Engine 850: B5252S/2.4/10v: Missfire/plug leads

[LPGjonderby]

Cat !

The way my gas system works, is that its computer piggy backs Volvo's system but ignores the lambda readings as they are not applicable. So it uses everything else, from timing to every sensor other than the emmisions. At least this is what I am told. It missfires on both gas and petrol, although in a different way. When on gas the missfire is much more violent, on petrol it results in a gutless engine that misses quietly most of the time.

[Timbo_1975]

On LPG the cat is safe with a misfire..

Anyhow, can you describe when it missfires, all the time, under load, at what revs? Hot or cold or both?

You can usually diagnose the cause from the symptoms of the miss..

Tim.

[LPGjonderby]

It missfires the most at 2,700-3,000 revs give or take. This is most noticable when you are crusing at about 80. You then accelerate without slamming your foot down and he shakes loads. If you hit the floor with the faster pedal it drives through the missfire, especialy if the box went down a gear.

It is a right pain when using the cruise control at 80-85, if decativated for traffic then switched back on it missfires loads.

You can see and hear the engine shaking as you feather the throttle with the bonnet up. It just won't rev smoothly.

Jon

[Mike_Brace]

To me it sounds quite possibly a plug starting to break down. I assume you are using a copper core or iridium plug as platinum plugs do not like lpg. If you are running mainly lpg the plug will still show the right colour as there is not the carbon there - hence cleaner oil and exhaust. For the price of a set of plugs I would definitely replace.

Mike

[LPGjonderby]

Yes it has NGK copper core plugs, although like the plug leads they have only done 2,500 miles. Will replace these I guess next week, along with some better quality leads. After that everything has been replaced, again.
Fingers crossed or its back to the drawing board.

[Timbo_1975]

What plug gap are you running? For LPG it's usually recognised to close the gap up 0.1 or 0.2mm as its alot harder to ignite being dry..

Tim..

[LPGjonderby]

Am running the plugs at 0.7 mm give or take a mm.

[Robos850]

If all the leads mis-fire at random as you have stated, there is only one coomon item to that and it is the coil. In excess of 80,000 miles they are known to start playing up. Check connections, earthing and security of HT lead into coil as sometimes it doesn't click in. I have just changed Dist Cap, Rotor, leads and plugs all from Volvoparts and they are OEM standard. All the leads are identical including Volvo markings.I have experienced this misfire problem on her indoors and after changing everything else it came down to the coil

[volvostu19]

Another problem these can suffer from is a faulty cam sensor, this can cause ruff running & missfiring but usually bring the lambda light on

[LPGjonderby]

I have some better quality leads on order, may be here tomo' from Fast Lane Autos. Am hoping this cures it for good.
I have tried a replacement coil from a 210k miler, didn't work at all, then a 75k miler from a 2.0 which have since sold on ebay, and the coil I am running now. This was bought from a salvage supplier also off ebay. This one is a replacement part on the donor vehicle. Car still missfires ! The original one and the 2.0 and present one were tested a few weeks ago at my local electrical specialist. All 3 working fine, although the original one was kicking out the weakest spark of all.
However they could not test the amplifier. Know one seems to know if these pack up ?
So am now only left with the leads !!!! If this does not work its time to buy a brand new complete coil.

With regard to the cam sensor ? Do these fail regularily ? If so, do you get violent missfire around 2,700-3,100 revs ?

Today Victor has been as good as gold for the 1st 10 mins of driving, then when fully warmed up the missfire returns. So am hoping it is the leads breaking down under load as they are pretty crap replacments.

Cheers guys