The car has ran fine for the past 12 months, but was slowly getting rougher, i.e. lumpy tickover etc, so i changed the plugs (cheap iridium ones, part
number for none LPG focus) and leads and it seemed to be a lot better. A few weeks down the line it started getting rough again, and is now only
running of 3 cyclinders. I changed the plugs again, this time to the the correct ford ones supplied by ford, but the problem still persists. I have
also put the old lead back on the offending cyclinder (cyl 3) but no change. It obviously still runs fine on petrol. The engine management light has
started flashing only when running on gas, but will go out when the car is under load, i.e. accelerating, but as soon as i back off the light comes
back on. I've not had the error code read, but assume its a lambda sensor error dud to the emissions.
Where should i go from here?? Its got be either a weak spark, maybe the coil pack is on the way out, or a gas injector problem.
Not sure if this is related, but i used different gas supplier, a couple of weeks ago, and they subsequently had some problems with @!## in their
tanks, but surely the 2 filters in my car would have filtered out any debris before it hit a single injector??? Could moisture mixed with the gas get
through???
A lot depends on the type of system fitted to your car and the exact engine type.
Generally LPG needs much narrower plug gaps than petrol and on modern Fords the plug gap setting for petrol is far too wide anyway, for first port
of call is to reset the plug gaps 20% narrower than standard. However if the plug gaps have been too wide the HT voltage looks for another route to
earth it can break down the insulation in the coil pack and the coil pack is history.
On the other hand it could be a problem with the gas injector valve sticking.
But I would also consider the possibility of a valve problem --- with after market LPG conversions some Ford engines suffer from valve seat
resession on LPG the factory fitted LPG Fords had special cylinder heads.
The place to get more info is here http://www.lpgforum.co.uk/
quote:
Originally posted by britishtrident
A lot depends on the type of system fitted to your car and the exact engine type.
Generally LPG needs much narrower plug gaps than petrol and on modern Fords the plug gap setting for petrol is far too wide anyway, for first port of call is to reset the plug gaps 20% narrower than standard. However if the plug gaps have been too wide the HT voltage looks for another route to earth it can break down the insulation in the coil pack and the coil pack is history.
On the other hand it could be a problem with the gas injector valve sticking.
But I would also consider the possibility of a valve problem --- with after market LPG conversions some Ford engines suffer from valve seat resession on LPG the factory fitted LPG Fords had special cylinder heads.
The place to get more info is here http://www.lpgforum.co.uk/
I'm leaning towards gas injector valve sticking as it seems ok for the first few minutes when cold, just wondering how i could test this, you can hear them ticking (this is normal), but they are under the intake manifold so very hard to get to
As above. Sounds like you have some dirt or something like it in a gas injector, especially if only one cylinder is affected
One thing you could do as a test is swap a pair of injectors round, then the misfire should move to the new cylinder.
Incase you don't know how to find a non firing cylinder, you take off a HT lead (or disconnect a coil pack depending on the engine type) one at a
time and the HT lead or coil pack that doesn't make the engine run worse is the cylinder that’s not working.
[Edited on 19/8/09 by Mr Whippy]
quote:
Originally posted by Mr Whippy
As above. Sounds like you have some dirt or something like it in a gas injector, especially if only one cylinder is affected
One thing you could do as a test is swap a pair of injectors round, then the misfire should move to the new cylinder.
Incase you don't know how to find a non firing cylinder, you take off a HT lead (or disconnect a coil pack depending on the engine type) one at a time and the HT lead or coil pack that doesn't make the engine run worse is the cylinder that’s not working.
[Edited on 19/8/09 by Mr Whippy]
The Ford factory fit system is very different from after-market systems check on the LPG forum they will be able to point you in the right direction with what goes wrong or where to get help.
this company seems to sell more of the parts separately rather than whole system kits
linky
If the car is running fine on petrol, but not gas you can discount al the common parts - coil pack, plugs, ignition leads, valves......
I would also suspect a sticky/not working gas valve (I've had this once in 180000 miles and it was a loose wire on the valve itself - recrimped
for nowt). I also had a seal plug perish on the gas mixer that had a similar effect, but was fixed for the price of a pint at my local gas place.
If its a ford fit job, does it still use the ford ECU when its on gas?. Mine is an aftermarket one and basically has its own, so in my case it could
be a cabling fault to or from the LPG ecu to any of the various sensors/parts. By the way , aftermarket systems often bypass the lambda sensor error
signal as it is often faulty - don't forget the stoichiometric mix is different for propane and petrol.
Hope this helps
Hugh
Sorry - just read the bit about removing the cable from injector 3. Does the system use the same injector for the gas and the petrol? If so, check for
wiring faults from the LPG ecu to the injector. Some older aftermarket system just inject the gas into the inlet manifold, and direct injection
systems sont use the injectors in this case. This usually results in the ends of the injectors melting off as they are protected by the fuel flow
through them! This happend to a friend of mine and was very expensive to correct.
hugh
quote:
Originally posted by hughpinder
If the car is running fine on petrol, but not gas you can discount al the common parts - coil pack, plugs, ignition leads, valves......
I would also suspect a sticky/not working gas valve (I've had this once in 180000 miles and it was a loose wire on the valve itself - recrimped for nowt). I also had a seal plug perish on the gas mixer that had a similar effect, but was fixed for the price of a pint at my local gas place.
If its a ford fit job, does it still use the ford ECU when its on gas?. Mine is an aftermarket one and basically has its own, so in my case it could be a cabling fault to or from the LPG ecu to any of the various sensors/parts. By the way , aftermarket systems often bypass the lambda sensor error signal as it is often faulty - don't forget the stoichiometric mix is different for propane and petrol.
Hope this helps
Hugh
quote:
Originally posted by hughpinder
Sorry - just read the bit about removing the cable from injector 3. Does the system use the same injector for the gas and the petrol? If so, check for wiring faults from the LPG ecu to the injector. Some older aftermarket system just inject the gas into the inlet manifold, and direct injection systems sont use the injectors in this case. This usually results in the ends of the injectors melting off as they are protected by the fuel flow through them! This happend to a friend of mine and was very expensive to correct.
hugh
Any progress?
It interesting that it doesn't happen when the engine is cold - not sure that helps much though! Does it imply the injector works ok?
Just a thought - can you check you are getting a signal through the injector wiring for no3 by plugging in an injector from the scrappies - saves
taking out the injector from your car then finding its the wiring not the injector. Make sure its the right type of injector though - there are
different sorts with different impediences and drive arrangements.
I like the tip about reducing the plug gap - just about to service mine so will try it.
Is it possible to use a long extension/angle drive etc on a socket set from below with the car on a ramp to get the injector out? I know its a long
shot and theres usually something in the way to stopyou doing this.
Regards
Hugh
quote:
Originally posted by hughpinder
Any progress?
It interesting that it doesn't happen when the engine is cold - not sure that helps much though! Does it imply the injector works ok?
Just a thought - can you check you are getting a signal through the injector wiring for no3 by plugging in an injector from the scrappies - saves taking out the injector from your car then finding its the wiring not the injector. Make sure its the right type of injector though - there are different sorts with different impediences and drive arrangements.
I like the tip about reducing the plug gap - just about to service mine so will try it.
Is it possible to use a long extension/angle drive etc on a socket set from below with the car on a ramp to get the injector out? I know its a long shot and theres usually something in the way to stopyou doing this.
Regards
Hugh
Apart from reducing the gap if it is also a good idea to go one grade or even two grades colder on the spark plugs -- on the Rover I use NGK plugs intended for the Mazda RX5 NGK BKR7E gapped at 0.025" in place of BKR6E