madteg
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| posted on 27/11/15 at 10:29 PM |
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Thinking of buying 3.9 discovery with problem
Car is on lpg and runs fine but misses when running on petrol. Am i correct in thinking it will be a injector problem. Any ideas welcomed.
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mark chandler
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| posted on 27/11/15 at 10:55 PM |
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Does sound like it, LPG shows up issues with poor ignition.
They only batch fire the injectors so you can swap the injector leads around to prove the fault if you can nail the errant cylinder.
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britishtrident
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| posted on 27/11/15 at 11:30 PM |
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It could be the Petrol Long Term fuel has gone way too lean because the LPG set up too rich.
I is also possible the problem is with how the LPG system is spiced in to the petrol injector loom. The LPG conversion loom can either use proper
Junior Power Timer male & female plug breakout leads to make the connection to the petrol injector loom or be spliced in , this is an obvious
weak point.
Another possibility is the petrol tank has been run dry a few times and the in tank pump damaged or a petrol injection pressure regulator problem.
My plan of attack would be :
(1) A visual examination of the loom and manifold for wiring damage and vacuum leaks.
(2) Use a scan tool to check the OBD2 data -- especially fuel trims, misfire codes, lambda output.
(3) Fuel pump pressure test
(4) Injector leak down test
[Edited on 27/11/15 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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britishtrident
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| posted on 27/11/15 at 11:39 PM |
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I forgot to say you can sometimes hear an injector that isn't working by holding the end of a large screwdriver firmly on the injector body and
putting your ear to the handle. A mechanics stethoscope also works but can be confusing as it will also pick up the sound of other injectors.
I also forgot to say use a test lamp to check all the injector are getting power and the earth side is getting switched by the ECU, Using a 5 watt
test lamp is a more reliable test than a NOID injector test lamp or DMM.
A 5 Watt bulb puts a more representative current load on the circuit than a NOID lamp which is very low wattage.
[Edited on 28/11/15 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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hizzi
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| posted on 28/11/15 at 08:53 AM |
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there is a known issue with the ignition amp modules on these. cheap as chips to replace, there is something about moving them onto a plate on
discoverys to stop heat damage
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Oddified
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| posted on 28/11/15 at 09:21 AM |
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Most 3.9's have a basic lpg system, tank, vaporizer and a venturi. On those the lpg system just disconnects the 2 banks of injectors with 2
relays. They then don't use any of the 14cux ecu or sensors on lpg, the dizzy and ign module are totally seperate. That's assuming
it's a basic lpg system of course...
Because they're not to good on mpg, most people run them on lpg pretty much all the time, so faults on the petrol side get ignored. Injectors
are normally fairly reliable but worth checking as mentioned above, then get a multi meter on the afm, tps, water temp sensor and fuel rail temp
sensor. A quick google will tell you what resistances and voltages you should see, it's all fairly simple.
Ian
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