When I started the car with the plug from cyl 5 out there was a lot of pressure /noise that came out the plug hole so maybe it’s still limping but I’ll try to check again in a better way.
I’ll check the valve clearance when I get a chance
@Frank_Andersen. I understand where you guys are coming from but I’m pretty sure what’s happening doesn’t have to do with running on 5cyls. Because when I bought this car it ran on 5cyls too but this hesitation and stalling never happened
But oh well. It still runs :). Also after I’ve retarted the timing by hand now the car runs better then ever I think and holds idle /doesn’t die at lower rpms compared to before when I started this post so there’s some improvement.
It maybe the o2 sensor causing my issues I guess I will replace it because I have a new one
Yeah definitely will do the clearance check when I get a chance. The car isn’t being driven right now because the xj12 is my daily. Oh and also check if it holds the pressure in there
Not my suggestion, the other David did. I maintain not to run it like this. The interior lamp covers are sparse but on ebay. Also I think Gary is making molds?
**
The O2 sensor, when hot(!) and working, detects oxygen in the exhaust, Jabraan - and if oxygen is present; it enriches fuelling. With #5 dead, incomplete combustion may leave enough oxygen - and the Lambda system will run the rest of the cylinders very fat…
Disconnect O2 sensor - if anything changes, the sensor is working. With a normal engine, properly set up, the 02 sensor makes no difference - what happens with an abnormal engine is anybody’s guess…
Incidentally, with the plug removed, air will blow out - with the plug in; the air blows out somewhere else. Unless you made an error in the compression test of #5; you have no compression - no ifs or buts…
**
Since there are likely 5 cylinders puffing out exhaust, Jabraan - it seems a rather dubious procedure…
But is sort of pertinent to find the specific cause of the lack of compression - even if you propose to go on driving rather than fix it.
A leaking exhaust valve is indeed likely, but bear in mind that the loss of #5 is most noticeable in idle. As the revs increase the engine smooth out due to inertia - and at some stage the engine appears to run normally. However, due to the loss of #5 it will be down on power (some 20%) - particularly during acceleration.
If #5 is allowed fuel and injection, and the mixture indeed ignites; hot gases will affect the leak area - hastening engine deterioration. The dead #5 will invariable consume power - it’s not worth while feeding it…
As a curio; injection is triggered by the ign amplifier, every third ignition pulse - the actual sparking at the plugs is immaterial. Also; which cylinder is firing, and is associated with the injector triggering, is purely random. As you crank; any cylinder may become the ‘third’ one - triggering injection.
Which means that as you start; #1 may be it, and the #6 triggers the next injection endlessly repeated. If #5 is the ‘third’, the #2 is ‘paired’ with it, as is #3 and #4. To the extent coincidence between injection and cylinder phase affects running, particularly with a dead #5 - you may have experience some different running each time you start up…
I thought I had a bad valve after doing the test yet it just ran badly. In theory it is a good test, but only if you know what to expect.
The nicest way to find a valve leaking is by means of a leak down test; simpler, by getting the cylinder to tdc and then pressurizing it with air; then listening to the escaping air: intake, exhaust, or breather/oil cap?
I doubt injection timing influences the running characteristics.
Maybe you can retest for compression before looking at fuel and spark again.
I decided instead of making it complicated try the easy things and that uneven running hesitation was because the o2 sensor. With it unplugged the car runs strong on 5 cylinders. I’ll either keep driving it or sell it
Jabraan,
I also recommend that you check the clearances of your intake and exhaust valves. My 1984 XJ6 Vanden Plas had a burnt #1 exhaust valve shortly after I bought it and when I measured the valve clearances I discovered that they had all closed up. My burnt valve might have been prevented if the prior owner or their shop had checked and adjusted them. This was when I learned how important the valve clearances were and how expensive and time consuming fixing a burnt valve was. You might be able to determine if tight valve clearances burned your #5 exhaust valve, and prevent further damage to your car’s engine if you measured the valve clearances to see if they are within spec (0.012-0.014 inches) or not. Adjusting valve clearances is a somewhat complicated process that requires specialized tools. But checking them would only require some common hand tools, a feeler gauge, and two replacement cam cover gaskets when you put the camcovers on.
**
The uneven running is caused by the missing #5, Jabraan…
The 02 sensor may cause excessive fuelling, but as the sensor is superfluous for running the engine in any case - leave it disconnected…
However, Paul’s argument is valid; if loss of the #5 was caused by incorrect valve clearances; checking and adjusting the others will prolong your use of the car…
David,
Thank you for that advice on disabling the ignition for a compression check. I will try that when I do another compression check soon on my 1984 XJ6 Vanden Plas that I did that engine swap on earlier this year. I have put about 3,000 miles on the replacement 4.2L Jaguar XK engine and it continues to run great. I just want to confirm the numbers now that I have some miles on it.
BTW, it is a breeze for me to do a compression check on these six cylinder engines because they are so easy to work on. When I do a compression check on one of our V12 Jaguars it takes me all day.
Conclusion to my xj6s rough running is that I still need to adjust timing and. I’m putting both my jags for sale whichever sells first goes and I’ll keep the other one.
It runs strong on 5cyls as In doesn’t have hesitation or feel like it’ll stall so it’s better then when we started. Tho other then the missing / bad cyl I started this post for the hesitation and stalling issues and that I feel like I fixed myself by disconnecting the sensor lol
