Range Rover Classic V8 misfiring intermittently - help!

[Harleyboy]

Hi all, my 91 RR classic is misfiring intermittently. It's a 3.9 V8. It overfuels a bit from cold but usually clears within a few minutes then is fine but since having it in May, it has every so often stuttered, not necessarily under load. It did it so infrequently i didn't bother but it missed several times on a 4 mile journey today, towing a loaded horsebox. It also did it once the trailer unhitched so I do not think it is load related. The only electrical items on were the heater on fan speed 1 and the headlights.

Annoying as yesterday i did 50 odd miles during the day and it never missed a beat.

It doesn't lose a few cylinders; its as if the whole engine is stopping for a split second.

Fairly recent fuel filter and spark plugs.

Anyone any thoughts or do i have an auto electrician look at it?

Thanks

[DKL]

Anything in the ignition system could do this. They are quite prone to plug lead deterioration and there are 8 of them.
I was advised to buy good ones - £80 or so - not the cheap ones. So far it seems sound advice.
Depending on your skills all these parts can be tested or just changed anyway if they are old.

[geoffphead]

mine was a set of faulty ignition leads and also the plug shields were not brilliant ended up buying 4 new ones

[Harleyboy]

Thanks chaps. The leads are most likely several years old so not a bad place to start. When it misses, the whole engine misses, it doesn't just lose a cylinder or two. I suppose the coil lead could have his impact though?

[plasticpig]

Running rich and cutting out and are also symptoms of a duff air mass ECU. The only real way of diagnosing this is to slot in a known good ECU and see if the problem disappears. Most specialist will have a known good one on the shelf to test for this. If it is busted don't worry too much as an early Disco one will work just as well.

[camel_landy]

Yep, lots of things can cause misfires on the V8... A blown head gasket can also sound like a misfire (though not the symptoms you describe).

FWIW - The Rover V8 is very fussy about the quality of HT leads. If you replace them, get good quality ones.

M

[Harleyboy]

Thanks for the replies. I think I'll go for some new leads - can't hurt as they are probably years old anyway.

When it misses, the rev counter drops which makes me think it might be wiring/coil/coil lead related. These seem the easier checks and cheaper replacements to try first.

Will go for some decent leads though - not some eBay specials!

[paintman]

Lead/plug/rotor arm/dizzy cap issues will cause a miss on one or more cylinders.
You describe it as the engine cuts completely & the alternator fed rev counter also drops which suggests a total electrical failure. Check all electrical leads & connections incl igniton switch for breaks or damage. Try a wiggle test - with the engine running wiggle the wires one at a time & see if it replicates the fault.
Check the engines earth leads for condition. The plastic covered ones can corrode to nothing in the middle.
As already suggested, if you can borrow a known good ECU test by substitution.
Have a look here: http://www.carelect.demon.co.uk/rrp2.html

Edited by paintman on Tuesday 14th January 08:41

[camel_landy]

Check & clean up the connections around the coil.

M

[Digga]

Harleyboy said:

Thanks for the replies. I think I'll go for some new leads - can't hurt as they are probably years old anyway.

I put some Magnecor leads on the Rover V8 lump in the Griffith I had and they improved things no end. Worth a look if you're changing. IIRC, Tim Lamont at ACT used to sell them.

[Jasper Gilder]

Did the orange light of death come on on the dash, if so it could well be a dodgy engine ecu connection. used to happen on mine until the driver seat ECU packed up and in refitting a lot of stuff got tightened up - hasn't misbehaved since. ( Main ECU is under drivers seat!)

[Harleyboy]

No, I don't recall seeing any lights coming on, the only visible thing I noticed was the rev counter dropping like a stone!

[JCW]

Another recommendation for Magnecor leads, pricey but worth it.

[Harleyboy]

Hi all,

So leads and rotor arm all changed, has made a big difference but there is still a misfire every now and again. Nothing like as bad but wondering if the coil needs a change?

[paintman]

camel_landy said:

FWIW - The Rover V8 is very fussy about the quality of HT leads. If you replace them, get good quality ones.

Even more fussy about rotor arm & dizzy cap. Don't use a rotor arm which has the metal strip riveted to the plastic.
Pattern dizzy caps can be awful. I had to use - on holiday & couldn't get anything else - a pattern one a couple of years ago. Immediately got an intermittent misfire under load at speed on both petrol & LPG. Once home replaced with decent one & no further issues.
So what's the difference between the two I've got?
The pattern cap plastic is much thinner, the turrets are shorter & much thinner (the LR lead shrouds fitted them about as snugly as a big bucket would fit your hand), some shrouding ridges inside the cap aren't present and the 8 pickups inside the cap are fully exposed (genuine one only the front faces were exposed, the sides were shrouded).

[TVRTRICEY]

Sorry to bring up an old post.. but do you have any pictures of the two different arms?

Tricey

[paintman]

Sample pic of non-riveted V8 rotor arm.
http://www.simonbbc.com/rotor-arms/v8-powermax-red...

This might be of interest:
http://www.distributordoctor.com/rotor_arms.html

And this, which is a TVR thread so might go with your username:
http://www.pistonheads.com/gassing/topic.asp?t=124...

Edited by paintman on Wednesday 27th May 19:12