I have started a new thread as getting no response to my old one. The problem is a lean burn misfire when going uphill, the car starts, idles and runs round town and on the motorway no problem, but as soon as I go up a hill it misfires and the CEL blinks so I ease off and it stops.
Work done so far after reading lots of threads on this problem, new Jaguar plugs, new coils, upper and lower manifold O rings, VVT and throttle body O rings, checked for leaks around booster and breather hoses. I have measured the earth wire on each coil plug back to battery negative and they have zero resistance.
I get random misfire on cyl 2,4,6, I think we can rule out airleaks as at idle when vacuum is high the fuel trims are spot on and same on both banks so that eliminates sensors common to both banks, i.e. Maf, Manifold pressure/temp, also the problem only happens at low vacuum i.e. when applying more throttle to keep the speed up going uphill. The only sensors unique to bank 2 are the O2 sensors and those are both brand new today. Cruising at 50 mph I get normal fuel trims on bank 1 and slightly negative on bank 2, when I accelerate the bank 2 short term trim goes negative to around -10 to -15 and longterm - 4 so its running with too little fuel on that bank. I began to wonder if I had a leaking injector that the ECU is trying to compensate for by cutting back the fuel on bank 2, however I have had the plugs out twice and they were all the same pale colour. I am running out of ideas now and having spent £500 so far I am reluctant to buy any more parts unless I know its going to cure the problem.
Any pointers much appreciated as I am getting very frustrated with this problem.

 

Blocked cat(s)?

 

That had crossed my mind, but the car will drive at motorway speeds as long as its flat and will rev to 4000 when first starting off, its just in higher gears it doesn’t like any increased throttle from cruising speed.

 

Too little oxygen (n the exhaust gas): air filter?

Is the 2.5L a direct injection engine? Or manifold injection engine? (Manifold injector cleaning is relatively cheap.)

Bank 1 and bank 2 mixed up?


Cheers, catfondler

 

The air filter is new, the V6 is manifold injection and I have run injector cleaner through it, its definitely bank 2 that is running lean from the colour of the plugs. Still a work in progress, I tested the cat on a 4 gas analyser and the values were spot on so the cat isn’t dead, but some have suggested it may be blocked but the car will do motorway speeds no problem. I have been working through the Jaguar workshop manual for lean mixture on bank 2 and it listed most of the sensors that are upstream of bank 2 as a possible cause so have a MAF on the way as a last resort before committing to replacing the cat if I can find one!

 

By the way: £ 500 isn't that much. - But it's also the parts cannon.

By the way (2): Pale spark plugs are normal with lambda control.

So you have the problem with becoming lean when cruising at 50 mph and when driving uphill.
And it affects the entire bank 2.

New lambda sensors can also be broken. Have you ever exchanged them from one to another (bank 1 <-> bank 2)?
Did you buy genuine Jaguar, Denso Direct Fit, universal, or no name? (Universal means generic here - not wideband.)

Do you observe the graphical curve of your lambda sensors live while driving?)

How is the fuel pressure regulation implemented? Two regulators on two injection rails? With vacuum control?
Did you check the bank 2 regulator?

Did you check the fuel pump / fuel pressure (while driving, too)?

What about a crack on the catalytic converter case or exhaust pipe?
Are the engine mounts ok? (Twisting of the drive train.)

A crack on the catalytic converter case could cause long term trim to positive, and a twist could close the crack, suddenly it's measured richer and regulated more lean.
Theoretically considered. (But you described long trims of -4...)

(Most things would rather make for enrichment. But think about it anyway. Especially fuel pressure.)

Cheers, catfondler

By the way: injector cleaning I ment with a test and cleaning device - no fuel additive. But clogged injectors are unlikely with random misfires on 2, 4, 6.

 

It's really strange: measure rich - make lean - too lean now.
Looks like a wrong measurement somehow.

What about exhaust gas recirculation?

catfondler

 

Thanks for suggestions, by the way £ 500 is a lot to spend when you didn’t plan to spend it and it hasn’t cured the problem!
Lambda sensors are new original Denso, I only use original or better on my cars.
only one pressure regulator on the fuel rail and it gives an electronic feedback signal to the fuel pump module, pressure is spot on under all conditions.
Engine mounts are fine.
I have driven many miles with my OBDII reader connected and the fuel trims are mostly negative the whole time on bank 2 while bank 1 has the normal fluctuations. I have also monitored all the other sensors while driving for anomolies.
Pretty sure there are no cracks on the converter or else where as the readings on the 4 gas analyser I used were spot on, and I have many years experience with gas diagnostics having sold over 400 of these machines to testing stations.
There is no exhaust gas recirculation on this engine.
It runs at fairly stable figures driving with the cruise control on, it only complains when I suddenly ask the engine to work harder as in overtaking or giving more gas to maintain speed climbing a gradient, as soon as I ease off or go back to level cruise its fine. Its just not getting that extra bit of fuel it needs to make more hp suddenly. It will go up to 70-80+ mph so I find it hard to believe the cat is blocked but who knows?
The official Jag diagnostics book under ‘lean mixture bank2’ lists all the common sensors as a possible cause also, I ran with the MAF disconnected and although I get the CEL light I don’t get the flashing misfire light when under load like before,so have a new MAF on the way as this seriously can affect the AFR.
Will keep you posted.

 

With a blocked cat you would see a bad monitor sensor signal on bank 2, don't you?

Dirty or old MAF sensors should show less air than is actually flowing through.
Could be a cause of general lean condition (decrease the amount of fuel).

Do you have an ambient temperature sensor? May be included in the fuel calculation. Does it show plausible values?

catfondler

 

Statement of the obvious: with annoying readings on just one bank it's hardly ever due to an item common to both banks.

Increased engine load as described tends to suggest a cat. conv. issue or possibly coils - but the latter normally give lean not rich issues.

 

Of course, but look what has already been checked and done.

Cat. conv.: he has a 4-gas-analyser. (But should check the monitor sensor signals, too.)
Coils: randomly 2, 4, 6? (Common ground problem?)

catfondler

 

Hi there, check to see if codes for the knock sensor are present.
A dramatic change showed up in my 02 x when it was replaced.

 

Just a thought to the collective intelligence out there....what would be the effect with Norcat's engine if an IMT was malfunctioning?

They are obviously there to alter intake performance to compensate for engine RPM and loading, conversely if one is not doing its job right could it be disrupting a single bank's performance to give rise to this type of behaviour?

 

Intake Manifold Tuning valve - very interesting. I didn't know this until now.

Perhaps a high potential candidate (like swirl flaps or variable-length intake manifold [I know from VW/Audi]).

Edit: Seem to be two of them: Thread IMT seals

catfondler

2006 X-Type 2.5 L V6:

 

They are a simple device. Driven with a PWM output from ECM but effectively that is just providing a variable DC input to the IMT.
They have a spring return force that the drive voltage overcomes depending on the voltage applied to the IMT.
IMT behaves like it has a gear reduction servo motor inside, as when drive voltage is abruptly removed the mechanical return is pretty responsive but not harshly abrupt.
I have bench run mine with a simple regulated DC power supply, and as you increase voltage to the IMT it has a proportional rotational response.
If I recall, I tested mine up to a drive voltage of around 7-8 volts which seemed to bring it to fully open. I think it took 2-3 volts to get it to start moving.

I don't know if a faulty (open circuit or jammed) IMT will lean out a bank, but it certainly would change the manifold performance in higher revs which might reflect poorly in some stats.

 

Well today I thought I had cracked it, after fitting the new MAF I did about 25 miles with no flashing CEL, then on a country road I hit the gas and it kicked down to 4th as if overtaking and the light began to flash. I was on the level with high revs so not under a big load like before going up hills. Really puzzled now as I hooked up the Icarsoft and looked at the fuel trims for the rest of the trip, the two banks are very close now without the huge negative numbers I had before on bank 2; in fact bank 1 which has never given any trouble had slightly more variance probably due to the O2 sensors being older. I still get random misfire on bank 2 but only cylinders 2 and 4, cyl 6 doesn’t show a fault now? I feel the engine hesitating before the light begins to flash and it feels like a good old fashioned misfire with a cylinder dropping out. I have tried 3 sets of coils on cyl 2,4,6 and 3 sets of plugs and checked the earth on each coil plug back to battery negative and they had zero resistance. I have never had a code for a coil.
Regarding the IMT’s I did wonder about those but the volume of air reaching the cylinders is the same just it goes a long path or short path which affects torque, I could try swapping them over.
I feel I am being pushed toward a converter, but firstly can’t find a supplier and all the gas readings say its working, but am afraid to lay out £6-700 on top of the £600 I have spent so far unless it gaurantees it will cure the problem.
I am going to try and disconnect the bank 2 injectors one at a time to see if it makes the same difference to the fuel trims to try to rule out a bad injector, also thought about briefly plugging in the good upper O2 sensor I have and seeing if the atmospheric O2 percentage of 21% makes the fuel trims go very positive.
Thanks for hanging in there with me, I appreciate the support, its very frustrating as I do diagnostic work most days on marine engines with more cylinders and hp than my Jag, and thought I had seen most faults over the years, but they don’t have converters.

 

I don't think unplugging the injectors is a good way to diagnose.

 

Well its definitely going the right way since I changed the MAF, it will drive for miles without the CEL coming on. It only does it when it kicks down from 5th to 4th and the revs are up around 3000, its blinks but as soon as it changes up or I back off it stops.The fuel trims at idle are almost identical on both banks and at 2500 the short term trims match going slightly positive and negative and the long term on bank 1 is about +8-9 and long term on bank2 about - 2 to 3. The bank 1 sensor 2 is the only one that hasn’t been replaced in the 7 yrs I have had the car so could be due for replacement as the 2 new sensors on bank 2 seem more agile in response. The other thing is its gone from random misfire on 2,4,6 to 2 and 4, and now just 2. Can it be recalibrating itself in the two days I have driven it since a new MAF?

 

Replacing of MAF sensor seems to be like replacing a battery due to incorrect resting consumption:
It changes something but doesn't remove the cause.

The (bank 2) monitor [!] sensor shouldn't change the mixture. So it should store a fault permanently (no blinking) for low efficiency if the cat converter is defective.
You can observe the monitor sensor. It's a voltage jump probe. It should show a rather flat wave near 450mV.

As far as I know, IMT does not change the air mass sucked in via the intake duct, but rather, via resonance effects, the filling of the cylinders with the air contained in the intake tract.

So basically different density of different air already contained in the intake tract.


I think a new MAF shows more air than an old used one, should be followed with more amount of fuel injection. -> You will notice less effects now.

Automatic mixture adjustment during two days: Why not?
The better way is to delete learned mixture adjustment values after a MAF (or O2 sensor) change.

Cheers, catfondler

 

Hi Catfondler, thanks for hanging in there with me. Today I zero’d the fuel trims and drove 15 miles town and country driving with my Icarsoft displaying all 4 fuel trims. When I accelerate gently from the lights bank 1 goes positive as you would expect but bank 2 went negative, this is around 1000 - 1500 rpm so I find it hard to think the cat if blocked can cause this seeing as there isn’t much exhaust flow at this speed and I have taken it up to 80 mph. At cruise the short term on bank2 was around 15 negative and on bank 1 2-5 positive, so its still seeing a lot of excess fuel or lack of oxygen. Could a leaking injector which would give low oxygen level in the exhaust make the ECU pull the fuel back enough on all 3 cylinders on bank 2 to cause this lean burn misfire I am experiencing. It can’t be an ignition fault as this would cause excess oxygen to be present and the ECU should compensate by going positive on fuel trims. In fact the only time I saw a slight positive trim on bank 2 was on over run when all the injectors should be turned off, but can deliver fuel if mechanically defect and leaking. Trouble is I gave no way of testing the injectors to see if one is leaking so it means I would have to replace all 3 to be sure. I am really digging deep here as the symptons can lead you in several directions, and I am trying to logically deduce what is actually happening, what do you think of my train of thought.