Does LPG affect O2 sensors differently?

[glengulliver]

thanks very much for all your expert advise. i am a new member and am experiecing all same problems with my 2002 v70 bi-fuel. 120,000 miler. when problem arises on lpg i get message to SLOW DOWN OR SHIFT UP. but seems ok in petrol mode. i too have eml on but unsure to replace lamba sensor as it clears after batt disconected. will try changing plugs first maybe. cheers glen

[capt jack]

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Well I can report that since removing the NGK and fitting the 'old' Denso plugs back into the car, the engine warning light has resolutely stayed off. The car hasn't had so much use over the past two weeks, and was off the road for a couple of days when the heatre matrix developed terminal incontinence all over the passenger footwell carpet, but when I'm back at work next week I guess I'll see whether the plugs are indeed the cause of my problem.

When you think about it, even one plug isn't firing properly on gas then the O2 sensor will see the unburnt LPG in the exhaust, which it will interpret as a change in the O2 content of the exhaust, and then throw a code.

And of course, as LPG is more difficult to ignite than petrol, a dodgy plug will show up with LPG whereas it may well be OK with petrol. Equally, a less-than-ideal set of plugs (too hot, too cold, wrong gap etc) could also cause incomplete combustion of LPG I guess. Interestingly, the NGK plugs I took out, even though they'd only done a few hundred miles had an odd look, with highly glazed and very white centre insulators and dry sooty deposits around the outer edges of the plugs.

Jack

[volvobaggen]

Your car is very similar to mine capt jack

I normally disconnect the battery when the car is in the deep freeze for over a week, and when I reconnected the battery at the cabin, I noted that the coolant expansion tank was empty and it was wet under the drivers side rubber mat. Added over a litre of clear freezing mountain water. The car now fogs like hell, and it is time for a new heater matrix.

When the weather gets better I´m also installing the Densos to see if it helps.

The 245 is also acting up in this wet cold weather. Won´t start probably due to bad ignition leads, stray sparks in the dark when cranking... Cheap ignition leads never pay off

[capt jack]

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I reckon that like the drivers, as these cars get older they generally do still work OK but sometimes need a bit of kind attention!

The heater matrix was a lot easier to swap than I had expected, and a lot cheaper. I asked Volvo for a price for a new matrix and it was £168 plus VAT and available to order only, plus another £5 for the O-rings. The local 'Eurocarparts' had a matrix in stock for £45 including VAT and the O-rings, although I did get the O-rings from Volvo anyway as I reckoned that they would be the best quality. I know it's not an original Volvo matrix, but at a quarter of the price, if it lasts a couple of years I'll be happy. The car is 16 years old and worth around £500 max!

The whole job took me maybe 90 minutes, and most of that was spent in getting all the trim panels back!

I tried to buy some more Denso plugs yesterday, but none of our local motor shops keep them any more, so I have ordered some online from Spark Plugs UK. Less than £10 for the set, plus £2.50 postage.

I realise that my old bus is now limping along a bit at times, and that it's going to need more and more litle bits and pieces. But I'm going to put off the inevitable day when I'll have to replace it as long as I possibly can. As much as anything else, my car is now an old friend - and I can't imagine any other car being even half as good as this one has been!

Jack

[volvobaggen]

Yes, cars needs to be taken care of. Im getting a couple of heater cores from over the pond, they supposedly better than the original Behr ones and very cheap.

http://volvospeed.com/vs_forum/topic...-heater-cores/

I have watched a few tutorials and I´m also doing the fire wall thermal coupler modification so I hopefully don´t have to deal with leaks for a while

http://volvoforums.com/forum/volvo-8...y-lines-46740/

[pistrix]

Hi guys,

I am also very sentimental towards my Volvo... And my oscillations now became like a challenge to me - or obsession if you ask my wife. In any case, I just must find the reason.

I am wondering about the Denso plugs. Jack, you said that Denso are hotter than NGK. But, shouldn't LPG plugs be colder than normal and not hotter?!?

Happy2013,
Jan

[capt jack]

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Hi Jan

The Denso heat reference number (20) looks to be further up the Denso scale, nearer to the 'hot' end in fact, whilst the NGK reference (6) seems to be in the middle of their range. However, if you go to comparison websites you'll find that the Denso 20 is the exact equivalent to the NGK 6! Looking at the two side by side, apart from the name on the side, I can't see any differences in the plugs at all. I really cannot explain why it should be that my car has got so fussy. And yet in the past when I tried Bosch superplus plugs and Champion, and Volvo plugs, I invariably got misfires (but no engine light) after as little as 3000 miles.

And yes, I think that most would agree that for LPG it's OK to go one grade colder than usual, and also to close up the gap by 0.1mm.

Perhaps my car is developing some cranky old ways as it gets older (a bit like it's owner maybe!).

Happy New Year to you too.

Jack

PS: The only other thing that I can think is that possibly in some way the NGK plugs don't create a perfect seal as they seat in the cyilnder head, and the Denos ones do. This might lead to a very tiny air leak that affects the fuel mixture maybe? Perhaps NGK use a different material in their sealing washer that reacts differently when hot? I don't know!

[Pete_c20]

Originally Posted by capt jack

My own V70 has ben playing up for a few months now. It's been hunting at idle, running rich, running lean, triggering fault codes etc etc - always on LPG.

I've yet to play with ODB readers, but is there one out there that will graph & trend sensor data for you? If you have a log of what's going it may be possible to see what happened in terms of input sensors. Could take a bit of looking at due to the various feedback loops in the system but you never know. It also seems like you know a couple of ways to 'play' the system up, or know when its going to play up. That could be really handy, if you can log what's going on.

[capt jack]

I don't think it's possible to set up something that gives live data for the Fenix 5.2 system. Certainly nothing the LPG company had would do the trick, and when I asked the local Volvo dealer they said that they didn't have the right software anymore. I suspect that they just didn't want to get involved with a 16-year-old car with intergalactic mileage in case things got messy!

Since the previous posts, I've swapped the NGK plugs that were in there for some new Denso ones - and bingo - there have been no issues since. (Hope I'm not speaking too soon!).

The engine is running fine on LPG and petrol, although for financial reasons LPG is the fuel of choice!

I'd got into the habit of using the Denso plugs and changing them every 10k miles, but just before Christmas the local motor factor stopped selling them, and so I went for the immediate alternative, the NGK.

Almost in desperation I ordered Denso plugs off the interweb, fitted them, and the problems went away!

Cheers

Jack

[CNGBiFuel]

I wrote a thread on this somewehre, in my case a pulsed idle was the Lambda, it ran fine on petrol, it was CNG that gave the issues.