It was said TWO countries away. Guatemala.

But yes, I did exaggerate a little bit on that first statement.

 

I also thought the cat would be a likely suspect but I checked for a block by doing temperature checks before and after. The cat is working as the temps were between 40 and 100F higher after going thru the cat. The RH side numbers were very similar to the left side.
The O2 sensor doesn't seem a likely candidate because the sensor (apparently) doesn't play a big role in the warm up phase anyway. (someone correct me if I'm wrong about that).
Spark plugs and coils have been eliminated.
Re: fuel pressure. Isn't the fuel pressure common to both sides? Why would low (or high) fuel pressure only affect one side? Unless you think it's because the RH side is farthest from the pump.
Re: Injector electrical harness. By the time I get down to access that I might as well replace the injectors on that side.
Now, a quick confession, I did acquire the car with a mouse nest in the LH fender and did find a couple of wires under the engine fuse box had been nibbled. In particular, the wire to the cigar lighter relay had been broken. But everything else looked intact. And if it was a dodgy wire, then it has to be a poor contact that is only poor when cold. Also unlikely.

 

I had very similar situation. 112,000 miles.
changed plugs. 2 not burning gas. Had to change a pump - C2C 1314. Found bolts on supercharger loose. Now runs very well. 2008 XKR.

 

I got readings to check out how the MAF sensors were doing from cold. Both sides seem to be within proper range but the right side was 25% less than the left.
The numbers rose with increased rpm but the differential stayed about the same. The left always reading greater flow.
Airflow at idle:
Left: 5.6 gram/sec
Right: 4.9 gram/sec

I also read the short term fuel trims for each bank from cold. Left side was normal but right side was pegged at -25%. So it was trying to DECREASE the amount of fuel going in.
However after a few minutes (I presume the engine had warmed up enough to go into closed loop and start using the Ox sensor reading) the value suddenly flipped to normal readings oscillating around +3 and -3%

Fuel pressure was 55psi

Not sure what to make of that except, whatever the computer was using to set the open loop trim values for the right bank was indicating that it should scale the fuel way back. What factors does it use to set fuel trim on open loop? I was thinking it uses the MAF value, temp and pressure and it's own internal mapping tables. That's why I checked the MAF readings.

 

Check the pump C2C 1314 and supercharger flange bolts. I had some symptoms of reduced forced power.

 

What connection does a coolant pump have to a misfire? I understand if the supercharger were loose that would be bad. If it's loose could I move it just by prying on it? I just tried that with no affect. I presume you mean the silver box is loose between the two silver supercharger coolers?

 

The coolant pump failure caused overheating of supercharger hence automatic performance reduction, safe mode. Spark plugs-misfire.

 

It’s a very interesting problem to solve, and I exerience a very similiar one with my STR... The only difference is I had a bad injector on cylinder 7 and a P0207 code for that from the very beginning (I bought the STR in that condition) as well as P0300 P0301 P0305 P0307 P0316 P1313. I tested the injector with a multimeter and it was toast. Supercharger out, used injector 7 installed, all injectors bench tested prior to install. All new gaskets and new intake elbow to brake booster notorious fitting. Random misfires, check engine, restricted perfomance and catalyst damage still in place. LTFT bank 1 at +20%, bank 2 at +5%. Audible vacuum leak where the PCV vent valve is located. Silicone sealant, replacement PCV didn’t help to sort that out, still have to smoke test for vacuum leaks. But misfires are gone. Now I only have P0171 wich is no surprise with those LTFT trims. Fuel rail pressure at 429 kpa, MAF 5.62 g/sec (there’s only one on STR). All that makes me think it’s the upstream air/fuel sensor (yes, those are not O2 but more complex air/fuel ones). My plan is to test upstream sensors (one way is to swap bank1 and bank 2 connectors and look for if lean condition goes to the other bank), clean/replace shoud need be, and smoke test for vacuum leaks. Common sence tells me that only having one bad upstream sensor on one bank could result in lean condition on one bank and not the other given I had injectors tested, all 8 cylinders show compression within specs (155-170psi), normal fuel pressure, normal MAF reading, functioning ECU and circuits, good coils (tested by exchanging between cylinders), new NGK spark plugs.

 

The O2 i.e. air fuel sensor does play a significant role in managing fuel trims after it heats up and kicks in (closed loop). You are correct in that it’s reading is not taken into account by ECU (open loop) until it’s in operating temp range but it takes the sensor about 30 secs to reach operating temp as it has a built in heater and doesn’t need the engine to reach the operating temp

 

I ran some more tests on Saturday in between spreading mulch (on the flower beds, not on the Jag).
Air flow on the RH side was 25% less than the left. So I swapped over the MAF sensors left to right to see if the sensors were misreading. Observed no difference, i.e. the right side had a more restrictive air flow than the left. So then I removed the air filter on the RH side. AIr flow dramatically increased to 2.5 times that of the LH side. But, despite all that, the car still misfired on the right bank and the short term fuel trim was still -25% at idle. Conclusion: Even with plenty of air, the computer is still sensing it's way too rich on the right side and trying to cut it back.

I also noticed that the big negative short term fuel trim was happening even after we went in to closed loop. If I brought the revs up it would eventually straighten out and come down to -5% or so.
Next step is a bit unclear. I have to assume that several injectors are bad on the right side, perhaps not spraying properly and that it's just coincidence that 3 or so are bad on the same bank OR the upstream oxygen sensor is bad and stuck at .9v giving the computer a false rich reading. Seems unlikely. My scanner has voltage readings for Ox sensor 2 but I don't see the listing for the upstream sensor. There something called "Commanded Lambda ratio" or something like that.

The scanner pics for the air flow is with the RH air filter removed.

 

I would have suggested the rt MAF sensor until you swapped them. Now I agree with others that you might be looking at a stuck/leaking injector which is making the right bank run rich and the ecu accordingly trying to compensate but reducing fuel flow. A lean condition on cold start would definately lead to rough running.

 

And now for a little more of the story, in hopes that someone else can help finish it:

There are a couple of other things going on with the car that might be related.
1. Coolant level is going down with no signs of a leak
2. From cold, there is too much white smoke coming out the exhaust - more so from the right side.
3. My new plugs on the right bank already have a chalky white deposit on the outside electrode.

The compression on all cylinders is fine. The white smoke doesn't really smell of antifreeze.
Here's my theory: There is a slow coolant leak inside the EGR valve or the Charge AIr Intercooler or the Throttle body (I think it has coolant)
The most likely would be the intercooler because my problem is sided, i.e. it is messing up the right side. And I don't thing the EGR valve only feeds the right intake side (does it?)
Anyway, so overnight a slow drip of coolant gets into the intake. From cold we have coolant and steam in the cylinders, hence the misfire and once the car warms up, the coolant burns off and at higher revs it's not so interfering.

So, does anyone know of cases where the charge air intercooler or the EGR valve leaked?

I can remove the EGR and test it, but the for the intercooler I have to remove the supercharger . Of course, the supercharger also sounds like its rolling marbles around when it starts from cold, so maybe I'll be forced to do that as well. Gosh, this stuff never ends!
Mark

 

On the charge cooler leaking, if ALL of the plugs on one bank are showing evidence of water in the combustion chamber, you might be on to something . If it is limited to just a couple plugs, head gasket is the likely problem.

 

I took the car to register it on Tuesday. 5 miles from my house there was a sudden burst of steam from the right front of the hood followed by a stream of red coolant over the corner of the windshield. I immediately turned around and drove home . . . ha ha ha, no sir! No, I parked miserably by the side of the road unable to see where this massive leak had come from.
A couple of hours later and after paying an expensive tow truck I was back in my garage. The top radiator hose has a T junction with two silver metal bands around it. The hose had simply separated from the T!! Really? What's wrong with a moulded piece or real screw clamps? My departed Audi S8 is looking really attractive right now.

So, now that the car had automatically drained the coolant for me, I started on removing the supercharger. Once I had the EGR out I smoke tested the coolant channel for leaks. Nothing. I then fed smoke into the coolant lines of the charge cooler and watched for leaks into the manifold. Nothing. So there goes that theory.
There's lots of inaccessible bolts to get the supercharger out so it's still in progress. Once it's out I'll work on a way to get the bearings replaced and then take a look at the fuel injectors.
Meanwhile, I'll guess I'll run a leak down test on the right bank to see if there's any head gasket of cracked head problem. (That the compression test didn't pick up.)

I'm not sure what my new theory for the right bank misfire now is:
1 Bad fuel injectors affecting the firing on adjacent cylinders?
2 Blown head gasket not shown by a compression test.
3 Mouse chewed through ground wire for right bank that makes better contact as the car warms up? (yeh, right!)

 

There is a thread in the DIY sticky: Valley hose replacement that has a great rundown on how to get access to the SC for removal. Great time to change the valley hose and your SC oil, provided you can get to the bottom of your original problem.

 

The supercharger is out and I'm waiting on getting a press to put all the new bearings and oil in.
The injectors are all off to Jim at Injector Repair in New York so meanwhile . . .
I ran a leak-down test on 6 of the cylinders and only one passed the test.

On all the rest air was leaking big time around the inlet valves! What the hec? (I can't see what the exhaust valves are doing)
This makes no sense. Why would all the valves suddenly stop sealing? Totally confused why this is the case. Could it be that as I pulled out all the injectors and disconnect the inlet stuff, that dirt drops down around the valve faces and then they don't seal? On one cylinder I tried using compressed air to blow the sealing faces clean but it had no effect.

On cylinder number 7 (on the bad misfiring bank) I also could hear air bubbling and coming out one of the disconnected coolant pipes!!

OK, I can understand the coolant bubbling if the head gasket is bust, but what I can't understand is why all the rest of the valves are not sealing? I basically rotated the engine with a stick in the spark plug hole and waited until the stick reached its highest point. I then checked the inlet valves were closed and assumed we were at TDC for the cylinder. I even tried 20 or 30 degrees either side to see if that made a difference.

I dribbled oil down around the back of a couple of inlet valves and watched the compressed air bubble out.

So really confused now and don't know how to interpret anything.
And all this from a misfire when cold on the right cylinder bank.

 

FYI ... I thought this might be helpful, about identifying cracked heads and blown head gaskets.
https://www.hagerty.com/media/opinio...urday_RoadTrip

 

Thanks for the link. They mention in that link that a crack in the head can often close up once the engine gets hot and that's why it's worse from cold. These symptoms fit my car very closely.
I think there's nothing for it now but to remove the head and inspect. And since the LH head inlet valves are not sealing either I'm guessing there might be heat related damage there too. So now there's a ton of work ahead and it's a bit disheartening.
Anyone know of a cylinder head removal DIY? I have the workshop manual, but it's not quite like having someone list out the steps.
It looks like the hood has to come off in order to get decent access to remove the front engine covers. At least the supercharger is already out.

Mark

 

At the moment I'm regretting my decision to remove the heads, but the alternative was to sell it as it was and take a big loss, so for now here's what happens when you begin stripping down to remove the heads:
I already had the supercharger out to replace the bearings so taking off the valve covers was quite easy and I'm replacing the hoses that lie in the V valley even though they look quite good.
To get the heads off you have to remove the front engine cover. To do that you have to remove the hood, the cross-bar support. the fan shroud, the crankshaft pulley, the P/S pump. the A/C compressor and all the other pulleys and idlers on the front. This is a lot of work!
The crankshaft pulley had me stuck for quite a while. It needs the special tool to hold the pulley and then the puller to pull it off.
I eventually used an old serpentine belt wrapped around the pulley and then around a 2x4 which was twisted up tight under the engine. Amazingly this actually holds it and together with a long steel pipe the bolt comes out. I used an Ares harmonic balancer puller with some longer M8 bolts to finally get the pulley off but it was a struggle.
The P/S pump and the A/C compressor are near impossible to get at, squashed between the body and the engine body. There's hardly any help from below because the sway bar and sub-frame obstruct everything. The long bottom bolt on the A/c compressor won't come out because it hits the frame and only when you jack the engine up a little and twist the compressor will it finally come free. And then you have to get the support brackets out from behind it for both the pump and the compressor. All this involves dripping power steering fluid, coolant and evacuating the A/C. And all the time I haven't even got as far as de-tensioning the chains to get the camshafts off. More and more it feels like, removing the engine might have been a faster way to go but maybe someone with experience can verify that.
So I'm about to undo the bolts on the front cover.
It's only take 3 weeks to get this far!!

 

For anyone still following this saga -
I finally removed just the right hand cylinder head this evening.

Before I unbolted it, with both camshafts out, I re-ran the leak down test. i.e All valves should have been closed.
From left to right (front) cylinders 7, 5, 3, 1
With cylinders 7 and 5 the compressed air bubbles into the coolant channels (I could hear it)
Cylinder 3 was also leaking, about 50% loss, I think through the valves not closing fully.
Cylinder 1 passed the test (less than 10% leakage) and was good.

There’s no visible breaks in the head gasket.
In the photos I have simply wiped the gunk off the surfaces but not cleaned them up yet.
There’s brown burn marks from cylinder 5 into the coolant channel and possibly from 7 into 5 or maybe to a coolant channel too.

I did a quick straight edge check on the head surface and it didn’t seem warped but maybe I need to get a lot more sophisticated and careful about that test.
So it looks like there has been leakage between the gasket and the nearest block coolant channels on cylinders 5 and 7.
Why that has happened, I don't know. the car was misfiring from cold before it went all the way from Virginia to Florida and back.
Maybe I'll clean up the head and see a crack right there but for now it's not obvious.
Those head bolt are very tight. It was quite a work out to undo them. I was scared I might strip the head of the bolt but they let loose with an initial crack and then a subsequent double crack on almost everyone.



Here’s photos of the RH, gasket, head and block.