Intermittent Engine Fail.

[Flappers]

Hi, I bought my Double Six about 3 months ago, (1989) just as the icy weather hit, I slipped on black ice, was just a passenger. I did some quite hefty damage to the drivers front wing, it needed a new front sub frame and jigging out an 1/4 inch. Anyhow, all good got the car back 2 days ago & drove it the 10 miles home and noticed that the engine would cut out, intermittently, not always when idling at lights but noticeable then because the engine would stop. (not allways stop, it dies for a half second and jumps in again) A turn of the key and shes fine again. I don't think its the pumps because this happens regardless of the tank used. Not sure its the bit of kit that kills the pumps & ignition on impact as I'm told its either on or off, not something that'll be intermittent .... So, the car took quite a bump and I'm wondering what its shaken up, can anyone offer any support please ?

[almcl]

You've only got one pump and the wiring for that runs from the radiator top rail all the way to the back of the car. So don't discount fuelling as an issue.

If you hit it hard enough to bend the front subframe, fuel relay damage (there are two involved) is a definite possibility but so too is ignition. If you give the wiring in the vicinity of the relays a good shake, can you provoke the symptoms?

Do you have a fuel pressure gauge? Could you fit it so that you can see it while driving? If so a drop in fuel pressure would be a big clue.

More random thoughts as they occur.

[Flappers]

Where would i find a fuel pressure gauge, & how would I fit that please ? And where would ... in fact I'll google the relays see if i can find where they are

Edit. Nope, cant find them : / I'm looking in the Haynes, nothing listed here as "Fuel Relay" would it have another name in the book ?

[mike020150]

If you have the same Haynes edition as mine, try pages 340 and 344 for the locations of the engine relays including the fuel pump relay. The latter is usually the second relay from the right looking from the driver's seat. Mike.

[Flappers]

Cheers Mike, I'm not sure we have the same editions but I see on page 340 the relay on the front of the engine bay in front of the fans, I'll go tinker

[Flappers]

This is what I see, I tapped each of them with the grip of a screwdriver (not to hard) and nothing, are any of these the relays please ?







This looks newish, could it be an issue with the ignition & is this the box that deals with that please ?

[almcl]

Lot of questions there, not sure I can answer them all, but

the item in your last picture is the Lucas AB14 ignition module. This has been replaced and the brand shown has a fairly dire reputation. The chip inside that fails is fairly easy to replace. It could account for your symptoms, although in my experience the engine dies and doesn't restart until it has had a chance to cool down. I have a stock of the genuine chips purchased for me by a friend in the US (they're unobtainable here.) PM me is you want to pursue this.

The two black Bosch relays are the ones that are labelled in The Jaguar wiring diagram as main relay and pump relay. One of them is twisted round a bit, the reason why might be worth investigating.

I think you are going to need a better manual than Haynes if you want to pursue this. The wiring diagrams on the JDHT supplement CD might help. Not sure if this will be allowed but a relevant segment from one of these included below.

[mike020150]

Hi Sam,

Intermittent faults are always the worst to diagnose because their unrepeatability makes it tempting to guess. The only real way to solve them is bottom all the issues methodically, one by one.

In the case of a suspect relay, substitution by an identical relay controlling an unrelated function can avoid the need to buy another before you are sure it's the guilty culprit. For the relays fitted to the radiator rail, another issue is earthing. Since you think the top rail has been disturbed, try checking that all the earth leads have been refitted and ensure each has clean mating faces. While you are there, check the wiring for signs of physical damage which could indicate internal breaks and then use a meter to check continuity whilst the suspect wire is wiggled. As Al mentioned, buying a fuel pressure gauge and fitting it would indicate whether you have a fuel problem or whether you need to be looking elsewhere. Mike.

[almcl]

Where would i find a fuel pressure gauge, & how would I fit that please ?

Google fuel pressure gauge. You need one that reads to 100 psi (a good fuel pump can manage that) but the range you are actually going to see is 25 - 40 psi.

It can be plumbed in anywhere on the fuel rail, via a T piece. One option indicated below.

[Flappers]

In the case of a suspect relay, substitution by an identical relay controlling an unrelated function can avoid the need to buy another before you are sure it's the guilty culprit.

Could you please tell me what relay I can safely substitute Mike ? And thanks all for your support, I'll get to it when the weather changes for the better.

[mike020150]

Hi Sam,

Over time and the various model series Jaguar used a variety of wiring options and electrical component suppliers so I can't give you a straight answer. However, take a look around the car to find a relay with the same part number, remove/disconnect it (after noting down where all the wires go) and if you are not sure what it controls, start the car and test to find what no longer works. I believe some models used the same type of relays for the fuel pump and for the cold start enrichment, so, as an example, swapping them and finding the car difficult to start from cold but free of the intermittent fault would provide a clue.

Alternatively, if you are unsure about swapping relays, just buy a fuel pump relay to eliminate it from the long list of possibilities but do check the earthing issues first to avoid renewing the relay unnecessarily and throwing yourself off the scent. Mike.

[Flappers]

Just to be sure, its the right relay i should be replacing here yes ?

[mike020150]

The fuel pump relay should be the second relay in, counting from the right hand side of the radiator rail. Disconnect one wire and insulate it. Then, try turning on the ignition. No pumping noise will mean you have found the right one. Mike.

[BobBate]

Hi Sam,
From workshop experience this fault is often caused by the inertia switch not resetting correctly after activation due to an accident. Suggest you trying pulling up and pressing down the plunger several times quite sharply then leave it down and carry out a road test.

If the engine cuts out try isolating the inertia switch by joining together the two wires. If the fault still exists it is elsewhere so please post a reply so I can suggest the next stage of diagnosis.

Bob Bate

[Flappers]

Thanks Bob, the engine cuts out for just a second and then jumps back in again. I was told by a mechanic that these switches are either simply on or off. If they shut the car down i was told they need resetting before the car will run again. So your saying it could still be this switch ? I am waiting for another relay in the post to swap them over before I was going to test and reply, but if it could still be this switch I'll go try find it ( where would it be on a 89 Double Six please ? ) and test as you suggested. Thanks for your time Bob.