Coolant temp sensor renix idle problems?

[Precious88xj]

1988 Jeep xj 4.0 4x4 aw4

So I recently swapped in a high output motor and forgot to install the coolant sensor that mounts to the motor on the renix. I kept my electrical system from the renix. Would that cause me a rough idle I don’t have it connected?
Also I won’t be able to install it to it’s original location can I adapt it to the water outlet where the temp sensor goes located for the H.O

[90xj06]

order a thermostat housing from a 93 4.0 and put your temp sensor in there. your going to need to make a longer harness.

it would change timing and mixtures a bit when its missing.

[cruiser54]

Originally Posted by Precious88xj

1988 Jeep xj 4.0 4x4 aw4

So I recently swapped in a high output motor and forgot to install the coolant sensor that mounts to the motor on the renix. I kept my electrical system from the renix. Would that cause me a rough idle I don’t have it connected?
Also I won’t be able to install it to it’s original location can I adapt it to the water outlet where the temp sensor goes located for the H.O

It needs that sensor for sure.

Too hard to get the plug out of the block now.

[JeepNoob]

Originally Posted by Precious88xj

1988 Jeep xj 4.0 4x4 aw4

So I recently swapped in a high output motor and forgot to install the coolant sensor that mounts to the motor on the renix. I kept my electrical system from the renix. Would that cause me a rough idle I don’t have it connected?
Also I won’t be able to install it to it’s original location can I adapt it to the water outlet where the temp sensor goes located for the H.O

Yes, it will cause idle problems. The PCM needs to know if the engine is hot or cold (among other things) to adjust fuel accordingly.

If your factory temp sensor will fit into an HO thermostat housing, I would simply cut the wires a few inches away from the connector and splice in some new wire. If you can solder, I would recommend that and some heat shrink tubing. If not, most parts stores sell butt connectors with a heat shrink plastic "jacket" that also work very well.

[Ecomike]

I am not sure, not convinced a missing CTS sensor will cause idle problems. Simple test is to connect one to the wiring, just do not install it in the block. Cool the sensor with cold water, then heat it with boiling water. That will tell you if it is affecting idle or not.

If the O2 sensor and IAT temp sensor are working I would think it could it idle fine (closed loop).

Not having a CTS can affect starting the jeep (probably hard to start, easy to flood sometimes)!!!!

And it can waste gas!!!

Old-Man had a bad one, it was telling the ECU the temp was 30F or something all the time, and his problem was the ECU would not switch to closed loop, and it stayed open loop and drank gas big time, but he did not mention an idle issue. I think it was Renix. I think the ECU will assume an acoolant temp, guess, and then use the O2 sensor to control fuel feed.

IF the O2 sensor is having issues, fuel injectors have issues, or a dozen other things, then that is the probable cause of the idle issue.

[cruiser54]

Originally Posted by Ecomike

I am not sure, not convinced a missing CTS sensor will cause idle problems. Simple test is to connect one to the wiring, just do not install it in the block. Cool the sensor with cold water, then heat it with boiling water. That will tell you if it is affecting idle or not.

If the O2 sensor and IAT temp sensor are working I would think it could it idle fine (closed loop).

Not having a CTS can affect starting the jeep (probably hard to start, easy to flood sometimes)!!!!

And it can waste gas!!!

Old-Man had a bad one, it was telling the ECU the temp was 30F or something all the time, and his problem was the ECU would not switch to closed loop, and it stayed open loop and drank gas big time, but he did not mention an idle issue. I think it was Renix. I think the ECU will assume an acoolant temp, guess, and then use the O2 sensor to control fuel feed.

IF the O2 sensor is having issues, fuel injectors have issues, or a dozen other things, then that is the probable cause of the idle issue.

I'll guarantee a missing CTS will cause problems.

[Hypoid]

Flores helped me diagnose a bad CTS: It idled great, ran great, never went into closed loop, could not pass emission testing.

[Ecomike]

Originally Posted by cruiser54

I'll guarantee a missing CTS will cause problems.

I never said it would not cause problems, but I still say it will not cause a bad idle/problem if the other sensors and hardware are working!!!

"Coolant temp sensor renix idle problems?" is the title of the OP post.

But I agree with you, it will cause many other issues. For one it controls the initial fuel feed rate when cranking on start up!!! Because at that time it has no O2 sensor data!!! It is critical for start up fuel rates!!!

[Ecomike]

Originally Posted by Hypoid

Flores helped me diagnose a bad CTS: It idled great, ran great, never went into closed loop, could not pass emission testing.

Well that confirms it. I am pretty sure old_man had the exact same story, his was sucking up fuel like a mad dog as the CTS was passing out bad coolant temp data to the ECU, claiming the block was always super cold, or something like that.

Depending on the bad data, random change in the reading, or always reading cold, warm or hot, would likely create different issues. One might be hard starting when cold, the other starting when hot. IMHO. But in Old_mans case it would not go to closed loop either, due to bad CTS, thus it wasted gas big time.

So a missing CTS needs to be fixed!!! But doing so fixes other problems, not a wandering idle!!!