help - cylinder misfire, shuddering
 

Any help is appreciated. My 2000 US S-type engine has started misfiring/shuddering about every 10-15 seconds ...

purrrrrrrrrrrrrrrrrrrSHUDDERpurrrrrrrrrrrrrrrrrrrr rSHUDDERpurrrrrrrrrr

The Check Engine Light came on for a few days and went away.
The stored code was P0308 - "cylinder 8 misfire"

I replaced one ignition coil but that did not help. I believe it was cylinder 8
but not 100% sure.

I will try replacing the spark plug.

Car is 2000 US S-type, 38000 miles.

FYI, can someone confirm location of cylinder 8 ???

FRONT of ENGINE 1-3-5-7 REAR of ENGINE
FRONT of ENGINE 2-4-6-(8) REAR of ENGINE

number 8 is back right side as youre looking at with hood open. on a car that age the coil connectors are notorious for coming loose since the retaing clips break off. but barring that change plugs. And are you sure its 8 doing it again, or is it another acting up now....which is often the case

Thanks Brutal.

I changed the plugs on the driver side four cylinders, and changed the ignition coil on cylinder #8, but I still have the same problem. The coil connectors on driver side bank looks ok. I will replace the plugs on the passenger side bank and see if that fixes the problem.

I notice, the "Average MPG" display on the console is between 8
and 12!! regardless of highway or stop-n-go.

I notice, the engine lurches/gasps when I go up a hill, or try to accelarate quickly.

The Check Engine Light is OFF. There are NO stored codes.

Easy OBDII live data shows "Short Term Bank Fuel Trim" running rich about 50% of the time. The "Long Term Bank Fuel trim" only shows a voltage but no status!

Could this be a fuel problem?

A month ago I ran the fuel tank through a can of Fuel system cleaner, but that did not help.

short term running rich is sign of vacuum leak and trying to add fuel to comphensate. Check for loose broken connection past the mass air flow sensor in intake and air tubes. If youre monitoring short term then spray with carb or brake clean and watch if it becomes ellivated, when it does you found the leak. these are good starts for diag, also if youre still getting a misfire on 8, swap coils with adjacent cylinders and see if it follows. since you pulling plugs, at least eliminate mechanical faults and run a compression test. V8 can tend to drop or get loose exhaust seats in the back cylinders from letting coolant get low and air in system. Although it doesnt overheat, it does create hot spots that can lead to dropped exhaust seats in the back cylinders

Thanks Brutal, great suggestion.

I replaced passenger side plugs ... great improvement BUT, the engine still shudders every 15 secs, at low speeds most visible around 600rpm and when car is stopped. The car no longer shudders/gasps when climbing a hill or during accelaration, hooray.

While replacing plugs I noticed the 2 back plugs looked really bad
some kind of white powder and lots of grease and some sand around
the back 2 coils almost as if water got through. Also there is almost
no clearance to work ... took me more than 3-4 hours to R&R all 8.

Where are intake and air tubes? Where should I spray cleaner?

Check engine light is long gone. No more stored code , no more misfire on cylinder 8.

Never done a compression test before ... do I need special tools?

I just had the exact same (sounding) problem as you did. I took my car to the dealer and they told me it was misfiring because of bad gasoline. I live in the Pacific Northwest and most major Metro areas are required to use Ethanol in their gas to help with lower emissions....well apparently a lot of Jaguars and BMW's do not like the mixture of Ethanol and it has the ability to create misfires and screw things up.

They replaced #5 ignition coil and spark plug, and flushed the injectors. $550 bucks later the car seems to be fine.

They had this problem a lot in the past year and said it has slowed because they think the cars are either adjusting to the ethanol, or the gas companies have lowered the amount they put in the gas....federal regulation limits it to a max of 10 percent. But when Jaguar brought in a Jaguar engineer to investigate this problem, after testing several samples of gas from cars that had problems like mine they found that the actual levels of Ethanol were closer to 20 percent. Turns out, the majority of the gas causing the problem was Premium Grade from Chevron Stations in the area.

Now one thing that threw me for a loop..... Jaguar Tech told me to run REGULAR grade gasoline in my STR every few tanks to help with this problem.
Call me crazy...but isn't that like really bad advise? These engines HATE Regular gas.

I dunno!! I just hope it doesn't happen again....

Anyone else ever have that happen, or ever hear of that happening?

hottienamedscottie - Glad to know your problem was resolved.

I did change all 8 plugs and #8 ignition coil, with partial success. My tests suggest that there might be more bad ignition coils. If that fails, I
will run another can of Fuel injector cleaner and replace fuel filter which has not been changed for a while. If these easy fixes fail, then take I will take it to the ***********.

It is odd that the Jag Tech advised you to use regular gasoline ... hmmm.

Update ... I showed it to a tech ... he says replace spark plugs and clean fuel injectors.

I changed the plugs to iridium.

Anyone have a DIY on how to clean fuel injectors ?

The gas tank method has been tried twice to no effect.

Any one ? Any one at all?

I had 2 more misfire codes on different cyclinders. So I change 2 more
coils. That did not fix it.

I had the injectors cleaned. That did not fix it either. Engine gasps and misfires when I try to accelerate.

After cleaning and driving around it I got 2 more misfire codes on cylinder 3 and cylinder 6.

I am now at my wit's end.

Try gas?
 

Do you use the same station to fill up? Had a lot of rain in your area recently? I'd next try some gas additive to dry out any moisture that may have accumulated in the tank, given nothing else seems to have worked.