XJR 308 Won't Rev!

[schueymcfee]

It just will not rev beyond 3k rpm! It has a misfire and I was wondering if there is some kind of safe mode for misfires?, it's like it's hit the limiter.

[vladman]

possibly a silly thought, but is this whilst driving? because if you're only revving it whilst stationery, i think they don't rev higher than 3000rpm (built-in limiter, only active when stationery).

[schueymcfee]

vladman said:

possibly a silly thought, but is this whilst driving? because if you're only revving it whilst stationery, i think they don't rev higher than 3000rpm (built-in limiter, only active when stationery).

Hi Vladman,

I hope that's true, if it is then brilliant.

[drummerboyXJR]

Yes, safety cut out at 3000 if in park or neutral.

[Jaguar steve]

Yes 'tis true, the R will not rev over 3000rpm in neutral.

Errrr... why do you need too? There was somebody posting on PH a while ago who repeatedly started and reved up his XJ because he liked the V8 soundtrack so much and wanted to share it with all his mates.

He ended up flooding it and had a whole load of grief getting it started again.

Not suggesting that's how you found the 3000 limit of course - but just in case you'd been tempted....

[schueymcfee]

Jaguar steve said:

Yes 'tis true, the R will not rev over 3000rpm in neutral.

Errrr... why do you need too? There was somebody posting on PH a while ago who repeatedly started and reved up his XJ because he liked the V8 soundtrack so much and wanted to share it with all his mates.

He ended up flooding it and had a whole load of grief getting it started again.

Not suggesting that's how you found the 3000 limit of course - but just in case you'd been tempted....

No, I have a misfire, and I was trying to see if it cleared futher up the rev range, so I was trying to work out if it was indeed a limiter or a serious misfire.

I'm losing water, presumably into one of the cylinders hence the misfire and the header tank stinks of exhaust fumes

Anyone know the cost to do the head gaskets on one of these things?

[Jaguar steve]

When does the missfire occur? Just under load or all the time? Is it regular and steady or intermittent?

XJs are a bit prone to coolant leaks - have a really careful look round the engine bay. Hoses can weep, the joints between plastic and metal components are prone to failing and the spring type metal hose clips fitted when new can loose strength. These could be the cause of coolant loss and the miss fire may be somthing else entirely.

Check all the plugs tips for colour, if one is markedly different to the rest then that's worth investigating too.

[NormanD]

schueymcfee said:

I'm losing water, presumably into one of the cylinders hence the misfire and the header tank stinks of exhaust fumes

Anyone know the cost to do the head gaskets on one of these things?

Are you getting white smoke out of the exhaust.

Quite a long job time wise on the XJR
If doing the head gaskets then change the chain tensioners at the same time.

I would say £1,500 by a good independant

[schueymcfee]

NormanD said:

schueymcfee said:

I'm losing water, presumably into one of the cylinders hence the misfire and the header tank stinks of exhaust fumes

Anyone know the cost to do the head gaskets on one of these things?

Are you getting white smoke out of the exhaust.

Quite a long job time wise on the XJR
If doing the head gaskets then change the chain tensioners at the same time.

I would say £1,500 by a good independant

That's a good point, I don't think there is any white smoke. The car will do about 50 miles before the "coolant level low" warning comes up on the computer. The heater goes through hot and cold cycles on max heat.

[schueymcfee]

Jaguar steve said:

When does the missfire occur? Just under load or all the time? Is it regular and steady or intermittent?

XJs are a bit prone to coolant leaks - have a really careful look round the engine bay. Hoses can weep, the joints between plastic and metal components are prone to failing and the spring type metal hose clips fitted when new can loose strength. These could be the cause of coolant loss and the miss fire may be somthing else entirely.

Check all the plugs tips for colour, if one is markedly different to the rest then that's worth investigating too.

I've had it sat running for 30 minutes and there's no drips of water on the drive. Heater cycles through hot and cold on max heat though.

The misfire appears to be on idle only.

[Jaguar steve]

Are you actually loosing coolant or just getting coolant low messages? The level sensor and connections can cause error messages even when the level is OK. If the heater is not consistent that suggests you either do have low coolant level or an air lock in the system. With the engine cold and the heater turned to Hi, park the car on a slope facing downwards, top up the coolant to the max level, replace the cap, run the engine for a min or so, then top up again.

Have a look at the plugs. If there's no clues there I'd get it scanned if I were you. You have to acertain exactly what's causing the missfire. It may not be anywhere as serious as a head gasket.

Could just be a faulty coolant sensor and a dud plug.