Engine Backfire?? air filter

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Pockers

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Ive got a P38 R reg converted to single point LPG

Recently (seems to be more when its been raining) i'm getting a backfire or three from the engine bay. Then the car wont start or if it does it wont get above 300 revs.

The pipe behind the air mass meter has loosened or blown off completly, on this pipe is an aluminium tube with an aluminium flap / valve. The back fire has caused the flap/valve to blow through the wrong way & deform.

Ive bent the flap pushed it back through & reshaped it & the car then works fine until the next backfire & the whole thing is repeated.

Any one any ideas whats causing the backfire?
Any one know what the aluminium tube with flap/valve is actually called so i can get a new one?
Is it the fact that the flap is now deformed so it doesnt seal that is causing the backfire?

Any suggestions greatly appreciated.

happy landying
Pockers
 
Yep,you have a choice - change it to a decent sequential system,run it on petrol or do nothing.The last is most expensive - you'll end up needing a new engine.The sequential system may not be cheap but is a long term answer,and I guess running on petrol could be expensive too.
Single point systems dont feed your engine well enough and the backfires will quickly total your airflow meter and even dent the bonnet.
 
Consider fitting a manifold DUMP VALVE no matter what else you do.

You WILL get manifold explosions running on gas, and because the V8 manifolds contain a fairly high volume of gas/air mixture, it makes a bit of a bang.

If you fit a DUMP VALVE with a very low setting, it will release the pressure before any harm is done.

That's the theory anyway

Hunt Google for dump valve.

CharlesY

LMA Motorsport - Dump Valves
 
CharlesY said:
Consider fitting a manifold DUMP VALVE no matter what else you do.

You WILL get manifold explosions running on gas, and because the V8 manifolds contain a fairly high volume of gas/air mixture, it makes a bit of a bang.

If you fit a DUMP VALVE with a very low setting, it will release the pressure before any harm is done.

That's the theory anyway

Hunt Google for dump valve.

CharlesY

LMA Motorsport - Dump Valves
Click to expand...
With the sequential system you dont get backfires,which is why I suggested it.But the backfires are nothing compared to the cost of another engine/head gaskets etc,etc.
 
I had a similar problem when I had A Jeep Grand Cherokee running on a single point LPG, it blew 2 air boxes up which are not cheap the installer really did not want to know, another garage found the system was out of tune and running to lean, it also needed a new Lamda Sensor. So with a combination of the tune and the new sensor that seemed to cure it. I was also advised to fit one of the Cone air filters (K and N type) so any further back fire could escape through that rather than be contained with in the air box.
I wonder if the flap thing you mentioned is a backfire flap which someone has installed to try and prevent a back fire from blowing you intake system to bit's, if it is then as you have found out they do not work.


Jim
 
my p38a has exactly the same problem after listening to guys as clued up as eightinavee and others regarding single point lpg`s unsuitability for the p38a 4.6 i decided to go down the path of buying a good sequetial lpg kit , try speaking to tinleytech lpg i found these guys to be absolutely unbiased in there opinoins and very helpfull , i will install the system myself but depending on your experiance you could buy the kit the get a decent place to install it for you , its not rocket science to do it , then it`ll be an end to what could be a potentially expensive problem , i hope this helps.
rick.
 
A ball park figure for the DIY kit would be great, also any idea what sort of tech knowledge / mechanical knowledge would it take to fit it?


thanks
 
crossa said:
Rick if you don't mind me asking how much did the D.I.Y kit cost as I am thinking of doing the same.

Jim
Click to expand...
hiya mate the kit to upgrade to sequetial lpg is about £640.00 ish + vat , not bad really i thought .
it cost me a total of £804.00 including vat , but i also bought some extra`s at the same time , like a ready made up injector loom just to save a bit of time really.
rick.
 
Re the Dump Valve

is there one made for the Range rover or is there another make that will do the job.
How esy are they to fit??
thanks
 
Pockers said:
A ball park figure for the DIY kit would be great, also any idea what sort of tech knowledge / mechanical knowledge would it take to fit it?


thanks
Click to expand...
its ok for me being an hgv mechanic , but looking at the kit and the instruction booklet and all the other bits and piece`s included it does`nt really seem to be a major undertaking and anyone that can read a curcuit diagram , and can carry out their own maintainance i would think would be more than capable of doing it themselves.
rick
 
Pockers said:
Re the Dump Valve

is there one made for the Range rover or is there another make that will do the job.
How esy are they to fit??
thanks
Click to expand...
its no good just treating the symptoms you need to treat the cause and thats the single point lpg .
rick.
n.b if you get it wrong and it goes belly up on you it`ll cost a damned sight more than an upgrade to sequetial.
 
The flap is a backfire flap. My hybrid has a single point LPG system and so did my old V8 Discovery. On my hybrid it tends to backfire when you try to run it cold. On the discovery it did it when it flicked over to gas while you were accelerating (i.e the engine was under load). It was a pain in the arse because you had to take the pipe off and bend the flap back - but that's what the flaps for. They are not the best system and if you didn't install it yourself then it might not have been installed properly. There are lots of DIY kits and it's better to spend a bit extra and have a proper installer do it. At least that way you get some sort of guaruntee/warranty.
 
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