Hunting For Revs When Idling

[LeeB]

Hi Guys

just recently got a 98 V70 2.3T T5 with a LPG conversion.

Car runs brilliant on petrol, ticks over bang on 900rpm

when on LPG it runs well through the revs (one or two flat spots but nothing major) BUT when idling it doesnt.

If i pull up in traffic, the revs will either 1) drop to 900 (good)... or 2) fall way below 900 then bounce back up to 900...

then with a few seconds the revs begin "hunting" and the engine shaking - its also cut out a few times! its an auto and if i put it into park it seems to hold the revs better but still feels lumpy!

obviously when driving in traffic and having to stop-start this is a nightmare... especially when part of my daily commute is a steep incline!


like i say when on petrol its great... it could be in my head but it also seems if i give it a good blast on petrol for a day then go back to LPG then this runs better for a few days... then reverts back again! altho this could be an over active imagination on my part! lol

any suggestions/help much appreciated - i have a few in mind but woulnt want to put ideas up before listening!

Thanks

[capt jack]

This might sound daft, but just because it's OK on petrol doesn't always mean the problem is with the LPG!

LPG is very intolerant of tired ignition components. I'd recommend replacing the plugs, leads, rotor and dissy cap (if fitted). Use single point plugs set 0.1mm less than the book recommends. This will only cost a few £, and will be well worth it anyway. Change the air filter while you're at it.

Have a good look at the LPG installtion and make sure ther's nothing obvious wrong - a poor connection to a solenoid etc.

If that doesn't help with this problem then you need to think about the LPG installation. Fuel pressure and the fuel filter spring to mind as potential problem areas. LPG filters need to be changed every 10,000 miles at least, and the pressure really needs a bit of attention from an LPG expert.

If the basic electrics service doesn't help, and as you're 'oop north', get the car to Autogas 2000 at Thirsk. There is nothing that John or Chris there don't know about LPG.

If the car runs fine on petrol there probably isn't anything fundamental wrong - just needs a bit of the right attention.

Cheers

Jack

[classicswede]

What make and type of LPG system do you have? Will need that information to give you any advice on what to be looking for.

[LeeB]

no idea on the make of the system, theres a certificate that looks like its in polish or something similar? its listed as LPG on the V5 too.

There is a box in the engine bay which has the name on it (begins with A i think) so ill check later tonight!

its getting a full service this weekend (plugs etc.) and a mate has given me a number for the local lpg expert who has all the tuning/mapping software or something - hes a mate of his anyway and he says he knows his stuff with lpg installations! so hopefully this should go a long way to clearing the prob.

One thing i have noticed is that the last few days when starting from cold the LPG doesnt seem to wait for any kind of operating temp before kicking in... it still waits until i hit a certain rev range... kicks in... then when i brake/stop the car cuts out. its ONLY done this the last few days - before that it would wait until the temp gage hit about two thirds before kicking in!

i ran it on petrol yesterday and today on LPG, once it had reached temp, and it ran fine - a little lumpy in traffic and definitely not "right" but no major hunting for revs.

Thanks for the advice on the plugs ill pass it on to the guy doing the service - ford mechanic, apparently they use the same engine in some of the ford focus STs?? so hopefully hell be able to see any obvious issues!

[classicswede]

If the system is Polish chances are it will either be a Stag system or KME electronics. Some photos of the major LPG components would be a help.
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