98 XJ8 misfire? Or something worse?
Discussion
Symptoms:
Cold engine runs fine, warms up on journey, then gets up over 50-55 and can't accelerate without a judder (similar to running on the rumble strips on the motorway). The symptom only happens when engine is hot. No steering vibration. Laboured acceleration (but she will accelerate).Get to a speed (any) and just cruise along and the noise/ vibration stops (normal feel to the car). Stop at a junction (with it in gear) and she tries to creep forward but has a lumpy feel. Take out of gear and normal idle. Pull away and it struggles. Reverse onto drive and it's very lumpy.
It had a gearbox flush last year.
Any pointers? Hope it's not what I think it may be.
Cold engine runs fine, warms up on journey, then gets up over 50-55 and can't accelerate without a judder (similar to running on the rumble strips on the motorway). The symptom only happens when engine is hot. No steering vibration. Laboured acceleration (but she will accelerate).Get to a speed (any) and just cruise along and the noise/ vibration stops (normal feel to the car). Stop at a junction (with it in gear) and she tries to creep forward but has a lumpy feel. Take out of gear and normal idle. Pull away and it struggles. Reverse onto drive and it's very lumpy.
It had a gearbox flush last year.
Any pointers? Hope it's not what I think it may be.
Symptoms indicate that under load when hot you have a misfire. Any fuelling or ignition problems have the potential to cause engine damage so best not ignore it. I've suggested on another post you check everything that's free first - have a read of Supermomo's XJR post for ideas of what to look for.
On a Nicasil engined car it's a useful check to lift the oil filler cap slightly at hot idle to make sure there is no excessive crankcase pressure or heavy oil mist. If you see evidence make sure the breather hose are clear and the calibrated 2.5 mm hole in the part throttle breather hose stub on the LH cam cover is not blocked. Once you're sure the pipes are clear it may be worth changing the oil as bog standard mineral oil tends to loose its hot viscosity performance and film strength when at the end of its sump life leading to increased piston ring blow by.
You may have a coil or plug breaking down or possibly a MAF gone out of spec or a air leak down steam of the MAF. Plugs should be changed at 70k on n/a X308s and gapped to 1.0mm. Remove the air intake trunking and check there are no splits or holes in it and have a look inside the throttle body to make sure it's clean.
Do the free stuff first then get hold of a OBD2 a code reader to see if any codes are stored. Write them down then clear them, run the car for a while and see if they come back.
On a Nicasil engined car it's a useful check to lift the oil filler cap slightly at hot idle to make sure there is no excessive crankcase pressure or heavy oil mist. If you see evidence make sure the breather hose are clear and the calibrated 2.5 mm hole in the part throttle breather hose stub on the LH cam cover is not blocked. Once you're sure the pipes are clear it may be worth changing the oil as bog standard mineral oil tends to loose its hot viscosity performance and film strength when at the end of its sump life leading to increased piston ring blow by.
You may have a coil or plug breaking down or possibly a MAF gone out of spec or a air leak down steam of the MAF. Plugs should be changed at 70k on n/a X308s and gapped to 1.0mm. Remove the air intake trunking and check there are no splits or holes in it and have a look inside the throttle body to make sure it's clean.
Do the free stuff first then get hold of a OBD2 a code reader to see if any codes are stored. Write them down then clear them, run the car for a while and see if they come back.
Gassing Station | Jaguar | Top of Page | What's New | My Stuff