Hello everyone,

I recently bought a 1986 XJS V12 that is not cranking. Put new battery and nothing but a click under the passenger gearbox when I go to ignition on. Found it to be a relay but don’t think that’s the issue. That relay is 33358B. I checked the starter relay and put 12v to the thick white/red wire and the brown wire. The starter starts and the engine spins. Any ideas on why I can’t get that to happen when I turn the key in the ignition?

 

Welcome to the Forums.

You dont say where home is, VERY helpful for proper answers.
Add that little snippet via the CP tab at the top, easy.

ALSO, I am OLD, too old, but lets get this Drivers/passenger side sorted PLEASE.

RH, or LH, as sitting in the car facing the Front is the correct terminology we ALL understand. The other depends on which side of the car the steering wheel etc is fitted, confusing for sure on a World Access Forum.

The fact the starter works with your By-Pass, is GOOD, so its upstream from there.

The gearlever has a neutral start switch fiasco attached, and different markets have different versions. Aussie fix, HOLD the key in the start position, move the gearlever through the gate and hold on. It should ONLY start in P or N, but age is against you here, anything could happen, soooo foot firmly on the brake pedal would be clever.
If that fails, that switch arrangement is highly suspect, not rocket science, Locate the switch, join the wires for now, and try again.

Failing that, the electrical section of the Ignition switch hates you, common as cold bear down here. Back to that starter relay, probe the White/Yellow wire, go for start, should have battery voltage. If so, that switch is fine for now.

I will return, I have some medical needs for my wife to attend to.

 

OK, thats sorted for a few hours.

Something else appeared in my thoughts.

Has the car been fitted with ANY form of alarm, Imobiliser, etc. IF SO, remove it all, return the wiring to OE pathways. Chasing other Wombat's wiring screw ups will cause you too much stress. Refit that stuff after the ca is sorted if you really must, I never did.

Some reading for you attached.

Any SOLID Brown wire is Battery HOT, so take care. Check that Brown wire at the starter relay for Battery voltage, could be the missing item.

Have a read of the Stickies at the top, much info in there.

 

To expand Grant's point about the safety inhibit switch: If you remove the console top you will see a microswitch attached nto the forward end of the gearbox lever chassis. When in Park or Neutral this witch must be moved to the "closed" position by the lever. If it goes out of adjustment then the inhibit circuit stays open.

 

See if these help the journey through the rats nest

 

The color schematics already posted should be helpful in understanding the system. As you're I'm sure aware, all relays have a load side and a control side. It seems you've tested the load side of the starter relay and it works when manually operated? (manually pressed or jumpered). (Jumpered doesn't really tell you if the relay is OK or not though...) This does suggest the main power cable from the firewall to the starter is OK w/o a problem at the bulkhead connector.

The control side of the starter relay is not directly via the ignition switch. It is via an "inhibit" relay. Essentially the starter relay control side on W1 cannot find ground (through the inhibit relay's load side) if the inhibit relay has not actuated.
I should note for other readers that later cars change this whole system and where the "inhibits" are in the circuit.

The inhibit relay's control side can only activate IF ignition power from the key switch flows through the inertia switch (upstream of the relay), to IRelay's pin 86, and ground is available to pin 85 of the IRelay's control side via the neutral safety switch. (i.e. you should check that relay and test the socket). You may have a bad neutral safety switch in the console, or somehow the inerta switch on the A pillar frame may have been pulled up for unknown reasons. Worst case you start testing continuity between the relay's wiring. The inhibit relay should be just ahead of and beside the starter relay.

~Paul K.

 

Ferrari Guy
I have a 1985 (UK non-cat) and it does not have an inhibit relay in the position your (I guess later- diagram) for a Catalyst-equipped car shows. In mine a fairly chunky white/red cable goes direct from the inhibit switch on the lever chassis to the starter relay. As far as I can tell no relay in that side of the circuit anyway.
I only mention this is the OP's car being a 1986 might be like mine.

 

First of all, Appreciate all the responses. Home is the US Grant, sorry for not indicating that in the initial text. But GOOD NEWS, I got it to crank today from the ignition! The previous owner installed a security system so I removed all those wires and set everything back to normal. Confirmed I was getting voltage to the White/Yellow wire and brown wire at the starter relay. I jumpered W1 on the starter relay to ground and the car cranked. I understand the point of the inhibit switch it to only allow the vehicle to start in P or N. So its either that the switch itself is bad or the wiring to it, correct? I still need to investigate this. I might have missed something that the previous owner tampered with.

So now with it being able to crank, its time to try and get it to start. I went to fuel first. I have verified a faulty fuel pump so I will need to order one of those. No sign of the system priming and removed the pump and put power to it and no sign of life. I confirmed there was power at the leads to the pump. Was able to make shift a system with a spare fuel pump I had laying around and was able to send fuel to the injectors just to see if it will start. No start so I turned to spark. Brand new spark plugs installed. Voltage is being sent to distributor cap but it doesn't seem like its being transferred to the HT leads. No change in voltage at the leads when cranking the engine. I'm honestly not to familiar with distributor spark ignition engines so any information would be greatly appreciated.

I appreciate all the quick and helpful responses and I've made progress so thank you all. Lets keep it going.

 

DAMN, drinks on you then, WELL DONE.

Simple cars these V12's, I say it again.

Spark to the cap, SWEET.

CAREFULLY remove the leads from the cap, LABEL THEM AS YOU GO.
3 screws hold that cap in place, and they are captive in the plastic.
Even MORE carefully f
lift the cap STRAIGHT UP to clear the long rotor inside, then fiddle it around to clear all the junk that may be running over the top, your market clogged things a tad.
Invert that cap, ;look at the centre post, ensure the carbon brush is still there, they can fall out when the cap if juggled into place, oops. Had that too many times.

If its gone, some parts people have just the brush and spring, if not, a new cap and rotor would be best.

 

Thank you! Took a look at the distributor cap and it looks good. I was actually getting spark on some spark plugs when I looked at it today. However some aren’t getting spark. However I’m not sure if it was enough, the spark seemed weak. I currently have the distributor dissembled since the rotor took quite a bit of force to spin and there was no spring back. With it off and compressing the springs, it doesn’t not retract. Could this be a cause of why some spark plugs aren’t getting spark?

 

In a word NOPE.

The rotor rotates (damn I need more coffee) and as the tip passes the probes in the cap the spark
"jumps" the air gap and the spark plugs get spark, the bang juice ignites, and the smile on your face is priceless.

Weak spark is a list on its own. Some common reasons are:
Ign coils are old and tired. Do an Ohms test (ALL wires removed) between +ve and -ve. About?? 1.2Ohms is the number. The coils are nothing special, so if and when replacements are needed, ASK, its that simple.
The WHITE wire to the Prime coil MUST HAVE battery voltage when the Ign is ON, and drop NO MORE than 2V approx while cranking. This is the key to the V12 coughing and starting. Ign Switch Electrical Section (see previous attachment), is the PRIME culprit here.
Inside the AB14 Amp (the black box bolted to the B Bank Inlet manifold, is a condensor looking thingy, tucked in one corner. REMOVE it and bin it. It was a noise seppressor and now they "leak" to earth, thus reeking havoc with spark generation.
HT leads are OLD, like me. They have an average life of 5 years on a V12, tough world they live in.
Engine Earth Strap fiasco at the LH engine mount area. Worst thing ever, so pay attention to it, clean it WELL. I replace them with a dedicated Engine to Chassis strap, and forget that nonsense.

Distributor Papers I wrote years ago attached.

 

Ok Sounds good! Reinstalled the rotor and distributor cap after cleaning it up a little bit. Did the ohms test on the coil and got 1.2 ohms so right on the dot. I removed the condensor thingy within the amp so that out of the way. I checked all HT Leads and found the resistance of them to be between 3-7k ohms depending on length so those seem to be good aswell. I did notice the white wire on the coil did have 12V when I'm not cranking but as I begin to crank it drops to 8-8.5 Volts so its time to investigate the Ign Switch you mentioned. Hope that's the case and I can find the culprit. Any specific things to look for?

Also want to mention that when I initially cranked it, I saw spark on one of the spark plugs but when I cranked it again, did not see any spark after. Any thoughts on this.

 

BEER.

I strongly suggest a relay in that White wire.

I did that to all mine, including the older Series 2 cars, 6 and 12.

Simple cube unit will be fine.

30/51 = battery hot, firewall post under the bonnet.
86 = earth
85 = White wire chassis side.
87 = White wire to the coil.

That gives a real clean signal to the coil, and takes the load off that ageing switch. That rekay wuill stay energised to about 7volts, so even with a dodgy switch, the Whote wire will have a strong 12V at all times.

I also did the Accessories wire, under the dash, and that livened up a lot of things.

 

Hey Grant,

Got that figured out reading about 11-12V while cranking but that’s it just crank at this point. Getting spark at the spark plugs. Have fuel going to the fuel rail. Still no life of starting. What do you thing the next steps would be?

 

Very close.

You need some starter fluid, and a helper.

Have them crank it and spray that Ether up the snout of one side, if the plugs are actually sparking it will cough and fart, so that will almost proves the Injectors are not spraying fuel. They may "click" but that only means just that. If the needle is stuck, lack of use, dried up old fuel, then they will need professional cleaning.

The EFI loom in the nottom of that "V" is getting quite popular in the failure stakes.

Try this:
Ign ON.
Open the throttle quickly to full open and LISTEN. You should hear a CLICK. This indicates that the Inctors are getting a signal, how god that signal is, who knows with that original loom in there.

One thing at a time, spray the Bang Juice, that will confirm spark inside the cylinders, then move to the Injection system.

Aussie Starter Fluid.

 

ALRIGHT! GOOD NEWS and bad news. Sprayed some of the bang juice and bang, it started!! Spraying the starter fluid in spurts and kept it running for about 10 seconds. I attached a sound clip of it running. But here comes the bad news. If you listen to the clip, sound like something is knocking. What does it sound like to you? The sound comes from near the LH intake manifold. Thanks for all the help so far!

 

Pre Ignition, plain and simple.

That Ether is NOT what the engien will run on, other than a cough or fart to prove spark inside said engine.,

WORRY NOT, but cease more attempts, please. You have proved you have spark inside, but NO fuel, so off to Injection area.

1) Are the Injectors "clicking" when the throttle is opened quickly with the Ign ON?
2) Are they spraying fuel, clearly NO. Why, is the SLOW and methodical process of elimination.

For all 12 to be inop, RARE, I would suggest electrical.

Confirm fuel AT the rail, disconnect the B Bank fuel hose from the FPR, drop it into a jar. Ign ON and OFF a few times, thus priming the rail and the overflow should be in that jar. Yes/No?

My sticky at the top No start....... has a lot in it, and maybe the answer.

 

You've got ignition which is good. And that's the first step. The ignition system is upstream of the EFI system in this car and the EFI system depends on the ignition system working in order to perform injection.

The AB-14 Amp which controls the coil dwell and spark initiation (via the distributer pickup 12 point star wheel & vr sensor) has a 3 way split in the negative pin of the GM amp within. One split is directly to the neg side of the coil (and when it goes open circuit a spark is generated), the other two splits are to the Tachometer and pin 18 of the EFI ECU via resistors in a white silicon blob you might have noticed when you had the amp open to dispose of the noise suppression cap that can short to ground with age.

The split to pin 18 of the ECU is via a white wire shielded wire and carries the RPM signal to the ECU. Without that single the ECU will not perform injection (well running injection). You CAN ask the ECU to perform an injector burst without the car running to confirm that the ECU is indeed awake and capable of commanding the injectors. To do this you need to turn the capstan to engage the Wide Open Throttle Microswitch with key-on but car off. You should hear all injectors click once due to that single. If you don't then the electrics to the Injectors or ECU need to be checked.

Its helpful to understand the ECU's wakeup routine. When you turn the key on, ignition power goes to the main relay in the trunk, which provides power to the injectors, and control side power to the fuel pump relay, as well as power to the ECU. The ECU upon first power, grounds the control side of the Fuel Pump Relay (FPR) for a few seconds allowing battery power to pass on the load side through the fuel pump on it's way to ground spinning it up and pressurizing the fuel rail. The fuel pump will shut off in the absence of the RPM signal. It will NOT re-engage until it gets the +12V signal from the starter relay and a continuing RPM signal from the shielded wire from the amp. In addition, the ECU has to have the RPM single in order to calculate injection. The next most important input is the Coolant Temp Sensor (CTS). Without this input being correct, the car will massively mis-fuel (usually over fuel) to the point of not starting (the ECU thinks the engine is off the chart cold as resistance is far to high or open circuit).

Assuming all is normal, the ECU will try to command the injectors via 2 channels (A and B bank) but separated into 4 groups of 3 injectors in a peak and hold system which means to open the injector group a direct ground is provided to 6 of them (wired in 2 groups of 3) and then in milliseconds handed off to the "hold" circuit that occurs by keeping the ground going for the duration of the injection via the Resistor Pack pathway - thus limiting the current and protecting the driver transistors in the ECU.

Common issues: No RPM single to the ECU (due to age and a brittle shielded wire); stuck injectors (some of them), inoperative relays (main or FPR), junk in the fuel line/fuel sock/fuel filter, bad fuel pump, bad V wiring for the injectors due to age/brittleness, CTS issue. a 6CU specific issue where it's fuel pump command circuit goes inoperative. A 1986 car probably has the 16CU though that does not usually have that last problem.

~Paul K.

 

Thanks for the replies @Grant Francis and @FerrariGuy .

I haven’t been able to get much work done on it lately due to being busy but got some work in today.

Confirmed injectors are clicking when ignition is set to on and throttle is opened quickly. I also disconnected an injector and confirmed that injector is spitting so there is fuel at the fuel rail. I did not check every single injector and confirmed they are also spitting. So I will need to do that.

One thing to mention that I will look at tomorrow. This might be the issue. The return fuel rubber hose going from the fuel rail to the FPR expanded and popped. Seems like the system after the fuel rail to the tank is plugged somewhere causing the pressure to build up. Also not allowing proper flow of fuel. Could this be the reason for the non-start. Everything else seems to be ok….. unless there is another direction I should go in.

 

Return .line blocked would give excessive pressure and cause lots of running issues., normally. In your case I reckon "flooding" and that is stopping running, I think???

Trace that hose to the spigot at the firewall, remove that hose and put the end in a jar. Switch ON the Ign to prime the rail and ensure you have flow that far down the line. If so, read on, if NO then the issue is possibly in the fuel cooler (I remove the fuel lones from them on ALL my V12's and 6cyl)

If tht test proves OK, then its time to get "down and dirty" with the beast, and follow the steel line towards the rear of the car. LOOK CAREFULLY around the jacking points, as tyre fitters are reknown for jacking cars wherever the pads hit, and crushing that line, I have had a number like that.

There is a hose in that line where it travels OVER the rear cradle, usually leaks fuel, but it may have collapsed internally and plugged itself. PITA to do with the cradle in the car, but doable all the same. You will need that warped sense of humour, and that whole new language you are learning quickly, haha.

In the boot, front corner, LH side, obviously, is the end of that pipe/hose, and it twists around to enter the tank in that corner. Usually no issues with that hose, as the Spare Wheel protects it very well.

Take your time, one section at a time.