dip stick on passanger side, one from the head to firewall, on drivers side, and the one at the battery. TEST the ground at each sensor, power off, with ohms! You want less than 1 ohm from sensor grounds to the battery negative post. Add new grounds if needed!!!!

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

well ima pick up a meter, since i dont wanna wait till i can borrow one. gotta get my ass to work will update tomorrow morning after i do some testing appreciatev the help mike

i have no technical input here whatsoever, but that is a clean looking MJ. congrats on the find

rweaver138 said:

but that is a clean looking MJ. congrats on the find

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This. So jealous. There's absolutely no way you're finding anything up here that looks even half as good, let alone even SEE an MJ on the road. 'Gonna have to go down south when I buy another XJ fo sho.

Thanks guys. When i saw how clean it was u knew it'd be worth it. Kid couldn't afford gas for it or try fixing it

just swapped out o2 sensors, its smoking a little more i believe than it was. hard to tell. ran a little smoother at start up. im assuming it will take a little driving to get the computer to relearn itself so to speak? bout to go test the map sensor see how it checks out

Driftingrz said:

just swapped out o2 sensors, its smoking a little more i believe than it was. hard to tell. ran a little smoother at start up. im assuming it will take a little driving to get the computer to relearn itself so to speak? bout to go test the map sensor see how it checks out

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there is no relearning in the Renix ECU. It's all real time. You're dealing with first gen fuel injection, so dumb down your expectations of what the ECU does.

the CTS sender on the side of the block is the one that controls open/closed loop. The one that drives the gauge in the back of the head has nothing to do with it.

You'll also want to check out the EGR system. THe link posted to the lunghd site is a good place to start.

alright well im no electronic guy, ive always had carbed motors. can someone help explain how to test the map sensor and others.. i dont understand how to get a reading on the diff terminals.. check the wire leading into the sensor itself? if so then the wire leading into terminal b had no change in voltage from a ignition on/engine off to an engine on idle... im new to this stuff so help me out

bdahlg said:

This. So jealous. There's absolutely no way you're finding anything up here that looks even half as good, let alone even SEE an MJ on the road. 'Gonna have to go down south when I buy another XJ fo sho.

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agreed. That thing is BEAUTIFUL! Mine is a huge rotbox by comparison.

I daily drive it anyways :wave: if you see a white turd of a shortbed MJ cruising around massachusetts with a lot of jeep parts in the back, it's probably me...

Assuming you already checked for exhaust leaks, especially upstream of the O2 sensor, this is what came out of the lambda calculator at the bottom of http://www.smogsite.com/calculators.html - lambda 0.6445, A/F ratio 9.474. You're running VERY rich. My bet is that your O2 sensor, MAP sensor, MAT/IAT sensor, or CTS sensor is hosed, or you have an exhaust manifold crack or hole in the downpipe above the O2 sensor.

First check for exhaust leaks, those will kill you. If there aren't any of those I'd next check to see if the ECU is going into closed loop mode, you'd have to check the CTS for this. If the engine doesn't get above 170 degrees or so (or the computer thinks it isn't because of a bad CTS) it will stay in open loop start-mode and dump extra fuel into the engine. After that I'd check the MAP and IAT/MAT sensors, since you already replaced the O2 sensor.

you need to backprobe the connectors at the sensors. The sensors are fed reference voltage from the ECU, the ECU measures the difference in voltage from the reference that it's sending and what it receives.

THings I would check first:

TPS sensor adjustment, it is very crucial.

Map sensor, also very crucial

CTS sender in the block, not so much

Here's a link to Renix sensor diags.
http://www.lunghd.com/Tech_Articles/Engine/Cam_Position_Sensor_and_Sync_Pulse_Stator.htm

Here's a forum link to a discussion about adjusting the auto TPS. Looks like you treat the 3 pin the same as you would a 5 spd TPS, the 4 pin is for the TCU.
http://www.naxja.org/forum/showthread.php?t=61772

no exhaust leaks I could find or hear while laying under. how could I check temp. I'm at work but I got a full weekend to get this thing running better

Backprobe? Sorry if I'm a dumbass.

Driftingrz said:

no exhaust leaks I could find or hear while laying under. how could I check temp. I'm at work but I got a full weekend to get this thing running better

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Put a meter on the tip of the CTS, ground the other side to the block, read resistance.

Driftingrz said:

Backprobe? Sorry if I'm a dumbass.

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You'll need some pins to stick in the back of the connectors. Multimeter probes are too big, and you need to see the voltage as it is connected to the ECU.

You can use pins to pierce the wire and get readings, it's easier, but I prefer to not comprimise the wire jacket like that.

Renix CTS has two pins and two wires, not a single tip. Best way to check resistance on Renix sensors is to disconnect them from the harness, and test with meter probes at the two sensor electrical tips (across the sensor connectors).

87manche said:

Put a meter on the tip of the CTS, ground the other side to the block, read resistance.



You'll need some pins to stick in the back of the connectors. Multimeter probes are too big, and you need to see the voltage as it is connected to the ECU.

You can use pins to pierce the wire and get readings, it's easier, but I prefer to not comprimise the wire jacket like that.

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guess ill try and figure it out in morning. probably have most trouble just using the voltmeter. things confuse me. all the different settings and ranges/ abbreviations dont mean anything to me.

what should my cts read when engine is at running temp?

edit: im guessing from statement

". Resistance should be less than 1000 ohms with a WARM engine (examples = 212* would be about 185 ohms, 160* would be about 450 ohms, 100* (not warm enough) would be 1,600 ohms"

i should be finding around 1000 if i get a crazy number ill look for a bad ground or replace the sensor