I took my '88 XJS into my mechanic to have some work done on it and we found a broken distributor cap....my mechanic said that he was really surprised that the car ran at all.
It had been hesitating upon hard aceleration and was behaving as gutless as a honda civic so I told him to replace the distributor cap and rotor, spark plugs, plug wires, ignition coil, ignition amplifier, vacuum advance, and I was having some mild trouble with the car getting a little too warm during hot weather in stop and go traffic, and I told him to replace the fan clutch, fan, fan belts, water pump, and I ordered an upgraded all aluminum radiator. So far it was only the fan clutch that was leaking oil a little but nothing serious, but it was on it's way out. I can't wait to take it for a drive after all the work is done.
ps what causes a distributor cap to break besides being BAKED in that hot engine bay?

 

Not sure why one would break. Pretty strange. Physical interference between the cap and rotor comes to mind.

In what way was it broken? Cracked, blown up, a giant chunk missing, or ?

A couple things, if it's not too late.....

While he has it apart ask him to check that the mechanical advance hasn't seized. If he twists the rotor it should snap back smartly. Also ask him to make sure the vacuum advance cannister is still working. Problems with the advance mechanisms will really reduce engine power.

The amplifier is very expensive....probably $250-$300. The main functional component inside the amp is the ignition module, AC Delco part number D1906...about $50. Only takes a few minutes to replace.

If there is any doubt as to their age, now would be the time to replace all of the fuel hoses in the engine bay. If the hoses are still original you'll see that some of them are part of a pre-made hose/pipe assembly. These are very expensive to buy. However, the hoses can simply be cut off the pipes and new hose sections installed...no need to buy new assemblies.

Cheers
DD



Cheers
DD

 

In the old days of distributor caps I remember so well, the constant high voltage and humidity would often cause a "tracking" either inside or outside the hard plastic of the cap; this could often be seen in the dark as a glowing line just like lightning but quite darkly. Inside of course you couldn't see it. We fixed them by scraping out the carbon with a sharp point and the judicious use of some Araldite. If you examine the surface of the plastic when it's off the car, you can just see it. Same could happen to the rotor arm. Effects were misfiring, hesitation etc. Good old boy mechanics would spray with WD40 wiping off the excess. The BMC Mini was badly affected by rain right onto the distributor at the front behind the grille. Many wrapped it up in a polythene bag.
Leedsman.
The high voltage leads to the spark plugs were suppressor leads (we called them 'graphited string'). These often caused misfiring as they went very high resistance. We replaced them with wire which was available then, and a single screw-in suppressor of 10Kohm. if you were bothered about causing tv interference.

 

hey what causes a broken distributor cap? just hot engine bays?
it's weird, I have never had a car of any kind with a broken distributor cap, my mechanic said he was surprised that the car ran at all.
the vacuum advance was weak so changed that.

the plugs are saying the car is running a little rich, do you other V12 owners know why?

 

Hi DD, the cap came out in three pieces~!~!~! I know....weird huh?
Haven't done the fuel hoses, but they look as if they had already been replace all except for one.
The small hoses that leave the fuel rail to the injectors need replacing, but my car is pissing me off so maybe I'll just leave them there and forget I ever heard of "engine fires" in an XJS....ha ha.....NOT~!~!...... so funny but ha ha ha anyway,if it was a horse I'd shoot it~!~! (sometimes a little sarcastic rant is good for the soul)
The company I bought my upgrade radiator off in Dallas said it was a direct fit.....bull**** big time......the rails and some other things had to be modified to get the tiny metal hoses on top to fit. **** me off~!~!~!~!~! ugh~!~!!
Don't ever buy from this guy in Dallas Texas, it took him about two months to send my stuff after I got the Dallas city police to knock on his door, and after I called the better business bureau.
if you know who I am talking about don't believe him it is all horse****.

 

thanks for the insight......I was thinking it might be the weather here in the north pole(canada) that was doing it, the really hot engine then 35 below Celcius......? Maybe???

 

I'm at a loss about the dist cap.

For rich running here are a few things to check:

1) coolant temperature sensor--skewed readings
2) excessive fuel pressure--faulty pressure regulator
3) leaking pressure regulator--raw fuel being drawn into the engine
4) faulty enrichment switch--stuck closed
5) lazy or dead oxygen sensor(s)

Your mechanic probably knows how to check these things but, if not, post back for details.

Cheers
DD