I bought a 88 xj6 for 500 bucks a month or two ago because its a no start and the old owner was tired of working on it, it says it only has 74000 miles on it so i hope i can get it running
He claims he changed the fuel pump, filter, and cleaned the injectors.
I changed the Crank positon sensor, Ignition coil rotater and cap
It seems like its trying to crank more than when i got it, and tonight i almost got it started
I turned the key, heard the pump prime, then started cranking it, then i pumped the accelerator and the RPM gauge actually picked up to around 1.5k, but it wasnt running corrext at all, it was sputtering and let out a large cloud of smoke and died as soon as i let off
Im excited because i know its close, it just needs a little something, tommorrow i think im gonna take a fuel line off in the engine and check if its getting fuel
Wondering if anyone has any ideas on what it could be
Without a doubt the first thing you must do is a COMPRESSION CHECK. Probably the easiest car in the world to do this on. Really no need to go one step further in your troubleshooting until you perform this 10 minute check.
Any questions on how do do this let us know
For $500 it’s really hard to go wrong with a 74K XJ40 (only a little over 2,00 miles a year, sweet !). Either you’ll have a nice runner or worst case if you sell a few part you’re already making a profit.
Regrettably I think you just found out why the price was so low. As a rule of thumb all readings should all be within 10-15% of the highest compression, so yes you definitely have a problem.
The next step is to squirt about an ounce of motor oil into each cylinder and do the compression check again. If the readings jump up to normal then the piston compression rings are at fault (the oil temporarily seals the rings). If the readings remain the same then the problem may still be the rings (broken rings) but most likely it’s the valves or possible a bad head gasket. Remember to get an accurate reading it’s very important when you do these checks that you have a fully charged battery and the throttle is held wide open.
Do you know how long it’s been since the car was running ?
Alright, on my next day off ill add some oil to the cylinders and see if the compression rises, ATF or normal engine oil?
No i didnt have the throttle fully open, i did just take the battery off the charger, do i need to retest the compression, holding the throttle fully open this time?
The old owner said it was running fine a few months prior, so it shouldnt have sat for more than 6 months, but the oil in it now does seem really old, the coolant in it was bright green though so it seems that some maintenance was done to it
I havent seen any evidence of heat warping in the engine or anything like that to suggest it was overheated and locked up
You mention you are an ‘aspiring mechanic’ so I’m reading that as not very experienced, forgive me if I’ve jumped to the wrong conclusion.
As Grooveman has already mentioned, it’s vital the compression test is performed correctly to be certain you are getting the correct readings. If you don’t have the throttle held wide open during the cranking it will affect the readings considerably. These engines can cover very high mileages > 200,000 without exhibiting piston ring / or excessive bore wear and in most cases of lost compression it is either the head gasket or burnt valve seats. If squirting engine oil into the bores does not raise the compression readings then removing the cylinder head to rectify either of these faults has been covered extensively on the forum if you search the archives. It is not a quick and easy job to do, but if you are methodical and read up on it first before starting it is an achievable DIY job. If it does turn out the rings / bores are damaged then I doubt it would be financially viable to repair that engine and would be far cheaper to source a used replacement engine and fit that if you really want to keep the car.
I think you’re very quickly approaching the “is this really worth it” zone, actually I think you’re well past it.
Your compression numbers don’t indicate normal wear and tear on a 74K engine, especially with a AJ6 Jaguar engine which is VERY tough and well designed motor.
Don’t let anyone kid you, pulling off the head is not an easy task. I removed the head on my 89’ a few years back and it’s a LOT of work and I’m a pretty experienced home mechanic with a large workshop and all the tools. It will be a miracle if you don’t end up stripping off a couple of bolts (and depending where they’re located that can be an absolute nightmare), have electrical connectors crumble away in your hand, or run into any number of other bugaboos. Remember your car is three and a half decades old !!
So the best you can hope for after removing your head is that it can be rebuilt and it’s not corroded away. Removing the head by yourself and having it rebuilt will cost you around $1000 for the machine work, full gasket set, fluids. and the other expenses that I guarantee you’ll run into.
And after all this there’s no guarantee that the bottom of the engine isn’t the problem which means a full rebuild.
If the rest of the car is in good condition … meaning no serious rust, and you want to keep it then you’re talking about an engine swap. And there’s no guarantees on the condition of the replacement unless you pull it out of a running car.
If it were me I’d sell whatever you can off the car and look for a much better one (that you’ve done a compression check on before you buy it ).
Hello maxole, what I would do is if you have the time and space and tools take the cylinder head off and see what you discover. You learn a lot along the way with the process. The cylinder head is already lost if you don’t do anything with it. You may discover that it can be fixed, plus the learning process will only make you a better mechanic. At least if you want to be one. It’s always easy to choose the simplest way, but you don’t learn anything from it. And maybe you will get it fixed and that gives a very satisfied feeling. I also once started a major repair job on a engine,i didn’t really know what I was getting into , but in the end I got it made and learned a lot. And maybe an most importantly when you get it fixed , you save an xj40 from demolition.
Not really useful as its been determined that it has a ring problem.
I go along with the idea to gain experience with pulling the engine apart, its toast already so its not going to be saleable but, stripped down theres a bit of aluminium (sorry for the spelling but I’m British/Kiwi) that can be sold for scrap.