Discussion
Hi all,
I bought my 2.9 XJ40 '89 reg about 8 weeks ago, drove it 200 miles home and
everything ok.
I changed the oil/filter, plugs and leads. (120k on the clock) Sent
injectors away to be cleaned. Drives really well.
Drove it the other Monday for about 30 miles, perfectly smooth it
was, parked up at home. Saturday morning, it started fine but had
zero pulling power, feeling like it was only moving on tickover.
Lumpy tickover and would struggle to rev up. I took the plugs out
and they were all very sooty black. Have since changed the
Coil
Temp sender unit (twice, after dealer sent wrong one)
Rotar arm.
Dizzy cap was recently renewed with old owner allong with fuel pump
and filter.
It starts but is still very lumpy idle and will struggle to rev up,
sometimes blowing back through airbox. Strange thing is, it is
slightly better with Temp sender disconnected (ticks over better
anyway)
Any help/ pointers appreciated because otherwise it has a big
stick waiting for it
I bought my 2.9 XJ40 '89 reg about 8 weeks ago, drove it 200 miles home and
everything ok.
I changed the oil/filter, plugs and leads. (120k on the clock) Sent
injectors away to be cleaned. Drives really well.
Drove it the other Monday for about 30 miles, perfectly smooth it
was, parked up at home. Saturday morning, it started fine but had
zero pulling power, feeling like it was only moving on tickover.
Lumpy tickover and would struggle to rev up. I took the plugs out
and they were all very sooty black. Have since changed the
Coil
Temp sender unit (twice, after dealer sent wrong one)
Rotar arm.
Dizzy cap was recently renewed with old owner allong with fuel pump
and filter.
It starts but is still very lumpy idle and will struggle to rev up,
sometimes blowing back through airbox. Strange thing is, it is
slightly better with Temp sender disconnected (ticks over better
anyway)
Any help/ pointers appreciated because otherwise it has a big
stick waiting for it
Calling Jaguar Steve!!!!Sounds like the fuel / air ratio is all over the place - which will be a tricky one without electronic diagnostics.
Heavy sooty deposits on the plugs indicate a mixture that's too rich while backfiring through the intake trunking and air box suggests the opposite - it's too lean.
Are there any fault codes on the dash?
I don't think ignition is the problem from your description but it's always the best place to start looking - so before you do anything else check everything you have done so far and make sure the timing is spot on.
The fact that it's running suggests the fuel supply and pressure is more or less right and consistent and the ignition system is firing all 6 plugs as they have become equally dirty.
Have a really good look round the engine bay. Disconnect all the electricial connectors and check for corrosion or broken wires especially on the air flow meter. Check none of the engine breather or air intake hoses have perished or collapsed and have a listen with a length of garden hose pipe all round the inlet manifold to see if you can hear any hiss of air being sucked in. If you find what you think is a leak dribble a little engine oil on the suspect area and see what happens. Check all the intake manifold bolts and fittings are tight.
Are the brakes OK? Make sure the vacuum pipe leading to the brake servo is sound. With the engine running clamp the pipe and see if there's any improvement. If there is either the non-retun valve connecting the pipe to the servo or the servo vacuum chamber has failed allowing excess air into the engine. Have you got a vacuum gauge? You should see around 25" / 2 Bar of vacuum on a healthy induction system at idle. If it's wildly out or all over the place then you have an air leak.
Take the air flow meter off and look inside the bore. If you can see a tiny wire at right angles to the flow of air - it'll depend on which type you have - then give it a spray with carb cleaner.
Next get hold of a Heynes manual and multimeter and check all the fuel system components you have data for. Next step is try substition - which with a 2.9 will be a bit tricky as they are so rare.
If none of this works then either join the Jaguar Enthusiasts' Club and get some free technicial advice or join the AA or pay for an hour's labour at a good Jaguar indy.
Fixing it should be easy - finding out what to fix is always the
bit.
Heavy sooty deposits on the plugs indicate a mixture that's too rich while backfiring through the intake trunking and air box suggests the opposite - it's too lean.
Are there any fault codes on the dash?
I don't think ignition is the problem from your description but it's always the best place to start looking - so before you do anything else check everything you have done so far and make sure the timing is spot on.
The fact that it's running suggests the fuel supply and pressure is more or less right and consistent and the ignition system is firing all 6 plugs as they have become equally dirty.
Have a really good look round the engine bay. Disconnect all the electricial connectors and check for corrosion or broken wires especially on the air flow meter. Check none of the engine breather or air intake hoses have perished or collapsed and have a listen with a length of garden hose pipe all round the inlet manifold to see if you can hear any hiss of air being sucked in. If you find what you think is a leak dribble a little engine oil on the suspect area and see what happens. Check all the intake manifold bolts and fittings are tight.
Are the brakes OK? Make sure the vacuum pipe leading to the brake servo is sound. With the engine running clamp the pipe and see if there's any improvement. If there is either the non-retun valve connecting the pipe to the servo or the servo vacuum chamber has failed allowing excess air into the engine. Have you got a vacuum gauge? You should see around 25" / 2 Bar of vacuum on a healthy induction system at idle. If it's wildly out or all over the place then you have an air leak.
Take the air flow meter off and look inside the bore. If you can see a tiny wire at right angles to the flow of air - it'll depend on which type you have - then give it a spray with carb cleaner.
Next get hold of a Heynes manual and multimeter and check all the fuel system components you have data for. Next step is try substition - which with a 2.9 will be a bit tricky as they are so rare.
If none of this works then either join the Jaguar Enthusiasts' Club and get some free technicial advice or join the AA or pay for an hour's labour at a good Jaguar indy.
Fixing it should be easy - finding out what to fix is always the
bit.Thanks for the response JS, Think I have fiddled and twiddled to the end of my knowledge and its time to give in and pay 
someone to sort it.
Pressure testing and electronic diagnostic equipment are beyond me.
I think it was only backfiring into the air-box when I disconnected the temp sender. It hadn't done it before, only yesterday when I fitted the new sensor. So I think it is a over-fuelling issue
Hopefully it turns out to be something simple that I just can't sort. Never had to pay a garage to fix a car before, hope they don't charge more than 10 bob.
someone to sort it. Pressure testing and electronic diagnostic equipment are beyond me.
I think it was only backfiring into the air-box when I disconnected the temp sender. It hadn't done it before, only yesterday when I fitted the new sensor. So I think it is a over-fuelling issue
Hopefully it turns out to be something simple that I just can't sort. Never had to pay a garage to fix a car before, hope they don't charge more than 10 bob.
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