I have just been given a 1985 XJ6 which wont run, previous owner used to drive it around but has since stopped running. its has fuel and spark but there is no signal getting to injectors other than the cold start injector. looked through the manual that was given to us but still no luck.

any ideas u have will be greatly appreciated

cheers kirsty and warren

 

There are several possibilities but here are some easy ones:

1) Look for a white/black wire coming off the negative post of the coil. It runs rearward along the water rail. check for breaks, poor connection, etc. It's the trigger wire to the fuel injection ECU.

2) At the rear of the water rail you'll find a bundle of ground wires under a bolt head. Make sure all the connections there are clean and tight. These are the fuel injection grounds.

3) On the water rail is the coolant temp sensor for the fuel injection. It's third from the from. Remove the connector and jump the terminals inside the connector with a paper clip or piece of wire and crank the engine. If your injectors work you have a very dead sensor or a poor connection.

4) On the RH inner fenderwell, well forward, approximatley across from the power steering pump, is the fuel injector resistor box. It's silver...about the size of a pack of cigarettes. Remove the connector and, with the key "on", check for voltage on the two brown/slate wires. You should have 12v. If not, post back.

Or.....simply check for voltage at one of the fuel injectors. With the key "on" you'll have battery voltage on both terminals of the injector if you are checking with the connector plugged in. If you remove the connector from the injector and check at the terminals inside you'll have voltage on only one of them.


Post back if more details are needed.

Cheers
DD

 

Thanks for the help, it sorta reluctantly ran for a rew minutes lol

1) found the white/black wire coming off the negative post of the coil, there was a poor connection halfway up the water rail, fixing this gave a signal at the injectors (I borrowed a little light that plugs into injector plug)
it ran but not very well and was very reluctant to start, running on about 4 cyls, wouldnt rev and evetually stalled.

2)found earth wires, nice and tight and clean.

3)coolant temp sensor, third from the front, the plugs all orange and yuck from water getting in there, bridging contacts does nothing and there is no power either side with key on or cranking.

4) found injector resistor box, it has power at both brown/slate wires with key on.

5) now these injectors, all have power on one terminal unplugged,but to acheve this, the whole lot has to be unplugged, if you plug No 5 or 6 into thier injectors it seams to backfeed and give power to both sides of the plugs of any other injector plugs you test.

using this little plug in test light and cranking the motor it flashes but man is it dim, its got to be dark to see it, put it on the cold start injector and its bright as.

 

Hmmm.

With the key "on" but engine off you should have 12v at both sides of all injectors if they are plugged in or on one side if they are not. If not I suspect a problem with the ballast.

With the engine cranking or running the ECU grounds one side of the injector (so that the injector operates) which the ballast drops the voltage.

I sorta thinking you have a problem with the ECU.

I'll have to mull this one over a bit. Others will chime in.

Cheers
DD

 

It's a long time, (too long !!), since I fiddled around with the fuel injection on a Series 3, but anyway, here are a couple of thoughts.

1. Your little plug-in injector test bulb is a really useful device, and should wink brightly as you turn over the engine, and also whilst the engine is running, (obviously the cylinder for the disconnected injector will not get any petrol). I still have my test bulb in my tool kit since 1995 !! Test each injector one by one with the bulb and check they all 'wink' brightly and properly. All the injectors fire together twice per engine revolution.

This is an early EFI, (Lucas-Bosch L-Jetronic), so is NOT digital, it is all done with discrete components inside the fuel injection control box, which, note this, has nothing whatever to do with controlling the ignition except that it relies on the ignition coil pulse to time the injectors. Combined all-signing, all dancing, digital engine control modules came later.

The wiring loom for the engine and injectors plugs into a socket on the scuttle, (or firewall), and there is another on the other side of the car for a few other things which escape me at the moment. This was always a place where the electric contact could deteriorate and thus cause injector troubles. Unplug, clean and replace it, but be careful, the heat over the years can make the wires delicate. On the plus side, just getting an injector pulse means the ignition coil pulse feed is OK, so it looks like fuel supply to the engine is the problem, and also you have been able to make it run, albeit not very well or for very long, but it's a start !!

2. Coolant temperature transmitter - one of the two big influences on injector pulse width, (the other being mass air flow from the MAF box), the other inputs are just trimmers. Driver input, (throttle) is picked up by the MAF, but there may be a couple of switches to detect closed, and fully-open throttle position.

3. Good quality fuel at the correct pressure is also essential, if this is too low the engine will not run properly even if everything else is OK. There is a pressure relief valve and this can fail thus preventing fuel pressure from being maintained.

4. There is a little pair of contacts inside the MAF which can fail to make contact over the years. The whole fuel system depends on these little contacts as they switch the fuel pump relay. However, check the first things before starting on this little job.

Anyway, here is a real expert on this engine : -
http://www.jagweb.com/aj6eng/42efi/index.php

 

Thanks very much everyone!
Hope you all had a great christmas!

Now everything has settled, I can carry on lol
Ive been cleaning connections, tracing wires and she runs on 5 cylinders now lol theres power to number 4 injector and coming out the other side of it, but from what ive lernt from you guys there must be stil a bad connection back to the computer or something so it can pulse.
are they usually this hard to start? the injectors dont show a pulse untill its actually running, to get it started the first time I have to mickey around with the cold start injector using its power to squirt the nerest injectors.

 

As far as I remember, the injectors are grounded via a resistor pack to avoid damage to the ECU in the event of an injector going "nil resistance". I assume your test bulb is not winking brightly, if at all on the dodgy injector, is this the case or not ?

Check connections to this resistor pack which is at the back of the engine compartment somewhere, (I think !!). The underbonnet looms and connections can get very problematic on a car as old as yours due to heat damage, and connection corrosion. It's a fact of like, I'm afraid. In the UK there is/was a firm making new injector looms, but don't know the name.

Doug probably knows better than me on this one, but read this one carefully, as the author engineer was there at Jaguar when the EFI was developed: -

http://www.jagweb.com/aj6eng/42efi/index.php

 

Actually, I re-checked and the resistor pack is before each injector, rather than after it, but the same checks apply. In the Roger Bywater article I mentioned, the injectors run on 1.5 amps - not a lot at the voltages used, so vulnerable to connections with high resistance from corrosion.

 

You might have a couple different issues here.

To clarify/backtrack a bit....

Voltage TO the injectors comes from the ballast pack. The ballast pack is segemented into two sections, each powering three injectors. Make sure you have key-on voltage on the two brown/slate wires to the ballast pack.

With the key on, engine off you will have voltage on each side of the injector. If you don't you have a wiring problem (common, as mentioned) or an injector with an open circuit.

The injectors are grounded by the ECU. It grounds one side of the injector so the solenoid operates. Tha ballast protects the circuit, as mentioned by Fraser, when the ground event happens.

If all the injectors have supply voltage from the ballast but one isn't working then you have an ECU problem, or a wiring problem (between ECU and injector) or a dead injector.



Should start with 3-4 spins of the starter.

The ECU gets a "cranking" signal from the starter circuit. You might wanna check this out....white/yellow wire at pin 4 of the ECU. If faulty, it might have something to do with the hard starting but won't have anything to do with one injector not working.

Cheers
DD

 

G’day to you all.
I have been looking at this thread as I have the same problem. Won’t start.
With all injectors unplugged I get 12v one side but if I plug one plug in I get 12v either side of the other 2 plugs.
1 plugged in voltage either side of 2 & 3 but not 4,5,6 and the same happens when one of 4,5,or 6 is plugged in.
the circuit diagram shows the resistors before the injectors so if the ecu is switching to ground then it would appear that it switches 3 together.
Does this sound correct?
tried a different ecu but exactly the same.
keep happy
Jim

 

Hi Jamwilblat
You might care to read the pages on the XK engine EFI system on this website:-

Fuel injection and the Jaguar XJ6 4.2 Series 3 / AJ6 Engineering

This system works by there always being 12 volts at the injectors, then, when a pulse comes from the ignition system, the ECU earths all the injectors together, so they all fire together, but twice per engine revolution. This system is an early analogue system, there is no fueling map or anything modern at all. However, it is extremely reliable. So what you have told us is correct, you should have 12v present at all the injectors. The key thing is - no ignition pulse=no injector firing. Pretty simple really !! So you need to check that the feed off the coil to the ECU, a single wire, is there and connected.

BTW Doug Dwyer runs one of these cars, or used to, and is a mine of info on them. I sold my 1980 XJ6 in 2002.

 

Was wondering since my timing was all moved around with new chains and turned out 180 degrees off not to mention the drive gear is probably not in the same position when I rebuilt the motor if that would offset the injector timing.

 

From where I sit, you need to start over and put the cam timing right before you do anything else.
If I'm understanding you correctly, these are Interference Engines wherein cam/crank timing is critical.
If you ever do manage to get it started (which seems doubtful to me but I don't speak FI) you could easily have a serious case of Energetic Disassembly or at the very least some Bent Valves.
(';')

 

No I'm well aware of not bending a valve that's why I don't want to mess with them again.

 

Not quite clear what is 180º out. The cams or the firing order?

Is the engine running at all?

The injectors are batch-fired from the ignition system; they don't know where the valves and cams are. Of course, if the ignition system is not in phase with the cams neither the spark nor injection will occur at the right time.

Cheers
DD

 

That's what I'm thinking , I need to get the firing order started at the correct time the injectors start. And engine has to be timed. I'm thinking my problem is where the lower distributor gear and crank connect along with the oil pump. Not thinking that will come out easily. Unfortunately. Got schematics of the pins and wire colors at the ecm and the power resister. Thinking 5 moves with wires it's either that our pull engine and oil pan .

 

I have a 1981 jaguar XJ6 and it only cranks. My fuel pump wasn’t getting any power, inertia switch was bad. I jumped it and got power to the fuel pump, but not my injectors. I’ve been reading the thread and I still need some help. The white/black wire that comes from the coil reads 12 V and my coolant temperature sensor wire is is completely corroded, getting no power. The fuel injection ballast that is across the power steering pump, the brown/slate wires are reading 0 V. What do I do? The injectors are reading 0 V on both sides.