The spark plugs on my 1987 XJ6 need to be replaced. This is a 4.2 l engine. What is the correct torque? I plan to buy the Platinum plus 4 that are pre-gapped.

Thanks for the info.

Neal Lewis

 

Went to the Library. The torque should be 27 ft-lbs. The gap (for plugs that need to be gapped) is 0.035". New spark plugs purchased. Plan to put them in tomorrow. I will see if that helps the idle problem. Neal Lewis

 

wnlewis, not to steer you away from the plugs you are looking at, but I have installed the Bosch +4's into one of my vehicles (97 Ford 5.4L motor) and noticed no performance gains. Maybe with the older engine you will see a slight gain, but don't be planning on gaining anything near what they say on the box. They were a good plug and I got lots of miles out of them, but if you are installing them with the intent of gaining more power, don't hold your breathe.

 

Old British cars and lawn mowers love Champion plugs. Seriously. If you want this old girl to run right, put the same Champion plugs back in there.

 

Thanks to both of you who responded.

I was not expecting major performance gains from the Platinum + 4 plugs. However I expected (and got) a bit smoother performance than the old plugs of questionable origin. This Jag had been purchased from an auto auction place as a "beater" for a friend's college son. When it did not prove to be dependable, cheap transportation, it came back to dad. The son was (I am pretty certain) most interested in not paying much for gas and turning the girls' heads at school. So, real mechanical issues were not addressed and things like an ear shattering speaker system were. When I appeared on the scene, my friend just wanted to get rid of the car (his wife really wanted it gone). The body is sound, the engine appears to be sound (the old spark plugs came out looking clean), the transmission is sound (it shifts well) and the interior still looks and smells nice. I saw an opportunity to nurse back to health one of the great cars and learn in the process. My degree is Industrial Engineering. My occupation is Technical Writing. And my passion is doing things slowly and right. Not the right combination usually for the present day.

The brake booster that was on the car was rusted (brake fluid had leaked on it where it bolted on) and appeared to leak vacuum. I replace it with a salvage unit (which may leak as well). Most of my work on the brake booster was done at the friend's house after work and in the dark in the company of mosquitoes.

Several parts came with the car and were either on the floor or in a Tupperware tub. One piece of hardware I think belongs in the brake equipment. It is a long "sort of bolt" with a short section of thread near the head and a long plated stem. It looks like either a stop device, or a metering device. I don't have the shop manual (it will take a few more lawns before I can afford that) to know if it does go into the brake system.

The vacuum system does hiss, so I know I have a vacuum leak somewhere. It could be the brake booster, it could be the old hard rubber tubing, it could be the part that I don't know what it is. I do know that most engines will not idle properly if the vacuum is not correct. The engine will not idle and will not run even close to smoothly below 1500 RPM. Before I put in the new plugs, the lowest speed was 2000 RPM.

This car has the Ducelier ignition system. I can't find the pickup coil by itself. The spark coil I have replaced. Although some members have said to forget the Ducelier coil, it appears to me that the engineers who designed it thought it was needed. Being an engineer myself, I am not about to argue with them (especially when I do not know why they did it). So I feel I probably have a questionable Ducelier coil. That could add to idle problems.

I changed the oil and put in Mobil 1 0w-30 synthetic. I have had very good results with that line in all sorts of engines and am satisfied it will work. The oil filter was replaced with a Wix brand filter.

The air filter was horrifyingly dirt. That is one place where I do question the judgement of the Jaguar engineers. That design is poor from a structural and air flow standpoint. It is almost impossible to tighten that style of air filter without warping it. A new air filter (AF852) is on order and should be here Tuesday.

I have new Borg Warner ignition wires on the car. The old ones were horrible and had been cobbled together to fit. The old coil had overheated and was leaking fluid.

The idle problems could also be (or so I am told) from a bad EGR unit or a bad idle solenoid (although that should cure after warm up). The mass flow sensor could also be bad.

The distributor may also be out of time (time for a trip to the library and a timing light).

I've not checked the compression on the cylinders just yet. That can be done fairly easily and will tell me if there is wear on the cylinders or a burned valve.

What else am I overlooking that I should consider?

Thanks for putting up with this long ramble.

I will try the Champions again when I can afford to buy another set of spark plugs (although right now I am not impressed with their quality control).

Neal

 

Only thing I would suggest, while you may have had good luck with that weight of oil elsewhere, these engines like to run on 20W50.

One other good thing, like Ken said, these engines like Champions, or if you don't like them, there is an NGK equivalent copper core also and cheap.

Just my 2 cents.

 

The NGK or Champion won't cost both arms and both legs. I'll try the Champions at next payday (or lawn mowing job, whichever comes first).

The oil seems to be doing OK, but I've only had it in a few days and have not been able to keep the car running.

I plan to replace all of the soft vacuum lines and the brake booster to see if that helps. The first brake booster tested bad. This is a salvage yard unit donated to me to get things running. I don't think it's any better.

Thanks again for the help and info.

Neal Lewis

P.S. Just got the SNG Barratt XJ6 catalog. WOW! WNL