P38 , 4.6l power loss and popping.

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AckAckFlack

New Member
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Hi all, sorry newbie here.
Hope this hasn't been covered to death.

I have a p38 4.6l 51 plate which has been converted to LPG
Recently it has developed a problem. It starts fine even from cold but runs on petrol roughly. If I try moving off on petrol when cold it is sluggish and lacks power.
I have been allowing it to warm and go to LPG - as soon as it kicks over the revs pick up and runs far smoother.
All is fine on moderate to slow acceleration up to 40 mph but then feels as though it has dirty fuel and pops (not a full blown back fire but a pop).
If I try to accelerate it will kick down a couple of gears and manage 60mph ish tops.

It has done 98,0000 miles.
I had the high tension cables replaced a week ago and initially seemed better but next morning back to square one.

Someone mentioned cats might be a problem.
When the airbox was opened (by garage when high tension cables changed) he found no air filter. (I bought it 10 months ago and have done 4k in it like this)

The exhaust isn't blowing smoke out of the back and starting is fine even in the -5 temp this am.
It isn't over heating and there are no errors on the dash.


Any of you guru's can give me pointers as to where to start or look.
Many thanks
 
change lpg filters had same sort of thing on my 1998 they said to change filters every 12 months
 
prolly maf, go get it on a camputer, look at the fueling, its prolly not getting the signals it needs from the maf!!

incidently cats are pretty insignificant in the running of an lpg car as they dont run on petrol long enough to make a difference, the fact that it runs better on lpg would suggest coil pack and plugs/leads are fine!! maff crank, cam sensors are the only ones that arent directly used by lpg but are by petrol
 
gavbriggs said:
prolly maf, go get it on a camputer, look at the fueling, its prolly not getting the signals it needs from the maf!!

incidently cats are pretty insignificant in the running of an lpg car as they dont run on petrol long enough to make a difference, the fact that it runs better on lpg would suggest coil pack and plugs/leads are fine!! maff crank, cam sensors are the only ones that arent directly used by lpg but are by petrol
Click to expand...

I see you are in Rotherham - do you have any recomendations as to good range rover mechanic/techies
 
AckAckFlack said:
It starts fine even from cold but runs on petrol roughly. If I try moving off on petrol when cold it is sluggish and lacks power.
I have been allowing it to warm and go to LPG - as soon as it kicks over the revs pick up and runs far smoother.
All is fine on moderate to slow acceleration up to 40 mph but then feels as though it has dirty fuel and pops (not a full blown back fire but a pop).
If I try to accelerate it will kick down a couple of gears and manage 60mph ish tops.
Click to expand...

I have exactly the same problem with my single point LPG install.

A reset of adaptive values with Testbook should solve your problem. Reset then run it 300 miles on petrol and have your LPG tuned.

Many people told me LPG Single point do not match with P38.

After 10 years of good running on LPG, bad running on fuel, i'm upgrading to Sequential Injection LPG in order to avoid that kind of problems.
 
Had look on internet and stargas do not seem to be around nowadays and the various garages I called didn't have the software to check it.

I managed to find the MAF sensor and even with my limited diy skill got it off. I have cleaned it with some kitchen roll and it definatley had 'muck' on it.
I put it back and went for a run. Defo better all round but the LPG flicked off once on an uphill- no significant backfiring either.

If I took it off again what else dare I clean it with? Soap n water?

I did see a replacement one on eBay and was 39 ukp and it stated they are lots more expensive from land rover- am I to have a punt for this price and simply get one or are the LR version what I need?

Thanks for the posts to this it has helped
 
MAF problems dont always show up on testbook

start the car, get someone to keep the revs up and disconnect the plug from the MAF, take her for a drive, if its instantly improved your MAF is fooked, dont be tempted to go for the cheap ones they dont last, get a bosch or similar from your local motor factors will cost around £150 ish but definately worth it.

The Maf is a service part these days i was told they last around 100k miles.

its a five minute job all you need is a screwdriver but a garage will charge you £200+ for the privilege.
 
robp38 said:
MAF problems dont always show up on testbook

start the car, get someone to keep the revs up and disconnect the plug from the MAF, take her for a drive, if its instantly improved your MAF is fooked, dont be tempted to go for the cheap ones they dont last, get a bosch or similar from your local motor factors will cost around £150 ish but definately worth it.

The Maf is a service part these days i was told they last around 100k miles.

its a five minute job all you need is a screwdriver but a garage will charge you £200+ for the privilege.
Click to expand...

Sounds good idea. Will try in the morning. Edit: just been out and tried it. Lots more power and got to 70 on LPG no pops but it did feel like it had a square wheel on it trying to shake it.

Mines done 98,000milez so it would suggest it is ready for replacement anyway.

Thanks
 
Last edited:
MAnaged to find someone with the same p38 and was willing to loan me the MAF to try.

It's far far better on LPG but is still rough on petrol.
I will replce the MAF and will need to investigate the petrol side of things.
I take it that the likes of the
Spark plugs
Ht leads
Air filter
Are all used by the LPG too so will be ok.

Are there any gadgets worth buying (like they use at land rover dealers ) that can help ?
 
Maf would be my 1st choice as well, STAY AWAY FROM THE CHEAP EBAY ONES!!!! All I have read/been told about the cheap copies are that they either don't work well from the start or they just don't last long, the problem I see would be that you could put a cheap one on and then think that was not the cure and keep trying other things just to find the new maf is the still the problem......too risky!

Bosch or Gen LR the only way to go.

LPG is very sensitive to plugs and leads, again use only quality or gen leads with quality plugs, lots rave about the magnecore leads others say gen LR ones are fine, both are expensive Magnecore with a big V in front! but again buy and fit once for long trouble free use.

Hope that helps, let us know how you get on!

Steve
 
Ohh yeah forgot to add you can use brake cleaner solvent to clean the MAF you should not be touching the wire as very sensitive, just spray plenty of cleaner around it and hope for the best....... I did mine, slight improvement but not cured so will be spending out on a new one but for now have water issues to sort 1st!

Steve
 
The borrowed MAF is far better on LPG but is still rough on petrol.
Bit confused now as I checked all the leads etc and seems ok.
Might need to give it back to the techie to see what his laptop says,

I have found out that there is no one around that can service the Stargas system I have. I may have to vignette bullet and re-convert, hopefully using parts I have already! Is this feasible ?
 
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