High CO

Now I realise there are several different ways of gauging emission results in different states & countries...

Over here in the UK, I passed on HC & Nox (no individual results given just a pass) but failed on CO. It is supposed to be <3.5%, mine was 8.31%.

Been reading up on all the latest Naxja gossip on this subject - 02 sensor is 2yrs old, started to think about the CTS. Never been replaced since i've owned it last 6years. Started checking online for a suitable replacement with pictures etc. Now here is where it becomes confusing...

The previous owner had changed the block to a later year HO, Not sure of the head -rocker cover is HO but all else is Renix - manifold etc. The knock sensor has been placed in the block and what I had thought was the CTS had been repositioned to the thermostat housing (like on HO models).

After checking the ACDelco catalogue, it seems that the switch I have in the thermostat housing could be the temp GAUGE switch. The jeep is in the shop at the moment so i can't just 'go and look' at it. I'll pop down there tomorrow but need my facts with me. If someone bodged this up, i'll need to find the wiring for the CTS. I have recently replaced the engine mount on the left side and I really did do a "spit and polish" on the drivers side when it was all apart, (show car shine) so i know there wasn't any wiring hanging around loose. If it has been cut-off or whatever, does anyone know what colour wiring I should be looking for? A photo of the type of plug I'm looking for would be good if possible.

Other than checking the manifold for leaks again i'm not sure what could give this high figure. I Seafoamed a few days before the test but saw no smoke exiting the exhaust manifold, just exiting the exhaust pipe.

Also, this model originally had a cat fitted, but was removed probably by the last owner since cats are not a legal requirement here till late1992. I bought another cat but haven't fitted it yet, the garage are a bit skeptical that it will make much difference

____________________________________________
1988 Cherokee Laredo 4.0Litre, 4WD Auto (Californian import)

If it is a Renix computer, make sure the air charge sensor is on the new manifold. It is a simple thermistor and can be measured using a DMM. Most people forget the sensor exists but can cause this problem.

old_man said:

If it is a Renix computer, make sure the air charge sensor is on the new manifold. It is a simple thermistor and can be measured using a DMM. Most people forget the sensor exists but can cause this problem.

Click to expand...

Yes, it's a Renix - just for the dummies:jester:...the air charge sensor is also known as the MAT sensor?
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

I'm pretty sure there is a pipe going to the manifold as in the above link - but I'll re-check it tomorrow.

You need to know what the O2 reading was along with the CO reading. If the O2 concentration reading was high, a new CAT might fix it, if the O2 reading was low, it is running too rich. Have you tested the O2 sensor voltage with a high impedance analog volt meter with the engine running, to see if it is running rich? Is there 12 volts to the heater inside the O2 sensor?

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

SuperRoo said:

Yes, it's a Renix - just for the dummies:jester:...the air charge sensor is also known as the MAT sensor?
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

I'm pretty sure there is a pipe going to the manifold as in the above link - but I'll re-check it tomorrow.

Click to expand...

And another is IAT.

Note from DJ
This is a picture of the Temperature Gage sensor relocated to thermostat housing.
http://www.naxja.org/forum/showthread.php?t=1062083&page=2
See Post #7 by ehall for picture; it is the single wire sensor.
Now by question is do you have the second sensor pictured behind the blue splice connector and is hooked up?

Thanks Ecomike, I confess, I haven't checked the 02 sensor voltage. Although it is only a couple years old with limited mileage on it, it is something that needs reassuring...and yes, it looks to be running rich...(tailpipe)

The jeep is still at the garage. Popped in there today to 'refresh' my memory of my engine layout...must remember to check things before engaging brain and causing panic writing...


Thanks for the link djgrayxj, I had 'forgotten' about the CTS at the back of the thermo' housing in mine, obviously I always seem to notice the gauge sender in front....


Now where I've circled in red -this is the MAT sensor? (No tube as in lunghd photo, just two wires on mine)
Circled in blue is a vacuum hose that seems to go to the vacuum canister (hose goes under the battery tray)

What I think I'll do is replace both the MAT & CTS sensors, I 'triple' checked all the vacuum hoses again while I was there. The sensors themselves are an unknown age to me and could very well be 20 years old and dead!

TPS was also replaced 2 yrs ago as well and that was re-checked by me only 2 weeks ago. Airfilter is new, jeep sounds like crap when MAP is disconnected so I take it, it is working. EGR valve stalls engine when lever is moved, again I'm assuming it is working. (believe me i'm really not one that relies on assumptions but i am tossing up age of components v's their culpability for high CO). Seafoamed her last week before test too...

You can test the temp sensors with ice water and boiling water, and an ohm meter against the OEM specs.

Have you checked the plug gap, and looked for black soot indicating excess fuel, running rich? Plugs, wires, rotor and cap new yet?

If it has any starting issues, or rough idle, check the fuel pressure regulator vacuum line for a gas leak while running. Bad EGR usually causes high NOx.

Lastly, some fuel injector cleaner may help the fuel spray pattern, and get a cleaner burn, lowering CO, if there is enough unused O2? That is why you need all the emissions data!!!!!

Note from DJ
If that is a HO CTS in your picture instead of a Renix CTS and your Renix ECU is looking for 185 Ohms of resistance from the CTS at full warm up at 212* but if you look at the second HO chart the coolant system will never get hot enough to produce 185 Ohms reading for the ECU.

If this is the case you Jeep is constantly thinking it must run in the warm-up mode

TEMPERATURE-TO-RESISTANCE VALUE for Renix
Manifold Air Temperature Sensor (MAT) and
Coolant Temperature Sensor (CTS)
Fahrenheit—Celsius—---Ohms
212*-----------100*-------------185
160*------------ 71*-------------450
100*------------ 38*-----------1,600
70*-------------- 21*-----------3,400
40*--------------- 4*----------- 7,500
20* --------------- 7* --------13,500
0* -------------- -18*---------25,000
-40*------------ -40*-------100,700

TEMPERATURE-TO-RESISTANCE VALUE for 1991 HO
Manifold Air Temperature Sensor (MAT) and
Coolant Temperature Sensor (CTS)
http://www.naxja.org/forum/showthread.php?t=1058341&page=2
See post # 17 by ehaul for table below
Fahrenheit—Celsius—---Ohms-- MIN.--- ------MAX.
248*-------------120*------------------370------------410
230*-------------110*------------------480------------540
212*-------------100*------------------640------------720
194*--------------90*------------------ 860------------970
176*--------------80*----------------1,170—-------1,340
158*--------------70*----------------1,630—-------1,870
140*--------------60*----------------2,310—-------2,670
122*--------------50*----------------3,330—-------3,880
104*--------------40*----------------4,900—-------5,750
86*----------------30*----------------7,370—-------8,750
77*----------------25*----------------9,120--------10,880
68*---------------20*---------------11,370--------13,610
50*---------------10*---------------17,990--------21,810
32*----------------0*----------------29,330--------35,990
14*------------- -10*---------------49,250--------61,430
-4*-------------- -20*---------------85,850-------108,390
-40*------------ -40*-------------291,490-------381,710

Renix goes closed loop at very low temps if the O2 sensor internal heater is working, and if the sensor is good, so while that might be a tuning issue, it would not stop Renix from going closed loop and using the O2 sensor feed back data.

Note from DJ
Just back probe the CTS for it resistance value at full warm up that will tell you which sensor it is.

Note from DJ

Even though the ECU is operating in closed loop mode doesn’t it constantly vary the injector pulse width with the information it is receiving from the various sensors?

If this is so, then I was thinking that cold engine resistance signal from a HO CTS might me causing the ECU to increase the injector pulse with to be lengthen out in the hope that the increase available fuel would raise the temperature of the combustion chamber; which would then raise the temperature of the coolant so that the CTS would transmit the right resistance numbers. This would then allow the ECU to return to a normal leaner operating mode.

Or in the worst case the HO CTS values may be so far off that the ECU is reverting to a preprogramed operating mode.

Ecomike said:

You can test the temp sensors with ice water and boiling water, and an ohm meter against the OEM specs.

Have you checked the plug gap, and looked for black soot indicating excess fuel, running rich? Plugs, wires, rotor and cap new yet?

If it has any starting issues, or rough idle, check the fuel pressure regulator vacuum line for a gas leak while running. Bad EGR usually causes high NOx.

Lastly, some fuel injector cleaner may help the fuel spray pattern, and get a cleaner burn, lowering CO, if there is enough unused O2? That is why you need all the emissions data!!!!!

Click to expand...

Plug gap is correct 0.035, coupled together with new plugs, rotor, wires & cap. This was all done a couple of weeks prior to the test. 'But' checking plugs yesterday & they did have thin soot across them

No starting issues & idle seems normal i.e. no hunting or roughness

NOx passed.

I only receive a figure if it fails, otherwise it shows 'Pass' on the screen & printout.

I'll pick up some injection cleaner for the gas tank. I did put some seafoam in there previously.
Thanks for the suggestions

djgrayxj said:

Note from DJ
If that is a HO CTS in your picture instead of a Renix CTS and your Renix ECU is looking for 185 Ohms of resistance from the CTS at full warm up at 212* but if you look at the second HO chart the coolant system will never get hot enough to produce 185 Ohms reading for the ECU.

If this is the case you Jeep is constantly thinking it must run in the warm-up mode

Click to expand...

I have no idea if it is an HO or Renix CTS since you mention it. I've never changed it since owning the jeep, hence my previous thoughts of replacing it . But as Renix Cherokees were never sold here, the later HO CTS 'could' have been used by the previous owner I guess. Thanks for charts DJ, I will back probe the CTS when I go back down there again

Ecomike said:

Renix goes closed loop at very low temps if the O2 sensor internal heater is working, and if the sensor is good, so while that might be a tuning issue, it would not stop Renix from going closed loop and using the O2 sensor feed back data.

Click to expand...

This is one-big-learning experience for me at the moment. A site I found lists 5 possible general causes for High CO
http://www.smogtips.com/failed-high-carbon-monoxide-CO.cfm
1. Dirty Air Filter
2. Faulty Oxygen Sensor (O2 Sensor)
3. Defective Manifold Absolute Pressure (MAP) Sensor
4. Defective Throttle Position Sensor (TPS)
5. Defective Engine Coolant Temperature (ECT) Sensor
For me,
1. Brand new filter & it is still clean
2. Replaced 2 years ago -will have to check
3. Same one since I've owned the jeep -
4. Replaced 2 years ago - was within spec's afew weeks ago - will double check it again
5. Same one since I've owned the jeep - will check, but likely to replace it

Note from DJ
This information may help you identify what the previous owner swapped into your Jeep
Block casting no location can be found hear in post # 2 by CJ7-Tim
http://www.jeepforum.com/forum/f11/4-0l-serial-number-location-995174/

Head casting number by years
It is easy to determine what head you have. On the driver’s side, about halfway down the cylinder head between #3 & #4 fuel injector but below the valve cover clean the lip of the head with a rag or solvent if really greasy. With a good light, you can read the casting number of the head.

Head casting number by years
Casting numbers are as follows:
Year............Casting No
1987-90......2686
1991-95......7120
1996-99......0630
2000-01......0331

djgrayxj said:

Note from DJ

Even though the ECU is operating in closed loop mode doesn’t it constantly vary the injector pulse width with the information it is receiving from the various sensors?

If this is so, then I was thinking that cold engine resistance signal from a HO CTS might me causing the ECU to increase the injector pulse with to be lengthen out in the hope that the increase available fuel would raise the temperature of the combustion chamber; which would then raise the temperature of the coolant so that the CTS would transmit the right resistance numbers. This would then allow the ECU to return to a normal leaner operating mode.

Or in the worst case the HO CTS values may be so far off that the ECU is reverting to a preprogramed operating mode.

Click to expand...

Yes, but it also uses the O2 sensor data in a feed back loop that corrects any other sensor data errors in the next injection cycle, like the CTS being off a bit. The MAP and TPS data are critical during rapid acceleration and deceleration.

A colder engine will use more fuel at idle, but only because the air is denser.

This part

"might me causing the ECU to increase the injector pulse with to be lengthen out in the hope that the increase available fuel would raise the temperature of the combustion chamber;"

is backwards, running the engine leaner warms it up, running rich is running cooler.

The OP might want to check the actual coolant operating temperature, see that the T-Stat is working, and that the engine is not running too cold.

djgrayxj said:

Note from DJ
This information may help you identify what the previous owner swapped into your Jeep
Block casting no location can be found hear in post # 2 by CJ7-Tim
http://www.jeepforum.com/forum/f11/4-0l-serial-number-location-995174/

Head casting number by years
It is easy to determine what head you have. On the driver’s side, about halfway down the cylinder head between #3 & #4 fuel injector but below the valve cover clean the lip of the head with a rag or solvent if really greasy. With a good light, you can read the casting number of the head.

Head casting number by years
Casting numbers are as follows:
Year............Casting No
1987-90......2686
1991-95......7120
1996-99......0630
2000-01......0331

Click to expand...

I'll be picking up the jeep tomorrow for hands-on investigation, thanks for the above info' it will help me to understand the 'frankenstein monster' i have

Ecomike said:

The OP might want to check the actual coolant operating temperature, see that the T-Stat is working, and that the engine is not running too cold.

Click to expand...

Thanks for the suggestion, i'll follow through with this when i pick her up tomorrow

It is called a FrankenJeep, LOL!