V8 Range Rover misfire

[Harleyboy]

Hi,

For some time my 91 Range Rover 3.9 efi has had an occasional misfire. It didnt bother me much so left it but over the osst few weeks its turned permanent.

I didnt think it was anything serious such as head gasket as it was intermittent. So far i have done the following:

1.Cleaned plugs. (6 anyway as couldnt get last two out). Pulling the leads on these last two made the running worse so think they are ok. Plugs are 4 years old/3000 miles
2. Changed distributor as the ignition module was suggested as possible cause
3. Changed leads
4. Changed coil
5. Checked timing post dizzy change
6. Injection cleaner (Redex).

I dont know what to do next other than compression test and find a specialist in north wiltshire.

Any thoughts or mechanic recommendations?

Thanks
Adam

[Harleyboy]

All and any. It would occasionally start rough then settle down. More recently it was worse under load not its just permanent.

Its sounds as if its running on only 5 or 6. Would barely pull itself up my slightly inclined driveway.

[Harleyboy]

Ill try the header temp next weekend. Thanks for injector suggestion - i will look into that

Probably worth changing the plugs again. I’m worried about the two stuck ones snapping. I had a long bar on them and they didnt shift!

Hopefully its not the cam!

[Harleyboy]

Thanks for the links - really useful. I shall spend some quality in the office tomorrow reading those!

I’ll take a look at the diagnostic tool too. It might sound stupid but I find anything diagnostic related really daunting. I can do simple DIY stuff but get myself so stressed out with anything else. However, I will give this a go!

Cheers

[Harleyboy]

tight fart said:

Have you changed any spark plugs or just cleaned 6 of them?

They aren't that old - maybe 3-4 years. At that point 7 of 8 were changed. 6 are now cleaned.

any tips for removal of sticking plugs? Someone suggested WD40 or spraying Coke around them. I have two long extension bars on them to no avail and am nervous about snapping them off. I pulled the plugs off whilst running and each had a negative impact on how the car ran. However, removing all leads one by one seemed to make it run even worse so I was unabble to pinpoint if I had issues with specific cylinders.

[Harleyboy]

Steve_D said:

Don't get stressed by Rovergauge it is very simple. It does not do any programming just shows some readings from which you can apply logic to understand.
Example....There are two temp sensors, coolant temp, fuel temp......if the car has not been started and you plug in RG both temps should read about the same and ambient. Logic says if one is reading way off then you have found an issue.
The same sort of simple logic can be applied to all the other readings.

If you want to have an in depth read try http://www.g33.co.uk/pages/technical_fuel_injectio...

Steve

Thanks - think its worth a go and not expensive to buy either

[Harleyboy]

Arnold Cunningham said:

Just to reiterate the above, all my Rover V8s have been very particular about plug leads & distributor cap. I also found once I replaced, for example, the leads, that this then showed up a weakness in the cap. And the cap needs to be a good one - I tried a cheap generic jobbie and it was no better than the cracked one it replaced.

Plugs - less so - I realised a while back that I was still running the plugs I'd bought it with in 2008 which were some crappy cheap brand - but it never missed a beat on em. Now changed, however....

I changed the leads even though the old ones are only 3 years old. The cap came with the Powerspark distributor and it runs equally badly with the old or new one!

[Harleyboy]

Just in case anyone is checking in, i have made some progress! Not exactly fixed it mind you but one of the stuck plugs is out and changed. No impact. The other one has snapped and im waiting to borrow the skills of a friend to try and get it out. Only the ceramic, not the thread thankfully.

Whilst i had it running, i pulled injectors and could tell no difference on one of the cylinders, possibly two so think this may be the issue. I need to get plugs in and then try the injector thing again before getting them off for cleaning.

Fingers crossed the plug comes out!

[Harleyboy]

Afternoon, so a further update for you:

All plugs now changed. Running nicely in neutral but no power under load. Will get to 50-60 on the flat but get to an incline and its down to 20-30 very quickly, albeit still running on all 8.

I took it to a guy who got it running much more smoothly and suggested to try an Mass Air Flow meter, then an ECU.

I know a guy who might have some known good units I can borrow for elimination purposes. Mechanical failure (cam, HG etc) seems to have been ruled out.

Thanks again for your thoughts/advice
Adam