There is a tire calculator in the Tools menu:

 

Thanks a lot,
On the picture of the car above it is visible too.
But would 4% lower rear wheel speed compared to front wheels actually freak out the cars systems without traction-loss signals to the driver?
I guess not. (searching the forum)
I also already thought not but am doubting everything with this the car...(but have some good leads to go on from earlier replies now)

Edit 23 Oct: I tried driving with both rear ABS sensors disconnected to eliminate tire size as the problem. Besides that it results in the fact that the car won't shift or indicate actual speed, it still stumbles under WOT so that probable cause can be put aside for sure now.
The car already holds back when WOT from start, and although I haven't measured fuel press under WOT, I believe fuel consumption at lower RPM and low speed (<20MPH) won't probably need 2 pump full capacity.
I think I might ask to borrow 2 knock sensors, connect them to the harness but tyrap them somewhere near for a moment to see what the effect is (engine won't blow in a second or 2 I hope).
If engine does not stumble under (only 2 sec) WOT I know knocking of some sort is the issue, or something wrong with the sensors.
If still stumbling it will be something else. (intake temp signal corrupted etc.)

 

The XK8 has a 'snow mode' where it reduces the torque delivered to the wheels, which is triggered when it senses all four wheels moving at different speeds. That isn't quite the same thing as mis-sized tires but probably should be corrected anyway. And I what I recall is snow mode is a feature of the transmission (increases the amount of slip) so would not expect the engine symptoms.

An XK* that doesn't throw a ton of codes is suspicious to me. Has it ever logged a code?

 

Actually it is a real XKR so meaning it had lots of codes but besides a few coils, only codes until recently where caused by power on with stuff disconnected.
however...
2 weeks ago, after the car was stationary for a while (week) outside..
It gave all kind of codes and warnings.
ACC, Trac, ABS, Transmission, Restricted Engine performance, and even brake fluid level warning. (brake fluid was up to full)
I did not mention it here because I was SURE the old batery voltage driopping to 12.3 in 2 days was the culprit..
So I installed a new A-brand 100AH battery last week before jumping into this forum for this problem..

But unfortunately,
Today all of these ACC, Trac, ABS, Transmission, Restricted Engine performance, and even brake fluid level warning came back while driving. The battery was 12.88 even an hour after shut down.
So I am in probably in the ECU / Wiring ball park now? :-(?

The externally installed knock sensors had no influence on the Stumbling. (so restriction not caused by actual knock)
The discinnected rear ABS sensors no impact as well.

So either a spooky (large?) air leak, a weird injector problem (only when hitting the pedal?), or a ECU partly burned out/ wiring connections corroded. (Unable to provide higher frequency steering signals to coils or injectors?, or get corrupted sensor signals)
CRAP..

Ow yes, slight chance of and fuel pressure issue, with 2 operating pumps and 50 PSI pressure at 11 psi boost but without actual consumption happening.

Might be preparing for nice Christmas fire..

 

Mind blowing indeed!
I believe in EU we call it Sports mode ;-)?
We haven't got Snow modes over here at least not on the R's.
In the meantime I am sure tire size is not the issue.

Take care

 

One way to "even things out" a bit is to try running the tires that have a smaller rolling circumference than they should at their maximum recommended air inflation (e.g. 36 psi), and run the tires at the other end at the lowest recommended inflation (e.g. 30 psi).

With all of those warning lamps illuminated, there have to be diagnostic trouble codes stored. However, they may not be Powertrain codes (P-prefix). They may be Chassis (C-prefix), Body (B-prefix) or Network (U-prefix) codes. Standard OBDII scanners cannot read these non-Powertrain codes - it requires better grade of scan tool/diagnostic system or the dealer-level IDS/WDS system.

While I'm thinking about it, please visit your User Control Panel (User CP) and edit your signature to add the year, model and engine of your Jaguar so these details show up in all your posts. I had to scroll all the way back to your first post to be reminded.

Thanks!

Don

 

Thanks Don,

I have edited the signature. Haven't seen it work yet but it will get done.
Tire size issue has been eliminated from the equation in the mean time as the car even stumbles when car has no wheel speed sensors at the rear to get a signal. (just for testing)
I was advised to change the pulley to original by the best specialist around here (they come from a day distance to him for Jag issues). I
I just need to get to it and do the job and see what happens.
It's just that I can't understand that knock sensors are not the cause of the enige holding back, when the pulley is the cause.
But hey, I am no specialist so must obey:-) .

Now with all these electronic gremlins coming back, I think I need to dig in and disconnect the main engine connector and see what is going on in there..
Maybe crished during engine swop? Maybe water ingress? Who knows anything could be the reason. It could even be also the cause of stumbling as we well.
Next is then to also open up ECU and look for anomalies.

 

It would be useful to know more about what is causing the stumbling. Codes may help.

Here's what I say to myself when I'm stumped: It's going to be one of these four things: Fuel, air, spark or timing. That helps narrow down what to look at.

 

So true,

As said it had no codes when stumbling.
But now it many intermittent issues reported on dash text screen.
I had cleared he codes t be able to get home, and now it only shows P1638.

I checked the schemics and see that the warnings it gave seem all ABS computer related?
ACC, Trac, ABS, are all ABS computer related I think?
And the false brake fluid low level warning also runs over the ABS computer in schematics.
Then the transmission fail warning...If no wheelspeed id available (perhaps ABS comp inop at that time?) also may be caused by same problem?
But not sure, suggestions are welcome.

Still think the stumbling has another cause.
Another observation is: On OBD reader (Phone/ELM327) , the engine RPM signal sometimes spikes to 16 thousand RPM!!!...(While dail pointer in dash is stable)

I have a Icarsoft LR2 but doesn't connect to the car fully (just some seat modules etc, no ECU and TCM etc.) (can't seem to connect to 9141 using protocol)Electronic issues are the worst

 

Still planning for a whole weekend of wrenching:-)..but not luck so far finding time.
Have cleaned grounds in engine bay area in the mean time, and disconnected connectors to all units and fuse boxes for inspection in that area.
Car has no codes now. P1638 is gone (but who knows for how long)
Next is instrument cluster and transmission tunnel for wiring check.

Here is the plan to get somewhere with the stumbling under wot.
My own fuel pressure gauge is on order and will get here this week, so I want to check fuel press unser WOT. (Static fuel press was ok and regulator responds to boost pressure.)
If that is correct I want to try investigating the charge cooler system. I discovered that the whining of the charge cooler pump gets different after a minute or so and it seems to just quit or at least not pump anymore at some stage.
OBD indicates inlet temp (coming from intercooler sensor) at 50 degrees Celsius (122F!!) which does probably result in ignition being retarded (!!) towards low value (what I see actually happening on ELM327)
Ignition retarding seems not caused by actual knock sensor activation.
The external knock sensors I connected to find out if the engine was actually knocking dit not result in a difference, still stumbling under WOT, still retarding ignition timing, no spark knock audible.
So charge air temp seems reason for ignition being retarded. (Other theoretical reasons could be TRAC intervention, and Transmission intervention, but both more or less ruled out)
Specialist was right to advise put original pulley on as this will give less heat (10% less charger RPM). At that time however the cooler pump did not stop working and was therefore not suspected.
Flushing the cooler system and installing a better pump could also be a nice try to get some improvement, is a good improvement anyways. (and can always go back to stock pulley)
So I got a Bosch pump, it came from an AMG (cheap, like I am:-)), the one with higher flow (010)

Step 1: Upgrade charge cooler pump and flush system.
Step 2: Replace Supercharger with one having stock pulley (Or if pump replacements helps, install my other charger anyway because bearings of installed charger are pretty noisy, and probably generate lots of heat as well...might then still use small pulley snout)
During this step while its open:
+ Get out the injectors and have them checked/cleaned.
+ New plugs for peace of mind.
+ Remove the large engine harness connector and inspect/clean connections.
Step 3: Get and install working cat-converters (I rather empty them but guess ECU will not accept...would like to drive without these restrictors s I plan to visit a few tracks to play arround when I get this all working. Can we fool ECU to avoid downstream sensors alerting? Tricks to pass MOT?
Step 4: If still not solved, put a cloth down the fuel tank opening and light it. (Take car outside the garage before this step)
No, Step 4 is to sell all luxury item from the car, the trans, the diff, and all boxes and put in a manual (S-Type 2,7D) in and a standalone ecu. but still think that is a waste of a nice car....

 

Most cars, the XK8 and almost certainly the XKR, have a special WOT mode that switches to a separate set of fuel maps, transmission programs and more. If there was damage to that separate and special programming, you would see it only under WOT.

In the XK8, there is an actual button under the throttle pedal.

If you disable that button, does it still stumble?

 

Thanks! Nice info!
Yes it happens already before button activation (kickdownswitch?)
The more the engine warms up the worse it gets (and earlier in throttle travel)
But when I stamp it to floor, it picks up somewhat better and the higher RPM makes the more it flies. (But flooring it under stumbling condition feels like I am willingly destroying the Engine..)

So maybe not in line of intended thought about WOT fuel map being the problem, but it can still help to find distinction for finding causes.

Will het there...

 

Slowly digging into the engine bay...
Main engine harness connector made accessible and disconnected.
Suspected water ingress confirmed. Not much but moisture consealed within connector housing environmental sealing...but stil...


Could have caused RPM signal spiking to 16000rpm, and high Charge temp signal even, and many other unpredictable gremlins..
Still not sure as I can't test now. Wil dig in further to remover Charger and intercoolers, even Cat-converters as access is a bit easier when some under-hood parts have moved to the trunk now😉

 

Not sure if I can help here, haven't read everything here as well, so apology if I ask things that have already been done.
Stumbling isn't good of course, so to have that under load is dangerous, so be careful not to do to much of these test runs.
I would 1st ensure that the MAF is good, is it an original one you have replaced it with?
Next have you measured the pressure after the supercharger? What where the results under full load?
Then just as important, what is the actual fuel pressure? It needs to be 43 psi + the air pressure as above, can you make that measurement?
Did you swap original coils, and are you sure they where good?

What makes you think the ECU is retarding the ignition?

 

Thanks Avos,

I would 1st ensure that the MAF is good, is it an original one you have replaced it with? --> it was a denso (correct P/N) but it gave only 250g/s value at WOT / high RPM. I replaced with non original MAF that now gives 350 g/s under same conditions. Stumbling was the same before and after.
Next have you measured the pressure after the supercharger? What where the results under full load? --> No I haven't measured. I do have 10% pulley upgrade btw. I took off the SC yesterday, also to get to the injectors, found a seal at the SC to IC plenum (lid) that was not perfectly seated (one of the round ones on top. Can't imagine this was a creating huge leak though)
Then just as important, what is the actual fuel pressure? It needs to be 43 psi + the air pressure as above, can you make that measurement? --> I have measured Fuel Press and it was around 40psi and it raised when applying air pressure to the regulator (up to ~50 psi max) Later I planned to measure while driving under actual WOT but never I came that far because my new measuring tool was not suitable fro the pressure range...(But it makes flow checked at disconnected filter housing, and pressure when no fuel being used..)
Did you swap original coils, and are you sure they where good? --> I did have some misfire issues last year. but replaced a few coils and no codes ever since. The engine runs really smooth when idle and even runs smooth when driving being real easy on the throttle.

What makes you think the ECU is retarding the ignition? -->When starting to stumble I see ignition advance dropping on ELM327. Can even hear it "burble"(;-)) from exhaust note when it happens. Short term left and right FT goes to 0% at instant. (also with external KS)

Stumbling not only under WOT but the hotter the earlier in throttle travel.
I am looking for IC heat issue also..
Was advised to take 10% pulley off te solve the issue. ( I will do it but causes little heart ache)

Thanks a lot!
I jumped in this older thread from post 12 onwards

 

Ok, non jaguar MAF is not something I feel comfortable with in the sense that you can tick the box for sure if you see what I mean. 350ish is more then normal iirc, but am not sure what you should get with your setup.

It would be good to know the air pressure, best is to measure it, as that will help to understand as well if the fuel pressure is correct.

At full load (so top rpm), if the fuel pressure is 43 psi + the air pressure measured, you can be assured that there is enough fuel flow. Now you still can't, so another tick that can't be placed in the box.

I have had on several occasions a bad coil, that caused exactly the same issues you describe, though it is not the only possible cause of course. At light load (and idle) the engine was running perfect, but as soon as you put serious load on the engine, it would stumble. I was pretty surprised that just 1 cylinder could cause so much power loss.
Coils can degrade in such a way that under heavy load they do not perform correct anymore.

I use a coil tester, with that I can check each coil under idle and by the performance shown know which one isn't correct:
https://www.jaguarforums.com/forum/j...tester-143357/

So if you don't know that all COPs are working as they should, you could still have a faulty one.

 

Thanks again,

MAF:
I still have the Denso, can change back any time to rule it out off course. My setup is AJ-27S with 10% pulley and 3" alloy inlet tube and "open" cone filter (alibaba quality...filter just keeps mosquito's out.)
Question: Is MAF wiring plain wire? or Chromel Alumel wiring? PO had it spliced for some idiot reason.
I also have replaced crank sensor, because RPM signal spiked to 16000RPM randomly which would trigger rev limiter I guess (RPM spiking only is visible on ELM once in while) Now I am assigning that problem to moisture in engine connector.

AIR Press:
I will check air pressure once all is assembled back together.
Now need to have injectors cleaned as they are out now and some were dripping after shut down. So brittle they are, I screwed up a few...! And 1 had been burned a bit on the tip from the PO drove with a valve seat dropped..(Injector on that cilinder now looks charred)
I wonder, can stock ECU mapping cope with higher cc injectors? (I now have stock blue injectors = 360cc I believe. They are just too expensive, and I expect to need 2 or 3.... Wanted to get a set of 550CC side feed injectors instead (cheap, just other connector)

COP:
Coils,...I wish I had COP tester but I don't...
COPs are all not original. I am also planning to put new plugs in. They are standard ones with now 0.9mm gap, which I believe /expect is right.
I have no oil in spark wells.
With Covid, and it not being summer I also can't offer you to stop by for a beach holiday in Prov. Zeeland:-)....and bargain you into bringing the COP tester along:-)..

Nice car:-):
And next to that, P1638...with a lot of fault messages leading to suspecting databus being interrupted somewhere...(The moist engine plug has no databus in it I believe, could be anything. Removing ACC radar connector gives exact same effect in fault messages, incl the brake fluid low msg.)
Icarsoft refusing to connect. ELM does.

I have this car to have somethin to wrench on, and to learn. Luckily not to drive with a destination purpose:-).

 

MAF:
Its normally wired, as long as you have almost 0% ltft+stft trims it would not have the highest prio imo for now.
The RPM is odd, am not familiar with something lie that.

Air Pres:
To change the injectors you would either need to re-program the ECU (not likely to find someone), or change to a MAF that provides than the right signal e.g. ProM 92. You don;t need higher flow injectors though, there is enough room with your setup.
Cleaning them is good anyway, after so many years of usage.

COP:
I live relatively close, with the right briberies I might be able to test your car, however for now with Covid and restriction of movement....
(PS you live then also close to G&G, excellent mechanics, have you ever checked with them about your problem?)

Nice C:
Do you also get the P1638 without the icarsoft? I can remember that some odb2 could trigger a can error.

 

Thanks Avos,
RPM thing is odd indeed. Hopefully solved by drying out connectors and cleaning up grounds etc.
Will keep the stock injectors, will ask G&G for some used ones to suit by "hobby" budget:-).
Will think of some briberies...My car was well driveable when behaving as granny... Thanks for considering! Will keep this in mind once all is back assembled and still no luck;-).

I know G&G well (who doesn't) and have been there for advice and with my previous XKR I was allowed borrow all tools for gasket change (for free!). Each time I step in there I am amazed by their skills and service.
That is where I got the advice to remove 10% pulley and go back to stock., which I am in the process of doing now.
I was just surprised that my KS hack did not reveal actual spark knock. So power must have been limited by too high Charge temp....(Trans and Trac ruled out)
I have learned that sometimes just follow advice of specialist even if you do not understand. (have some trouble with understanding:-) so will ask when stopping by for injectors, I just don't want to waste their time too much as it is an actual business. (and for me it is like collecting poststamps (lol), take my mind off other things)
Would have loved to keep 10% pulley though..

Have now the bigger SC pump installed (old one whined irregularly) and flushed the SC radiator. (doing lots at once now, I know not good for fault finding...but now it is apart anyway
Before re-assembly of the whole, I will take cat-converters out as well. I don't trust them until I can look inside from manifold side.

P1638 also happens without OBD reader plugged in.

Thanks again

 

No need to take the 10% pulley off, but I understand the reasoning of course from a shop like G&G, you want to spend your time wisely and addons/changes from stock add complexity and makes troubleshooting more difficult because of the unknows.

But its not the pulley, except a little higher flow/air pressure might aggravate an issue, that's it.

Sorry, not sure what you mean with power limitation, is that the stumbling you mean, or was there another issue before?
The ignition shown by the ECU is just for 1 cylinder, so not a way to check if there is a retard or not, especially not due to the low updates on a ODB2 device compared to the revs. Hence my question why you thought the ECU was retarding the timing.
There are checks on the IAT2 sensor, so as long as the intercoolers feel cool after a drive with engine still running, that should have been ok.

Fully understand the DIY part, that is how I started with my car and know it now pretty well now ;-)