Just picked up a 1984 XJS a week ago and have been having some issues with it.

First of all, the car had been sitting for almost 10yrs when i picked it up but there is very minimal amount of rust and the interior is flawless with only 64k miles.

Anyways, so i drained and flushed all of the old fluids out and put in new fluids including all the injectors cleaners and all that jazz. Replaced plugs and wires, ignition amplifier, fuel filter, oil filter, air filers, fuel pump, etc etc.

Here is my problems im having:

First of all, the car will only start for a few seconds and then die out, for those few seconds it sounds great but after about 5-10 seconds it just stops. Sometimes it just immediately stops, sometimes is slowly starts dying out and stops.

Second, it seems random, but sometimes the car will start and stay running, but if i touch the gas pedal it will die out or will start bogging and backfiring into the intakes.

Third, when the car is actually running i can hear the injectors working fine, but if the car does die out the injectors stay wide open and floods the engine to the point where buckets of gas are flowing out of the intake manifold into the air filters.

And last of all, when the car is in the on position, but not running, the injectors randomly pulse in no rhythm whatsoever.

I have attached a video of the injector ticking problem.

84 jaguar xjs v12 randomly ticking problem HELP! - YouTube

Anyways, any help is appreciated guys, i really want to get this cat up and running and start working on the cosmetics of the car!

Thanks!

 

Good grief!
I'm just spitballing here, but is this an ECU problem?

 

thats what im kinda leanin towards but i think there are other bad parts along with it..... hate to say it but ive been looking into the v8 swaps kits, they make some real nice crate engines with all the bells and whistles now adays

 

It's difficult to tell from the video, but to me it sounds like electrical arcing....... also, at about 0:15 in the top right hand corner of the frame I can see some smoke wafting up......

Was the engine running during this video ? or you only have the ignition on ? I would perhaps try this again in pitch dark and see if you can see any electrical sparks coming from anywhere inside the V

The injectors make a very very slight ticking noise when they are running...... this does not sound at all like injectors

 

These are THE classic symptoms of the injector loom failing and arcing to earth, meaningthe injectors stay open and flood. The injectors are permanently live when the ignition is on, they are triggered by being earthed by the system. If the loom gets cracked, the injectors fire randomly/all the time/not when they should etc etc, as the triggering goes haywire from the uncontrolled earthing.

The loom is clipped to the bottom of the V, mainly, and comes to the engine from the RHS inner wing just behind the headlight nacelle, where it plugs into the power resistor - the silver thing about the size of 2 cigarette packets on the inside of the RHS wing (fender).

I suggest that you take the loom off, unclipping from the injectors and marking where each one went, bit of a pain as unbolting the attachments in the V is fiddly and will need the cruise bellows removing. I bet the loom insulation is baked to a crips in places - both outer and the inner insulation on each of the two wires.

As a test you could carefully reinsulate it with tape, ensuring the wires do not short to each other, as well as that the outer is unable to sort to the engine, and temporarily install it on the top of the fuel rail, hood up, and start the car.

If that does it, either buy or make a new loom. If it is better but not perfect, the throttle position sensor under the capstan might be a candidate for changing too. A duff signal to the ECU could produce some of your symptoms.

My car had exactly this problem, so I've been there too!

best of luck
Greg

 

I think that's my best bet is to make a new harness, either way it needs to be done if its the problem or not. If not at least I'm narrowing it down to the ecu.

And the smoke in the video is my buddies cigarette lol. I don't think I'd be running the car if smokes billowing out haha

 

There are a couple of ways you can go about this.

You can buy a new V12 injector harness for $500 from V12s - This is a plug and go solution
v12s - Official Website

You can build your own using these connectors.
BMW E30 fuel injector connector m3 m5 m7 318 325 ev1 | eBay
and silicone insulated wiring
Wiltronics - Silicone Insulated High Temperature Wire

or you can buy 2 BMW 6 cylinder harnesses and wire them together - these are good harnesses made from high temperate insulated wiring.
eBay Australia: Buy new & used fashion, electronics & home d

Which ever way you go I would use fire sleeve in the engine bay to shield the wiring from the heat.
Aviation and Aerospace Firesleeve AS1072 AS1055D
or this
High Temperature Heat Resistant Wire Jacketed Fiberglass Rope Seal Gasket

 

Sorry it took so long to get back. I made a new injector harness for the cat and still, same story... Injectors randomly ticking.... Any other ideas?

From what i THINK i can tell by feeling each injector as they are ticking is that its all 12 of them firing, not just a certain batch..

On a side note, where can i find the CTS and MAP sensors on the car, ive looked briefly but have been to busy trying to solve the injector problem

 

I did also notice that the resistor pack was VERY hot when i touched it

 

As it starts time and time again and all 12 injectors go wild my guess is the ECU. Typically electrolytic capacitors may have gone bad. That is certainly the case with pre-HE ECUs.

 

I am also assuming the ecu, and the car is an HE.

 

There is a shielded wire going to the ignition box that becomes brittle with age and it is responsible for telling the ECU when to fire the injectors. When mine went bad I also assumed the ECU, but after switching it out there was no difference. Once I repaired that wire, the flooding, stalling, etc... all stopped.

 

Ignition box as in the black box atop the right side intake manifold?

 

Yup, that's the one! It's a solid white wire thats a bit thicker than the rest. If you strip the insulation back you'll see it has a wire within the wire. Very poor design.

 

Supercharged 3.8 Series II for me! its gonna be bad to the bone, light, and 35+mpg highway.


ive also got a DIY injector harness in my for sale thread in my sig. a lot of painful hours wrapped up in it.

ive got a resistor for sale as well.

and an amplifier

 

Ummm... nobody mentioned the TPS (Throttle Position Sensor) If it is electrically wacko...it will fire the injectors as well.

Dave
Atlanta
1994 XJS 6.0L Coupe

 

All of the wiring related maladies will normally mean getting the thing to start is a painful experience. As long as it starts fine every time I would rule out "permanent" issues like faulty wiring or accidental shorts. (I assumed the 84 would be the Lucas double coil (Digital P IIRC) system where the ECU fires the injectors directly.) So still ECU for my money.

 

Pity you are giving up on the V12, but then why not a 4.0 from a '96-'97 XJR? Supercharged out of the box (or engine bay of a derelict XJR). That would bolt pretty much straight in.

 

hmm.

i guess because my 3.8 is $300 and a blown 4.0 is probably out of my price range by... a lot. not to mention availability. clearing the bonnet will be difficult with a I6, let alone one with a blower bolted on top.

plus im actively involved in several grand prix and W/H/G/F body platform forums that have mountains and mountains of technincal, mechanical, and wiring info.
plus i can get tons of performance parts (hot cams, pulleys, upgraded blowers, intercoolers) on the cheap. and not to mention that the fastest blown 3.8 runs a 10.89 1/4 mile and the fastest turbo conversion runs 8.56 1/4 mile.

and then theres the torque. :O

 

shot you a pm about the ecu

TPS tested fine, but it is old so i will likely end up replacing it soon

the 84 does have the Lucas double coil, i will be changing it over to the single coil also



Thanks for all your help guys, i really appreciate it.