XJ6 & XJ12 Series I, II & III 1968-1992

Lacking power

 
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Old 10-15-2014, 01:21 AM
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Default Lacking power

Have a problem with the car, an XJ6 Series 3-81, lacking power after some time in the garage. It runs OK on idle and gearbox works fine but it feels tired lacking power to reach 50 mph. Just like the motor its weared down but oil, oil preassure and the compression is OK. Could it be the AFM that needs cleaning or replacement after a long standstill
 
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Old 10-15-2014, 02:27 AM
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Originally Posted by amazontommy View Post
Have a problem with the car, an XJ6 Series 3-81, lacking power after some time in the garage. It runs OK on idle and gearbox works fine but it feels tired lacking power to reach 50 mph. Just like the motor its weared down but oil, oil preassure and the compression is OK. Could it be the AFM that needs cleaning or replacement after a long standstill
Hi Tommy

How long has it been in storage?

Does it have a fresh tank of fuel?
 
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Old 10-15-2014, 04:37 AM
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Default XJ6 lacks power

The car has only run some 50 miles over the past years but has fresh petrol in the tank. I have recently replaced the cylinder head gasket.
 
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Old 10-15-2014, 05:13 AM
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When you replaced the head gasket, did the cam timing get dialed in correctly??

That alone could/will give a sluggish engine.

Also the ignition timing is probably in dire ned of checking/resetting.

Blocked fuel filter now comes to mind, as does a lazy fuel pump.

AFM sticking is more common than dirty.
 
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Old 10-15-2014, 03:48 PM
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Originally Posted by amazontommy View Post
The car has only run some 50 miles over the past years but has fresh petrol in the tank. I have recently replaced the cylinder head gasket.
If the car basically starts and runs OK but lacks overall power, Grants suggestion sounds like a most likely area to look at given the recent work you described. If you have fresh fuel, its not dumped on a load of old stuff and its had time to run through then its probably not that. That was a problem I had when I first started working on a little BMW I had a couple of years ago. It had the symptoms you are experiencing.
 
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Old 10-16-2014, 10:20 AM
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Default Still sluggish

[QUOTE=Grant Francis;1078749]When you replaced the head gasket, did the cam timing get dialed in correctly??
Timechain was not removed and special Jag-tool for tensioning was used. If ignition timing is off the car would run instable on idle speed, wouldn't it?

I have not though checked the fuel pump filter yet.

That alone could/will give a sluggish engine.
 
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Old 10-16-2014, 10:37 AM
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Originally Posted by amazontommy View Post
Timechain was not removed and special Jag-tool for tensioning was used.


Did you use the camshaft positioning plate? Or at least ensure that the camshaft notches were absolutely 90 straight up from the plane established by the cam cover mating surface?

And then, after assembly, roll the engine over and recheck the cam timing/position? It can vary several degrees depending if you installed the cams with the chain slack or taught.

Cheers
DD
 
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Old 10-16-2014, 10:40 AM
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Actually, no. Late ignitio0n timing would mean a nice smooth idle and possibly off idle, but just sluggish when driven. Well worth checking at least the static timing.
but, if the vacuum advance diaphragm is bust, that will cause timing issue. Also, stuck
mechanical advance weights.


My personal diagnostic protocol calls for getting the ignition right first, then if noi fix advance to fueling.


As to the basics, you've done that with a compression test.


All the tuning in the world will not fix weak cylinders.


Hope it helps.


Carl
 
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Old 10-16-2014, 03:32 PM
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[QUOTE=amazontommy;1079474]
Originally Posted by Grant Francis View Post
When you replaced the head gasket, did the cam timing get dialed in correctly??
Timechain was not removed and special Jag-tool for tensioning was used. If ignition timing is off the car would run instable on idle speed, wouldn't it?

I have not though checked the fuel pump filter yet.

That alone could/will give a sluggish engine.

Fuel filter issues normally result in a go/no go situation as you add gas, rather than overall poor performance e.g. cuts out above "x" speed or cuts out when you floor it to overtake.

Timing is worth checking. The car may start and run apparently OK but be gutless to drive. Will be interesting to see what you find.
 
 
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