Hi everyone (Oracles included!),

I have developed a most vexing problem / issue.

Mid last week I was driving along, minding my own business when without warning, the ignition just simply cut out. No warning what so ever.

Unfortunately, whilst intermittent, it is persistent, which is testing for the nerves in modern day traffic (ie. others not paying attention to what is going on around them).

What I have done recently to the car (no major mods);

New ignition amplifier module
Wires from said unit to coil upgraded to thicker speaker wire.
Fitted a 'serviced' and set for unleaded distributor (10 Deg BTDC)
New old stock 2PR Ignition Resistor Pack
New old stock Red Pektron Diode / Resistor module on firewall
Replaced other two 'blocks' next to said diode on firewall with modern Bosch brown blocks

And still is starts to fluctuate and then stall, just when I would prefer to be moving forward with the traffic around me.

My gut feeling is that is is electrical as once I pull over and stop and turn the ignition off, it will immediately start again without issue (Not fuel then).

I also note that when this happens, all other electrical systems continue to operate (Radio, Windscreen wipers, Indicators and as I have become proficient with this issue, hazard lights as well).

Because of the quiet nature of the engine, usually the first inkling of a problem is heavy steering and or lack of propulsion. A quick look at the rev counter confirm the problem when I notice that the needle is lying under the '0' reading on the left of the dial.

I have been thinking voltage fluctuations and or spikes but don't know how to test and or where to look for them.

The coolant sensor is 6 months old, so doubt that is a problem.

Any help, insight, ideas would be much appreciated.

Cheers,

Test Pilot Nigel

 

Can you recreate the issue by jiggling key in ignition??
What are circumstances when it usually happens? Doing 70 on freeway? Pulling away from a stop? Or does it not matter, just happens when.it decides its most inconvenient for you?

 

Yeah, I am with Darren.


A several month old tussle with my car involved what
was a "just plumb tuckered out" ignition switch.


The electrics in them are a bit puny to begin with, and a heavy key
ring don't last forever. Or is over thirty years, reasonable service???


A good taut used one via David Boger fixed so much in my car.


Carl

 

Reading the first post, you do not say whether the ignition coil (not amplifier) has been replaced. Another possible cause.

 

Hi Everyone,

Thanks for the responses.

To clarify;

Ignition barrel is a bit 'loose' and key does stick occasionally, but jiggling it does not affect the running of the engine.

Driving conditions don't dictate the event. Coasting, accelerating, sitting in traffic. It just goes when it goes.

Temperature doesn't appear to be linked to this issue either. It has happened shortly after starting and one day I managed a couple of hours of driving before it presented itself.

I have noted that once the problem starts, it re occurs fairly regularly thereafter. So once triggered, it gets progressively worse.

I didn't mention that I did suspect the coil so swapped in a spare one to be sure. (I use DLB198)

With the car idling in Park I can mimic the instant shut down by unplugging the red Pektron diode on the firewall.

As they say in the classics...This one's a doozy!

Cheers,

Nigel

 

Let's go a bit further. Remove the driver's under-dash trim panel. With the engine running reach up and gently jiggle the actual wires at the ignition switch. Any reaction from the engine?

Do the same jiggle test with the underhood wires at the coil, amp, firewall relays, etc





That cuts voltage to the fuel pump.

Try this...

Get a jumper wire with some alligator clips. Start the engine and then attach the jumper wire to the battery "+" post and the coil "+" post. Go for a drive, or perhaps several drives. Has the problem disappeared? if so, then you have a voltage supply problem to the coil. Note: do not leave the jumper hooked up 24/7. Disconnect it when you are not driving.

Next, unplug the fuel pump relay and locate the white/green wire (or wires...you might have two) in the relay socket. Using a jumper wire apply 12v from the battery "+" post to each of the green wires. One of them goes to the fuel pump so you should hear the fuel pump run. Now start the engine and go for a drive, as above. Any change? You've bypassed the pump control circuit so if the stalling out appears cured, you'll know the problem is in the pump circuit

Cheers
DD

 

Hi Doug,

Thanks for that.

I did wiggle the ignition barrel wires whilst I was in there and there was no effect of the running of the engine.

I will do the other tests as suggested even though I don't think that it is fuel supply related. Simply because the car doesn't cough or splutter like it is starving of fuel.(Unless this fault affects fuel pressure enough that the ignition thinks that it doesn't have fuel and shuts down?)

The ignition just simply cuts out. It is a complete and instantaneous shutdown.

The engine does not power down, slow down or even lose power gradually, it just stops as if a kill switch has tripped (Not the inertia switch either).

I was lead to believe that the red control module governed the injectors, not the fuel pump?

Cheers,

Nigel

 

It has been quite some time since I worked on a Series 3 XJ6, but have you checked the inertia relay designed to shut off fuel in a severe accident?

On a RHD vehicle, it would be located near the lower portion LH side of the fascia.

 

The XJ6 S3 has an Achilles Heel situated within the Mass Flow Meter. Within the compartment covered by the black plastic cover are a pair of contacts that are open until the flap valve opens. This action closes these contacts. They are really tiny contacts and one does wonder at the engineering judgement of the Bosch engineer who designed them. What they contacts do is maintain the voltage supply to the fuel pump relay after the engine has started. On start-up they are bypassed when the ignition key is in "Start" position. It was designed as a safety feature so that if the engine stopped with the ignition on, the fuel pump would stop as well. Over time the springiness of the contact supports diminishes so occasionally contact is lost the fuel pump relay opens and the fuel pump stops.


With me it happened mostly when I was overtaking something and was on the wrong side of the road. Brown trouser time, basically ! Eventually I tracked the problem down with the help of a local expert. A bending of the contact supports to give more closing pressure cured the problem.


Of course it could be something else entirely with your car, but even so, it is mentioned by Roger Bywater, an ex-Jaguar engine development engineer in his article on the XJ fuel injection. Look here on Air Flow Meter problems: -
Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

 

I'm inclined to agree but sometimes finding the fault comes down to process of elimination.

No, the ignition system is that smart. is has no idea what the fuel system is doing

My gut says you have a poor connection somewhere along the line. But...we'll just have to wait 'n' see !



Nope. The red diode pack is like a switching station for the fuel pump circuit. No interface with the injectors. 'Tis the ECU in the boot that controls injector operation.

While you're noodling about, double check the white/black wire that runs aft along the water rail from the "-" coil post. This is the trigger wire for the fuel injection system and the one place where ignition and fuel injector cross paths.

Also check the bundle of ground wires at the rear of the water rail. The fuel injection electrics, including the ECU itself, ground/earth at this point

Cheers
DD

 

Hi Doug,

Just an update.

After posting this stuff this morning I went out to start the car.

Well.

It didn't want to start. Turned over, but took a while to catch on.

Then it chose to idle at 1100 RPM although when the climate control kicked in it dropped to 900rpm which is two higher than usual readings.

Almost immediately the 'flutter' in the revs kicked in, usually meaning this problem is about to happen in my experience.

I selected reverse and the revs dropped to 400 ish and the engine was struggling to run.

The last time I tried to move in this situation, the load on the engine was too much and it stalled, so I didn't bother this time.

I had to go to work so abandoned the project until this afternoon.

SO

This afternoon, when I started it, the engine behaved however, the rev 'flutter' was evident straight up.

I jumped a lead from Bat + to Coil + but the flutter was still there

I jumped a lead from Bat + to green wires (There were two) in pump relay.
Pump hummed and revs fluttered.

I'm going to try and clean out the relay / diode pack female connectors over the weekend and see if that makes any difference.

Cheers,

Nigel

 

I love these problems, you learn so much about the weak points of the cars just from the suggestions from people that have worked through these issues before.

My 20c would be to check that the earthing points (or erffing in Australia) are clean and tight.

 

Hi Steve,

Thanks for chipping in.

Earth straps / points have been checked previously and are good when I was chasing other gremlins.

BTW We all love these problems whilst they are someone else's !!??

Cheers,

Nigel

 

This is good. The more constant a problem becomes the easier it is to solve


Ok, you positively eliminated a problem related to the ignition switch and associated wiring



You eliminated the fuel pump control circuit as a possible culprit



Good.

Years and years ago I had a cutting-out problem wit my Series III. It ended up being a slightly loose connection at the 'main relay'. One of the terminals in the relay socket just wasn't gripping the relay post very tightly.

Cheers
DD

 

Yep you get all of the learning and none of frustration, but also none of the satisfaction when the fix is finally made. Sounds like you are homing in on it.

 

ive seen this before.... its the ignition coil.
when they wear out, they become temperamental and sensitive to heat.

this is why as you are driving it cuts out. then a short time later you can start and keep going like nothing ever happend. 80's Ford had the same problem.

 

Very plausible. The coils are known to give trouble, for sure.

But the coil as already been swapped in this case.

It's possible, I suppose, that the replacement coil is faulty

Cheers
DD

 

Hi Joel,

Thanks for your input, but I swapped in a new spare coil to eliminate this as a source.

I tinkered with and cleaned the electrical connections to all the relays and diode packs over the weekend, but still can't pinpoint the problem.

I have too much on and I need the car for work, so limped it to an auto electrician yesterday.

I managed to drive over 15km in light midday traffic by keeping one foot on the accelerator and moderating my speed with the brake pedal. I found that by keeping the engine above 1200rpm it didn't stall once.

Not ideal and the gearbox didn't know if it was Arthur or Martha, but at least someone with a proper workshop and diagnostic tools will hopefully nut this one out.

I'll keep you all posted.

Cheers,

Nigel

 

Hi All and anyone interested in this thread,

So, I left the car with an auto electrician for a week.

The problem presented itself once a couple of hours after I dropped it off to him when he had decided to take it on an errand to see what would happen.

Unfortunately he was in heavy traffic and was unable to do any diagnostics on it.

For the remainder of the time that it was with him, it didn't play up once!

He was very gracious and did not charge me for not finding any fault, besides he quite enjoyed the beautiful ride as his daily driver for the week.

Getting back to the problem (what problem?)

The only thing that I did before dropping it off to him was remove all the diode packs and relays and clean out the connections.

It did play up after that, but the auto electrician did also remove and refit all the said packs to check them as well.

The only thing that I can think of that may have changed is that a combination of cleaning connectors and perhaps the 'cleaning' effect of sliding said packs on and off the connector pins a couple of times has cleared the problem up.

I picked the car up this morning and drove 70km's around town without any fuss today.

Go figure.

Sorry that I couldn't give a definitive answer like the fan belt broke?! (A cheap dig Steve if you read this)

Cheers,

Nigel

 

Nigel:


Perfect. A classic solution for these and other critters. Seems more so here, though???


Jaguar Mantra, clean, tighten and ion places lube connectors to solve mysteries.


And, yes disconnect and disconnect fixes bad connections at times.


I suspect many a component has been needlessly convicted and replaced.
The remove and replace fixed the issue, not the "new" component.,


Enjoy your victory and save the result in memory for possible reuse,
"way down the line".


Carl