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[Rank]

Had a new cambelt fitted on my 2.5 V6 at the main dealer just before Christmas and got them to put a new set of spark plugs in at the same time.

Ever since it has had a slight misfire under load, mainly below 2000rpm which is worse when the engine is fully warmed up. It misfires both on petrol and lpg in a similar manner.

Took it back to the dealer who did a diagnostic check  (£50) which came up with no fault codes. All they could suggest was to change the leads and dis pack, charge me £600 for the parts with no guarantee that the problem would be solved.

The plug leads have only done 40,000 as they were changed last time the cam belt was done and there were no problems prior to its recent visit to the dealer. I still have the previous leads as they were not found to be the cause of a problem at that time. (It was LPG related)

My starting point would be the plugs and possibly the purchase of another new plug and replace each one in turn but any other thoughts or helpful comments would be appreciated.

[markey mark]

more likely to be dispac  

[feeutfo]

here we go, firstly if the fault was not there before the work, then cant really see how its not related to what they did. And then to charge you 50 quid to diagnose what they did is a bit rich tbh. So i would be going back for moan esp. as they have left you without a diagnosis haveing paid for one and not found the fault.
 May be worth checking all the plug caps are fully home and seated on the plugs, and the leads are fully connected to the dis pac itself and not damaged. Hth.

Ps. They obviously did not mention oil in the plug wells?

[feeutfo]

pps, thinking about it, any issue with the ignition system is usually amplified when running on lpg afaik. So given the symptoms are the same on both fuels, would this point to an issue with something else?

[Rank]

Had that problem in the past- changed the rocker covers to solve it.

Only problem before the new cambelt and plugs was an occasional slight misfire when the weather was damp. Only happened now and then again at low revs under load. Now it is a constant problem

[Pete Elite]

They possibly damaged a lead when pullingyanking them off so try and remove each lead one at a time to see if there's any difference but first try spraying the leads with some WD40 or damp start .

     HTH,
           Pete .

[ngrainqey]

as markey mark said further up really, if it's missing under load then it could be dispack but if it's missing in general then it's likely a damaged ht lead (possibly chaffed after getting trapped) but check for oil in plug wells as non Vx cam cover gaskets dont last long (especially if breathers havnt been cleaned)
HTH

[Marks DTM Calib]

Yep, miss fire under load is normaly a HT issues as you require max volts under that conidition, I suspect that if you floor it you can accelerate through the miss fire (unless its getting really bad).

This is most liekly due to one or two things.

Plus
Leads

Check the ends of the leads for damage and them going hard, under the current wet and cold condition some moisture can cause tracking round the plug insulators causing the miss fires as a result of damaged leads.

[Rank]

Update on problem- cured itself after a couple of long trips up the motorway (40 miles +). Misfire has now gone so I can only assume it was a bit of crud on a plug.

Downside is the LPG system has packed up so back to the installer for that one.

[MutantCav]

Might be that as the LPG system has packed up the misfire is no longer being amplified by the LPG system and its now just about coping...I will bet if you get the LPG system working again it will go back to misfiring!

[Rank]

Might be that as the LPG system has packed up the misfire is no longer being amplified by the LPG system and its now just about coping...I will bet if you get the LPG system working again it will go back to misfiring!

Before the LPG packed in it was, the misfire was present both on LPG and petrol- I checked that by switching between the two in case it was connected with the LPG system

[MutantCav]

As said...leads or dispack...any oil in plug wells?

[Rank]

An update on this problem.

LPG issues due to corrosion on the connector plug to the ecu. Required a new ecu and new lpg wiring loom- Ouch!

With regard to the misfire, which returned in the wet snowy weather, the following was carried out.
Changed the dispack first which made problem worse. Then changed plug leads and plugs and found problem- Two broken plug caps!!!

Alll was fine before it went to the dealers to have the cambelt and new plugs fitted. Misfire was evident from the moment it came back from the dealers. Dealer failed to find the problem when it went back to them after I complained about the misfire.

Also the plugs that were taken out looked like they had done a considerably higher mileage than the few hundred they would have done between when they were "fitted" by the dealer and when they came out again.

Draw your own conclusions, but I have ben in touch with trading standards and will be taking the matter further as it cost around £600 in parts and labour to resolve a problem that wasn't there before the dealer changed the plugs.