Haha well Im grateful for any help from a far!

Yea im starting to think that it's not the plug too, however I'll swap it to a brand new one to see

I think Mikey might be on to something, the gap between the shell and the ceramic has the same amount of carbon in there as on the tip.

So as far as I believe, we have proved it's not the plugs, the leads, the injectors or the exhaust.

I'll focus on the wiring loom today and then move onto the coil.

Jag-o-nomic: Thanks! I'll attach that today. Thanks for taking the time to snap a couple of photos! I don't know what I'd do with out everyone's help!

 

Ok so reporting back again, with a list of ruled out issues and such.

As I mentioned I was going to try the new injector in the cylinder that seemed to run better. Turns out that it was just perceived, no change.

Swapped Coil for a spare I had - No change.
Swapped Power resistor with a spare - No change.
Disconnected Lucas Ignition Amplifier - Car didn't start, so Assume that this is in good nick.
New Leads - No change.
Checked FI loom for damage/wear and tear - None found.
Reattached loose ground to ground wire found under FI loom - No change.
Put new injector in one cylinder at a time - No change.

Well I'm completely stumped, stuck in the mud.

I might just have to live with this miss haha.

 

Well, it is fundamentally operational, at least.

Since we're grasping at bit it couldn't hurt to open up the amp and see of there's a cruddy connection, chaffed wire, or such. Or perhaps replace the module (AC Delco D1906) on a wish and a prayer.

Cheers
DD

 

I'm still hung up on swapping in a fresh plug. Higher heat range.
But, some just say I'm stubborn.


Carl

 

A new plug of any heat range from hottest to coldest will fire the cylinder properly until it either melts from being too hot or fouls from being too cold. Neither of these eventualities occurs instantly.

The electrodes in the existing plug show no signs of melting or fouling.

 

Haha keep it cool guys, for the sake of a couple of dollars and world peace I'll grab one today and try it out, who knows it might just work.

If it does work for awhile and then gets worse again then that will help with diagnosis anyway.

I think the next step is abit more serious too, a leak down test. As I've found that the compression gauge I use will not show me if the cylinder holds pressure, as it has a valve in it. Silly me haha

 

That's fine but I could use a memory refresher on the exact nature of this misfire. How intermittent is it? Any pattern? Only felt at idle? Engine hot? Engine cold? Only after xx-period of driving? Is it just a single 'bump' sensation like one cylinder dropping out for one instant? Or several bumps as though more than one cylinder was acting up?

My experience with burned or leaky or otherwise faulty valves is that the missing is felt only at idle. Off idle, the engine momentum masks any misfire sensation. Unless of course the valve problem is so severe that the cylinder can't develop compression

A 'sticky valve' ...rare occurrence....might cause a misfire sensation but it'll he hard capturing the event on your leakdown test

Cheers
DD

 

Ok so here's the detailed run down on the misfire.



Felt at Idle - Can feel the car shaking from the engine shakes.

Worse when idling in D or R, Eg lower RPM. But can still be felt in P, the shaking speeds up with the idle.

I can visually see the engine shaking, there are moments where it sits nice and still as if is running smoothly.

Not felt when driving, If I floor it there seems to be plenty of power.

Felt and seen when Hot or Cold, even after a run on the freeway.

Felt as soon as the car is started, at all stop lights for the duration of the drive regardless of how long, and felt when I finally park her back in the shed.

Generally if I have been driving and then come to a stop at the lights I'll idle fine for maybe 30 seconds and then the car will start shaking, not terribly but enough to notice.

The engine shaking is not really intermittent, this just happens at idle.

About once a minute it will miss a lot worse on what seems to be a single stroke, this one can be felt in the car with a more pronounced bump or at the exhaust pipes by holding a hand at the exhaust and feeling a sudden gap in the exhaust. This is the single bump that you speak of. The engine is still shaking about unevenly and rocking the car for the entire time while I wait to feel the bad miss at the exhaust. I think that its missing gently or one or more cylinders aren't doing 100% which is causing the shaking and then I get a full miss once in a while (felt at the exhaust or in the car with a more pronounced bump).

The engine visually shakes around about about 5 to 10 mm, mostly on the rear end where there is less support, not evenly though, it seems to shake around semi randomly.

Here is a video of the shake, the Iphone camera is not very good so its hard to see to with the whole engine in frame, I move the camera closer to get a better look at the shaking towards the end.

https://www.youtube.com/watch?v=xfGflqGSQcU



Thanks,
Harry.

 

You said the cap inside looks fine? Take it out and use a magnifying glass and look for carbon lines, sometimes not usually seen by naked eye. when it builds up enough to trip and get a miss the flap in the air box. Either one can make it a heavy miss. I bet on electrical, plug is dry, so it is firing somewhat. I have had the coils loose contact with loose terminals that richens and dies or falters. But that would be a hard miss and kill. Listening sounds normal, vibration doesn't bother me, have seen that before, numerous times. The miss and falter, is where I'm searching my archives to remember. Been on these 6s for 52 yrs., and yes this would get me too. Your compression is fine, something like a 20%-25% between cylinders is a killer.

 

I'd reclassify the symptom from "intermittent misfire" to "Rough idle"....very common and frustrating complaint on the Ser III 4.2. I've driven many that idled as yours does; my own was about the same. Difficult to solve; in fact I've never heard of anyone fully solving the complaint. The best improvement I made on mine was richening the idle mixture at the AFM but, trust me, some roughness remained!


Rough Idle Fixes, 4.2 EFI


How long have you owned the car? Has it always been like this, or is this new development?


Cheers
DD

 

JagFixer: Ah good point I haven't gone through and tightened all spade connections, I'll do that.
And your point about the cap is good, I'll have another look.
I'm very glad that you are not too concerned about the sound and the shake! This is the only Series 3 that I've ever even seen or heard running in person, I've been dying to have something to compare it to!

Doug: I've had the car for about 18 months, all of which its been a project, I've only added 1000km to the clock while its been in my hands.
Its always had this idle/miss.

In those 18 months I pretty much have worked on and refreshed everything that I could get my hands on, I have an expansive list somewhere.
18 months ago I had no idea how an engine even worked, I just brought this on a whim to learn about cars, I'd still be off the road if it wasn't for the helpful people here so my thanks goes to everyone!

I'm starting to agree with reclassifying the symptom to "Rough Idle", I'm sorry guys! I didn't mean to start yet another rough idle thread

As for the "Rough Idle Fixes" I have done a lot of that already, as such:

Replaced all rubber seals on the injectors, pintle caps and connectors.
Replaced all vacuum hoses that are in the engine bay.
Adjust valve lash (I call it clearance).
Moved ignition leads out of the way of any other wires.
Checked the distributor diaphragm for leaks.

However I'll approach the list in a more methodical way and see how I go.

 

Also consider, if you haven't already, the cone-like seats for the fuel injectors.....

Jaguar FUEL INJECTION CONE.

If they're cracked and crumbly you'll have a leak

Cheers
DD

 

Well I don't have those at all! But there are small rubber rings that go around the cap to seal against the intake manifold, these are new too, replaced them a couple months ago, the ones I removed were the exact same.

Well bad news my trouble shooting has come to a halt, I took the missus and my little brother for a drive to get ice cream and my fuel pump died haha.

So I'm currently working on replacing that and the fuel hoses in the boot.


I'll be back when I've got the old girl back on the road haha.

 

OK, so I'm back on the road again, and unfortunately I think I'll just have to live with this idle for now, I'll be working through the rough idle list again to see how that goes.

Once again everyone, thanks for your help! Much appreciated! Happy motoring!

 

Been looking back over the years at my previous builds and owns. You adjusted the valves which means cams were removed to install proper shims. Were the bearings wore or corroded? Were the tops of the valves clean? The heavy miss at idle can be an old sticking valve. I have run a few quarts of transmission fluid in the block to soak and clean the engine. Was a 50/50 mix trans fluid with proper oil for a moderate driven 500 miles and change. Yep, lots of oil changed twice. Have also hooked a vacuum hose to a vacuum port and stuck in a quart of trans fluid and flushed thru the intake to cut carbon on valves. Old fashion remedy, works sometimes, sometimes still have to tear down. Some run of the mill remedies that might work without killing the bank. Or some Lucas Valve cleaner pulled thru a vacuum port. Just another thought.

 

Bearings seemed to be fine, no extreme weather and the tops of the valves weren't too bad, I've just come across a local guy who knows this engine and he said he would have a look at it to see what he can find. I found him at the pub the other day haha