HD fan clutch upgrade...

Please, before you argue the facts. Please google the information. I am not your "wife's" nor am I into arguing facts. Get educated before you challenge someone's post/reply to help others. Once you read a little, you will find my facts are correct regarding the relation to open/closed loop on OBD systems. Read the post, others also agree.

Have a good day.
 
ehall said:
doesn't have anything to do with OBDx and everything to do with emissions

anyway the engine computer wants to see a specific temperature range, so unless you can reprogram the computer you need to stay there for optimal efficiency
Click to expand...

I have run several older vehicles with 160 F T-Stats and passed local Texas (Houston) emissions tests and been at 5% or less of the limits for CO, NOx, and HCs. My 87 just passed in 36 F weather with a 180 stat, and the engine was still warming up, 266,xxx miles.

The running temp (emissions wise) may be a bit of an issue in tight limits places like Calif. And may have been an issue at the factory in meeting off the dealer lots (factory) emissions limits, and may have been a fuel economy target/design issue, but what we are saying is that as we went from pre Renix, to Renix, to OBD-I, to OBD-II, there was an OBD trend in raising the operating temps and in raising the op temps required by the ECU/PCM logic to switch to closed loop, and especially in OBD-II versus Renix, there was shift in the computer logic that lets Renix go closed loop, essentially cold (80 F for sure), while holding OBD-II XJs open loop until they are hot (130-160 F minimum as I recall, maybe a little higher).

The op-temp programing shift for closed loop ops in OBD from Pre, to I to II was a shift to OBD and in OBD and a shift in emissions controls, so it really is both.

I try to keep in mind that my profession has been after EPA to reduce NOX since the 70's as the worse smog culprit, and not to raise NOx emissions to reduce HC emissions, but that has gone on deaf ears until recently. I would rather have less NOx, and a little more HCs and run a little cooler, if it still passes the states/EPA limits. I am finding 180 F to be near perfect for Houston, except in 20 F hard freezes, but that may just be a 22 year old, dirty heater core. 195 F t-stat is too high for hot humid climates like Houston, IMHO.
 
Last edited:
ehall said:
open/closed loop is about getting the O2 sensor and cat converter to temp <-- emissions

the diagnostic interface (aka "OBDx") is wholly unrelated. coincidental
Click to expand...

Yes, in part, but the OBD also designates the computer control generation of the system, not just the diagnostics. There is, IIRC a real temperature, CTS computer difference from I to II, regarding when it switches to closed loop. The Renix is definately different, pre-OBD.

Also, the computer decides when to switch to closed loop, not the Cat converter or O2 sensor. The computer does not care, or monitor the Cat temp on any of these three. On Renix it immediately checks the O2 sensor for a proper voltage range and resistance, and as soon as it sees a proper O2 reading, it switches to closed loop. OBD-II requires a proper O2 value (which requires the O2 sensor to be hot, which is accomplished in several seconds by the electric heater in the O2 sensor after start up), and also requires at least a CTS temp above some lower limit, which I think is above 160 F (IIRC).

Am I not understanding the point you are trying to make?
 
ehall said:
I don't want to dialog, just stop saying stupid crap like temperature is based on version of OBDx. Other people expect these boards to be informative and accurate.
Click to expand...

Fine, I am done trying to reason with you, and I have no intension of getting into a pissing contest with you by trying to claim your "saying stupid crap". I don't see anyone else in NAXJA disagreeing with what Jeep4cern and I have posted here. My statements are based on reported actual tests by other NAXJA members here in other threads, and based on my own extensive tests on Renix, and based on extensive discussions with one of the Bosch O2 sensor design engineers that has been around O2 sensors since the Renix era.

To clarify so there is no further miss understanding. OBD-II XJs will not switch to closed loop operation until they have a valid, hot enough temperature, signal from the CTS.

Renix will switch to closed loop if it has a valid O2 sensor reading, even if the engine is still cold.

I think I recall posts here in older threads where others here confirmed that OBD-I year XJs would go closed loop at low engine temps (based on the CTS reading being fed to the engine computer) than the OBD-II year XJs.

Perhaps some links will help:

http://www.obd-codes.com/p0125

I have looked, and run out of time, trying to find the older posts here by others, that tested the temps that theirs would go closed loop, or stay open loop (I and II), but they are here in NAXJA somewhere.
 
89xj said:
not true, renix uses coolant temp to for input.

page 79 of the 4.0 liter multi-point fuel injection has the inputs for closed loop at idle.

http://www.lunghd.com/Downloads_and_Links/Jeep_Renix_Fuel_Injection_manual.pdf
Click to expand...

Please try quoting others accurately. I did NOT say Renix did not need a CTS sensor input to go closed loop. It does need one. I said the engine could be cold, 70 F, and go closed loop in a matter or seconds after engine start up if it had a valid, accurate working O2 sensor reading that the ECU accepted as valid.

That does not happen if there is no CTS reading for some reason , or no O2 sensor reading in a proper range, which requires a good O2 sensor, a good 12 volts to the O2 sensor's internal electric heater, a working O2 sensor heater relay, a working engine, a working battery, a working ECU, and so on......etc.

So yes it needs a CTS reading in the proper operation range of the CTS that the ECU will recognize, to go closed loop, but the CTS does not need to be hot for Renix to go closed loop.
 
Just read 14 pages, was ready to run to Advanced Auto till i read the reported 2MPG loss a page or two back.

Has anyone else experienced a loss in fuel economy?
 
OverlandXJ said:
Just read 14 pages, was ready to run to Advanced Auto till i read the reported 2MPG loss a page or two back.

Has anyone else experienced a loss in fuel economy?
Click to expand...

Probably depends on gearing and tire sizes. If you stay around 2000 rpm, like mine does (1600 to 2400 max), I doubt you will see a difference. I did not. Some run their XJs at higher engine rpms, lower gear, than others.

I did not see much difference in MPG. Little loss I did see, if any (?) was probably due to the engine running cooler, not due to the clutch losses, in my case.
 
Ecomike said:
Please try quoting others accurately. I did NOT say Renix did not need a CTS sensor input to go closed loop. It does need one. I said the engine could be cold, 70 F, and go closed loop in a matter or seconds after engine start up if it had a valid, accurate working O2 sensor reading that the ECU accepted as valid.

That does not happen if there is no CTS reading for some reason , or no O2 sensor reading in a proper range, which requires a good O2 sensor, a good 12 volts to the O2 sensor's internal electric heater, a working O2 sensor heater relay, a working engine, a working battery, a working ECU, and so on......etc.

So yes it needs a CTS reading in the proper operation range of the CTS that the ECU will recognize, to go closed loop, but the CTS does not need to be hot for Renix to go closed loop.
Click to expand...

must be my reading comprehension, but on page 2 of the maunaul, the OPEN LOOP OR CLOSED LOOP DETERMINATION paragraph reads differently. to me it reads that when the engine gets to suffienct operating temp(result of the engine coolant and manifold air temp sensors) the engine goes to closed loop. then the o2 determines the air/fuel mixtures, but not until it reaches operating temp.

i dont see how you can have a cold engine with hot coolant.

yes the o2 controls the air/fuel in closed loop, but it wont go to closed loop until a certain temp is reached.

the way im reading what your saying is that the engine goes into closed loop from a reading from the o2 sensor, which is contrary to what the manual says. the o2 sensor controls air/fuel yes, but the o2 sensor does not put it into closed loop. even the renix needs to be at a suffient operating temp to go into closed loop.

maybe the problem im having is that the manual only says "suffient" operating temperature and does not give an exact temperature. but to say that engine temp or coolant temp has nothing to do with whether the renix goes into closed loop is contrary to the manual im reading.

maybe 100f is suffient, but non the less, the renix also uses temp as a condition to go into closed loop.
 
89xj said:
must be my reading comprehension, but on page 2 of the maunaul, the OPEN LOOP OR CLOSED LOOP DETERMINATION paragraph reads differently. to me it reads that when the engine gets to suffienct operating temp(result of the engine coolant and manifold air temp sensors) the engine goes to closed loop. then the o2 determines the air/fuel mixtures, but not until it reaches operating temp.

i dont see how you can have a cold engine with hot coolant.

yes the o2 controls the air/fuel in closed loop, but it wont go to closed loop until a certain temp is reached.

the way im reading what your saying is that the engine goes into closed loop from a reading from the o2 sensor, which is contrary to what the manual says. the o2 sensor controls air/fuel yes, but the o2 sensor does not put it into closed loop. even the renix needs to be at a suffient operating temp to go into closed loop.

maybe the problem im having is that the manual only says "suffient" operating temperature and does not give an exact temperature. but to say that engine temp or coolant temp has nothing to do with whether the renix goes into closed loop is contrary to the manual im reading.

maybe 100f is suffient, but non the less, the renix also uses temp as a condition to go into closed loop.
Click to expand...

Your position is well stated above. Nice job! As you pointed out the question that is not answered in the manual is what is sufficient operating temperature.


Let me explain the difference between the manual you are quoting and my hands on test results with Renix. I use the O2 sensor data as proof that the engine is running open loop (O2 sensor reads extremely rich continuously) or closed loop (in closed loop the voltage oscilates back and forth slightly from rich to slightly lean, rapidly across a 2.45 V target, which indicates the ECU has switch to closed loop). I have consistently (100%) found that Renix will switch to closed loop (based on multiple tests on different days, and years even, empirical test data that I did personally with a calibrated analog volt meter), at temperatures below 100 F. Most of my tests were run (started) at ambient temps around 70-85 F. Engine coolant and intake air temps were no higher than about 90-100 F when I got back under the hood to see it was already closed loop within in seconds of engine start up from a cold (overnight) start.

I do not know the exact CTS or MAT temp limits that the ECU uses as a go/no go limit for switching to closed loop operation, but I do know it is not way up in the 160 F plus area, and even if my sensors are off some, it appears to me from my tests (multiple) that it goes closed loop at under 100 F on both the MAT and CTS temps. That includes tests over several years, on an 87 and 89 model.
 
ehall said:
3-wire O2 sensors have an internal heater, which allows the sensor to reach operating temperature faster than the vehicle.
Click to expand...

Yep, so do the more recent 4 wire O2 sensors (has 2 separate grounds and ground wires internally)

One mistake some people make is to replace the OEM style (3 or 4 wire) with a universal 2 wire O2 sensor. Bad idea for two reasons. Has no heater which wastes gas (takes longer to reach closed loop operation, and can switch to open loop at extended idles like stop lights as most O2 sensors do not stay hot enough at idle to continue working). Second reason is the newer OBD-II set ups seem to be able to eventually detect the missing wire(s) on the 2 wire sensor.
 
Ecomike said:
Yep, it is a matter of balancing competing issues or forces, that we optimise to minimize the bad, and maximize the good. At some point, temp wise, too cold lets water build up in the oil, leading to damage to the oil and to the metal. At another extreme the oil and metal is damaged by high temps. The older engines do better with 180 F. The newest OBD-II seem to prefer 190 F. In fact some of the OBD-II hardware kills gas mileage at lower temps, while the Renix is OK at 160 F.

I have noticed that even the Renix gets a little better gas mileage at 220 F than 200 F, or 200 versus 180 F, apparently due to the hotter intake manifold thinning out the air at letting the engine run leaner per stroke at idle and cruise. But I have also confirmed that Renix will go closed loop at 100 F while OBD-II will NOT!

Point #2, is that the answer (optimal temp) does vary with use of dyno oil versus synthetic, and Renix, versus OBD-II controls. One can not make universal cart blanche statements, unless you want to get nailed here by old timers who know better.:scottm:

IIRC, someone a while back confirmed that OBD-II XJs do not like 160 F T-stats, or a lack of a good, minimal CTS temp reading at the ECU in that range of 180 F or higher, IIRC. Seems they stay open loop at much higher temps than renix before going closed loop, but I don't know the exact critical temp, may be in the 96 FSM.
Click to expand...


G'Day ....

Since OBDII Loop changeovers at coolant temps of 190'f are mentioned in this thread .......

.... and Im getting Loop changeovers at 68'f from a cold start .... 182' / 188' / 192' / 195' thermostats ... or NO thermostat ...:shocked:

.... And the gauges are correct since others get similiar ....
winking0061.gif


Whats the likelihood that theres some computer programming done on a location of sale basis ???

Any chance cold climates vehicles are preset for loop changeovers at higher coolant temp from a cold start ??
Any chance hot climate vehicles are preset for loop changeovers at lower coolant temp presets from a cold start ??

Only asking coz I wasted two days a while back ... stripping harnesses and plugs to get the "police ext idle" function working ... and the only reason I came up with - for it not working ... was coz it was a RHD "export" model and probably didnt get programmed for it.
mad0078.gif


But the idea might conflict with the fault code listed in the manual ... that occurs if the engine is running too cold for too long at 20'f.

You fellas ever tried to get a list of same same computer XJs and compare a bunch of vehicles coolant temps / locations / ambients, when the Open/Close Loop change over occurs ???

:cheers:
 
bigalpha said:
Everyone prepare yourself, I will attempt to make an analogy:

Pretend you have cancer and this cancer made you run a very high fever. Instead of diagnosing and treating the cancer, the Dr's only treat your fever. Well, your fever may go away, but you still have cancer.

This is sorta the same thing.
Click to expand...

Wouldn't the cancer be the Chrysler beancounters that put the inadequate cooling system in the XJ?? So the cure would be upgrading the cooling system with HD ZJ fan clutches, better radiators, or whatever.

I'm trying to decide whether I want a ZJ clutch. I've been overheating because my old clutch is bad, but I'm not sure if I'll have any overheating with a new one. On Maui we don't really get above 85F. I don't want the noise and possible overcooling if there's no benefit.
 
You must log in or register to reply here.

Similar threads

N
Fan clutch for 2001 4.0?
Replies
7
Views
441
maxbraketorque
M
C
Renix Engine Coolant System Updates
Replies
5
Views
243
Saudade
Saudade
T
Another Cooling Issue Thread - 99 Cherokee 4.0
Replies
18
Views
492
Black1990jeep
B
S
94 XJ Running hot running out of things to check
Replies
13
Views
719
PLRX
PLRX
V
High temp woes
2 3
Replies
56
Views
4K
Vitzaa
V
Back
Top