Renix 4.0 high warm idle

[RustyRodder]

Yes, another renix thread.

My 1988 4.0 starts with a normal idle, then creeps up until it idles at 13-1400rpm (stabilizes there). 

I have cleaned the grounds, the C101 connector, and relays.  I did do the TPS calibration per cruiser.  I also didnt know when the O2 was replaced, so that was done with a new NTK unit [although the idle issue started a bit after this].  according to my REM, it pulls 20in of vacuum when idling like this (17ish when at normal idle). 

What should I be checking? I havent found any vacuum leaks, and most searches find guys firing the parts cannon, or saying "it was fixed" without an explanation. 

[Ωhm]

Check both Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) using your REM, between normal idle and high idle.

[RustyRodder]

water temp at high idle fluctuates between 190-200, depending on if the fan is on (Coolant is vanishing, so I am watching this)

[Ωhm]

Wonder how REM handles Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). What kind of numbers are you showing there? Do numbers move during idle? Do these numbers reset (128) after KEY OFF?

[cruiser54]

what does the REM say about TPS?

[RustyRodder]

Sorry for the delay- Truck is stored at my parents.

ST/LT fuel trim both reset to 128 when the key is off.  Here are some pictures off the REM:

 

Key off, before any start:

 

Post-Start, these were the numbers:

 

the short term increased once it hit closed loop, starting in the 200-range, and dropping as the temp rose.  It was crap weather, so I didnt get to drive it and see how long term was effected. 

 

O2 heater was sitting around 12.4V, and O2 voltage was fluctuating between 1.4 and 2.9v.  TPS sat at 17 the whole time idling.  Engine vacuum between 17-20. 

 

Also noticed its been taking 8-10 seconds to fire up.  Tried to test the CPS, but for some reason my cheap hobo freight multimeter won't read the voltage.  Could this be a CPS issue?

 

 

[cruiser54]

O2 should go from .1 to 4.9 rather quickly. 

 

Have you snugged up your intake manifold bolts? Done tip 5? 

[RustyRodder]

1 hour ago, cruiser54 said:

O2 should go from .1 to 4.9 rather quickly. 

 

Have you snugged up your intake manifold bolts? Done tip 5? 

I will check them- Is there any way to get at them without taking off the heat shield? I did find 2 of the top exhaust bolts loosish a couple weeks ago.  

And I have, but I will double check it again.  Wouldnt be the first time I missed something.

[Ωhm]

Fuel Trim values look good (my concern was leaky injector(s)). O2S is running on the rich side. Was engine at normal operating temperature? TPS(17) and MAP(10.8) values also look good for engine at idle. Air leaks will cause high idle, as cruiser suggested, check intake manifold bolts.

[Warren Mohler]

cruiser54 has very good info available to you and you should follow his advice I have looked at his links and this really takes me back in the late 80's jeep had many complaints of high idle with warm engine but was almost always about 3000 rpm as I remember TSB said it was do to bad ground through TPS and I replaced many of them for this problem I am not sure what output voltage should be at idle when replacing TPS as I always used MS1700 to adjust other vehicles I have worked on have been about .5 volts good luck and don't fire that cannon.

[Kjell]

If you change /swap anything on the Renix system take of the +from battery  and hold it against -  think this resets the ECM/ECU .

And check/ clean the connectors on the ECM/ECU.

 

EDIT After looking at wiring schematic and measuring volts on the ECU and found that connector pin B7 on the ECU are "hot at all times" battery + ,so the ECU has + when key is turned off. iI have no idea if it stores anything in memory or what ever it does  i rephrase my tip .

 

If you change /swap anything on the Renix system take of the +from battery.  I do belive this makes sure  that the ECU has no power and  restarts .

And check /clean the connectors on the ECU, found some bad connected ones o my ECU

 

[JustEmptyEveryPocket]

8 hours ago, Kjell said:

If you change /swap anything on the Renix system take of the +from battery  and hold it against -  think this resets the ECM/ECU .

And check/ clean the connectors on the ECM/ECU.

 

Cleaning the connectors is an okay thing to do, just be careful if you use any solvents. No need to "reset" the ECU though. Renix does not have adaptive memory, so it doesn't do anything. Every time the engine starts up is like a brand new start from ECU perspective.

[Kjell]

6 hours ago, JustEmptyEveryPocket said:

Cleaning the connectors is an okay thing to do, just be careful if you use any solvents. No need to "reset" the ECU though. Renix does not have adaptive memory, so it doesn't do anything. Every time the engine starts up is like a brand new start from ECU perspective.

Had some problem when i replaced the trottle body couldent get the TPS/idle motor to work right (high idle bad gas respons) after disconnecting reconnecting tps and turn key off and on twentyeleven times , did the vodoo magic reset and it worked fine. Maby disconnecting reconnecting the battery + resets the idle motor

[JustEmptyEveryPocket]

Kjell: My guess would be the trick was unplugging and replugging the TPS connector. Probably helped seat a pin better or some such. Either that, or you have a 91 or 92 MJ with the HO motor. That ECU has adaptive memory. But Renix is basically a complex series of switches and nothing else, no memory anywhere, etc.

 

OP: I would listen to Ohm and Cruiser54. They should get you to the answer soon.

[cruiser54]

CRUISER'S MOSTLY RENIX TIPS

RENIX SENSOR GROUND TEST

OCTOBER 30, 2015 SALAD 14 COMMENTS EDIT

 

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.

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.