running rough

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worrall1959

New Member
Posts
13
Hi guys, can someone please advise me on the following i have just bought a 1999 p38 4.6 which has a lpg conversion, it runs really rough when it switches back to petrol !!! currently knocking and banging when ticking over.
Any ideas please.
 
How does it run on LPG...??

What system, single point or multipoint??

Multipoint:
Could be the Fuel trims are out when running on Petrol...

The ECU 'Learns' the way the engine burns the fuel, prolonged period on LPG will make the ECU Fuel Trims learn the burn on LPG, when switched back to petrol the fuel trims are out and as such will run rough....

First thing is to reset the fuel trims on diagnostics, and see if that makes any difference....

Single Point:
Could be the MAF is faulty....start engine run on petrol, disconnect the MAF - any changes? No Change - Suspect MAF, engine running worse - MAF OK
 
Hi saint .V8, thanks for quick reply, car was initally running on gas all the time, when it ran out on the motorway when collecting car it switched to petrol however no power and was running rough, have had dianostic reset and now its worse than ever !!! it will start but its knocking and banging when running on petrol or gas
 
Hi Saint.V8, it was carried out by K Motors in leyland lancs who are a Land Rover specialist, it showed up to have 3 pages of faults which he cleared, think the main ones were showing mis firing on some cylinders, he did not touch any of the leads etc, like i said its running worse since being reset that it was before !!!
 
worrall1959 said:
Hi Saint.V8, it was carried out by K Motors in leyland lancs who are a Land Rover specialist, it showed up to have 3 pages of faults which he cleared, think the main ones were showing mis firing on some cylinders, he did not touch any of the leads etc, like i said its running worse since being reset that it was before !!!
Click to expand...
So all they did was reset the faults and not reset the fuel trims??

I know you may not know, but could be worth asking the question...clearing fault codes won't make an engine all of a sudden run better unless the root cause of the faults have been rectified...

You mention misfires...I am thinking iff HT leads, Coil Packs breaking down, Lambda issues, MAF sensor issue or Fuel Trims being wildly out...

If it is doing it on LPG and Petrol, it points to ignition or fuel/air mix problems....
 
As Saint originally said, the LPG system is probably putting the long-term trims out of kilter, now they have been reset they are wrong for petrol and LPG. The LPG should only ever be tuned when the car is running well on petrol, then the LPG fuelling is set to run nicely on correct petrol fuel trims. Get the car to run properly on petrol worry about the LPG later.
 
Last edited:
Hi Saint hope alls well need to pick your brain again, changed battery on P38 and its locked me out !!! cant seem to reset it using the emergency entry code, alarm keeps going off and draining the battery !!! tried the code on the card that came with it but no joy !! however there is a printed out sheet that also came with it, instructions turn key left so many times press top button then right so many times and press top button etc, which is the top button the lock one or the one that pops the key out of the fob !!!
Hope this makes some sense !!!! Regards phil
 
Sounds like you need to resync the key to the Car....

If it is 99 onwards, all needs to be done is to put the key in the ignition and turn the ignition to pos 2

For earlier cars, the resync can be done by putting the key in the door lock and turning to lock and press the lock button then unlock and press the unlock button, then start the engine....

You will need a working door lock mech and a working RF unit for this!

Send a PM to Mozz Smith, he has much luck with getting the keys and car synced and started...he seems to know the process exceptionaly well!
 
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