Long shot, but you didn’t set the points gap with the distributor on the bench, did you? If there’s any play in the shaft, it will alter the points gap when installed.
Hi Kevin, the original distributor was setup each time before installation with different caps. I replaced it with another dizzy from another car with low mileage, but the results were the results. . At this point I don’t believe the distributor is the problem, but possibly faulty wiring. That will be my focus today and I’ll keep you posted. Have a great day…
Have you done a resistance check with the assembled wiring and cap - that is from the contact inside the dist. cap to the contact inside the plug cap. Also what is the total resistance in the system? Some folks have resistor plugs, resistor spark plug caps, wires (including the cap to coil wire), and a cap with a resistor brush in the center.
Do you know anybody with one of the old ignition analyzers with a scope? They really do work at pinpointing problems.
I’ve mentioned this “long shot” many times in the past. Corrosion between the distributer plates can cause the centrifugal plate to stick (not return to the stops) after the engine is revved. On my car the problem was very elusive as the plate would stick in various positions…so the timing was always changing. Another problem I’ve encountered is #2 and #6 plugs not firing. Turned out to be the rotor was not set square on the shaft and angled “up” when it passed by those two brass terminals inside the distributer cap. Both weird long shots, the second was obvious when I looked more closely at the rotor.
Several of these hypotheses can be tested with a timing light.
Using the light in the usual manner at idle does the timing mark jump around? That can suggest a wobbly distributor bearing causing the points gap to vary.
Revving the engine does it return to same advance each time at idle? If not that could be the weights hanging up.
Connecting the light to the plug wires other than 1 & 6 do the timing marks still appear every once in awhile? That could be a crossfire occurring.
Terry I wish I had, but tomorrow I’ll be taking the distributor with the points wires and everything intact to Brian Meleski from Motorcraft limited (Jag shop) here in Rutherford New Jersey to analyze this puzzling issue. They have been servicing XK’s XKE’s and jaguar in general for fifty plus years and counting, I was told they have an e-type engine at the New York Art museum on display for many years. Lets see what he discovers, i’m sure it will be a learning experience. Cheers!
Wow that’s interesting, it seems mine does not fire on #2 and #5; I’ll give an update tomorrow, cheers!
Sorry, no video. If you are still living with points and condensers, you really need a dwell meter to confirm your points are set correctly. A vacuum gauge is also very helpful in trouble shooting sick engines. I assume you have a timing light to confirm your timing is proper and consistent. Old school tools help to analyze these old school engines.
What dwell is considered optimal for the XK engine?
Or is it enough to observe how steady it is?
Hi Eric, I did check the shaft and it does not seem to have any wobbly movements. I’ll try what you have suggested before having it checked by Brian, thanks and have a good evening…
Hi Kris, I’ll give it the timing light in the morning thanks…
I shoot for 35 degrees dwell
Same as for a stove bolt… or a Porker… or a Bentley…
30 to 35 degrees.
2 Likes
I was surfing the net when I I found this after suffering to no end with the annoying missing and misfire. I tried new wires, rotors, points and condensers all with negative results. So far it turns out that the rotors mybe the culprits. You may have an issue that also developed or developing and this could be an eye opener. Though I’ve not recieved the new oem rotor I’m hopeful it will solve the challenges. Please take a look at this video, it may save you a few dollars/quids When the new rotor make sure to ask for the red OEM rotor…
Indeed: poor quality plastic in a rotor can drive you NUTS!
1 Like
After months for trying to figure what was causing the misfiring popping and back firing, a friend who was vacationing from Jamaica worked on these cars on the Island as a certified British car mechanic. After five minutes of telling him what my challenges were, he quickly pulled the the ignition wires of and figured number one on the firing order and jackpot, the for month issue was resolved.
It turned out the distributor was 180 degrees out causing the horrible running and misfiring. I quickly understand, this is a very common mistake with mechanics putting these engines together, When I replaced the wires I had no inclination the firing order was not in sink causing such a nightmare for something this simple, there were no indications that the engine was touched but later discovered the PO had a friend who was a Porsche mechanic did tune-ups etc.
Though he did some work on the car he did not realize British cars especially over head cam designed Jaguars are not mechanically the same or designed as Porsche’s.
These engine were meticulously designed and to but to be done by the book and not a common sense approach.
One may ask why didn’t I take the car to a certified jaguar mechanic? Firstly the car ran well before changing the spark plugs wires etc and thought the matter was a simple one and did not want the expense of having it towed back and forth, diagnosed and charged for a simple fix, nuff said!
Hi Garth I think one of the problems here was an inadequate description by you of the problem you were having. A misfire is something different from popping, back firing, and horrible running. The latter suggests exactly the problem that was observed and correctly diagnosed, the former is something the responses were trying to deal with.
1 Like
It must’ve been a different problem, because you can have a distributor, 180° out, and if it’s properly timed and properly wired, it will not cause a running problem.
Thanks Terry and my apologies I thought I was being clear and the description adequate; however I’m happy the matter is now resolved but I’m going to make the corrections needed as per the Jag manual cheers!
What Paul; (Wiggles) said…so there was something else…such as, also likely not wired up correctly. Does the 4.2 have a distributor drive dog that allows 180 out? or…was it out in the drive gear, or internals? Nick