Jaguar S-Type Misfire
On the S-Type a misfire is nearly always an on-plug ignition coil — usually one at a time, often after rain, a car wash or oil seeping into the plug wells. I'd read the code to find the cylinder, then swap that coil to another cylinder and see if the misfire follows it. On the V6, cylinders 1 to 3 sit under the inlet manifold, so which bank it is decides the bill.
How bad is it · Garage, carefully
Drive gently to a garage, not long distances with the light flashing
A flashing engine light means a misfire bad enough to damage the catalytic converter right now. Hard throttle can also drop the car into limp mode.
Which one applies to yours depends on your symptoms, your model year and what has already been done to it.
Likely causes, most common first
Read the check cost before the odds: a free check that rules a cause out beats a likely guess that costs money.
A failing on-plug ignition coil
Every cylinder has its own coil sitting on the plug. The insulation breaks down under load, so a coil can arc to earth only some of the time and still pass a resistance test off the car.
A judder on gentle throttle around 1500–2300 rpm or a steady 40–50 mph that vanishes when you floor it, because the gearbox changes down; a small kick at idle; the engine light flashing. The code can take weeks to appear, and sometimes never does. A bad coil can also bring up a gearbox warning and restricted performance.
Read the codes: P0301 to P0308 name the cylinder. Move that coil to another cylinder and see whether the code follows it. With no code, live oxygen-sensor data or the scanner's mode 6 shows the bank; then fit one new coil in turn across that bank.
Replace the coil that carries the fault. Buy Denso, Delphi, NGK or genuine — cheap online sets have died within weeks; the same coil is listed under the 2001 Lincoln LS 3.9. Early green-label coils were superseded by black-label ones, and if the originals keep failing one after another, a whole set saves repeat labour. On the V6 the coils under the manifold tend to go within days of each other, so with the manifold off it pays to do all three; on the V8 they come out one at a time. When one coil is fixed, a second can show up on the other bank.
Water on the coils after rain or a wash
Water gets past the seal at the back of the bonnet and through the cowl, and drips onto the coils and into the plug wells. A wet coil shorts; one left wet long enough corrodes and dies.
The misfire starts the morning after heavy rain, a car wash or a degreased engine bay, often with the amber engine light flashing; several cylinders can log codes at once.
Lift the plastic cover over the coils and look for water or tide marks round the plugs and coils. Give the car a long run to dry out before buying anything. A scanner can show a pending misfire on one cylinder before the lamp comes on. Don't rev it hard while it misfires — that is how the catalyst goes.
Drying out alone can cure it. If the misfire stays, replace the damaged coils and clean the coil connectors, then stop the water: Jaguar revised the cowl piece and the coil cover, and on the V8 the cover has no separate seal — a new cover or a bead of silicone.
Worn or fouled spark plugs
The factory plugs are long-life platinum or iridium, but the electrodes still erode and a plug can work loose. A worn plug makes its coil work harder and kills it early.
Misfire on acceleration or at a steady speed, smooth at idle, often with no code; or rough running after the engine was flooded on starting. A miss around 1500–1700 rpm that appears straight after new coils or plugs points at the wrong plug type.
Pull the plugs and look for eroded or rusty electrodes, a loose plug or wet fouling. Realistic plug life on both the V6 and the V8 is about 50,000 miles, short of Jaguar's 60,000.
Fit a new set gapped to Jaguar's figure — for example 0.051–0.056 in on the 3.0 V6. Change plugs as soon as misfires start, before they take a coil with them. These engines are fussy: check the part number and gap yourself rather than trusting the parts counter.
Not a misfire at all: torque converter lock-up
In the top gears the torque converter locks its clutch for efficiency. A worn lock-up clutch shudders in a way that feels exactly like a misfire.
A stutter only in 4th to 6th, accelerating gently from about 30 to 50 mph; the rev counter jumps in steps of about 50 rpm; no misfire code, and new coils change nothing.
Read the codes first: a misfire code points back to the coils. A shudder with clean codes, only in the high gears, points here — bulletin S307-13 covers converter lining failure.
A replacement torque converter.
Oil in the plug wells from the cam cover gasket
A leaking cam cover gasket or plug-tube seal lets oil fill the plug recesses. Oil soaking into a coil breaks its insulation down, and the cylinder starts to miss.
Oil on the plug and the coil boot when you pull a coil; a misfire that comes back after new coils.
Pull a coil and look into the plug well for oil. The variable valve timing seals can leak too.
Worth renewing the cam cover gasket together with the small O-rings that seal the plug tubes. A gasket alone won't fix a coil that's already damaged — do both.
An air leak at the inlet manifold or a perished breather hose
Air that gets in after the airflow meter leans the mixture on the cylinders nearest the leak. Several cylinders misfiring at once is more often a leak than several coils failing together.
Codes for three cylinders together or P0300 with P1316, sometimes P0171; worse once the engine is warm.
Read the fuel trims: well positive points to an air leak, well negative to a rich mixture. Then smoke-test the intake, and look at the rubber breather elbow and hoses under the manifold. On the supercharged V8, the O-ring for the brake servo line in the throttle body is a known leak.
Worth doing whenever the manifold comes off for coils: new manifold gaskets and the breather elbow underneath. Have a spare for the small plastic T-piece in the coolant hose nearby: it goes brittle with age and often snaps when disturbed.
Water in the boot soaking the electrics
The battery and a lot of the electrical equipment live in the boot. Blocked boot or sunroof drains let water collect there, and wet connections bring random running and gearbox faults.
Random misfire codes or restricted performance warnings, the gearbox misbehaving, water under the spare wheel or heavy condensation in the car.
Lift the boot floor and check round the spare wheel; clear the boot drain hole and the sunroof drain tubes.
Worth trying: dry the boot out and clear the drains.
The order to check them in
The point of the order is money: each step either rules a cause out or makes the next one worth doing. Green is free, amber costs a little, red is the one to arrive at last.
Read the codes
P0300 is random; P0301 to P0308 name the cylinder. A cheap reader will do — and no code doesn't clear the coils.
freeRain, a wash or an engine clean lately?
Lift the coil cover and look for water. A long drive may dry it out.
freeSwap the suspect coil to another cylinder
If the code moves with it, the coil is dead. Cylinder 4 on the V6 and 5 on the V8 sit at the front on the left, seen from the driver's seat.
freePull the plugs and look into the wells
Worn electrodes, a loose plug, or oil in the well.
a set of plugsSeveral cylinders at once? Fuel trims and a smoke test
Strongly positive trims mean an air leak at the manifold or a breather hose, not a set of coils.
free to a few poundsReplace the coil — on the V6, by bank
On the 3.0 and 2.5 V6, cylinders 1 to 3 sit under the inlet manifold: with it off, do all three, plus the plugs and the VVT solenoid screens. V8 coils come out after the cover's six bolts, two bolts each; taking the cross-brace off helps.
a coil; manifold labour on the V6Clean codes, shudder only in top gear? The torque converter
Only once the coils and plugs are ruled out.
a torque converterWhat it usually isn't
Don't spend money here first:
If none of this finds it:
On jagaux.com
- Jaguar S-Type Gearbox Fault, Transmission FaultIf the codes are clean and the car shows Gearbox Fault rather than a misfire.
- Jaguar S-Type Rough IdleIf it idles rough but pulls cleanly once moving.
- Jaguar S-Type Won't Start, No CrankIf it won't crank at all after coil or plug work.
- Jaguar S-Type Restricted PerformanceIf the dash shows Restricted Performance or Engine Failsafe Mode, or the car cuts out.
- Jaguar S-Type OverheatingIf the misfire followed steam and a burst coolant hose.
- Jaguar VIN decoderConfirm your exact model year, engine and factory options before ordering parts — free.
Ratings, fuse numbers and torque figures vary by model year and market. Read the legend on your own car before pulling anything, and use the figures in the manual for your car, not the ones in a video.
Check your VIN: exactly which car you have and which bulletins apply to it.