Hi again. I'll try to make this long story as short as possible.

Jasmine is my very late production '96 XJS, 4.0 litre six. She has 105,000 miles. I've had her 20 years and 75,000 of those miles, before this worst problem was a starter.

For several months my temp gauge read very low. I wasn't very worried, because better low than high right? A few weeks ago I got an CEL, code, P0116, low engine temp. I still wasn't worried (better low than high, etc.) but now I figured thermostat stuck open. Then after driving two weeks like that I was coming home from a 60 mile trip, car drove great, stopped for gas, and then car kept stalling. I could start it, but it wouldn't idle and I had to keep revving it to get home. Now I had three codes, the P0116, and P0727 and P1775. I have read those last two basically mean it's stalling. Now I had to fix it so I got a new thermostat. Put the car on ramps to drain coolant, went to take car off ramps, suddenly it wouldn't start and seemed to lose all compression. Yikes! Long story short I discovered something called bore wash, had never heard of it in about 35 years or amateur mechanics. I ended up replacing cam cover gasket and spark plugs because I had taken those apart before I knew about bore wash. And I replaced the thermostat. And I tested both temperature sensors (ohmmeter and boiling pan of water) and they seem fine. Got it all together again, cleared the codes, and she started up, and ran great. I let her warm up for 15 minutes or so, temperature gauge read N for the first time in months. So thermostat definitely was bad, right? So I shut her down, put down the top, got my wife for a celebratory joy ride (about 20 minutes all this), started her up... and back to not idling. Smells like running very rich. No new CEL.

So, ideas? Why do I have no CEL if it's running that bad? Wouldn't most of the usual things cause a code to come up?

Very confusedly yours,

-mB

 

My first immediate thought is CTS is bad. I would start there. Make sure you get the original correct part as there are two for AJ16, if I am not mistaken

EDIT- this code is for part LHE1600AA , the CTS. An archive search shows I had the same problem myself with my AJ16 a few years ago ! The CTS will cause over fueling and other problems. I don’t think your engine “running cool” was ever the problem. It probably wasn’t running that cool anyway, there is a wide “normal” range of for the operating temperature in the AJ16 and as long as you operate within that range you are fine......It is false that you have to constantly reach 200-210 or the car will have issues. That high temperature range is there for emissions and other purposes. I have been running my AJ16 with a slightly cooler thermostat for a long time- this was way after my CTS went bad- and nothing terrible has happened other than the car seems to stay a little cooler at speed and seems to be able to handle being in stop and go longer before in passes the “N” (as all AJ16 XJS’s do).

 

Hi Mike

If you do decide to replace the (CPS) Crank Position Sensor on your AJ16 Engine, this is how I did mine

(1) Don't try and do it from under the Car as you will be there all day! (6 hours in my case!)

(2) Go in from on top from under the Bonnet/Hood, where if you've never done this before you may find it easier to remove the Crank Sensor together with it's Bracket (only 2 bolts) but behind it is a Blanking Plate which easily falls out!

So do watch out for that one, though fortunately its quite heavy, so if it drops you will probably hear it

(3) Going in from under the Bonnet/Hood there is no need to remove anything, as this is a job that is done by feel rather than eyesight

(4) If you don't remove the Bracket (where the only reason to do so could be the awkward plug) then replacing the CPS is in fact a very easy job, where having been there and done it then it should take no more than 10 minutes

Where in an Emergency situation, if you have a Spare CPS, then this could be very easily done by the side of the road providing you have a long extension (pref) 1/4 Socket

How to remove and then Replace the Front Crank Position Sensor on a 4.0L AJ16 Engine in about 10 minutes

 

Hi OB!!

He needs a CTS- coolant temperature sensor, but changing his CPS if he is over 100k is not a bad idea either!!

 

Hi Spike

My Bad, I thought it was CPS (too many late nights!)

 

I will replace the CTS; after all I'm not going to get advice from experts and then not heed it. But I am skeptical for two reasons. One, replacing the thermostat did make an immediate and obvious difference in the running temperature (from barely into the low normal bracket to at or a little above N). Also I have been driving this car for 20 years, and it always runs around N; the much lower reading was a recent change. Two, when I tested the CTS off the car (pan of boiling water and an ohmmeter) I got all the right readings; started out at about 2300 ohms, gradually went down to about 280 ohms when water was not quite boiling.

Are CTS's the kind of thing that fails intermittently? That would explain a lot.

Anyhow I'll replace it but would also be curious about other possibilities.

Thanks,

-mB

 

There’s the coolant temp sensor, and then there’s the sender. Two different parts. It’s absolutely plausible that the sender is reading correctly and this your gauge is showing the accurate temp reading.

At the very same time, the sensor could have failed, which is read by the ECU. Basically the ECU thinks the engine is cold and therefore making poor fueling decisions.

Its an extremely easy part to find, cheap to buy and easy to replace.

At the other end, it could be the TPS. Impossible to conclusively bench test, expensive to buy, somewhat more involved to replace, including a reset by a Jag diagnostic computer. It’s a part that, when failing, can cause mysterious and inconsistent problems....like yours.

 

CTS is part number LHE1600AA and it is completely unrelated to your gauge. This tells the computer what your temperature is and causes the codes and symptoms described. I recommend you buy it directly from JCP in the U.K.

The sender is part DAC11079 And it is NLA. I managed to get NOS parts that popped up on eBay, but other than that we have not yet found a suitable replacement.

 

I bought a new CTS and I'll put it in as soon as it arrives, and cross my fingers.

I think the sender is okay- at least the dash gauge gives reasonable readings. And even if it were bad it wouldn't cause a drivability issue.

I'll just hope I don't need a TPS.

Wish me luck, and thanks again for the help.

-mB

 

Doubt its TPS. Failure mode in my 95 AJ16 was sudden cutout (even at high speed) when the acceleration required I give the car gas, suddenly decrease and then increase again, as it is sometimes necessary. Sometimes my would just die when decreasing speed to make a turn. It was almost impossible to diagnose and required an adaptation after it was changed.

 

Hi everybody. Just wanted to let you know that after replacing the CTS and after now having done several long and short test drives, that was the problem. No more engine lights, and she drives great. As I said I had tested the old one off the car, but seems like the old one would go bad intermittently.

This weekend in particular I did a lot of SoCal freeway driving with the AC on, which seems to heat the car up a lot with its combination of high speeds followed (abruptly) by stop and go, all in hot weather. With the new thermostat in she still runs hotter than I'd like, but probably not so hot as to be harmful. It used to (a couple years ago) always run right around N. Now it seems to run at 1/3 or 1/2 the way between N and H. It seems like the thermostat opens at 1/3 of the way up from N (because as soon as she warms up she goes there) and hard use can make it peak a little higher.

After all the fiddling about I think the following is the timeline of my cooling systems issues:

1) about two years ago the original thermostat got sticky, causing her to run hot.
2) last year I replaced that thermostat with a parts store one. And then the car sat for months as I was busy moving from Colorado to California.
3) Early this year I started driving her in earnest, and the new thermostat stuck open, causing very low temperature readings on the dash, but no real problems.
4) After months of that, unrelated, the CTS went bad. This at first caused a Check Engine Light (probably only happened for a second at first) and then caused the car to become basically undrivable.
5) As a result of the super-rich condition that was causing I learned first-hand what Bore Wash is. Such fun.
6) When I finally got it back together with a newer waxstat thermostat the CTS worked again for a while, making me briefly think the thermostat was the whole problem. Then the CTS conked out again half an hour later.
7) I replaced the CTS, following advice on this forum, and now she runs great again, albeit a little hotter than I'd like. Many thanks to the forum. I really didn't think that was the problem because i had tested the durn thing, but it was, and I'm glad I listened.
8) Almost beside the point, somewhere along the line the heater stopped working. I had thought that might be connected to the very low temperature it was running at, but even with the car well above N I can't get any heat to come on. AC works great though.

I think I'm done with this particular problem, until further notice. Now I'll start asking about the next problem...

Thanks again,

-mB