Gurus,

Sorry, this is LONG and DETAILED ...

I have been eliminating issues and codes after an initial issue popped up.

This is on my 2001 XJ8 X308 North American and Normally Aspirated, 106k miles VIN series F23776, no TSB's recorded anywhere
.
I bought this car at about 86k miles and it has always had intermittent restricted performance Bank 1 or Bank 2 too lean issues that would appear, then disappear for long periods, then reappear, mostly when driving at highway speeds over 75 mph for long periods of time or when filling the fuel tank. The restricted Performance mode was always the restriction of 3000 RPM and Bank 1/2 too lean codes alternatively, but I could never find any vacuum leaks using propane/carb cleaner/smoke and no obvious broken hoses or o-rings.

Here are the symptoms that finally forced the issue into deeper problem solving:

Driving down the interstate at 60-75 mph, (at around 106K miles) the engine seemed like it dropped 2 cylinders, loosing power, not accelerating. ECU went into Restricted Performance mode.

I hooked up Torque Pro, ECU was showing P1313/1316 and cylinder 5 P0305 and cylinder 8 P308 misfires, and injectors 5 and 8 disabled explaining the restricted performance.
We were close to our destination got to the parking garage and parked as we were going to be late for an appointment.
Upon returning a couple of hours later,I checked the codes, saved them, reset them, and the engine started, idled and accelerated fine, then the condition repeated after reaching normal engine temp and attempting highway speeds, but would come and go.
This time, only cylinder #5 misfire. I stopped at my son's house, swapped coil 5 with 3, reset the codes, misfire symptom remained but as a "general misfire" code and no cylinder #5 or #8, and not #3 as expected.
After carefully driving home, 3000 rpm limited only with general misfires, eventually there were codes for all 8 cylinders misfires, bank 1& 2 upstream sensors too lean etc. etc. all most likely caused by limp home mode being activated.

At first impression I was thinking the battery, it was after all, 6-7 years old. So I checked the battery and even though it was showing 12.6 volts and 14.6 with the engine running, I decided it was best to replace it before winter sets in. So a MAXX8 Everstart battery is the perfect spec and I have run it also in my 2000 XJ8, having 900 CCA slightly more than OE spec and it fits properly too.

Still having issues, thinking it might be throttle body or fuel, key on, engine off, pumped the throttle full range 3-6 times, key off, key on, engine start, and engine ran perfectly, then after a few miles or normal running, 1313 and general misfires, but no specific misfires. It seemed odd that that process would seem to correct the problem for a few miles then the 1313 and general misfires 0300 would come back with no specific cylinder - but 0305 did occasionally come and also disappear.

Starting on the low hanging fruit when I got home, I pulled all four connectors off the throttle body, gave a close inspection with a jewelers loop magnifying glass with high intensity light, and contacts were all dry and clean without corrosion and on the TPS, gold pin sockets, no pushed back pins as the pin keepers were also intact and not broken. So some contact cleaner in both sides, and some seat/reseat operations a few times to assure good connections Engine ran fine for a while with no codes, then bank 1 and 2 lean conditions, 1313 and 0300 general misfires. Not making any headway, I swapped Bank 1 Coils with bank 2 coils, and still 1313 and 0300 would return after a short run, but no acceleration issues on low to medium throttle until after 3-4 drive cycles.

Next thought was fuel pressure / flow, so fuel pressure gauge installed and yep, fuel pressure was going in and out of spec. So I replaced the old and stiff vacuum lines to both the fuel pressure regulator and the Emissions Purge, Fuel Rail pressure regulator and the fuel pressure was restored back to spec 38-44 PSI throttle/no throttle.
Perfect, that was supposedly one of the P0300 problems with no supporting cylinder issue and I was sure that would correct the problem ... wrong!

Next I would check the coil circuits, spark plugs, etc. With no firm misfire identified - only general P0300, I found the Spark plug gaps were way out of spec and electrodes looked crappy, - okay classic issue so a set or NGK Iridiums were ordered also on the list for P1313/0300 symptoms. Coils were actually rusty on the metal coil plates indicating there had been moisture in there, but no oil or water actually in the spark plug wells, the coils were not showing any heat / stress cracking of the potting materials, no arching or cracked boots, and no corrosion on the coil electrical connections, no apparent broken wires, no blown ECU fuses, and Relays were all swapped for other areas that would quickly demonstrate a bad relay - likes seats and seat heaters...)
Since I was essentially doing a full 100k service I found a full set of new coils, the engine had not had a major tune since I purchased it, and while performing a major tune I figured it was time to replace all 4 O2 sensors as I did on my 2000 XJ8.

Next I located every ground connection stud in the engine bay and trunk. removed the wires, brass brush cleaned every connector ring, post and nut and retorqued, metered the wires from each coil, each O2 sensor, throttle body connector to the ECU for opens/shorts/resistance/ and harness all good well within spec.

Also replaced the fuel filter, air filter, removed checked and sealed the Full Load and Part Load hoses and replaced the O Rings, including the Air feed hose to the Fuel Injection rail connection and at the TB, checked the wires from the Mass Air Flow to the ECU and the Mass Air Flow sensor wires. The Throttle Body was sent off to ASI for what they call "re-manufacture", which I am very disappointed to report is actually just a bead blast of the outside and not very good one at that, a throttle plate clean, and break apart the TPS sensor and "repair" I renewed the Throttle Body gasket on reinstalling the TB.

I also removed the fuel injectors, found a few cracked O rings on two of the injectors, ultrasonically cleaned the injectors in ChemTool, then used a fuel injector cleaner adapter to reverse flush each injector and forward flush each injector to show a perfect spray pattern, renewed the O rings and Air seal ring on each injector.and reinstalled.

Upon reassembly, I attached the Fuel Pressure gauge and primed the fuel rail, I started the car, did a "propane" test, "smoke" test and carb cleaner test around each fuel injector, each port of the intake manifold, each connector and the full lengths for the Full /Part/Air hoses, emission purge lines and the whole length of the intake plenum - everything appears sealed up nicely showing no increase in idle (Digital RPM monitored) or no sucking any smoke.

Now all that should fix the problem, yes? Wrong again ...

So here is where I am now:

Engine starts, warms to temp and and idles perfectly. On slight to medium throttle, immediate hesitation and undefined misfires, no power, slow acceleration. On full throttle to the kickdown switch ON position, the engine leaps to life, revs up to 6k + RPM, shifts perfectly through the gears and gets to over 100 mph quickly throwing no codes other than P1646, fuel pressure remains perfectly steady going from 38 to about 44 psi (gauge sticking out of the hood) . No P1313/1316 or 0171/0174 codes, and no rich codes UNTIL ....when I try to drive normally, I get hesitation, no power, gradual and throaty acceleration and misfires.

Checking the Throttle body response with Key on and air plenum off to observe the throttle plate, the throttle plate responds with no hesitation, smoothly and full range the the throttle pedal. No throttle body codes have ever come up.

On low to medium throttle acceleration, no proper throttle response or acceleration, I get intermittent misfires, I clearly hear a throaty intake sound, sounding like it is a fuel starved bogging carburetor - but fuel pressure is spot on and every injector tested perfectly, I will eventually get misfire codes on all 8 cylinders if try to drive normally. Full kickdown throttle the engine jumps to life, but any throttle position in between delivers slow acceleration, no power and misfires.

So the P1646 code I believe might be a defective O2 sensor out of the box as I can swap it with the other bank and the code moves so I will replace it. I have used the same manufacturer O2 sensors Up and down stream on my 2000 XJ8 with no problems, resolving the lean bank issues on the 2000 xj8. But I don't believe for a millisecond the P1646 code would not give the throttle response and misfire issues, I drove my 2000 XJ8 for a couple of weeks with no issues with those codes until the new sensors arrived, and I had no throttle or misfire issues, only in/out of restricted performance.

But the low to medium throttle issue, well the only things left on the list are pointing to compression/valve spring, but idle is perfectly smooth and I do not hear any tappet or other noises. And the Full throttle with no misfires smooth and quick up to over 100 mph when in kickdown switch is really bothering me, with a bad spring the engine would have self destructed on the first couple of 6k shifts, or the Variable valve timing would have thrown codes.

When I blip the throttle, the lag is a textbook lean stumble while the fuel pressure remains perfectly within spec, but and I do get a corresponding noise around the mid engine intake plenum that I cannot describe or pinpont using propane, carb cleaner or smoke, and the sound disappears instantly as the revs start to pick up responding to the throttle. It really does not sound like a vacuum leak, an intake leak on the manifold or seals sound would not disappear almost instantly and would also get louder as engine speed increases, and I would probably also throw P0171/0174 codes. Not getting any of that, just the lean lag with the corresponding noise that "might be" a chain rattle taking up slack when the throttle is blipped.

I have never heard a loose timing chain in one of these X308 engines. Could it be the timing chain skipped / tensioner/ guide as opposed to valve spring/compression? I would think I would hear some sort of classic timing chain rattle on cold startup if the tensioners or guides were toast - maybe that is the noise when I Blip the throttle ...

So at present it is sitting in the driveway while I scratch my head and come up with the next things to check.

Any of the gurus have some pinpoint short list of checks?

I am thinking the next step is pull the cam covers to check the timing chain and tensioners and possibly the intake manifold, all while hoping the CATS have not packed up, but I really cannot check for broken springs unless I pull the cams, and I need to clear my lift in the garage before I dive in that deep
.
Maybe simpler, would a failing Mass Air Flow give an instant lean stumble or no low/medium throttle acceleration but still allow full throttle perfect acceleration?

Experienced Suggestions please.

Cheers!

 

Possibly a broken strata inside a cat. converter? Restricting exhaust on light/ medium throttle then being forced away on full throttle? I've seen pieces of converter in mufflers as well causing restriction.

 

A faulty (or dirty) MAF sensor could certainly cause problems that you are having. On some cars, the ECU will ignore the MAF signal at full (or close to full) throttle and go by its own fueling map which, if it is also the case on Jaguars, could explain why your engine runs well at wider open throttles.

I suggest you have a look at the MAF sensor and clean the sensing element if dirty. Poor contacts at the MAF connector could also cause problem with engine throttle response so have a look at these also. If you get improvement after cleaning the MAF sensor, it may be good for some time but the problem may reappear. In this case, you will need to replace the MAF.

 

I would want to fix the P1646 before putting in more effort or thought.

I would not be surprised if there's major cat damage given the scary history.

 

Thanks for the reasoned responses!

One nice thing about having Jaguar twins is that I can organ donate from the working one to the problem one for some troubleshooting - just as long as they are not both exhibiting the same problem at the same time - had that ...with both failing the HO2 sensors within a month of each other, not to mention within 3000 miles difference on the odometer.

So I swapped the MAS between my 2000 XJ8 to my 2001 XJ8. Not the MAS, and I did clean both between the swaps. Odd thing is, the 2000 seemed to run a bit better but I did seal up a typical crack on the intake plenum I found at the sound tune/deadening tube connection while swapping MAS sensors.
On the 2001, after swapping the MAS and not resolving the problem, I did adjust with the TPS until it threw hi/lo idle codes, then centered between closest places to get a smooth return to 650 rpm idle after throttle .. that made only minor overall improvements but still have the lag/hesitation and intermittent misfires with no codes.

Since the CATS are a pretty major effort requiring getting my Stag-under-restoration off my lift, those are last on the list after resolving the P1646 - but I have been suspecting the CATS as a cause because of the starved Carburetor throaty bog sound when moderately accelerating, and also from driving 25 + miles in limp home mode - but I bet the lean limp home mode tries to protect the CATS to some degree.

But here are a few questions about CATS and the Upstream/downstream O2 Sensors relationships for diagnostics:

1. if one or both Cats were broken, would the corresponding downstream O2 reflect a higher reading due to a broken CAT, or
2. if one or both cats were burned out / plugged, what would be the diagnostic pinpoint tests - without using a emission test rig, I think I saw a procedure that swaps out the HO2 and O2 sensors for testing the CATS and I don't have that. It is cheaper just to replace the cats than have a diagnostic done to determine they are bad. I will see if my video probe is small enough to see into the HO2 and O2 holes.
3. where is the best source for replacement cats that actually fit and don't cost more than the car is worth?
4. PRO/CON about replacing with the so-called High Flow CATS?

I also spent about a half hour with my engine stethoscope probing 4 points around each cylinder, heads, intakes, injectors, throttle body while blipping the throttle, spraying volitiles and I can't detect any significant issues on any cylinder, injector.
The throttle blip lean hesitation noise is probably not timing chains, it is louder without the stethoscope
But I will spend a bit more time since it seems to be mid engine but will probe the CATs for rattles and insides if my probe fits.

In the mean time, pinpoint tests for P1646 AGAIN to see if I missed something the first two times before I order a replacement HO2.

Thanks for more reasoned troubleshooting ideas!

 

This saga has moved to another thread .. as the heads are coming off now ...
https://www.jaguarforums.com/forum/x...8/#post1994844