I‘m pretty sure I have some left over. You‘re welcome to have one I‘ll post it to you if you send me your address pm.
Martin
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Please don’t drive it. Do the head or send it in for repair. It’s not too expensive.
This way you will not enjoy driving it, you will break it big time and it is avoidable.
Do not drive it.
The bright side is that you found the problem. That is a huge thing. Not that it matters, but, the PO might have learned that… Sold, cheap…
It is a great looking car…
The cylinder might be “merely” weak and not quite “dead”. Explains why it runs a tad better with the spark plug working!! At cranking speed, zip in compression… on number 5!! Up the RPM’s and it might “hold it’s own”, that is not a drag on the live 5 cylinders. Or even contribute a teeny bit.
Against the wisdom of some here, I might consider just drive it. It will not get better, it will get worse. I don’t see the best coming from a refreshed head on a 212 K engine!!! One of the other cylinders isn’t that healthy either!!!
1, Find another DOHC. A decent one from a rust bucket?? Good idea to run a compression test on any candidate. Might David Boger have a decent DOHC?? …
- An SBC swap??? Not cheap or simple. Read in the lump section Shop. Jpohnscars is near to you, in Fort Worth. Or Jaguar-Specialties. San Jose, CA.
Aye, born and raised in El Paso. Greed and ambition brought me to CA in 55 !!!
The best of fortune in whatever you choose…
Carl
. …
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Hey what do you mean by at cranking speed get compression. I tested the compression by cranking engine with starter. Are you saying I should perhaps do the compression test with the engine running?
I know the previous owner. He didn’t know about this issue till yesterday either. But he didn’t drive the car much
It does definitely run better with the wire plugged in but I will see how it behaves with injector disconnected
By looking at the compression test numbers the engine is in worn health anyways. But it doesn’t make any noise so I think it may keep working
Just one thought, did you have the throttle fully open when you did the compression test?
It has a very lopy idle and shows low compression on just one cylinder. Of course it will still contribute but not much.
And it will break and then he‘ll be sorry. I‘m not exaggerating. I can’t find the numbers?
Oh and about the oil pressure, that’s bad so maybe you should get rid of it before it stops altogether and let someone else worry about it 
I actually didn’t have the throttle open one any of the cylinders. So no the throttle wasn’t open @davidsxj6
. The car isn’t running constantly tho. Sometimes it’s strong idling at 1k and sometimes it starts dipping low. I put the compression numbers up again on this pic so if you don’t see it let me know
Oil pressure for Jaguars is measured at 3000rpm and should be <>40 psi from memory.
Low oil pressure at idle and just off could well be old oil that has been thinned out by contamination.
Oh thank you. I must have missed them. You should redo the test with the throttle wide open, however it very clearly shows trouble on 5… No need to retest.
But if it runs and accelerates well once in a while you might have messed up testing 5 somehow (and I know you retried with atf). Is there absolutely nothing if you crank it and put a finger on the spark plug hole? 0 might be a little low in all cases, no?
About the oil, on the gauge in the video it looked similar to what I have, and I‘m thinner than 15W40 right now.
When I bought it it didn’t make noise but it was the thinnest, darkest oil I had ever seen.
Sure low pressure at idle but so low that it starts knocking strongly implies that there is absolutely no lubrication somewhere.
I will take the plug out and try to look inside and also see if there’s any pressure The car never clears up but i was talking about the idle. It’ll be sitting normally at 1k and randomly start to hesitate and sometimes recover sometimes stall
You should check the valve clearance on that cylinder, there may not be any, and the valve not closing properly.
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Even with a dead cylinder, the idle can be set at will, Jabraan. And with the uneven compression in the other cylinders the idle will fluctuate - sort of an extreme case of the xk 'uneven idle…
The point of compression test is to verify that the compression is even between cylinders - within 15% of readings is the min spec. Which requires that the same procedure is used for each cylinder. You can run the test either with one plug removed at a time, or all - but no mixed procedures. Faster cranking usually gives slightly higher readings, but does not influence evenness…
Generally; fully floor the gas pedal and crank for 4 seconds. Read and note gauge reading, zero the gauge - and repeat.
A complete test involves a ‘wet’ test; a spoonful of oil is added to the cylinder - and retest. The oil added will counter bore wear - raising compression if wear is the cause of low pressure. To be compared to the ‘dry’ test results…
Given the already unstable idle; I doubt if the effect of the plug firing is reliably detectable…
Be aware that if the injector is working; the mixture in the cylinder is blown out through the leak. A sparking plug may ignite it at unwanted places. Adding that a leak will reduce the amount of air/mixture ‘sucked’ into the cylinders. Which is one reason for ‘no compression’ - nothing there to compress…
Foggyoo’s point of checking the valve clearances is easily followed up - but will need some interpretation…
Frank
xj6 85 Sov Europe (UK/NZ)
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Interesting thought as to how to check compression with the engine running. I’ve seen it, done it or read of it.
Not my point. My point is that the rpm is is low when cranked. And is the compression in the weak cylinder. It rises at a higher rpm. enough to fire at least weakly.
I know of at least one engine in my past. That would not start at all unless it was cranked for an extended period. That would enable one or more cylinders to “pump” up enough PSI to fire and get the others going.
I had a derlict pair of Ford V8’s. Lousy idel. Attributed to burnt valves here and there. but, ran decently once the throttle was opened.
My 50 Chevrolet burned a valve as I came hoe across the USA Drove it for a time, til I pulled the head ands swapped in a machined spare. OK after that. shook mightily when cranked ad at idle. Not hard on that OHV 6.
My DOHC quit. Zero on all six…
Carl
Hey Frank I understand that the idle is adjustable to where I want it even with 5 cylinders. And I have set it around 1000 since that works in park and drive and it won’t stall out. But sometimes while just sitting there the idle will bogg down the car sometimes stalls. Seems like something electrical changes something and the car starts hesitating. It does recover sometimes after I hit the gas or restarting the car after it stalls. I’ll see if I can get a video of what I’m talking about
I did the compression test by removing one plug at a time and at the end all 6 were out. I did the test with the throttle closed. And I did wet test cyl 5 and got no change
The plug firing or not is pretty easy to spot/hear/feel as with it plugged in the car runs unevenly but with the wire out it runs even but loping like a cammed engine. I think it’s better with wire on, since off the line response is better
And the point on checking valve clearance seems like a good idea but I don’t know how to do that.
Jabraan,
When I have done compression checks on my Jaguars I first get the engine up to operating temperature and then turn off the engine
Then I remove all the spark plugs, hold the accelerator at Wide Open Throttle (WOT) with a piece of wood, disable ignition by removing the coil to distributor wire, and disable the fuel.pump by removing the Fuel Pump and Main Relays before cranking the engine. I don’t think that this makes a difference with an engine with a cylinder at zero, but it is a consistent way to evaluate relative performance in cylinders in an engine without major problems.
Do you have a copy of the Jaguar Series III Service Manual? Procedures like valve clearance checks and adjustments are complicated tasks that in my opinion require the proper documentation to do without causing further damage or personal injury. I highly recommend that you get a copy if you don’t have one.
Paul
I have a Haynes repair manual for it. And I just made a video of the way it’s running but I ended it before the car recovered which happened like 10-15 secs after I ended it so not long this time.
the car come to a steady 1k idle after this period of hesitation which is right after a cold start. It starts and rpms go up like normal but then they fall too hard lol. Sometimes it recovers sometimes dies. It recovered this time
Edit. Right after this I started it again and I got a better video I’m about to put it up
So this is the better video which is after the first start I started it and there was hesitation so I shut it off and made this video. So even after the 2nd start and clear up it did this again on the 3rd start up.
Guys don’t mind the steering wheel it’s only temporary so my legs aren’t smashing into the big stock wheel
I just streched and broke this. Now both are broken. Does anyone know where to get some? There isn’t any xj parts cars around me from what I know. If not I’ll just put leds there with no covers so atleast it lights up
Jabraan,
I’m not sure how much help I can provide because you are trying to run your engine in a condition that it was not intended to run, on only 5 cylinders instead of six. I can imagine that lots of unintended or unusual things may happen that have no explanation.
Paul
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To be expected, Jabraan…
The injectors are not synchronised with the valves - they spray once every revolution. If valve, say #6 inlet valve is open and ‘sucking’ as the injector sprays - valve is closed at the next spray. Other cylinders are in different states as injector sprays - there is an inbuilt difference in cylinder performance…
This is cyclic; sometime the cylinders are ‘in phase’ - sometimes they are not. Overall, the engine power varies slightly, most noticeable at slow rpms - part of the ‘uneven idle’, loping. The injectors actually spraying into the manifold, and cylinders are to some extent crossfed from all injectors - normally smoothing out the effect…
However, with one cylinder dead and not participating in power production; the ‘phase’ effect is grossly magnified - and the engine, loping excessively and may indeed stall.
No other factors needs to be involved; as Paul says, the engine is not meant to run on 5 cylinders - and unusual things will occur. There is no way of compensating for a dead cylinder - your whipping a half dead horse…
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As plugs are removed one by one, you ran the last with the engine spinning much faster, which tends to increase compression - as will flooring the throttle. As the intent of the compression test is also to verify evenness between cylinders - changing parameters for each cylinder is not ‘best practice’…
However; your #5 is dead, most likely, but not necessarily, a leaking exhaust valve. Petrol may or may not ignite, but such force exerted is dissipated through the leak. If unburnt; petrol will accumulate and backfiring may result - but the leak must go somewhere. The risk with running the cylinder…
Increased compression by higher revs is academic - the lack of compression during the normal compression test is proof enough. Running the engine in this state is unchartered waters - you do what you like…
Frank
xj6 85 Sov Europe (UK/NZ)
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No. The spark still wants to go somewhere from the coil. Better to remove the connector for the ignition amplifier from the distributor or to give the wire a few mm to ground so it can spark.
Remove all plugs and turn the engine by hand. Does it suck/push against your thumb on the no. 5 spark plug hole? Does that pressure hold for a little while?
Clearances; remove the valve covers. Try to fit a 0.016” or so feeler gauge under the heel of the cam (lobe sticking up). If it fits it is excessive. Then crank or turn to the next tdc, etc.
Also try to fit a 0.010 and if it goes in it is too small. Spec is 0.012-0.014”. Engine can be cold.
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