Temprature & enriched Fueling in OBD1 Jeeps.

[djb383]

I give up........the ScanGauge lies, our '98 XJ never goes into closed loop, doesn't get mid-teens mpg city, low 20s hwy or run like a top........and it does all that with a 180F t-stat.

 

[orange]

Antique cars- carb, manual choke.

Cold start needed choke on to richen it to even run. As it warmed up, the choke was GRADUALLY reduced. Took several MINUTES running to run smooth with the choke off. (All the while waiting for even a little bit of heat from the cabin heater!!)

The Jeep 6 cyl. is almost the same engine as those old ones and takes the SAME amount of time to warm up. There is a lot of (mass) metal, oil, etc. which takes a while to heat up. Jeeps, BBQ's, frying pans, ALL take much more than a few seconds to warm up.

Not saying it couldn't be done, but no references show it that way that I know of.

Regards,
Orange

 

[djb383]

....but a heated O2 sensor only takes a few seconds to heat up and send rich/lean info to the ECU.

 

[joe_peters]

....but a heated O2 sensor only takes a few seconds to heat up and send rich/lean info to the ECU.

Except the ECU/PCM ignores the HEGO until closed loop.

 

[xjbubba]

My OBD-I 5.7 doesn't have to be at 190* to "go" into closed loop. I've ran numerous scans with both an AutoXray and also with scan software on my laptop. I'm too lazy to dig out the "stats". Operating temp, as far as the ECM is concerned when deciding to proceed into "closed loop" from "warm up" mode, is a broader range than designed operating temp (generally 190*). As I recall, engine coolant needs to be around 150* minimum, as determined by the CTS. What matters, is an incorrect reading from the CTS can cause the engine to run rich if the ECM is unable to adequately trim the fuel ratio while in closed loop. If it's far enough out, the ECM will set a code and go to open loop. The Renix systems didn't have a "check engine" light, so you wouldn't know a problem exists, other than poor fuel mileage.
All the 4.oL Jeeps have a heated O2 sensor; however, Not all OBD-I vehicles do. Some, like my manual trans equipped '94 5.7 had a one-wire O2 sensor, while the automatic equipped version of the same truck had a heated sensor. I now have a heated sensor on my engine, and it does not go into closed loop any faster than it did with the unheated sensor. As far as when the sensor begins generating a signal is concerned, what matters most is where in the exhaust system it is located. Mine is located in the exhaust manifold, while the 4.0 Jeeps are located further down stream, in the exhaust down pipe. The further away from the exhaust manifold the sensor is located, the longer it takes to heat up--thus the need for a built in heater.
Some/many (?) of the OBD-II cars have a much more sopisticated system controlling the heat of the O2 sensor. The computer senses current flow through the heater, and adjusts voltage to vary the sensors temp, so one "shoe size" does not fit all "feet".

 

[djb383]

Except the ECU/PCM ignores the HEGO until closed loop.

......then how do u explain the ScanGauge (OBD-II) display going from open loop to closed loop in less than a minute after cold engine start-up?????

 

[joe_peters]

......then how do u explain the ScanGauge (OBD-II) display going from open loop to closed loop in less than a minute after cold engine start-up?????

1. Bad CTS--the ECU/PCM thinks the engine is at normal operating temperature.

2. Bad ECU/PCM.

3. Bad scan tool.

 

[carves]

1. Bad CTS--the ECU/PCM thinks the engine is at normal operating temperature.

2. Bad ECU/PCM.

3. Bad scan tool.

http://www.naxja.org/forum/showpost.php?p=244885562&postcount=217

 

[joe_peters]

http://www.naxja.org/forum/showpost.php?p=244885562&postcount=217

Good read in that link.

I'm not sure of what years the PCMs were "flashable", but it is possible that "extreme" climate/region vehicles could be dealer flashed to meet environmental conditions--cold, heat, altitude, even poor fuel. Trying to have a supply train of PCMs pre-set to meet all of the variations would be insane, but flashing as part of the dealer prep before delivery would certainly be doable.

Back in the Renix years you could purchase a high-altitude CPS/CKP crank sensor to change the timing on the 4.0 engine.

 

[djb383]

1. Bad CTS--the ECU/PCM thinks the engine is at normal operating temperature.

2. Bad ECU/PCM.

3. Bad scan tool.

With all that stuff bad, that would explain why our '98 XJ gets mid teens city mpg and low 20s hwy mpg and why it runs like a top. I guess all 3 ScanGuages are bad as the one in our '06 Vue and '09 Corolla also show the systems going into closed loop within seconds of cold engine start-up.

 

[joe_peters]

With all that stuff bad, that would explain why our '98 XJ gets mid teens city mpg and low 20s hwy mpg and why it runs like a top. I guess all 3 ScanGuages are bad as the one in our '06 Vue and '09 Corolla also show the systems going into closed loop within seconds of cold engine start-up.

Well, you have just provided anecdotal evidence that the Scangauge product is a POS.

Good info for anyone that had considered buying one.

 

[carves]

Good read in that link.

I'm not sure of what years the PCMs were "flashable", but it is possible that "extreme" climate/region vehicles could be dealer flashed to meet environmental conditions--cold, heat, altitude, even poor fuel. Trying to have a supply train of PCMs pre-set to meet all of the variations would be insane, but flashing as part of the dealer prep before delivery would certainly be doable.

Back in the Renix years you could purchase a high-altitude CPS/CKP crank sensor to change the timing on the 4.0 engine.

Since "flashable" computers and extreme climate/regions may have some rellevance to the pre OBDII issue .....


... And presuming windchill factor on a radiator is one of the biggest issues to consider when contemplating the cooling needs of a vehicle ... besides faulty components and poor servicing ....

Do you think ave 20'f winter lows in Toledo ... compared to average 90'f summer highs in Houston ... might constitute "extreme" climate / regions ???

Makes sense to have an engine AND cooling system running hot ... in cold temps ...
To ensure snowbound vehicles dont end up with a radiator "slushy" like from 7-11.

Dont make sense to have the cooling system at high temps somewhere like Houston tho .... Even if the factory did offer "max" cooling radiators / 180'f thermostats and stuff to try and maintain a farcical "one temp suits all" engine temp.

A radiator in Houston needs well cooled coolant to let the engine heating device ... the thermostat ... do its job by, regulating coolant flow, so as to maintain a selected operating temp for the engine ... ......... A lower temp thermostat assists in that procedure by not cooking up the engine temp too high ... Either that or bigger / better radiators & fans should be fitted from stock ... hmmmm .... maybe the factory copper/brass one they had on Saudi models ???

Just seems pointless feeding real hot coolant, into a hotter engine, in an attempt to cool the engine down when its running hard in hot weather temps ...


Selected Op temps:

Only three reasons I can think of - to run a 195' thermostat in an old clunker engine .....

Emission legislations,
High fuel economy targets as a sales pitch,
And a nice warm in-cab heater for snowbound moosehunters ..............


Over here the biggest rumour is that you MUST run a 195'f thermostat in all 4.0l XJs coz if you dont .....

Welllll ... put it this way ... theres a heap of doomsday stories .....

Myself and others over here and probably those in the U.S. hotspots have found ... if you run a lower temp thermostat ( not too low mind you ) then a stock, export ( max cooled ? ) XJ / TJ will do the light stuff at approx 190'f temps and then nicely "overheat" to that mythical "designed" 210'f temp when in traffic, towing, 4x4, uphill runs etc .... a bit of a generalisation and a bit ambient temp / t'stat version dependant ... but its worked for me for 12yrs ... and 80% of most "normal" vehicle use for most people anywhere ... would be those conditions I just mentioned ... that FSMs just happen to acknowledge as "overheating" causes.

So I guess for 80% of the time ... I'm running "normal" temps .... :laugh:
Fixed that problem recently though ... some better/different gear and running 195'f almost constant - Only need to pick up a 5'f lower thermostat now to get it just right for next summer.

Mythical "designed" operating temp ???? ....

............... :laugh:

anybody ever seen a FSM stated, actual 'f temp to use instead of the FSM "normal" word ??? .... or is just based on the wobbly meanderings of a barely accurate, dash temp gauge ???

Problem is of course ... the stupidity of high engine temps in hot climates can only be justified so as to meet fuel & emmission targets .... so we are presuming that the computer looks after that stuff ... and NEEDS to see hot temps to get all its parameters right ........

But there seems to be an awful lot of info around that indicates the computers DON'T need to see temps provided by a 195' thermostat .... especially a thermostat that according to available chrysler specs isnt even fully open until 218'f.

Will be good when its all sorted and the fairey stories and logical guestimations can be replaced with some fact about how these XJs & the computers actually work in all areas and conditions.

:cheers:

 

[djb383]

Well, you have just provided anecdotal evidence that the Scangauge product is a POS.

Good info for anyone that had considered buying one.

ScanGuage just displays info from the ECU through the ALDL port, just like most other scan tools including the ones at the dealership.......and I'm still gonna keep 'em as they are much better than any opinion or guess.