Thread: D2 V8 intermitent misfiring

Barnsey,

It could be and probably is something quite minor, but it also could be an early indication of liner slippage.

Looking back to our experience (99 V8 Disco 2), the first symptom was an intermittent misfire which was first picked up on the fault codes. But we could not reproduce it when needed for diagnosis. So after checking all that we could, we changed both coil packs and leads in the vain hope that that might fix the problem.

Then the misfire became significant enough to be noticable on occasions while driving. It was always of relatively short duration, and again, looking back, it happened mostly when the engine had been worked hard and had been shut down for only a short period before restarting. Then it would misfire badly before magically clearing itself and working normally.

About this time it started occasionally clunking briefly on start up from very cold, almost exactly like an old Falcon with a slow hydraulic tappet.

Very soon after this first started happening, leaking combustion pressure overpressurised the cooling system to the point where it tore the T join out of a brand new radiator hose.

We found the cause of the problem when we pressure tested the system after replacing the hose.

I hope that is not your problem, but you can check fairly easily by removing the plugs unless they are too new. If there is a liner slipping, the plug in that cylinder will be spotlessly clean, while the others should have normal deposits on them. In our case we had two slipped liners. Scratch one engine. The good thing was that it gave me a watertight (no pun intended) excuse to upgrade to a 4.6!

Slipped liners can be a problem, but given how many V8s are running around fine, its rare - of course you will see them on forums because the people who post are usually on here because of that (or other) problems in the first place. I am not being critical about the above post, but dont jump at shadows and dont sweat the big stuff (as a potential only...) when the small and more obvious stuff is not accounted for. Misfire - timing/spark and fuel metering first before assuming combustion problems. The fuel injection systems on these tigers shouldnt need touching for a VERY long time. You would have to be very unlucky to have a dodgy injector at 90,000k...so look for spark as the most obvious cause.

If the plug leads have not been done before then 90,000k and they are shot. Replace them before doing anything else. Also at 90,000k its is possible that the coil packs are shot. If they have not been replaced they are probably on borrowed time. At 90,000k knowing what I know now if I had a Disco that had not had them done I would get the coil packs and leads done at the same time and not look back for another 90k odd.

Cheers

A slight misfire on mine was down to plug leads, the heat can cause them to break down pretty badly even if it's not overly visible. With mine they came apart as they were being removed they were in such a state leaving bits attached to the plugs and all sorts.

Replacing them is a bugger of a job, best enslave a child with small hands to reach in behind the block to the coil packs to change them. I didn't get them all on securely enough first attempt so the issue came back a few days after i changed them, making sure they were securely on the plugs and coil packs sorted it though.

I have had an ongoing issue with my Disco 2 V8 ever since i got it, slight misfire about 3200 RPM under acceleration. I replaced plugs and plug leads, MAF and oxy sensors and to no avail. Gradually over 18 months the misfires began getting worse and the idle got more rougher... the motor was even rebuilt in this time due to slipped liner but the problem remained. Finally replaced coil packs on the weekend and now it runs much nicer, more torque, smooth idle and no misfire.

if its the coil packs(and they do fail--)
the job CAN be done WITHOUT the removal of the Plenum chamber(less $$$)
but only if you have the hands of a small child


buy GOOD leads,,,,

Had the same issue with my 01 V8 approx 3 months ago. Misfires/pings when cold particulalry when under load say going up a hill, then as the engine gets hotter it's alot less and infrequent.

They changed the Maff made no difference. Turned out to be the exhaust sensor on the right which adjusts air fuel mixure ratios. Cost me a few hundred bucks but it has now stopped missing/pinging.

And yes I was running Premium petrol.

Hope this may help.

Cheers

I replaced the leads and plugs in my 02 V8, had 7mm Spiral Wound leads made by Qld Ignition Leads for $100. They can also do 9mm leads for $120.

I also had faulty airflow meter and both oxygen sensors, and had all replaced with genuine parts, but now it is that smooth you cant really tell it is even running at idle and power delivery is smooth right through the revs.

By the way, I changed the leads without removing the intake plenum and although not a hard job, the small space tends to claim some skin. Easy way to get the old plugs of is bend a screwdriver to lever the boots of the coils, easier than using force by hand and skinning knuckles.

Thanks to all, for your great info, I'll go leads and coil packs and see how it goes, I'll post a reply and let you know the results, thanks again.