I bought a spark plug tester and tested plugs on both sides of the engine and I have fire on both. What next?

 

Geez, I'm gone for a day and look at all the posts! I'm glad to see others jumping in though, it's always nice to see others opinions!
Cassidy, if you have good spark at the plugs on both sides, then you can rule out bad coils and ignition modules. So perhaps we're trying to diagnose a problem without knowing the exact symptoms. You said you lost power and the exhaust smelled funny. I'm going to guess that if you weren't getting fuel to one side, then you wouldn't have a strange smell in the exhaust. So my next thought would be the catalytic converter is plugged, or at least partially plugged. Before you take this to heart I'd suggest discussing it with others to see what they think. I will say that if it is the cat-converter, this may not be a project you want to take on yourself if you don't have the time and the tools. It certainly can be done, but it is a royal pain.

 

Hi Cass,

There are so many things this could be,
- slipping transmission.
- engine miss fire. and this could be ignition (spark plugs for instance) or fuel.
- and many more internal issues you probably dont want to know about.

Did you test every spark plug on both banks?

cheers W

 

I did not check every plug. I checked two on one bank and one on the other (my battery went dead before I could check others). I'm stumped. All signs pointed towards ignition trouble. I really want to fix this myself, but I'm close to taking it to a mechanic.

 

Possibly my dumbest question yet: While testing the spark plugs I of course tried to turn the engine over several times. The door was open most of the time and the interior lights were on. When I try starting the car now, all it does is "click." I assume the battery got worn down, but at this point I'm so bewildered that I don't know. What do you guys thing? It's hard for me to imagine something else has went wrong during this process, as the car hasn't moved nor been started in over a week. A friend is going to come over and give me a jump in a while, so I guess I'll know soon enough.

 

Ok. I hooked everything back up and got a jump (it was the battery). There was a loud squeaking (I'm thinking a belt) and the exhause was very weak on one side (the right). I double checked every spark plug and I would describe each as weak (although I don't have anything to compare them to). I tried to start the car again to take it for a drive and it would not turn over. I'm lost.

 

The alternator belt is probably a little loose. When the engine started the alternator is working extra hard trying to charge the weak battery. The drag of the alternator was causing the loose alternator belt to squeel. Best guess :-)






Well, weak exhaust on one side *suggests* some sort of Marelli failure but weaks spark on both sides suggests...something else. Perhaps both coils are getting weak? I dunno. Stranger things have happened.

A "good" spark would be bright blue. A weak spark would be yellow or orange.

If you have a voltmeter you can make sure that the coils and modules are getting 12v. If they aren't perhaps you have a wiring and/or wiring connector problem. The engine bay heat can deteriorate the wiring. You might wanna visually inspect the wiring to the coils and modules.

At this point I'm not sure what to suggest. I hate the idea of throwing parts at a problem but at this point you may have to. Replacing the cap and rotor, plugs, and wires is sorta considered a good step on general principles if the age and history is unknown. I'll add that old plug wires with (possible) high resistance and/or incorrectly gapped plugs (should be .025") can play hell with the Marelli system.

Actually, what I do...and many others do as well...on the V12s is what we call "doing the Vee". Remove everything out of the "Vee" of the engine and replace all ignition parts, fuel hoses, vacuum hoses, and repair all the crispy wiring. It's a pretty involved job, though. I can't even promise it would fix your problem...although it might. But the idea is to save lots of duplicated labor by doing everything at once.

Wish I had a concrete answer for you.

Cheers
DD

 

I'd suggest putting the battery on a charger overnight before checking the strength of the spark. Even with a jumpstart you may not be getting full juice to the coils if it has to pass through a nearly dead battery.

 

If you want to fix this yourself you need to start from the beginning again - forget anything that has happened. Charge your battery ready. You have an XJS if you don’t have a Battery Charger go and buy one.

Diagnosing any fault is a process of elimination starting with the easy obvious fixes first. Being a Marelli car this means checking the ignition again from scratch.

Did you actually pull the plugs out or just check between the lead and plug? I have just replaced the plugs in mine and I had more than 1 that was not in good condition.

You said the exhaust is weak on the RHS, is the car miss firing there should be a constant stream of gas with no PPPing. Or is it a weak constant stream?

When you do start it does it fire into life within 5 seconds or do you need to crank it for more than 10 seconds?

 

I got to thinking about something you said...the exhaust is weak on the right side...but if the car wouldn't start how could you tell?

 

It started (just like always aside from the squeeling) after I got the jump. THen I turned if off, tested the plugs, and tried to start it again and it wouldn't turn over. Sorry for the confusion.

 

I had the battery fully recharged and connected -- but the engine
still wouldn't turn over. My thoughts: either the feul pump relays
are not adequately installed, or the spark plug wires are loose.
What does everyone else think? I mean, it started just fine with a
jump start yesterday then all of a sudden wouldn't turn over. It's
too dark now and I'm leaving tomorrow after work to go out of town
for the weekend, so it appears I won't be back under the hood until
Sunday afternoon at the soonest and more likely Monday afternoon
(first day of a trial prep week, so my time will be limited). I
will probably be noticeably absent but rest assured I'm checking
the site as much as time allows to see how we can sort all this
stuff out without invovling a professional. My email is
anderson_cassidy at hotmail.com if anyone feels the need to converse
in that fashion. Thanks again. Let's all be glad we have a XJS --
the good and the bad. And here's to an enjoyable weekend, whether
your tearing up the road or getting grease under your fingernails!

A synopsis of my troubles:

Loss of power (exhaust weak on one side); squeeling when starting
(who knows) now it won't start at all -- but it sounds like it
wants to so bad.

 

If the exhaust is only weak and not pulsing (miss firing) your problem is most likely unbalanced throttle bodies, NOT something to worry about at the moment.

Mine is weak on the RH bank due to badly worn (read non existent) bushes in the throttle linkages.

 

if this were one of my patients I'd say it sounds like Fibromyalgia!

 

Jamney . . . this is not reassuring!

 

Can anyone post a step by step guide for checking the ignition? What is the easiest way to extract all spark plugs? I think I'm going to go ahead and replace all plugs and wires (as suggested by Doug) and go from there.

I just can't figure out why it won't start now. Why would it go from starting just fine (but having weak exhaust on one side and no power) to just not starting at all?

 

DON'T PANIC

If I understand correctly the engine will not crank at all now is this correct?

If so my guess will be the starter motor. This happened to me with the car 4000km from home and yes that is 4000km. The starter motor had decided to pack it in.

But first do you have power ie do the headlights come on (don't leave them on too long)

If you have power when you turn the key is there a single click from the engine.

 

Just to give everyone an update: After a grueling trial I was pretty much exhausted and just didn't have it in me to work on the car any more before I left on a two week vacation. So, before leaving, I searched around, got some references and took my car to a reputable mechanic that has over 25 years experience with jaguars -- and has personally owned a few XJSs. I come back from vacation yesterday and the car is still parked in the same spot outside of his garage as it was the day I left. I tried calling him for a status update, left a message, and haven't heard from him since. I understand he's busy (like everyone else) but I was really hoping that he would at least have the problem diagnosed by the time I got home. Regardless, that's where I am on my little quest. Hope everyone enjoyed the last few weeks of spring -- it's in the mid 90's here with 90% humidity.

 

Just got a call from the mechanic. His prelimiary diagnoses is a bad fuel pump and he hopes to give me a definitive diagnoses on Thursday. Re re-read the comments on this thread and noted that no one every suspected a fuel pump as the source of the problem. What does everyone thing? Is a bad pump consistent with what I've been experiencing?

 

Did you ever get her up and running?