Picked up a 2004 XJ8 with 49xxx miles for my wife because she refused to quit driving my 08 vdp everywhere. Car had some basics I worked through quickly like bulbs and such

On her first drive out of the driveway she drives it about town a bit and when she parks at the bank drive through the car puked everywhere and overheated.
i\It was a hot day and the car was sitting in park with AC on. Car was towed home

To top this all off, the car throws NO overheating codes, not a single 1

So I begin the quest of resolution and upon popping the hood , Found a hairline cracked nipple on overflow tank. Replace it , test drove while watching the temp values on the obd2 . The car would drive fine staying about 190 to 200 depending on terrain. AS SOON as the car stopped and idled the temps would progressively climb to 220 and beyond

I let it hit 240 once before i realized it weasnt goinf to stop . Through all my testing ( probbly 20 test drives ) always shut it down at 220 or before

Since the new coolant tank did not fix the problem decided to replace the ENTIRE thermostat heart valve assenbly. Did so, refilled coolant and after a bunch of burping test drive the condition remained the same .

Then notice my fans arent spinning and decide they must be broke. So i order a used unit off ebay and did a test fit to the cars connector with the unit sitting out of the car. Plenty of slack on the cable. The new fans spins at 1/2 mph . so slow i could stop it with my peter. This is EXACTLY how the in car unit was behaving. spun so slow may have even been the wind turning it.

Began check fuses , ALL were good.

Then find out the fan is directly controlled by the ECU which triggers operation based on temp sensor readings. I know the temp sensor is good because i can read it on the obd2 and watch it climb from ambient air temp to the 192 thermostat and hold.

THAT means this HAS to be the ECM. Began sourcing the ECM on net and found

1. new dealer installed ecm is $2k+

2. ECM cannot be repaired , internal proceesers are largely unable to fix and profesional jaguar ecm repair shops WONT repair it

3 I can get a remanufatured unit with a warranty for about $500 BUT it needs to be security programmed by a local locksmith in the car. week of research and i found a local locksmith who new exactky what to do.

I now currently have the car sitting with no ecu . I wanted to make sure i would be capable of removal / install. so yanked her out.

so my advice request before i throw $at a new ECM is

1.Have i exhausted all possibilities?

2.Anyone else had or heard of this problem?

3. should i go the new ecm route

4. looking for anything here, or perhaps a miracle

Really just looking forward to getting this cat sorted and on the road. The above process has been about 4 months of a little at a time with a ton of frustration in the middle

 

Fans should be on, so you're heading in the right direction.

If you look at the workshop manual (free download) you'll see the PCM (aka ECM) commands the fan module (see fig 03.4).

Slight snag is the PCM uses a PWM signal to do it so realistically you could do with a 'scope to see it.

Generally the PCM on these era cars is bullet proof so you probably have an issue other than it.

 

The harness going to the fans has 2 plugs under the bumper (behind the rhs fog lamp)

If you disconnect to small plug the fans will go into full speed mode

Full details here
https://www.jaguarforums.com/forum/x...an-mod-104790/

Cheers
34by151

 

[QUOTE=JagV8;1789852]Fans should be on, so you're heading in the right direction.


Slight snag is the PCM uses a PWM signal to do it so realistically you could do with a 'scope to see it.

Generally the PCM on these era cars is bullet proof so you probably have an issue other than it.

Sort of what I was looking for , but i know nothing of oscipoes

1. Is there a base ( inexpensive ) handheld that can detect . I noticed some scopes are 1k +

2 . How in the world is is signal traces. I'm lucky I know how to read voltage of a battery so a scope is out of my league. You tube videos


So basically you are saying

I should see a scoped signal from the ecm when ac is put on OR when car hits like 210+ degrees. Seeing that signal would prove the ECM is good and leave my problem beyond it.

Perhaps a scope investment and figuring out how to use it is a decent investment


on the jags , is a scope a valuable tool to have or is its use so random it just may not pay for itself. ?

 

Unlikely to pay for itself. Borrow one / find someone with one?

Not every problem can be DIY by everyone, sadly.

 

So sounds like my best course of action unfortunately is

Bring it to the Indy with the proper equipment and have him confirm the problem

 

been poking around and found testing software . sds / mogoose/ laptop

look at the screen , it has a trouble shoot section right down to inoperable fans

only seems to be sold as a complete set in england though

 

Two things come to mind on your problem -

- water pump - is it pumping OK ? It's not unknown for pump impeller blades to break off and partially jam the outlet pipe. Coolant flow is therefore reduced but the additional cooling when the car is moving compensates for that.

- head gasket failure- combustion chamber gases enter the coolant jacket and force out coolant. Key test is to check whether there is any pressure in the coolant jacket when the engine is stone-cold. Easy to do by just taking off the pressure cap. A rush of air/gas out is a sign of HGF. Shops have testers to check for presence of combustion chamber gas products in the coolant.

 

my wife removed the resivoir cap today. has been sitting for 6 day un driven so it was cool. NO hiss or whoosh of pressure at all.

hoping that is a positive sign

 

I had overheating at idle problems with my 2005 XJR in very hot weather and it turned out to be tired fans, although I also replaced the radiator at the time.

When it started overheating at idle did the air conditioning also start blowing hot?

You said you bought a used fan on eBay. You should test that as well to make sure it’s not old and tired too.

 

This is the exact version I have. Run it on a $50 laptop with no issues.

 

Really odd you ask about blowing hot because it did. When at idle the AC would definitely turn warmer, but it seemed like it would cycle a bit unless i did not realize we were moving again .

The car was new to us and my wife picked up on that imidiately . The problem was so obvious i researched and diagnosed the compressor control valve which controlled air con at idle must be bad. I purchased a new one and have it ready to install but have been until after i get this overheating sorted

so my big question now is , great diagnosis but are they related ?

And tired fans?? maybe thats why they spun at a speed of 1/16 a mile per hour. i did try the bypass method a thread showed to jumpstart the fans and got no movement.

i have every confidence that the only reason the car overheats is because those fans arent spinning.

Feel like i am getting closer here , but still just out of range of that finish line.

thanks for the help

 

Yes the answer is to replace the fans with fans that you know are good. I bought a new OEM unit with along with a new OEM radiator which together were an arm and a leg. Completely fixed the problem.

I read that at idle on a hot day the fans need to run hard enough to displace an equivalent amount of air as driving 50mph does.

The fan unit in the jaguar is “smart” and has an ECU to control fan speed which can go bad.

Your AC stops working because it gets so hot in the engine bay that the compressor overheats.

I did a lot of research on this topic when I was troubleshooting my overheating problem (which only happened at idle on 85+ degree days)

 

thank you mike , and here is my plan of attack considering my odd circumstance of having a full function 08" in the driveway as well

step 1 . start 08 vdp and monitor the fans reaction to temperature and ac status under proper operating conditions.

step 2 . remove the fan in 04

step 3 swap known good fan from my 08 to the 04 and test to see if problem corrected.

i truly have no desire to remove the fan from my 08, BUT if it solves the problem is corrected i will just install the brand new unit in my 08 and consider it an upgrade.

i am trying to exhasterbate all possibles before going the ecm route,


Sure hope this works, will have time to do the job the day after thanksgiving.

 

With the car cold and ign on the fans wont be running
If you disconnect the smaller of the 2 fan plugs (located behind the fog lamp cover) this will disconnect the pcm from the ECU to the fans.
If the fan module is OK it will respond by turning the fans on full

If this works you dont have a fan issue and your issue is wiring or ECU

If you get no response from the fans first check the headlamp earths and the connectors for corrosion then measure the resistance to ground and confirm you have power at the plug. If these all pass power the fan directly at the plug. If all of this fails replace the fan.

Cheers
34by151

 

ok, this testing can be done pre removal of fans and will proof the fans with certainty, but i want to make sure i fully understand. I have been into these 2 connectors already as i have mounted a fan externally as a test. unfortunately i believe my test fan may have been garbage as well.

1. so you are saying if i JUST unplug the small connector, the fan will instantly go on FULL. ( if the fan is good )

2. IF the fan does NOT go on full i need to verify the headlight grounds ( i am familiar with these from all the cursing i did trying to replace a bulb with them in the way).

If the grounds seem good next i need to check voltage at the plug, and this is where you lose me

my assumptions are it would be at the big plug, since it seems the small plug is more of a controller signal.

So checking the big plug, i am assuming i will see 12+ volts?? will it be on one pin only?

i understand electric enough to realize i dont fully understand it . I can work a voltometer and am getting better mostly because im being forced to learn .
all advice on the electrical proofing portion is appreciated.

As a final note, i did try the unplugging and jumpering tests previously using your post and another gentlemans , and as i remember i got no reaction from the fans. I can not remember though if i did it with the car running or not so i will follow the testing procedure 1 more time .

 

Take a look at my fan mod here
https://www.jaguarforums.com/forum/x...an-mod-104790/
All we do is break the PCM wire to make the fans go on full blast

The Small plug has the PCM signal and ign power
The big one has the fan power and ground

If removing the pcm signal does not make the fans go on full you either have a Fan failure or a power failure

If you supply power and ground to the large plug and power to the small one you can then prove the fans are ok.

This is the bringing wire in the fan mode post.
I did that to supply power but remove the pcm signal

Testing the supply side of the large plug will tell you if you have power and ground.

The most likely cause of failure is the ground behind the headlamp and or one of the fan plus is corroded

As for the spare fans, simply supply power and ground to the large plug and power to the small one. IE no pcm signal = full on

This will test your spare fans as they may be dud ones.

To test the supply side of the plug check the power wire for 12 or more volts.
Check the resistance between the body and the ground wire. If you get any resistance you have and earth issue.

Cheers
34by151

 

so i was able to put a days effort into trouble shooting and though I feel I made progress the car is not fixed nor do I have a clear solution. The car with the fans that does not work is the 04xj8. To aid in the troubleshooting I have a used but new to me fan assembly as well as my 08vdp which is in proper order.

1. First step was to remove the small plug to the fan as suggested by 34x151. The fans did NOT kick on full .

2. wondering what my 08vdp would do i unplugged the small plug and the fans also did NOT kick on full. Now wondering if it is more than just unplugging the small plug but is actually unplugging AND jumpering one of the wires. I did not jumper the wire because as i read it , just unplugging the small wire would be all that was needed.

3. Tested voltage at the large plug and easily got 12+ volts.

4 Tested resistance at the the large plug and got 0

5 Decided to test the extra fan and got my 08 vdp warmed up then plugged the extra fan in externally and right at 196 the fan kicked on 1/2 speed then at about 199 the fan on kicked on full. spun like a raped ape.

6. Plugged the extra fan into the 04xj8 externally and it would kick on when ac was turned on or when hot and would spin at 1/8 speed. Clearly spinning just very slow. Stopped it with my hand and when released it would begin spinning again. Considering it would be triggered on with ac or temp i feel it was being signaled on .

7. The original fan which i thought didnt work, does turn on slowly exactly like the extra fan did .

so my conclusions are

1. My extra fan is a full functioning unit
2. My original fan is full functioning unit ( because it behaves exactly like the extra)
3. Have good power and ground at the ( big ) power plug

qustion

1. seems like i need to test the +voltage at the 1 wire in the small plug . what would that voltage be?

Only thing i wonder about now that i did not try is the unplugging the small plug . I read it as suggested that Just unplugging the small plug would trigger the fan FULL. is this actually the case or is it unplug the small plug THEN jumper the power wire to trigger the fan full. If that is the case it would seem i need to confirm + voltage on the power side of the small plug.

thoughts?

 

Remove the small plug
Jumper the pins as per the picture I posted
https://www.jaguarforums.com/forum/x.../#&gid=1&pid=2

Turn on the Ign
The Fan will come on full

The fan module is mounted on the fan
The PWM sent via the ECU is a square wave

See here https://learn.sparkfun.com/tutorials...dth-modulation

If the signal is 0% duty cycle (which equals 0 Volts) the fan is on full
If the signal is 100% duty cycle (which equals 5 Volts) the fan is off
If the signal is 50% duty cycle the fan is on half

ect.ect

Check the fan with the pin jumpered as per the pic and report back, we can go from there

I suspect you have a ground fault at the headlamp. Assuming you have not upgraded the ground points I would do this now. Even if they are ok the will cause chaos at some point.


Cheers
34by151

 

after much back and forth and some serious kitty tail chasing i have resolved the issue

as stated by 34by151 , the ground behind the headlamp was corroded/broken .
visually it looked fine, but when i put a socket on it , it snapped revealing extensive corrosion.

fix was simple. after the stud was removed i simply wire brushed the hole where stud was and ran a bolt/nut/lock washerthrough.

fans kick on now and all is well.

big thanks to all those who helped out.