OK, mud a tad clearer now.

Those revs are OK for now, at least its cleaned out.

Leave the filter where it is, I moved mine from the boot TO the engine bay.

Lean fuel mixture is now my best guess, and that will be the fuel filter as a starter.

 

New fuel filter will then be the fix of the day...

 

Back again...

I did actually change the fuel filter Wednesday, but I found the state and routing of the fuel line after the filter to be too bad to use even for a test drive.
The hose was as close as 2-3 cm from the exhaust manifold. It still had the heat protection sleeve in place, but still not good.

New hoses mounted, new Bosch filter moved up a bit and a good distance kept to the manifold. I heat wrapped filter and hoses while I was at it, can't harm as long time as the fuel tank is cooler than the engine bay air...

Engine started and allowed to heat up. Engine stopped and allowed to deliver some heat to the fuel lines for maybe 3 minutes. No issues when I started and took it for a drive, but then after appr. 3 km it started hesitating and backfiring badly, and this time got it on video. I had to push the accelerator almost to the floor before I got propulsion. After that it drove fine again, so the intermittent part of this issue is for sure real...

Ambient is 28-29°C today, probably the warmest weather I have tried to drive car in.

I opened bonnet at return to feel/smell for fuel leaks and was surprised to find air filter boxes really hot, but they will of course be heated by sucking engine bay temp air through.

Youtube video:

 

Leo
The backfiring is inaudible to me, anyway, on the video. I think you need a plan!

• Have you tried an alternative known-good amplifier?
• Have you checked the wires from the bottom of the dizzy (the wires that come from the hall effect sensor activated by the starwheel in the dizzy) to the amplifier and the earth strap?
• Have you got a new injector loom?
• ave you tried changing to known good/new coils?
• Have you tried a known good ECU?

I think eliminating these would be my next step. Basically something is failing when it gets hot, and that is making me think electrics rather than fuel blockages.
Greg

 

Thanks. I agree, it's not easy to hear. I had to listen to it on my PC speakers to hear it. The sounds are not bangs, but poofs. There is 2 at 2-3 sec and several at 13-18 seconds. If you're still unable to detect the sounds, watch the RPMs. They drop after the turn, and my right foot is at the same time sinking deeper until it eventually goes and RPM rises to around 2k.

Your plan is good, but I will have to team up with someone with known good parts in stock to do it. I have nada on my shelfs for the V12 except consumables as V12 ownership is still new to me.

 

And you were right, both of you. I removed the condensor, and did 3 drives 25-30 km long with 15-20 minutes pauses, and it runs well !
It must therefore be either the condensor or something I have disturbed in the neighbourhood of the amp.

Thanks !

 

Good for you Leo. Grant (the WoOz) is always the one!

 

AND YOU LIVE WHERE FOR DRINKS???????

Maaaaate simple cars for us simple folk.

WELL DONE.

 

Thanks Grant and Greg

For the drinks Denmark is pretty much on the other side of the globe for you, Grant. For Greg it’s not too far, 1000-2500 km depending on where in France you are located...

 

HA,

Greg can be there in a few hours and drink mine for me.

I will get it back when I catch up with him eventually.

Well done again mate.

 

The issue has returned after 3-4 drives and 250ish miles.

First time it was my wife, that experienced it. It drove well for a short 3-4 miles drive, but acted up on the return drive after 8 hours, so the engine was neither cold or warm. Ambient temp has dropped to 17-20°C, not warm at all.

Second time was today, where I have done the 17 miles commute to work. Hesitation/bad throttle response started after only 1,5 miles, so engine bay was still cold. The thermometer had only just started climbing. Pushing the accelerator pedal helped as usual. The last miles in city traffic (after motorway driving) was just as troublesome, so temperature may not be as big a factor as I thought.

I think I will go for a new TPS as it seems extremely connected to throttle position. I have the small red TPS, any suggestions for a source for this (preferably inside EU as Danish import tax fee is 20£...) ?

 

Leo
I think the amplifier is more likely than the TPS. The red TPS is very reliable, and you can reliably measure its performance with a voltmeter. SO why not do that before paying for a new one.
I had a very intermittent no-start problem for quite a while and in the end a new amp fixed it. I am furthered in my belief as you had the amp open and it did have some effect, so you might have nudged some failing component into temporary action.
Manners have them, not too bad price-wise
Jaguar Partno_DAC2673#_IGN.AMPLIFIER EARLY XJ12 SER3/XJS 81-84_David Manners Group with Alts

 

Thanks Greg

You're right: My handling of the ignition amp is likely likely to have disturbed the failing parts and thereby causing them to work for a short period. I will try to find a known good amp to borrow for a test.

Rookie question of the day: Where is the socalled dreaded wire located ?
I thought it was the wire going from rearward facing side of my ignition amp, but this wire is actually 2 wires with a shield grounded securely under one of the amp's fastening bolts, but I should as far as I understand it be looking for a single lead co-axial cable in same style as used for antennas ?

BR Leo

 

The DSW is one of the four which emerge from the inwards-facing edge of the amp. One is the coil +, one the coil -, one the tacho, and one is a very thin white insulated wire that goes rearwards to the loom. It connects to the loom with a connector and the LOOM wire is concentric, the inner is the connection to the ECU and the outer is a woven shield wire; the two are referred to as the DSW because the white inner cooks and shorts to the shielded outer - which is should not do. The shielded outer is to protect the inner from electromagnetic interference, but whether it is needed of not many doubt, including the Great WoOZ. If yours is cooked you unwrap the loom at bit, CAREFULLY, you will see the shield has a big soldered wire bit on it and this is the shield's earth. peel it back until you get to a bit of the thin inner where the insulation is not cooked, and splice in a new bit of wire.
The plug on the rear-facing edge is the signal to the amp from the dizzy starwheel, it is what triggers the spark, and the earth wire you mentioned is another important earth, but not the DSW!

 

Temperatures are now moderate (15-20°C) in Denmark.
I had my A/C filled this morning, meaning I now have a functioning fuel cooler and a nice climate in the cabin

The misfiring issues have none the less become worse. It's running well at 100+ km/h (60 MPH), but lower throttle opening is crap. It runs worse after motorway driving and does now also somestimes misfire at idle. It actually died on me once, never tried that before. Steering becomes HEAVY...

I'm most inclined towards TPS failure as moving right pedal towards the floor makes it run again. A few days ago it was also bad, but I then found a good speeder position giving me adequate propulsion for city driving. I could then adjust speed when needed by applying brake and keeping light throttle on...

 

BUGGA>

TPS must be flaky, not common on the Redish ones, but who knows.

Since it is heat related, sort of, it is hard to "make" happen.

When this event happens, quickly open the bonnet, "feel" the coil. It will be hot, obviously, but if its HOTTER than the surroundings, it could be breaking down due to heat, BUT, that does not answer the throttle position you are able to find to actually drive the thing, but well worth a check.

 

Thanks

The coil is new(ish) and the modern single coil type from the 6 litre: DAC 6093 from SNG Barrett. I suppose it must be good. I did by the way have same issues before coil was changed, so I think it can be forgotten.

The fact that the car runs better at more throttle indicates it is NOT ignition related as I see it. More throttle will mean more air/fuel mixture in the cylinders = It's harder for the spark to jump

I think I will just change my TPS...

 

New TPS EAC9634 mounted and adjusted to 324 mV. The existing TPS was the original Lucas dated 2788 !
No test yet as my exhaust lies on the floor under the car...