Is the idle ok now, or still a bit rough? And have you tried it 0-60 in 2nd gear only?
I haven’t timed mine, but I would guess 60 in 7-8 seconds, which I think is normal so you’re not that far off. Hopefully one last tune up issue, like cap, rotor or wires?
I am hoping to get mine to 60 in 6-7 secs once I remove mid mufflers. Beyond that, the only real thing to do is convert to manual. One day!!!
The warm idle is the same - its hard to describe though. On the tacho it’s perfectly stable and listening to it from outside the car it sounds stable, but you can feel the car just rocking slightly and if you put your hand on the exhaust it has the odd uneven pulse…
I believe that all the HEs are a bit like this though! Cold idle is perfect.
The cap was allegedly replaced recently, and I’ve done the HT leads, coil and plugs, none of which made any difference. It starts immediately from hot or cold.
What I haven’t really looked at yet is fuel pressure or potential blockage (sump filter etc)… but I dont know if that would produce these symptoms…
Years ago I had an odd low power problem with my 1988 XJS V12. Long story short, the torque converter had failed. Felt like I had an anchor attached to the rear bumper. A clue was an abnormal whine from the transmission
More thoughts…
Is the vacuum advance working? Is the centrifugal advance stuck? Both common problem areas on these cars.
Others mentioned checking the fuel filters but I don’t see any mention of you doing so. Perhaps I missed it?
Cheers
DD
Clogged filters would indeed cause low power. No question about it
Cheers
DD
I know the main tank was replaced quite recently as it was rusting away, so I wonder if maybe the crud has made it to the sump filter… I changed the separate fuel filter and that didnt make a difference.
Timing makes a big difference for power and smoothness…at idle the vacuum advance will get about 8 inHg, enough to advance the timing slightly out of a rough retarded idle.
When at high rpm, the distributor’s centrifugal system will advance the timing quite a bit. This could be the issue, it’s a lot of work, all in the book, but a very common issue, Kirby calls it a 100% failure rate.
After reading that part of The Book, I yanked the distributor out, overhauled it, oiled it, and replaced vacuum advance. Even though all my parts seemed ok, they were original, so to me preventative maint.
Jaguar recommended them, primarily to address a detonation problem. But many have reported their cars run much better.
I’ve already tested the vacuum level at the advance capsule, and that it does move inside the dizzy, and that the centrifugal advance is not stuck. It runs considerably worse if I disconnect the vac advance!
Actually, clogged filters would more likely cause burnt pistons. THAT, of course, would cause low power!
No doubt ! But before the pistons melted I’ll wager the driver would feel a loss of power.
Cheers
DD
A little gas additive and seafoam down the intake may be worth a shot.
You might also want to check for a plugged exhaust system. One quick test is to unscrew both oxygen sensors and take the car for a drive. If it runs much better, the exhaust tract is obstructed somewhere rearward of there. If it makes no difference (other than more noise!) you still might have an exhaust obstruction, just forward of there – in the cats in the downpipes.
Another test, IIRC, is to check manifold vacuum at several RPM points. As the RPM increases from idle up to perhaps 3000, the vacuum at steady state should be higher. If it drops off instead, that supposedly indicates a plugged exhaust tract.
There are no oxygen sensors, it’s a UK car. It’s also had its middle silencer removed, so would have to be plugged in both silencers to be a problem I think?
I’m pretty sure just plugging one side will make the car really slow. And there are several ways for it to get plugged. We’ve had reports of people finding the connecting pipe between the downpipes and the middle silencers, which are double-layer, had the inner layer collapse.