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don't know where to start so I'll just start typing in my situation. I bought a engine analyzer from nickintimes web site to help me diagnose engine problems and I have a general idea of what I looking at but not sure where the problem is at or what its telling me. this is on my 88 MJ 4.0l, a/t, 2wd. recent tune-up, new o2 sensor.

 

when I wrote down these readings the engine was at idle 750-800, engine water temp 195-205.

MAP-   12" @ idle...………...10" @ partial throttle

CTS-    170 degrees  @ CTS …………………………...:L:

MAT-     135 degrees @ 195  temp...……………..141 degrees @ 205 temp...………...seems to high

VLT-     12.5v on analyzer…………...13.5 @ battery

Vo2-      2.09-4.50 +/-v...………………………………………………...:L:

EX-       rich/lean...……....………..:L:

Vht-     12.5v...…..oxygen sensor heater relay voltage

LOOP-      closed...…..engine warming up it went open/closed, but when engine @  operation temp it stayed in closed loop .:L:

EGR-    closed/on...…………..:L:

TPS-    17 @ idle

TH-      closed.... throttle position

IGN-     14 degrees @ idle

KNO-    0...…….never changed

ms-      6ms @ idle...…………..normal 4-8 ms

%dc-     4.4% @ idle...………..normal 2-10%

SYN-   cycled between -/+

ST-      stayed below 128 about    60 or so...….........……..short term fuel trim:L:

*LT-      128...……………………………...........................................................this # didn't change………………………………………...long term fuel trim

 

* indicates things are out of the norm to me

 

 

 

 

Edited by a bum with money
UPDATE:............changed out cts sensor
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You didn't flag "LOOP" as an issue, and that's the issue. It needs to be in closed loop for the O2 sensor and other inputs to control the air/fuel mix. That's related to the coolant temp sensor, because it won't switch into closed loop until the temperature is above 165 degrees.

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1 hour ago, a bum with money said:

before replacing the cts I would want to check the voltage supply. would it be battery voltage? or something else.

thanks for replying

 

 

CTS (ECT) uses the 5 volt reference.

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1 hour ago, jdog said:

I would change the cts first. The thing is still thinking is cold so it's ignoring the 02 sensor and giving you all the base line readings.

Sent from my SM-N950U using Tapatalk
 

 

14 minutes ago, Eagle said:

You didn't flag "LOOP" as an issue, and that's the issue. It needs to be in closed loop for the O2 sensor and other inputs to control the air/fuel mix. That's related to the coolant temp sensor, because it won't switch into closed loop until the temperature is above 165 degrees.

 

I'm starting to understand now. I didn't know that about the CTS. doesn't that MAT reading seem a little to  high, 135-140 degree manifold air temp? that would cause the fuel to go lean, right?

 

3 minutes ago, Ωhm said:

 

 

CTS (ECT) uses the 5 volt reference.

 

yea, had just checked that. good to know. doesn't that voltage apply to all the engine sensors?

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1 hour ago, a bum with money said:

 

I'm starting to understand now. I didn't know that about the CTS. doesn't that MAT reading seem a little to  high, 135-140 degree manifold air temp? that would cause the fuel to go lean, right?

 

 

I don't think it makes any difference what any of the sensors read. If the ECU isn't in closed loop mode, it ignores sensor input and operates on a pre-mapped fuel/air curve, which is programmed to be rich so the vehicle can operate during warm-up on cold days, when cold air is most dense.

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40 minutes ago, Eagle said:

 

I don't think it makes any difference what any of the sensors read. If the ECU isn't in closed loop mode, it ignores sensor input and operates on a pre-mapped fuel/air curve, which is programmed to be rich so the vehicle can operate during warm-up on cold days, when cold air is most dense.

That's a good point, it never was  closed so it didn't matter what any other sensor was reading. So doe's that mean the the cts is the source of the problem? Or we looking at the ecu it self. What exactly controls the closed loop process?

 

15 minutes ago, DirtyComanche said:

 

What was ambient temperature?

 

It was about 70 degrees out, maybe the heat generated by the hot engine caused the intake to get warm. after all the truck was stationary.

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1 minute ago, a bum with money said:

That's a good point, it never was  closed so it didn't matter any other sensor was reading. So doe's that mean the the cts is the source of the problem? Or we looking at the ecu it self. What exactly controls the closed loop process?

 

 

It was about 70 degrees out, maybe the heat generated by the hot engine caused the intake to get warm. after all the truck was stationary.

 

The CTS is almost certainly the problem.

 

The IAT likely was fairly correct given those ambient temps and the vehicle being stationary.  The intake manifold gets heated badly by the exhaust.

 

You can actually test both the CTS and IAT in water with a multimeter if you really want to.  The resistance table is on here somewhere, or I can dig it out if you really need.

 

 

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The ecu will see that all the sensors are operating as they should, and that the engine is at operating temperature then it will go to closed loop. If one of the sensors does not read as it should it will stay in open. I would look at replacing the cts, sounds like the ecm is doing what it's supposed to

Sent from my SM-N950U using Tapatalk

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I have the same issues that Bum has.  My REM will switch to closed loop after about 2-3 minutes of operating.  It will then switch back to open and remain in OL.

 

I have on the display: Eng Temp, O2 v, heater relay v and Open/closed Loop.  (mostly open.)

 

My eng temp is consistently 190* +/-

Relay volts are consistent 12.5 v +/-

O2 v starts out at 4.98.  As the engine warms up, the volts drop.  Once it reaches operating temp (190*) it runs at 2.0 to 2.3.  Occasionally, it will drop below 2.0.

 

The Renix ecu is supposed to run in open loop until the O2 heater reaches operating temp (~1200*).  If the O2 sensors are "operating" as their supposed to, then why does to switch to open loop?

 

The O2 is relatively new: ~1 yr.  I installed NTK/NGK sensor.

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15 hours ago, Ωhm said:

MAP, CTS, MAT & TPS all use ECU outputted 5 volts.

AND, share the same GROUND!!!!

 

The sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate.

Set your meter to measure Ohms. Be sure the ignition is in the OFF position. Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector of the TPS . The letters are embossed on the connector itself.Backprobe 2

Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall. If you have an 87 or 88 with the C101 connector mounted on the firewall above the brake booster, wiggle it, too.

You want to see as close to 0 ohms of resistance as possible. And when wiggling the harnesses/connectors the resistance value should stay low. If there is a variance in the values when wiggling the wires, you have a poor crimp/connection in the wiring harness or a poor ground at the engine dipstick tube stud.

Refreshing of the dipstick tube connection is covered in Renix Ground Refreshing, and the sensor ground upgrade is covered in Tip #6 – Sensor Ground Upgrade.

On 87 and 88 models, you could have a poor connection at the C101 connector as well. See Tip #2 – C101 Refreshing and Tip #27 – C101 Elimination.

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9 hours ago, 87MJTIM said:

I have the same issues that Bum has.  My REM will switch to closed loop after about 2-3 minutes of operating.  It will then switch back to open and remain in OL.

 

I have on the display: Eng Temp, O2 v, heater relay v and Open/closed Loop.  (mostly open.)

 

My eng temp is consistently 190* +/-

Relay volts are consistent 12.5 v +/-

O2 v starts out at 4.98.  As the engine warms up, the volts drop.  Once it reaches operating temp (190*) it runs at 2.0 to 2.3.  Occasionally, it will drop below 2.0.

 

The Renix ecu is supposed to run in open loop until the O2 heater reaches operating temp (~1200*).  If the O2 sensors are "operating" as their supposed to, then why does to switch to open loop?

 

The O2 is relatively new: ~1 yr.  I installed NTK/NGK sensor.

O2 sensor should be switching rapidly from .1 to 4.98. Never still after it warms up.

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14 hours ago, 87MJTIM said:

I have the same issues that Bum has.  My REM will switch to closed loop after about 2-3 minutes of operating.  It will then switch back to open and remain in OL.

 

I have on the display: Eng Temp, O2 v, heater relay v and Open/closed Loop.  (mostly open.)

 

My eng temp is consistently 190* +/-

Relay volts are consistent 12.5 v +/-

O2 v starts out at 4.98.  As the engine warms up, the volts drop.  Once it reaches operating temp (190*) it runs at 2.0 to 2.3.  Occasionally, it will drop below 2.0.

 

The Renix ecu is supposed to run in open loop until the O2 heater reaches operating temp (~1200*).  If the O2 sensors are "operating" as their supposed to, then why does to switch to open loop?

 

The O2 is relatively new: ~1 yr.  I installed NTK/NGK sensor.

 

do remember what your cts was reading? mine never read above 110 degrees. I have a new cts sensor NAPA p/n ts 5018 that I'm getting ready to put in. stay tuned. 

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The REM takes the temp from the CTS.  The gauge take the temp from the sensor on the back of the head. They're not connected.

 

The REM gives the reading of 190 - 198*.  It will fluctuate depending on outside temps and how fast I'm moving.

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On ‎7‎/‎23‎/‎2018 at 11:59 AM, a bum with money said:

don't know where to start so I'll just start typing in my situation. I bought a engine analyzer from nickintimes web site to help me diagnose engine problems and I have a general idea of what I looking at but not sure where the problem is at or what its telling me. this is on my 88 MJ 4.0l, a/t, 2wd. recent tune-up, new o2 sensor.

 

when I wrote down these readings the engine was at idle 750-800, engine water temp 195-205.

MAP-   12" @ idle...………...10" @ partial throttle

CTS-    160-170 degrees  @ CTS …………………………...:L:

MAT-     135 degrees @ 195  temp...……………..141 degrees @ 205 temp...………...seems to high

VLT-     12.5v on analyzer…………...13.5 @ battery

Vo2-      2.09-4.50v +/-...…………………………………………………:L:……………. cruiser was correct, as usual! :beerchug:

EX-       rich/lean...……....………..:L:

Vht-     12.5v...…..oxygen sensor heater relay voltage

LOOP-      closed...…..engine warming up it went open/closed, but when engine @  operation temp it stayed in closed loop .:L:

EGR-    closed/on...…………..:L:

TPS-    17 @ idle

TH-      closed.... throttle position

IGN-     14 degrees @ idle

KNO-    0...…….never changed

ms-      6ms @ idle...…………..normal 4-8 ms

%dc-     4.4% @ idle...………..normal 2-10%

SYN-   cycled between -/+

ST-      stayed below 128 about    60+/- or so...….........……..short term fuel trim:L:

*LT-      128...……………………………...........................................................this # didn't change………………………………………...long term fuel trim

 

* indicates things are out of the norm to me

 

 

 

 

 

I changed the cts and that fixed the open loop signal and settled some of the other #'s as well. haven't been through DEQ yet but can tell it runs a 99% better. I still need to burb the cooling system too. I really appreciate the shared info I got to fix this rig, and have a much better understanding of the ecu system and how it works. also the REM was awesome to use to help with finding what was not correct. made it so much easier for me to understand a little better.

 

20 hours ago, jdog said:

The ecu will see that all the sensors are operating as they should, and that the engine is at operating temperature then it will go to closed loop. If one of the sensors does not read as it should it will stay in open. I would look at replacing the cts, sounds like the ecm is doing what it's supposed to

Sent from my SM-N950U using Tapatalk
 

 

thanks jdog for the simple explanation about the ecu system. sometimes I need it explained in to me in simple terms. appreciate that a lot.

 

thanks to everybody for taking the time to chime in!       :comanche:

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