• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

CTS wireing Question

xjtrailrider

NAXJA Forum User
NAXJA Member
Location
Roanoke VA
I am haveing a cold miss/stumble on my 90'. I have narrowed the problem down to the CTS wireing circuit or so I hope. With the CTS unhooked I am getting a solid 5 volts on the "beige" wire, The "brown w/white strip" wire is showing that it is grounded. I have traced the wire all the way back to the ECM and have not found a short/ground anywhere.

I've tested the sensor and it is reading as it should, High resistance cold and low resistance when warm.


What can it be?


The XJ runs great with the CTS disconnected but when its connected it runs bad untill it warms up.


With the CTS connected it runs very lean and has a good bit of detonation.


Will it hurt the engine and/or sensors to run it without the CTS connected?


Please help!!
 
Last edited:
Sounds like your CTS is starting to get odd on you.

The Coolant Temperature Sensor is a thermistor - a resistor that changes value with temperature. It should respond on a predicable curve, and it sounds as though its low-temperature response is starting to get problematic (even if there's no voltage applied, it still changes resistance with temperature.)

Since you're getting +5VDC, your reference voltage signal is just fine. I'd just replace the sensor.

Come to think of it, I've got to replace just about all of the sensors in my 88 sometime soon... They're all original - except for the TPS...

5-90
 
This is my 3rd CTS 5-90(in 2 months), and all the others check out good also!

I'm at a loss for what I should do or check next!

Could my ECM be bad?

What else could be making it run lean when its cold?
 
More info on this temp sensor. I back probed a volt meter to the CTS connector with the CTS connected and cold started the engine. The voltage dropped as the engine warmed up. Shouldn't this voltage increase since the resistance is dropping as the coolant heats up?

Is it possible that the connector could be reversed? Or does it matter?
 
Shouldn't matter.

Do you need the temperarure/resistance curve to check your sensor's operation?

"Lean when cold" could also end up being a HEGO sensor - if it's taking a long time to warm up (probably due to a shot heater element,) then it won't generate the "trim" input that the ECU needs to balance and trim fuel delivery - which could be a problem until the sensor warms up. Heated, the sensor should be warm in about five minutes. Not heated, it could take a half-hour or so.

5-90
 
I've got the RENIX FSM, I ve checked the CTS both in and out of the car. Its reading in the curve very close. At 100* it reads 1575 according to my memory.

O.K., What is the HEGO, Thats a new one for me or are we talking about the 02 heater.
 
HEGO - Heated Exhaust Gas Oxygen (sensor.)

They've got a spec life of 80Kmiles or so - but I've seen them go 150 or so without any trouble. Typically, either the heating element fails (common) or they get crapped up with carbon (which is supposed to burn off, but sometimes doesn't.)

5-90
 
My 02 is new from the dealer, but that doesn't meen its any good. I will check tomorrow a.m.

I drove it again a few min. ago. it misses with the CTS hooked up and doesn't with it unhooked.

I'm going to try the same with the MAT also and see if I get similar results.

My thinking is maybe everything is good and working as it should but this new motor may need more fuel than the stock set up is giving it since it has been bored over stock, milled and decked.

What about stock 5.0 Ford injectors(19#), would they give it a little more fuel? I've got a couple dozen laying around I could try.

I'm going to keep digging untill i find the problem, please keep sending ideas my way.
 
19# is about the same size as what you have in there already...

Depends on how far "lean" you're running - but I'd consider swapping in a set of 21# injectors (if you have them handy,) and probably building a MAP adjuster to tweak the input voltage to the MAP sensor.

5-90
 
Slight miss stumble at idle is a classic EGR renix problem, So after you chase down everything else. make sure the the egr solinoid works that the rod on the manifold goes up and down. and that it has vacumn. good luck.
 
Thanks XJING, I'm 99% sure after performing some checks/tests that the EGR and solonoid are performing properly.

I drove the Jeep today with the MAT disconnected and it ran better, the richer mixture is either masking the problem or is getting it away from the lean run condition. It was crisp outside this a.m., 30*. My MAT as well as my CTS all test good according to the FSM, but if I disconnect either one it runs better cold and about the same warm.

I have to find an alternative to just unhooking sensors to fix this problem due to the fact that the ECU will never close the "loop".

It looks like possibly a adjustable MAP or larger injectors or both to eliminate the "lean" condition I'm experiancing from idle to WOT.

Everything in the RENIX system tests good and most of it is new also. I think that the system is working properly its just not giving the engine the fuel it wants to run properly.
 
Back
Top