85 XJ6 Running Poorly/Rough

image Damn someone stole that. Or it fell off but I haven’t even driven the car… anyone know where I can get that from. Pass front side light lens. Edit. Lol I found where it fell off cuz I only drove it a tiny bit

I just did the compression test here’s the results

Now that does suck. But I still wanna make it run a tad better because I think I can keep driving this because there’s no rebuilding this 212k miles engine anyways. The timing is probably off so fixing that should make improvements. Idk what else. What would cause cyl 5 to be dead atf in the plus hole made no difference.
Spark plugs image

Probably a burnt valve, a 5 cylinder engine is never going to run well.
A leakdown test will show if it is a burnt valve as you will hear air escaping from the (normally) exhaust pipe.

When I take the wire off the cyl 5/bad cyl. The exhaust sounds is more even loped like a cammed engine with the wire In it sounds weird and all sputtery. Idk how I should run it

And yeah I understand this car is never gonna run smooth I just want it to work as good as it can how it is. I’d like to know if it’s better to leave the plug wire connected to the plug or not. Or should the fuel injector stay plugged in etc

Leave it in but pull the head off and change the valve. If it breaks off all is gone.

I would but. I don’t have any tools or a garage. Have never opened an engine before more then taking off intake or valve covers. And I got this car for cheap. Also. I just retarted the timing a bit and the car runs better I think. And I got the idle as low as I can. I haven’t gotten it to stall yet but it might. Maybe getting the timing better and it’ll go lower but idk

No, that’s not good.
If you have two weeks with good weather ahead and some spare time we could walk you through it. I replaced my head gasket not long ago and it wouldn’t have been hard if I hadn’t broken a few head studs. You need a helper to pull the head off the car but otherwise it is not as big of a job as it seems.

What can happen is that either a valve is bent and will eventually collide with either piston or the other valve, or it is burnt and can melt. In both cases the valve might break off and destroy an otherwise good engine, both head and possibly the block as well and all that while driving.

I‘m sorry. But no-compression valve issues are my one fear, otherwise I don’t care too much as it’s a fine engine. And setting mine right has turned out to be a great way to spend time, so I‘m absolutely in favor of keeping the car and looking at the valve.

Look at the room you‘ve got. This was me:
I had a competent helper but I didn’t need him much and three days of relaxed work was all it took discarding the few issues I ran into. I‘m 22 and learned a lot on my own yet it is still running great several thousand miles later and with some shady repair tactics. You can get a really sweet XJ for another $200 or so.

This being an old jaguar I expect my head bolts will break too. lol. And that would leave me with a car less usable then it is right now. And also. Do you know approx how much it’d cost? I think I’m gonna have to sell one of my jaguars. Either this series 3 with 212k miles and a potentially bad engine. Or my 94 xj12 with 100k miles purrs like it should needs shocks and paint. Don’t know what to do :confused:

edit. Does anyone know where I can get a front side marker lens for a reasonable price

Ebay or David Boger or a junkyard. You‘ll have to do something. I would prefer doing the head on the S3 and then selling it for good money or keeping it, but the way things are it won’t last. Shocks and paint are far more expensive, but sounds like a great car otherwise. Your choice. I tend to opt for as many cars as possible but that’s a disease…

The early XJs are almost indestructible and mostly easy to work on. I like them.

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I think I will continue daily driving the v12 and keep the s3 as my side car and keep it easy with that one till I can afford to fix it time and money wise.

I can get shocks from fcpeuro or amazon for cheap under 40 a piece so I can have both fronts done for about 200. I can get the car painted any color for 500 from my friend. I was thinking stock color with flake but I’m not sure yet. The car doesn’t soak bumps very well and is lowered in the front on cut springs done by the previous owner but that’s for another post In the xj40 section.image

I have seen zero compression twice in my Series III XJ6s over the past 15 years or so. The first was in my 1984 XJ6 Vanden Plas due to a burnt #1 exhaust valve. I removed the cylinder head, took it to a machine shop for repair, reinstalled the head and drove it for another 100K miles until I removed that engine due to low oil pressure.

The second time was when the #6 piston rings failed in my 1987 XJ6. I removed and replaced that engine with one that I got from a 1986 XJ6 parts car.

I can’t imagine driving on only 5 cylinders in a six cylinder engine and when I had that happen to me I found a way to fix it. I have no idea what the long term effects on the engine are of driving it with a cylinder that doesn’t burn the fuel but dumps it out the exhaust system but it can’t be good.


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Hey Paul. You got me thinking. I do remember this car was losing oil pressure at idle a few times and I’d hear things getting rattly and boom comes back and cleans up. So I don’t know if it’d be a good idea for me to open that engine up which is something I’ve never done to fix one issue only to find that’s there more bigger issues. Tho it’s possible it just needs an oil change maybe clogged filter

How hard is it to swap an engine comparing to replacing a valve and most likely breaking a couple head bolts.

And driving wise. Idle isn’t pretty haha. But it accelerates and runs better then ever right now after I retarted the timing and fixed a vac leak while replacing the crank pulley. Oh and I’ve only had this car with 5 cyls so I can’t say how it was before… I’ve put about 2k miles on this car like it is

Edit. So what do you guys think about the engine Health based off of the compression numbers. No point in babying a worn engine when another one could be put in. If this engine is worn I’d like to continue using it till it stops working then put a nice working engine in there

If you are going to continue driving the car on 5 then I would suggest you disconnect the injector on that cylinder, you are throwing fuel into a pot thats doing little to no work.

I was thinking about that but then I wondered if an engine can run lean and melt things when there’s no compression? If not then I’ll definitely to that to save some fuel and fumes

No fuel=no burn so not lean, however it might throw the o2 sensor out of whack (if there is one)
Just hypothesising on that as I haven’t owned a S111

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Ok cool I’ll see how it runs disconnected. There is a 1 wire o2 sensor tho probably fouled from the all the missing. I have a new one but I won’t waste it rn

I have removed and replaced several Jaguar XK engine cylinder heads. I have also removed 5 Jaguar XK engines and reinstalled two of them. I would say that removing and replacing an engine is easily ten times as difficult as removing and replacing a cylinder head.

With either job there are many tools required and dozens of things that can go wrong if you don’t know what you are doing, don’t have the correct tools, don’t have the proper repair manuals to follow, and don’t have a lot of patience and attention to detail.


I agree with Paul on the engine swap v cyl head. You will need some sort of engine crane to remove the engine and transmission, the bonnet/hood will need to come off as well.

There is absolutely(!) no point in running an engine at all with ‘0’ compression, Jabraan - it will cause further, and unnecessary, damage…

In a life and death situation, or to get somewhere to fix it: absolutely disconnect fuel injector on that cylinder - and there is no reason to have the plug sparking either…:slight_smile:

If you do not plan to repair/change the engine; sell it - explaining the problem to the prospective buyer. As the problem with uneven running is now clear - it saves a lot of useless work. But do not drive that car - and don’t fiddle with it!

xj6 85 Sov Europe (UK/NZ)

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Well I’ll see how it runs best. It does run better with plug wire in rather then unplugged. I got this car for 1k. I don’t think It’d sell for much more then that so I don’t see the point in selling it. It does drive and I’ve driven it 2k miles like this and the previous owner drove some too

If the engine lasts maybe it’ll get opened and fixed. If it breaks it can get changed or sold then. It’s not like a 212k mikes worn out engine is something to be worried about lol

Other then having a less then premium idle. Kinda sounds cammed which is cool :slight_smile: it drives great. Suspension seems ok condition, interior is great exterior is great. Even has a good sound system. I think I got the heater working earlier too

I would like to change the engine in the future to something fresher. Maybe a manual transmission. I think anything with less electronics will work. I wonder how much those V8 swaps cost. Ik ppl are against those but some are pretty cool. Or if I could find a cheap xk and have someone put it in for a reasonable cost