I’m new here so, if i do something wrong please don’t kill me
I have recently bought a XJ-SC V12 5.3 from 1987 with the hope of restoring it and using it for my wedding.
So far it has been what you expect from a Jag : issues, issues and issues.
For informations here are the new parts (less than 200kms, parts tested and OK) :
Air filter
Fuel filter
Oil filter (oil change done with 20W50)
Gearbox oil filter (oil change done with Dextron III oil)
Battery
Coolant hoses (all replaced after two cracked one in the same week…)
Coolant
Temp Sensor
Both coils
Ignition Amplifier
Ignition rebuild (seized distributor, now OK + new vaccum advance, arm, cap)
Advance setup following the Book (18° before TDC at 3000rpm)
Vaccum lines seems OK, waiting for a vacuum tester.
Sparkplugs looks OK and gap is good on tested one (change planned)
All the parts were replaced by new from SNG Barratt France.
Here is the issue :
The car was running great before the amp died a few month ago.
Now the car starts great but run a bit high at idle (1300/1400rpm). When hot I can’t rev it past 4500/5000rpm. I’ve tried to do it by slowly rising the load, flooring the pedal, running, in neutral…
After all my troubleshoot and changes on the car I’m a bit confused…
I’ve checked the forum for similar issue and found some but without solution or ones that didn’t work for me.
Next step for me is to change the admission and valve cover gasket. I’ll change the sparkplug with new NGK R in the same time just to be sure.
If this issue ring a bell for you or if you have any idea, i’d be happy to hear it!
PS : Sorry if my english is not perfect, I’m french after all…! :)£
Thanks!
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
I’m guessing here: Lucas ignition? Two bottle-shaped ignition coils, one in front of the radiator?
Whatever you do, don’t change the cam cover gaskets without first reading up on half moon seals and replacement screws.
Your first symptom sounds like AAV could be stuck open a bit causing high idle. Very common if still original. John John here on forum does reputable and inexpensive rebuild if you ship to him.
Second issue is almost always related to ignition coil. The secondary one may be bad. I recommend buying new single coil from SNG, that’s what i did. But first replace spark plugs, because that could be it too.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
I thought of the AAV too, but i can’t figure out how it would impact the RPM range…
Both coils are new and the wires ares good (check with multimeter)
The gap on the new sparks were checked and are at .025"
I didn’t try full cold (it’s winter here in france…) but testing at mid range between Cold and Normal, it’s the same.
I forgot to add this in the first post :
I have test without the air filter to check the throttles : they open both at 100% and same issue.
Remembering this post [xj-s] 5.3 91 XJS won't rev past 5000 - help!
I had in mind to test without the exhaust line since the B bank pipe is damaged (hole at the connection with the mid suppressor).
There is a weird thing maybe due to that :
A bank exhaust is constant
B bank exhaust is pulsing (i don’t know how to describe this)
I’m concerned about the cat converter too. There are 4 on mine (California import), and checking them sound like a good idea to me.
Any replacement options for those? (i don’t mind not having converters and/or only 2.)
Thomas, you didn’t mention looking at the filter/screen located in the small sump tank below the battery. It could be that you are running out of fuel at higher RPM. A pressure gauge on the fuel rail would help.
I would be looking at the distributor; check timing at idle (4 degrees BTDC with vacuum disconnected) and at 3000 rpm (18 degrees BTDC with vacuum disconnected). If you don’t see these figures, there is a good chance that the centrifugal advance mechanism below the rotor and flash shield is seized.
Warm engine up and check timing with vacuum connected, should be about 14 BTDC, unplug vacuum and should drop to 4 degrees; this checks your vacuum advance capsule.
At hot idle, remove left air filter and block the port to the AAV (to the rear of the throttle body); idle should drop to 300-500 rpm- if not, AAV is stuck.
The distributor has been rebuild (the mecanical advance was seize).
The vaccum capsule is new, same for the distributor arm and cap.
Advance is set right
The theory is, there’s a small screen sock filter in that small tank. Over 30 years, there could easily be a lot of dirt/sentiment at bottom of that small tank. As you drive, it gets sucked up and clogs the filter, not allowing the fuel pump to get enough fuel. Once you shut down the car, the dirt/sentiment falls back to the bottom of the small tank.
Mine was actually quite clean, but there was a bit of sentiment at bottom. Worth cleaning out if yours has never been open. The earlier cars had smaller filters that easily clog, but the later years like yours and mine have a much larger filter that works well. I left mine in, not worried about it.
You will find out about this car, there are MANY failure points. Glad you took care of the distributor already. You may go through several until you find the actual one causing an issue. But once you’ve gone through them all, your car will be in very dependable condition. That’s what I did.
Had similar issue - turned out to be a partially blocked Cat - found it by running and then measuring the cat temps and compared; one was running much hotter than the other.
It ‘could’ cause both…but just be ready, as I’ve found with my car, it’s never the first thing I fix that solves an issue, but at least that first thing is taken care of!
It took me about 2 years to really straighten my car out, but now it drives so well and dependable. Such a joy. Just keep reading ‘the book’, and asking questions here. It’s not too expensive to fix all the issues, it’s just time consuming. A lesson in patience for me!
It was the RPM issue. Car ran pretty well at lower RPM, but as the RPM built over 3500 it had a hard time - maxed out at about 90mph no matter how long I had the pedal down.
Although it didn’t affect my driving or rpms, when I changed my exhaust, I found out that one of my cats had a hole in the middle of the material, with chunks of catalytic converter littered down the pipe. So it could easily be an issue.
I can’t give better advice than all the experts , but depending where you are based in France, I may be able to help for vacuum tester of similar tools
IMHO, 1300 or 1400 rpm at idle is more than “a bit high”
either the AAV is blocked in the “cold” position, or you’ got some air leaks in the inlet
get in touch with John_John for a rebuild of the AAV, or a rebuild kit
also worth checking the butterflies close properly and equally at idle : the gap is small
you said you changed the coolant hopses and sensors, but did you change the thermostats ?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
20
With a vacuum gauge you can perform a quickie test. With the engine idling, note the manifold vacuum. Slowly raise the RPM. The manifold vacuum should increase. If it decreases, that’s an indication of an obstructed exhaust system.
