Opel Astra F knock sensor

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Re: Opel Astra F knock sensor

Postby Fat Freddy » Mon Apr 28, 2014 12:40 pm

Regarding LPG for engines designed to run on gasoline, there are numerous additives and "valve seat savers" that are alleged to protect the engines from premature seat wear, but in my experience with Toyota/Lexus, none of these have worked


I will try and check that out Steve. There is a bloke next door who specifically does LPG conversions (Generally non Euro but plenty Toyota), I'll pick his brains on that. I know he has fitted valve seat savers.

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Re: Opel Astra F knock sensor

Postby cristi0001 » Tue Apr 29, 2014 11:32 am

I hoped that my car had an electrical/electronic problem but it seems not... so, I'll take the car to my mechanic on thursday, he is an old fashioned mechanic, good on the mecanical side but with limited knowlegde and equipment on modern electronic car systems, anyway I'm looking forward to hear his diagnostic.

Thanks everyone for your willingness to help me fix my car! I'll tell you after this what happened
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Re: Opel Astra F knock sensor

Postby cristi0001 » Fri May 02, 2014 10:44 am

I went to my mechanic with the car started and run on gasoline - no problems.

I told him under what conditions my car won't run well and he told me to try something: always start the engine on gasoline, and after the engine is warm switch to lpg. I tried this and I have absolutely no problems, starting is very good, running under load is flawless.

What I did wrong was that I always started on lpg directly and probably when the engine was cold and lpg is used something happens to the ignition timing (on my engine ignition advance is calculated by ecu). The strange thing is that when the temperature outside was lower (2 to 5 degrees Celsius), I did not get this problem. I got this problem only when it warmed outside (10 to 18 degrees Celsius).

So apparently there was nothing wrong about my car, just a little crucial piece of information :D
Thanks
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Re: Opel Astra F knock sensor

Postby Fat Freddy » Fri May 02, 2014 12:02 pm

Thanks for the update.

We all probably should of asked one question early on "What type of gas system do you have? Venturi, vapour injection, liquid injection?" and "When did the fault occur".
But yes poor performance on start up with gas is not unusual. At 8am and 25*C it will still perform badly during the initial few minutes until warm. Ironically at 40+* ambient you can still run into converter freeze up problems if the wrong type thermostat is fitted.
I had a chat with gas guy (all he does and being doing it for20+yr's, very smart man). Additives, like Steve mentioned, he considers Snake oil. You will inevitably suffer valve problems (many miles) without valve seat attention. He considered Toyota to have a reasonable (each to their own) resilience to gas, Nissan and some Mazda's are worse (Asian market) but considered Euro not to bad. And one car he considered indestructible by LPG is the Ford Falcon (Au build). 4.0L straight 6 and in my mind a dinosaur of technology and not available in the UK.

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Re: Opel Astra F knock sensor

Postby cristi0001 » Fri May 02, 2014 12:39 pm

I have a gas vaporiser heated by the engine coolant and its' output is connected through an adaptor between the base of the throttle body and the intake manifold where the gas is mixed with air.

The fault occured only when I started the engine on lpg from cold. Starting the engine directly from lpg was a "bad habit" I developed in the past few month because I did not understand the reasons why should I start first on gasoline and then switch.

The strange thing was that if I started the engine directly on lpg and the fault being present, a switch to gasoline would not cure the fault (I tried this only for 10 seconds or so, maybe I should have waited longer), anyway if I start the engine from cold on gasoline, wait for the engine to warm - temperature gauge needle above blue zone, and then switch to lpg, the car runs and starts perfectly.
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Re: Opel Astra F knock sensor

Postby Fat Freddy » Mon May 05, 2014 12:20 pm

It all makes sense. It's a very basic gas system. Usually programmed only to switch over after a predetermined period (certain RPM reached). The convertor absorbs a lot of heat from the cooling system to 'convert' the liquid LPG to gas. On that type of system problems can be caused by incorrect start up procedure, low coolant levels, incorrect thermostat for gas applications. One symptom you may see is frost on the convertor.
While running LPG make sure plug gaps are correct. It's very hard on ignition systems. My advice is to have it serviced by a shop that works on LPG.

HTH
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