Hi All, I have an 84 XJS HE. Just checked and cleaned the injector resistor connector and all seems to be ok.
Fault I have is that I can only just get my car to start. She will only run with a bit of pedal, she won't tick over on her own. I'm getting obvious misfire, dangerous amounts of unburnt fuel and black smoke from exhaust. Stings your eyes, and the noise from the exhaust, sounds like a loud drunk orchestra wind section! My battery light is dull, and after a few seconds goes out before cranking the engine. The alternator has been off twice, new reg, then I thought best check the diodes, and I'm told they are good too. I'm convinced the battery light fault is connected to poor running issues as described but i'm stuck now. Any ideas? So far replaced distributor cap, ht leads, rotor, plugs. All sensors check out ok and have checked them at the ecu end too. No O2 sensors on this car, uk spec. Fuel regs have also been changed, and the return pipe is good as is flow to fuel rail. Fuel is new too. Removed the surpressor from the ignition amp. Oh, injector harness is new, as is fuel filter.

 

Well, the V12 is not that familiar to e as others. But, all IC's have a degree of commonality.


Compression, fuel, air and spark, each in the right amount and at the right time.


So, diagnosis is isolating each to test for function.


I usually choose spark. A crackling blue. A wimpy yellow will not get it.


And fascia indicators are only that, no more. A meter is an essential on "modern cars". I used to get along with test lights alone. Still good in some things.


1. Check the battery. Volts just under 13. Any less is marginal.


2. Remove the battery cables at each end, clean lube and tighten.


3. Down under. Find the chassis to engine braided ground. Clean lube and tighten it.


When and if you choose to take this assignment report back.


Carl..

 

If it is pooring out fuel, well, then check the fuel side Leaking injectors are common...

 

ing coils might be OLD and failing...

 

Thanks for guidance so far.
Main coil is new, aux coil checks out ok. I know the injectors are not leaking, I lifted the rail when I had the cam covers powder coated, new gaskets on the inlet manifolds, and I can't see anything trapped there. I have not checked the amount of fuel coming out when cranking though? She has been in my garage for the last 13 yrs, but v dry and part of the house, so not really deteriorated as far as I can tell. I noticed the last time I used her that there was a relay type clicking noise that was causing the battery light to come on and off. Can't say I hear any relays when turning the ignition on now, apart from the fuel pump running for a few seconds as it should. Is there a main ignition relay or module I should look for?

 

Again, Thanks for this, I will check these as suggested. I know the earth straps are present, as I found them when crawling underneath to replace the coolant pump, and resistance seemed low, but I will check on my next day off, next Wednesday now!

 

Forgot to mention, I checked the spark earlier from one of the ht leads and pretty faint yellow spark being generated, although I didn't check the plug on the main ht lead to the cap. I have battery power at the coil, but it's generating this pretty poor spark, as mentioned the plugs, leads, rotor, main coil and cap are new, so this must be an earth or ground issue?

 

If the battery is weak then the ignition voltage will be low, a few volts low on the battery will be 1000's after the coil.

Check spark at the HT lead from the coil to the distributor.

Check connections on ignition module on the LH intake manifold.

 

All good apart from battery, although i have been using a pack to start her, and then alternator should take over?

 

If the battery has lost a cell it can clamp the alternator voltage low, this will also put more load on the alt. Do not run the car without a battery as the battery acts like a capacitor and smooths the voltage produced by the alt. Running without the battery can damage electronics namely the ECU's

 

Thanks again, i will replace battery, it's a bit old, was bought new for the car in 2011. I had it tested the other week and it seemed to charge really quickly although it held the charge over night OK? I haven't run the car without the battery just used booster pack to get her going, then removed the pack leaving the battery on. According to the gauge, the car was bang on producing @ 14v. I'm OK with mechanical stuff just the electrics that i haven't got a clue with.

 

With the bonnet up, you should hear a distinctive "click" as the starter relay engages when you turn the key. But...if that was the problem then it shouldn't start at all, so that is a bit of a mystery.

I take it that (if I'm reading things correctly), all the fuel hoses in the engine compartment are fairly old? Probably a good idea to replace them in any case even if they are not showing signs of rot.

Have you tried a completely different battery? Sometimes a continuously clicking starter relay is a sign of low voltage/bad grounding.

Good luck with it!

John
1987 XJ-S V12

 

Don't go by the gauge, use a multimeter on the battery, 14v is good for charging.

I would replace the battery first. Then next the ignition module on the LH intake manifold would be my next suspect.

 

Going to borrow a battery tonight and swap it over, so i will report back tomorrow.

Thanks again,

 

I am a persistent guy. I don't mean to be pushy.


1. But, the battery has two cables, each with an end connecting to something. I suspect that until your remove each and clean, lube and tighten them, that your trouble will persist.


2. As Warren suggests. Get a meter. A cheap one will do. Mine have papers in them showing the rudiments of how to connect them. Reading volts is the easiest. I use it a lot. Even good to check household batteries.


Yup, til that wimp spar leaves and a really not crackling blue one comes on, it ain't gonna run decent.


Carl

 

Battery change has had no affect. Still struggles to start and then runs very rough as described. The faint battery light concerns me, as it didn't used to be like this, and before cranking the engine it eventually goes out by itself?? I will report back once all the battery connectors and earths i can find have been cleaned.

 

OK, a tad late.

You had the inlets off???.

In the centre of the balance pipe, at the rear of the engine, and facing downwards, is a 10mm spigot, That spigot has a vac hose attached. Is it attached and clamped?????.

That hose is the vac signal TO the ECU, and the ECU works thus:

LOW vac, lots of fuel
HIGH vac, less fuel.

At idle there is HIGH vac, and the ECU will use this for small amounts of fuel.

That is a SIMPLISTIC explanation, as I think you have a vac supply/signal issue TO the ECU.

I had one here years ago, engine fire, got "sorted" by someone else, and had exactly the same running issues as you have, ended up here on a truck.
Eventually I found almost NO vac signal to the ECU, the hose was attached?????. Days later I found a wad of fire fighting foam inside that hose. Blew it out, car is still running sweet today.

Check that hose, it would have been disturbed to get those manifolds off, also look at the ECU end, as they do split right at the ECU spigot.

 

Forgot, it happens.

At the rear of the RH (A side) Inlet and about 5A area, is a bolt with a number of earth straps under it, and I forget how many, but more than 1. Make sure there are NO errant earth wires looking for an earth point. Some of those are related to the fuel system.

 

when i 1st started playing with cars,and more so electronic cars, i learned that a BIG ground/earth cable from engine block to a good rugged part .like firewall, frame, even some run all the way to the Negative battery terminal.

it cleared many small issues and large one also! some times two cables, just to be sure, like one cable on one side another on opisite side of engine.

really helped computer cars!

 

I'll check that vac hose tomorrow, i'm going to check the earths again too. Really great advise. Let you know, fingers crossed.