Disco 1 misfire,1995 3.9 V8

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V8demon

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Location
Wiltshire
As above, 95 3.9 V8 with a misfire under load.

So far I’ve changed the plug leads which made the issue worse so to me it’s definitely an ignition issue, tell me if I’m wrong.

I know Rover V8’s can be plug lead fussy and the brand I used is all my local car spares can get. There more than likely cheap Chinese junk!

Which plug leads do you guys recommend? I was also thinking of changing the Champion plugs to NGK, purely because NGK are top notch, is this a wise move?

Thanks in advance.
 
Haven’t a clue on a misfire under load, other than the usual suspects dealing with the ignition system, the coil top connections is my favourite as I has an issue there once long ago.

Strange that replacing the leads shouldn’t make things worse, where ever they are manufactured. As for plug lead fussy, I had factory fitted leads failing within 4 years from new, these were replaced with ‘genuine parts’ leads again and they sill going strong with out any problems 16 years later, because 3.9 leads are not available as a set, I had to use 3.5 leads, no issues other the king lead is unusable because the 3.9s coil is located in a different position so the factory fitted king lead remains.

As for plugs, I’ve never has any issues with Champion in my 31 years of LR V8s, after all that’s what’s fitted in the factory, presently my disco has NGK fitted and I’ve found no difference at all from Champions even the price was the same, the Champion plugs that the NGK replaced are on the shelf as spares to reuse whenever.

So u don’t have any problems on starting from cold or when the engine is idling, was the engine running ok one day and not the next??
 
Last edited:
Update...

Replaced all ignition components, plugs, leads, rotor arm, dizzy cap and coil, used Lucas as generally they make good parts.
Misfire is still there!

I also replaced the stepper motor as the idle was up and down, this didn’t change much but it helped, I’m assumingbthe misfire is responsible for this issue.

Google searches show that it ‘could be’ the fuel temp sensor, is that so?
I’m running out of ideas now to be honest!

Plugs were all covered in carbon, quite badly except for one.
If your stood in front of the vehicle, the first plug on the left bank (drivers side of the vehicle, plug closest the slam panel) was wet with fuel, the rest all dry with a large amount of carbon build up.
Any ideas folks?

Thanks all.
 
A compression test would not be a bad idea...might be a valve or a lack of compression but if the cam lobes are knackered and the valves are good you will still get some compression Rocker cover off and turn the engine over, watch the rockers to see if they move the same distance as the others.
 
In different words you’ve said pretty much what my father said to do haha.. I’ll try and make some progress this weekend and see what the verdict is, I’ll keep you posted.

Thanks for your help so far :)
 
Update!

I found the cause of the misfire... Injector plug connection was badly coroded, seems to have cured the misfire anyway.

However... I now (did) have an idle issue straight after curing the misfire, It’s intermittent, if I’m driving along and then pull up in traffic or at traffic lights the idle falls right down and it will cut out. It does fire right back up though (every time) and idles a lot lower than usual, around 500rpm or I have to keep it revving in order to keep it from cutting out.

This evening I travelled 22 miles ( round trip) on the way I experienced the above issues, on the way back it happened once but the ‘check engine’ light flashed 3 times and immediately after seeing the light the engine cut out and then the light went out and the engine ran fine again.

In an attempt to fix the issue I have cleaned all electrical connections on the induction system, removed TPS & stepper motor and refitted/resealed (Stepper motor is brand new, TPS is old). Removed all vacuum hoses and induction hoses, cleaned, checked for cracks and refitted with new jubilee clips. Haven’t cleaned air flow meter as it appears to be relatively new and shows no signs of dirt or debris.

I took it for a quick spin and it seems to run like a dream.

Thought I’d mention this incase anybody has anymore input on the issue and for future reference for others with similar issues.
 
Started up and parked the Disco tonight, backing on the garage I shifted from Drive to reverse, feathered the throttle and it cut out again. Started back up quickly on the key and idled high (just under 1000rpm) for a moment and then dropped to just under 750 rpm. I continued to reverse with no issue and then selected ‘park’, the idle was a little up and down before settling just under 1000rpm again.

I’ve replaced the stepper motor, are there brands that are no good? From memory I think is Britpart. Is it worth changing TPS and/or Air flow meter?
 
If you've seen my post re. TPS they are virtually impossible to buy new, they are obsolete everywhere, every supplier says the same.
 
V8demon said:
Update!

I found the cause of the misfire... Injector plug connection was badly coroded, seems to have cured the misfire anyway.

However... I now (did) have an idle issue straight after curing the misfire, It’s intermittent, if I’m driving along and then pull up in traffic or at traffic lights the idle falls right down and it will cut out. It does fire right back up though (every time) and idles a lot lower than usual, around 500rpm or I have to keep it revving in order to keep it from cutting out.

This evening I travelled 22 miles ( round trip) on the way I experienced the above issues, on the way back it happened once but the ‘check engine’ light flashed 3 times and immediately after seeing the light the engine cut out and then the light went out and the engine ran fine again.
Click to expand...
Maybe worth checking that the ‘base idle’ is to spec. also, info on how to do that is in the various workshop manuals and it’s a simple procedure.
The lack of idle as u describe isn’t unknown, so clean or replace the crankcase “flame trap” breather and it’s connection hose to the plenum chamber also use a fuel injectior cleaner (redex) in the fuel, both things I do every couple of years, it’s part of main service schedule when done by a main LR dealer.
 
Last edited:
discool said:
Maybe worth checking that the ‘base idle’ is to spec. also, info on how to do that is in the various workshop manuals and it’s a simple procedure.
The lack of ideal as u describe isn’t unknown, so clean or replace the crankcase “flame trap” breather and it’s connection hose to the plenum chamber also use a fuel injectior cleaner (redex) in the fuel, both things I do every couple of years, it’s part of main service schedule when done by a main LR dealer.
Click to expand...

Thank you, I have Forte fuel treatment/cleaner in at the moment, I’ll give redex a try afterwards.
Never thought about cleaning the flame trap breather, I did remove and inspect the hose earlier on today though and it was relatively clean.
I don’t have a manual, is there anywhere on this forum that has the base idle ‘how to’?
 
V8demon said:
Thank you, I have Forte fuel treatment/cleaner in at the moment, I’ll give redex a try afterwards.
Never thought about cleaning the flame trap breather, I did remove and inspect the hose earlier on today though and it was relatively clean.
I don’t have a manual, is there anywhere on this forum that has the base idle ‘how to’?
Click to expand...
Haynes but LRs manual Rave can be easly down loaded Just Google
 
discool said:
Just did it for u. http://www.d-lander.com/manuals/D1_Workshop_Manual.pdf
Click to expand...

Thanks.

I’ve looked through that manual twice and read that the base idle procedure is found in the ‘fuel’ section (19) but I’ll be damned if I can find it! Need to look again.

After reading I’ve found the location of the fuel cut off switch, I didn’t clean that connection so that’s another to do today, every little helps I suppose.
 
Started up this morning, idle ran slightly high as you’d expect from a cold engine, selected reverse idle drops to just below 750rpm, feather the throttle and idle drops to approx 300rpm before picking back up and driving. Completed manoeuvre with no other issues, select park and idle sits at usual rpm, between 750 & 1000 (cold engine)

Just keeping everyone who’s following this updated incase symptoms trigger a thought towards an issue.
 
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