V8 spark plugs

E

Ethelred

Guest
I have a problem with one of my V8s - it has been running sweetly all year but has suddenly gone into 'grumpy mode' again.

I took the car to a mechanic here in the Isle of Man - he told me it was missing on two cylinders and that he changed the spark plugs. Unfortunately he is away this weekend so when I picked the car up this morning, I couldn't tell him that the car is just as rubbish as it was when I dropped it off.

Is the V8 engine fussy about its plugs?

I'm no mechanic but I am a decent troubleshooter so I decided to eliminate the fault, even if I can't resolve it.

I disconnected the fuel line and there seems to be plenty of fuel issuing. The electric fuel pump sounds the same as it always does.

I know it isn't poor air supply.

This car has had the wrong firing order in the past and I know what that does - I believe the firing order is correct.

The engine sounds very sweet when running idle and it isn't lumpy or rough.

This car had the carburettors rebuilt in January and it has been sweet ever since. I am very, very suspicious of the spark plugs - they might be of the wrong kind - maybe making very weak sparks. I can't see it being one of the carburettors because the engine would be uneven and the problem would come and go as the stuck float/jammed needle/<insert failed component of choice> would move about within the chamber.

Any ideas why my car is poorly again?
 
The V8 is sensitive to the position of its ignition leads. Check they're properly clipped into the holders and none are touching so it can't cross fire.
 
Thanks for that. I just took a look - one bank was neat and tidy, the other was a rat's nest. I tidied it as best I could and took it for a quick drive but it is still the same. It's getting dark so I will have another look tomorrow. I will also double-check the cables are in the correct order.
 
It may be worth running engine at night time ( darker the better) and watch plug leads for shorting / cross firing quite common with carbon/ old leads.
Clive.
 
clive P62 said:
It may be worth running engine at night time ( darker the better) and watch plug leads for shorting / cross firing quite common with carbon/ old leads.
Clive.
Click to expand...

Thanks for that. Will it be obvious - i.e. if the engine was healthy, would I expect to see nothing in the way of arcing, sparks etc?
 
Can be intermittent,try getting someone to rev the engine as this puts it under more load.
I remember my dad's 3500 running poor /misfiring when it was only about 3 years old and it was the leads.
You will still need to check the basics like cap/ rotor ( if you have fitted new as the are some cheap/ crappie ones out there).
and the plugs aswell , I only use NGK BP5HS if short reach fitted.
Clive.
 
There's a picture in my Range Rover workshop manual of where the leads should be routed. I don't know if there's something similar in the P6 v8 workshop manual.
 
I've just driven the car to an unlit side road and popped the bonnet, Even with squeezing the throttle linkage there's no sign of any arcing, sparks etc. I will check the other bits in daylight.
 
Looking at the dates of your Rovers, I am assuming it is still running a 10.5 : 1 engine? If so, Champion spark plugs work best. Don't use NGK plugs in these engines as they tend to misfire. The NGK plugs were perfectly well though in the 9.25 : 1 engines.

Ron.
 
Hi Ron

The car does not have its original engine - it has the lower compression ratio version which runs happily on 95 unleaded fuel.

Best wishes

Chris
 
to save the messing about i'd change the leads cap and rotor arm for one off your other cars as you have more than one v8.... even more suspicious if the fault then swaps between the cars....
 
hi there,
my car is becoming very difficult to start, 15 mins with a liberal squirt of "start U bastard" and eventually it bursts into life.
Mentioning this today on a club run to Harrington , about 30 mins drive north of Taree, I was told that the Rover would benefit from "hotter " plugs, because the Australian fuel is so Crappy, I use 95 octane..
I have a set of new NGK BP5HS plugs and this is one step hotter than the recommended on the NGK website. Later this week I will fit them and see if it makes a difference to starting?
Peter
 
Peter,

start with a tuneup - new plugs, leads, points and cap. Pay the extra for a set of Magnacore leads as they last forever and do give a much better spark. I also only use 98 octane with the timing set a TDC. anything else pings. I also experimented with a number of spark plugs but wound up with the standard Champions (copper core) as nothing else lasted very long. My car sat for a good five years and started straight away. While getting the carbs right is important the ignition is what really counts on the V8. The brighter the spark the better. My car never ran better than when it had CDI ignition and 1mm plug gaps.

M
 
mikecoombs said:
Peter,

start with a tuneup - new plugs, leads, points and cap. Pay the extra for a set of Magnacore leads as they last forever and do give a much better spark. I also only use 98 octane with the timing set a TDC. anything else pings. I also experimented with a number of spark plugs but wound up with the standard Champions (copper core) as nothing else lasted very long. My car sat for a good five years and started straight away. While getting the carbs right is important the ignition is what really counts on the V8. The brighter the spark the better. My car never ran better than when it had CDI ignition and 1mm plug gaps.

M
Click to expand...
thanks Mike for the advice.
What are magnacore leads, (full copper wire) ? or the graphite type?
Peter
 
ButterFingers said:
hi there,
my car is becoming very difficult to start, 15 mins with a liberal squirt of "start U bastard" and eventually it bursts into life.
Mentioning this today on a club run to Harrington , about 30 mins drive north of Taree, I was told that the Rover would benefit from "hotter " plugs, because the Australian fuel is so Crappy, I use 95 octane..
I have a set of new NGK BP5HS plugs and this is one step hotter than the recommended on the NGK website. Later this week I will fit them and see if it makes a difference to starting?
Peter
Click to expand...

I use 91 RON for mine and have done so for almost 20 years, no trouble starting and no pinking at all, mine is a 9.25:1 engine however I have run one step hotter plugs since the change to unleaded fuel and that made a bit of a difference back in the day but at that time the first batches of unleaded were pure crap! and I had to clean the plugs after 2 starts due to fouling....things have improved quality wise when it comes to unleaded fuels.
I also run a high energy ignition though I dont believe that made a diference starting wise but it does make a difference at higher RPM as the dwell is more extended than basic kettering and standard points allow well that and the 10's of thousands more volts than a standard coil :D


Graeme
 
SydneyRoverP6B said:
Hi Peter,

Magnecor leads are not the graphite type. I used my first set for 19 years, and they were in still in perfect condition. I only changed them as I was fitting a new engine, and wanted ( wanted, not needed ) a new set.
MAGNECOR Race Wires: WELCOME TO MAGNECOR!

Ron.
Click to expand...
Hi Ron, thanks for the info, which type did you use on your car, in reading there website, its a bit confusing as to which ones would suit my engine?
Peter
 
Hi Peter,

Pretty sure mine are the Electro-sports 70, in black. I went to the Magnecor factory in Sydney, and they made me a set whilst I waited. You tell them the make and model, they have all the info so the lengths and the ends are exactly like the original Lucas factory set, which is excellent.

Ron.
 
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