My first time on this forum but I have to give everything a shot.

2001 Jaguar XK8 lhd

I am a professional Jaguar mechanic and I am stuck.

Heres the story. I did a head gasket on this car due to a valve seat that dropped from the head causing the valve not to return all the way.

First time (yes I said first time) I did this cylinder head (Right bank) I replaced timing chains, tensioners, rails, obvious gaskets, seals, etc..
I used an aftermarket head gasket set. When I reassembled the engine I started it and it seemed to run fine. The second time I started it, the check engine light came on. The codes I retrieved were

P0301- Cyl A1 mis
P0302... A2 mis
P0303...
P0304...
P0300- random misfire detected
P1316- Misfire rate excess emissions

These codes were retrieved using a fully updated Autologic unit. So I ran all the normal checks. My compression was about 35-50 psi lower on the right than the left. So I took it all back apart, used an OE head gasket, and put it all back together. Same codes. I have eliminated, compression, ignition, fuel injector spray pattern, crank sensor, air flow meter, VVT assemblies on both banks, cam sensors, timing chain related components, fuel pressure, vaccuum leaks, and an ECM.

Parts installed other than the obvious:

Crank Sensor
R&R ECM from another car in my shop and reprogrammed
ALL t/c components are the updated parts
All new ignition coils, and plugs

Info that might help:

The computer (does not matter which one of the 2) is reading STFT as Long term fuel trim and vise versa (i have never heard of this happening before)

Exhaust reading at idle for right bank "HC-9ppm CO-.07% CO2-14.8% O2- 0.1% NOX-52ppm)
Right bank at 2500 rpm (HC-6ppm CO-.01% CO2-15.5% O2-0.0% NOX-47ppm)

Left bank idle (HC-15ppm CO-.02% CO2-14.0% O2-3.2% NOX- 217ppm)
@ 2500 rpm (HC-5ppm CO-.00% CO2- 15.5% O2 .1% NOX-177ppm)

Kind of seems like an exhaust or vacuum leak on the LEFT bank. But there isnt one, and the misfire is definatly the right hand bank. It is an EXTREMELY slight misfire, you can hardly tell its there unless you do a lot of work on these 4.0 V8 motors.

Please tell me there is someone out there that has ANY clue as to what this might be. Thanks for looking.

Dan

 

This is way above me (and I suspect most of us - hence no replies!) but could it be the re-programmed ECU - in other words the figures you're getting are not real?

 

being you had the head off and are you a Professional JAGUAR mechanic? Reason I ask is IF you didnt get the chain slack on the correct side of the tensioner, when you start the cam timing will be off for the bank and youll get misfires and rough idle just for that bank. go check the flats are correct side to side between both cams and the crank sensor, and its slot in the flexplate. Also did you replace the offending valves? Ive never seen straight valves when that type damage happens

 

There you go, Brutal is to Jaguars what the Stig is to Top Gear so do what he says !!
(I bet it's the ECU though )

 

thanks for the shots guys, but I know the cam timing is perfect I have done the cyl. head twice, the damaged seat was removed and replaced, all valves were lapped and properly set. Both ECM are reacting the same way, with the same misfires.

 

Ide run a leak down check now, especially if your that far down on compression for a bank. Its going some where, intake, exhaust or past the rings.

 

My WAG would be a grounding issue: Check and clean the ignition coil and ECM grounds.

 

I hope I don't offend you by asking a stupid question, but is the head surface flat?

 

Head surface was machined, 1 valve was replaced, all valve guides were replaced, 1 valve seat was replaced, all other valve seats ground and lapped. Compression was low on the first install because it was far thicker than OE gasket, Upon re-installation I used an OES Genuine gasket. This fixed the compression issue, leakdown test shows these readings

Cyl 1: 5%
Cyl 2: 5%
Cyl 3: 5%
Cyl 4: 8% (this cylinder has an oversized valve seat. Enigine is holding compression, loses the extra 3% into intake.)

Misfire is random across these 4 cylinders.

Brutal- In answer to your question, I am a professional JAGUAR mechanic. I have done these jobs multiple times, did the proper procedure as usual. Unfortunately because this car was serviced at the dealership until it came to my shop, with this valve seat problem, I don't know of any running concerns before this problem occurred.

 

Be patient guys. Between the two of you you'll find it and we all want to know what it is.

EZDriver

 

That's a little wierd, compression is off alot, leakdown is not. Difference is whether or not the engine is turning. I would immediately think valve timing, but you've checked and rechecked, plus you're a Jag tech who has done this many times ( as am I, Brutal, and others here on this board). So I have to assume valve timing is fine. STFT and LTFT being swapped is also pretty wierd, how do they compare right to left?

Edit change: I just reread your previous and realized you fixed the commpression problem.

 

The exhaust readings on the left identify as a lean misfire. High O2 readings and high NOX readings. The LTFT on the left bank is +19.8

The exhaust readings on the right bank look perfect. LTFT on this bank is reading -4.1.

STFT on both banks is 0.0

And of course they are swapped.

The readings did not change when I swapped computers from another car
(both have AJ27 engines, though the computer came from an XJ8. Both cars, swapping computers did not change the running or FT values on either car.)

 

I'm in the same ballpark as White XKR. If what he said checks out, I'd also carefully inspect the wiring harness to the coils. If it was bent back out of the way, even carefully, some of the wires may be damaged. Ten plus years under the hood takes it's toll on everything. Hate to sound simplistic but even the chance of sparkplugs being freshend up on reassembly and not quite correct (heat range, gap,make) should not be overlooked.
Other than electrical the only thing across that bank that comes to mind which may lean out things is intake manifold gasket leakage. Any chance they're not off quality as the first head gasket? Hell'uva puzzle, & sincerely the best of luck.
Cheers
TheCounty

 

I had a weird problem similar to this that turned out to be O2 sensors swapped. B1S1 went to the B2S1 harness and vice versa. It's a long shot, but who knows?

 

if the upstreams are swapped you would get the ecu reading a bank as rich when its not and leaning it which would be the other bank instead it would just make the issue worse and worse. Ide swap upstream o2 and see what happens, if the issue moves with swap. But first do a hard reboot of the battery to erase LTFT. Remember if you dont the ecu will never be able to adapt faster than old parameters screw it up even more. Make sure you start off with cleared LTFT.
@+19 thats a big lean which will misfire.
those are low(really good leakdown rates, better than my race car with total seal gapless rings)
BUt for ***** and grins. swap out the MAFS from the other car. Ive never looked into why, but over the yrs have gotten lean or rich single bank codes and it was the MAFS.
another thing Ive seen on this issue is a dropped intake seat and customer drove with it firing into the intake and it melted/blew a small hole in the bottom of the plastic intake that we didnt see creating a rough idle and lean engine. And one that warped the intake manifold flange from overheating. Also the NUMBER ! reason for a dropped seat especially the exaust in the rear cylinders is running thew car too hot too long when overheating. And or letting a coolant leak go which creates air pockets in the cooling system. Engine doesnt show it was overheating but it is in localized spots. Hope some of these outloud thought help

 

+1 to what Brutal said about MAFS. I had left bank showing lean as a result of bad MAF once. Of course, the MAF was the last thing I troubleshot. Cleaning it multiple times had little effect, but replacing it solved everything. If you have the ability to switch it out, given that it can be done so easily and quickly, do.

 

Of all the parts installed but,

New plugs, new coils, new intake gaskets

Idle is at 650

MAF already changed

checked signal, power, and ground at ignition coils. They have a single power supply for all 8, they are signaling properly, ground is good.

The O2 sensors- this car had a rebuilt transmission installed at another shop. Paint looks new on it. Since they had to remove the catalysts to take the trans out, swapped wires would be possible, but the harness isnt long enough to reach the other side. But what the hell I said i would try anything so I will swap them and see what happens.

 

swapping the O2 sensors to the opposite harnesses did a couple things.

The STFT and LTFT started reacting going to -25 on one side and +25 on the other. It leveled out in about 1-2 minutes. Then as the car warmed up it started going to max again one side max rich other lean. car was misfiring on every cylinder randomly. So it was not a swapped harness issue.

Another weird thing is if I disconnect the PCV hose to the left bank, (the one that runs under the manifold that I am sure we have all broken at least once) the O2 sensors react to the vacuum leak, but the ECM does NOT add fuel. Sooooooo wtf?

 

Bearing in mind that I am not in any way an expert

Have two coffees, a cigarette and a beer.

Then ..

Make it a rule for this job to do a ECU reset after each step as advised above so that you get true baseline readings on fuel trim without prior adaptations getting in the way.

Is this from a DVM or a code reader? If from a DVM, it is a stronger possibility, but either way ...

requalify all of the O2S sensors and related wiring harness.

The wiring diagram(X308) shows a "O2S HEATER RELAY" that is not really mentioned often, but it is going to have an effect on the sensors as the system warms up. So, it would pay to check this circuit for the sake of completeness.

The line of thinking from your opening post was "faulty sensing is driving the system into over compensation on a logical level and causing a physical misfire".

Bear in mind that the above could be completely wrong headed.

 

!