missfire

[STEVE AXWORTHY]

hi im having trouble with my early v8 i when you drive first off everything is fine it runs like a dream then when you have done around 10-15 miles it starts to miss fire gradualy getting worse and if you try to accelerate it feels very jumppy i have had new plugs/leads and cap recently but problem still same, i feel it may be fuel related any suggestions much apreciated

[lee celtic]

Has it got an auto choke??

could be stuck which is ok when it needs it (starting) but will over fuel when warm...

I had the same problem on a old mk2 transit after fitting a manual choke it was fine....

[Range Rover Blues]

What carbs have you got? sounds like the old SUs when the damper oil was running out.  They work fine with just a littl eoil, they work fine full (over full) of oil but as the excess oil starts to become consumed they are terrible.

[STEVE AXWORTHY]

forgot to add its an efi

[Eeyore]

We had a similar problem on the racer (also a 3.9 efi) and it took us months to find what was causing the problem. In our case we found (and I kid you not) that using a better quality engine oil cured the problem. What we were experiencing was a pumping-up of the hydraulic lifters (which stops the valves doing their thing properly). It doesn't take a lot of wear in the cam-train to inititate pump up, but instead of changing the cam and rockers etc etc, chaning the oil eeks the parts out for a good while longer.

Not saying it's whats causing your problem, but you never know!

[Range Rover Blues]

Is it a pre-cat model?  if so try disconnecting the EFi temp sensor at the front of the inlet manifold and drive it like that, it will use more fuel.

If it runs better then youhave a fuel issue, perhaps the MAF meter.  Hot wire EFi has many stages of cold start fuel enrichment, the last stage lasts up to 80 degrees.
If it's running well cold but not hot I wouildn't suspect over-fueling straight waay or you'd be getting unburned fuel when cold.

Have you tried injector cleaner?