I have a 90 XJ with 4.0, AW4 and 231. The coolant temp gauge on the dash reads 180, the CTS the ECU uses reads 160. I have NickinTime's reader tied into my diagnostic port, that's how I'm seeing the CTS reading. Is this hurting anything? Will the ECU adjust the tune based on the perceived cooler temperature? I'm hesitant to mess with it, if it isn't hurting anything - sleeping dogs and all that.

 

I think 160 is around where the ECU decides to shift to closed-loop? Does the reader indicate whether the O2 sensor is being used? How's your fuel mileage? Got an IR thermometer you can check what the temp really is?

 

Your dash gauge reads off a different sender located on the rear of the head. It only provides input to the cluster. You can use an IR thermometer to "sanity check" the readings. Next, I don't find the gauge reading to be very accurate in an absolute sense, but I do know where the gauge reads under normal conditions and when it reports something's wrong.

Does the NIT say you're in closed or open loop? If you're in closed loop at idle (or cruise) and fully warmed up, you're OK.

If you haven't done so yet, got to Cruiser54's website. Under Technical manuals, you find the Renix FI manual.

 

It is going into closed loop. I've had the jeep for five years now and have gone through Cruiser's site. The jeep runs fair. Have been looking at it lately to try to get better economy and performance out of it.

 

When is the last time you replaced plugs, wires, cap and rotor?
Have you ever snugged up your intake manifold bolts? Cleaned your throttle body and IAC?

 

Plugs, wires, cap and rotor probably have 10k miles on them. Will replace the intake manifold gasket in the fall, the exhaust manifold is leaking at the block. Just cleaned the TB and IAC yesterday. Thanks cruiser!

 

In the meantime, make sure the intake bolts are tight.