So our 1996 xj6 is running rich and I'd like to tweak that if possible. Googling this issue brought up a list of possibilities, which started with the engine temperature sensor being bad, causing the ECM to add more fuel to the mix. I've checked the engine temperature sensor (just in front of the fuel rail) and it reads ~ 2300 to 2400 ohms across the terminals (harness connector not connected) when cold OR hot. Is this a valid way to measure whether it is good/bad? I've seen a you tube video where they put in a couple jumper wires to the harness and instead measure the voltage drop across the terminals. It seems odd that I get roughly the same readings (cold or hot) because the dash temperature gauge does appear to be working correctly.

Also, if this matters, I did note that when the engine is started cold the cooling fans come on immediately. From what I've read they should not come on till the engine is up to temperature, or the AC is on. Is that correct?

Thanks for any help/tip and trick with this.

Bobby

The coolant thermostats in these cars do go bad and the engine will run too cool and will run too rich. If you look at your temp. gauge it should be about in the middle when the engine is warmed up. The fans always run when the engine is running.

There are a number of other things that can cause too rich a mixture but this one is a cheap and easy fix.

Thank you, the temperature gauge sits just a bit more than 1/3 the way up. Definitely not near the half way point. You right, they are not expensive, so it can't hurt the try that first.

Bobby

If you replace your thermostat you may be able to reuse the old paper gasket, do not use a big rubber 0 ring type if it comes with it. I just replaced mine recently and got the 192 degree unit.

the SENDER that actuates the needle on your dashboard is not the same as the SENSOR that is read by your ECU.

Technically, you could have an engine being read by the ECU as being too cool even though the needle on your dash would show an accurate reading.

I just had that happen to me on my XJS. I thought it was the thermostat, and after replacing, my car could not get hotter than 179F. After replacing the sensor, I’m good at 192F. The needle was always showing I was in the middle....that should have been the dead giveaway that the thermostat was fine, and revealed the sensor as the culprit.

"2300 to 2400 ohms across the terminals (harness connector not connected) when cold OR hot. Is this a valid way to measure"


Yes it is a valid way to measure, and yes your sensor is dead.

Resistance should fall as Coolant temperature increases. 2300 ohms should be about 20 Deg C.

Vee, I can't recall for certain, but I think that on the X300 the sender was eliminated and the ECTS supplies the coolant temp signal to both the ECM and IC.

Bobby, Your sensor is telling the ECM the coolant is much colder than 14F/-10C. Here's the resistance chart from the Engine Management System manual:



Cheers,

Don

Hey Don

I feel a bit like a student questioning his university professor, but @Vee is right, there is a separate sensor for the gauge (on my X300 at least).

Also, I think you are misreading the table of temp/resistance. The OP reading was 2300-2400 ohms, which equates to around 20C (2.5KOhms)

The original OP may have two problems going on at the same time, a bad thermostat that does not allow the engine to get up to the correct running temperature and a bad ECU coolant temp. sensor that is telling the fuel system to enrichen the mixture.

Hi Brendan!

Thanks for the corrections on all counts. We just moved and apparently my brain is even more fried than I realized! I should have known the X300 still has the separate sender for the gauge but I don't have one here at the moment to check and was too tired to pull up the schematic. Obviously my eyes were too tired to read even the resistance chart!

Cheers,

Don

Thanks all for the great info! I've ordered a new ecm coolant temp sensor. Along with a new top radiator hose. I think all the hoses might be original as they look really bad. So the bottom hose that runs under the intake manifold, can that be replaced from under the car on a lift? Or will the manifolds have to be removed?

Bobby

"can that be replaced from under the car on a lift? Or will the manifolds have to be removed?"


The hose under the manifold is commonly know as the bast*rd hose. Guess why.

A shop I use told me that the ******* hose can indeed be replaced without removing the manifold.

That shop was in the midst of replacing that hose while I had the intake manifold off because of a failed intake manifold gasket. Looked difficult to get to, but I would think if I had a lift, it would be doable.

Why aren’t you replacing the lower coolant hose, or the octopus hose? That one hose has more chances for failure than the upper does, for sure. And since you’ve already drained the system....kinda makes sense.

Hi Vee. I'm replacing the upper hose because it's easy to get to and I can do it without any major work.. We're planning on going after ALL the remaining hoses after my son gets another vehicle to use while this one is apart. Hopefully by the fall. I'm just gathering info on the remaining hoses now so I can maybe be prepared as to what what will need to be done at that time.

Thanks!!

Bobby

Today I received the new coolant sensor. Unfortunately the connector is wrong. The original uses the same metal clip that the injectors use. The replacement I received uses a different mechanism to hold the connector in place. They will not fit together. So I checked with some local parts stores (O'Riley's, Advanced, Etc...) and two of them had the part for a 96 XJ6, also sporting the same wrong connector. I'm wondering if I maybe look for a sensor from a different year might bring up the proper connector? Or I can make a pigtail with small spade connectors? Ideas? Pics Below.

Bobby

NOTE: Searching through the various parts stores, starting in 1995 they list this new part. If I look at 1994, they show the sensor with the proper connector. I wouldn't think a couple years would make a difference(?), Would it be OK to use a sensor for a 1994 XJ6? Or should I look at replacing the connector so that it fits the new style (because any time it needs to be replaced in the future it'll have the current connector)? Opinions?


Original Sensor




Original Connector




New Connector

Wow, I just recently replaced mine. There’s plenty of options, and I believe many cars used that same part, so it’s quite common. They just goofed.

Replacement parts may have a black, brown or green plastic section (or even metal) but they all look the same, other than color.

They just sent you the wrong part. LHE1600AA, right?

Hi Vee. Admittedly I did not go by the jag part#. I just ordered it by the year, make, model. Apparently they all have it wrong for the 96. I'm just back from O'Riley's Auto Parts where I asked them to bring up the part again for a 1996 XJ6, and the picture was of the wrong one (the same that I received). Then they brought up a 1994 and the picture was of the correct part. Since they can have it in by tomorrow morning I had them order one. We'll see what comes in.

Thanks,

Bobby

Trust me on this one, going forward, always use the part number. What each car part store has in their databanks cannot be relied on. I find tons of errors when trying to purchase parts. You will be more knowledgable than the guys computer....most every time.

Ideally, you bring the old part with you everytime you can....just like my dad made me do when I used to go to the hardware/car parts store....before the internet....

Thanks Vee. That's sound advice for all cars, but especially (it seems) Jaguars. We finally have the sensor installed. Not sure from here how we tell if it's made a difference?

Bobby

Look at the LTFT for the car.

Drive it for a week.

Check LTFTs again. Is there a change?