So in one of my posts, I asked about how to adjust the mixture on the EFI. someone said look at the temp sensor. I think it was Doug. said the third one. I’m looking at replacing all of the sensors because it doesn’t appear to be warming up very well, even though I swapped out the thermostat when I did a coolant flush / replace in May '19 the car warms up to about 75-80c
So I’m thinking replace all of the sensors, and maybe just maybe it will fix the aux fan too
I have the center single pole sending unit - I think this one goes to the temp guage.
the other three? not yet.
The others elude me. each has a different part number and some are not available. even though the parts look the same I’m guessing internally these aren’t the same.
I think the last one triggers the air pump. the others not a clue.
Front one is thermotime switch that closes the cold start injector. If it’s faulty the cold start injector will be providing extra fuel when hot. Also check the cold start injector doesn’t have a physical leak.
Middle one is temp transmitter sending signal to the temp gauge on the dash.
Third one is coolant sensor sending temp data to the ECU as input to the injection system. A fault in this might cause the ECU to run the injectors too rich.
The last one is not present on my car but I think your assumption is correct.
You may be able to get good used ones from David Boger at everydayxj.com.
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The coolant rail sensors have no bearing on how fast the engine warms up, Mark…
Only the thermostat can influence warm-up time and control engine temps. Basically the engine should warm up to thermostat temp in about 5 minutes of driving. Are you sure you fitted the correct thermostat - and with a 82 or higher rating…
If the engine is running too cool, and with long warm-up time, it is a sign that the thermostat is malfunctioning. And running cool, the engine will soot up like your spark plugs show.
There is no point in changing the sensors at this stage; they can be easily tested - and changed only if they are outside specs. Your thermostat warrants some action - new or not…
However; get an infrared thermometer to read exact temperatures - the dash gauge is not really to be trusted unless verified…
Not an in-depth thing but it gives you some basic ideas
Right.
It works in conjunction with the air switching module which is a multi-function device and a bit mystery to me. But, in any case, it almost certainly has no bearing on your rich running or cooler-than-normal running temps
This would require an unusual double failure scenario. While cold start injector gets grounded by the TT switch, which certainly can fail, it gets “+” voltage from the starter circuit… the idea being that it will operate only when cranking the engine. So a faulty TT switch would need to be coupled with some sort of weird circuit/wiring fault for the CSI to operate when the engine is actually running.
Good idea.
Temporary removing the fuel supply hose to the cold start injector, and seeing if anything changes, might be a short cut in eliminating it from the ‘could be’ list
I kinda more or less figured was afraid of that. I’m not looking forward to pulling the radiator. I’m considering an upgrade to a larger radiator with electric fans. Why, because I can; and I have lots of extra money to waste – NOT!
Seeing that I just swapped the coolant out less than a year ago, I’m not really looking forward to going down that rabbit hole again. But I’m quite use to eating my words with a dram of scotch.
Yes, Frank. I know that. I may be blonde headed but I’m not… well… that “blonde” I’m pretty sure it was a 82c thermostat, I’m not 100% sure thought,
I’ve got a stack of thermostats because I was having a tough time getting the Series II to a point where it wasn’t overheating. I may have gotten the boxes mixed up and put in a 72c thermostat instead. I will bust out the IR thermometer and check.
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Emphatically ‘bust out’ your IR thermometer, Mark - it’s an invaluable tool for coolant problems…
I’m not sure a 72C thermostat is a direct replacement to be used in S3 - does it actually have the long shank that closes the bypass as the thermostat opens? In any case; running the engine at low temps leads to fatter mixture - fully explaining your sooty plugs.
However, a properly working thermostat will still quickly heat the engine to the thermostat temps. But it is also important that when thermostat is fully open, recirculation is closed - otherwise part of the coolant will bypass the radiator. Which will raise the engine temp somewhat above the thermostat rating - with no fault with the radiator’s cooling…
The IR will remove all doubts; aimed at the base of the temp transmitter it will show water rail temp. Which should nominally be some 82C - which is a usual thermostat, though a higher temperature is beneficial for the engine…
With the engine temps sorted, you can review the sensors - if the engine runs cold, perfectly working sensors will still soot the plugs…
I probably won’t get to it for a couple days. The joys of being self-employed – I will be driving the truck for work. I will keep you posted with my findings.
Come to think of it, I do have a complete XK6 4.2. If need be, I can pilfer parts off of it. On another note, I’ve been kicking around pulling the fuel rail and related parts, rebuild it then put it on the Series III (green one) then rebuild
the green one put it on the gray Series III then rebuild that one and put it back on the spare engine. Project for another day.
What about your timming maybe it’s a little retarded. Or thermistor thinks it’s cold causing injectors to over fuel? I have all the sensors in a bag if you need some ohms measurements to compare?
I just did a tune up on the '85 XJ6. The ignition is spot on. Fires right up. runs great. I’ve had cooling problems in the past. the last coolant related issue is the upper radiator hose let go sprayed coolant all over the place. Right after I cleaned the engine. Go Figure.
I’m pretty confident that it’s the termo-thingy that regulates the fuel mixture based on temperature. I’ll check the specks on it. sometime. I just got insanely busy. My day started at 6am and I just got home at dinner and it’s 11:30 and looks like I’ll have another 4 or 5 days of this. yeah me…
I just put a tune on it. it was a bout 2 degrees retarded. That may have something to do with it. I would think so though. I’m leaning towards the Thermo-meter thingy that regulates the fuel mixture (when cold). I had cooling issues
a while back. This has turned out to be layers on an onion. The temp comes in at 72c, The Aux cooling fan won’t shut off – I ended up unplugging from the relay to keep the battery from draining.
I haven’t got any time right now to investigate it any further. Keep you posted.
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Incorrect timing does not really promote good combustion, Mark - but setting timing to correct values is required anyway. And too little advance tends to make the engine run hotter…
If you read 72C at the water rail; you have a thermostat problem - to be rectified. At that temp, given by the CTS, the ECU will run the engine fat. You can measure the temperature at the base of the CTS - and compare it to the spec resistance for that temperature. If it complies at various temps; the CTS is OK.
The continuous Aux fan is a separate problem - it will not cause cold running. With the thermostat closed, as it should be until the engine is a proper operating temp, there is no circulation through the radiator - and ‘no’ cooling…
and looks like I’ll have another 4 or 5 days of this. yeah me… 