Running a little rough

merlinpjl · Aug 15, 2012

4.6 V8 2000 Model

Ok, regular contributors will know that I have put in a new engine from Turners and have sorted lots of little faults but I still have one big one!

Before I take the P38 to a specialist, I'm hoping someone can help.

From battery disconnected for 30 mins, runs great on petrol, no mis-fires or coughs. Swap to LPG and there is the odd misfire and a lack of power above 3000 rpm.

Swap back to petrol and it runs rough, Hawkeye registers misfires on some cylinders, more on petrol than on LPG.

Disconnec t the battery for 30 mins and the car fires up properly on petrol, swap to LPG and here we go again.

I replaced the coil packs and HT leads this morning and running became much smoother in general, but still have the above issue.

Also replaced the CATs this afternoon as they were making a racket internally.

Any ideas welcome?

StuckAgainSteve · Aug 15, 2012

Sounds like the LPG system needs tuning, when it's on LPG it's putting the fuel trims out in the ECU, when it goes back to petrol the mixtures are now incorrectly trimmed. When tuning the LPG system the guy doing it should have the car hooked up to diagnostics ensuring it's tuned to a point where the lambda figures closely match how the car was running on petrol.

I wouldn't have bothered changing the cats unless you failed an MOT. Just stick a couple of self-tapping screws in them to stop the cores rattling around. P38s can get through MOTs with barely working cats as the softly tuned engine is pretty clean to begin with.

mozz smith · Aug 15, 2012

hi, either have the lpg trims reset and fit new filter ,then either change maf sensor or clean with thinners or nail polish remover and make sure its air dried before re-fitting or it may just go BANG !!!!!!

merlinpjl · Aug 15, 2012

Ok, there is a specialist LPG place not to far from my house, what sort of price should I expect to pay for the trims being reset?

When you say "fit a new filter", which filter?

Consensus seems to be that if I change the MAF, original is the way to go, or is a Britpart or similar version OK?

Saint.V8 · Aug 16, 2012

merlinpjl said:
Ok, there is a specialist LPG place not to far from my house, what sort of price should I expect to pay for the trims being reset?

When you say "fit a new filter", which filter?

Consensus seems to be that if I change the MAF, original is the way to go, or is a Britpart or similar version OK?

Get the LPG set first before you pay out on a MAF (OEM is best - steer clear of Britpart if you can)...

If the misfire happens on LPG - thats the problem - stuck injector - clogged filter - low tank pressure etc etc.

The engine has knock sensors so when it senses a knock due to misfire, the petrol ECU ill try to compensate by adjusting timing etc, so when you go to petrol the timings and trims are out of true....

LPG service first....

merlinpjl · Aug 16, 2012

Right, I took it to an LPG specialist today on the off chance that they could have a look. They didn't have time to hook it up, but did say that I should probably replace all the injectors before they tune it.
The car had done 70,000 miles on LPG before I put the new short engine in so still has original injectors that were put in by the LPG installers.

What do you all think, just shell out and do it?

Datatek · Aug 16, 2012

merlinpjl said:
Right, I took it to an LPG specialist today on the off chance that they could have a look. They didn't have time to hook it up, but did say that I should probably replace all the injectors before they tune it.
The car had done 70,000 miles on LPG before I put the new short engine in so still has original injectors that were put in by the LPG installers.

What do you all think, just shell out and do it?

Personally I'd want a second opinion. Petrol and diesel injectors often manage 200K miles or more, I see no reason why gas injectors should only last 70K miles.

Saint.V8 · Aug 16, 2012

datatek said:
personally i'd want a second opinion. Petrol and diesel injectors often manage 200k miles or more, i see no reason why gas injectors should only last 70k miles.

+1....

merlinpjl · Aug 17, 2012

Thanks guys, I have found a few more specialists in the area, so going to try them first.

I'll let you know what happens.

jerrytlr · Aug 17, 2012

Datatek said:
Personally I'd want a second opinion. Petrol and diesel injectors often manage 200K miles or more, I see no reason why gas injectors should only last 70K miles.

+2

The injectors in my Legacy are now on 45,000 miles and working perfectly

The setup should not be too expensive - most decent LPG systems have an 'auto calibrate' mode which get you pretty close to the ideal values, that alone should be enough to establish if the poor running is a setup problem or if something needs replacing.

Another thing to consider is the LPG filter - perhaps it is clogged - I know mine was very dirty (though not enough to affect running) after 20K miles, I think they are supposed to be changed every 10K miles...

HTH

Cheers

Jerry

merlinpjl · Aug 21, 2012

I managed to buy some software and leads to cover every type of LPG system.

Also changed the MAF today and ran the auto calibrate.

The car runs smoothly now and has the power of an express train! on both petrol and LPG.

LPG filters and Lambda sensors due tomorrow so will fit them and re-calibrate.

Things are looking up now, very happy with progress

merlinpjl · Aug 22, 2012

Lambda sensors and LPG filters arrived today, installed them, engine smoother than ever now.

Also did the EAS valve block 'O' rings and compressor rebuild.

It's like a new motor now.

Thanks for all the info chaps.

Running a little rough

merlinpjl

Active Member

StuckAgainSteve

Well-Known Member

mozz smith

Well-Known Member

merlinpjl

Active Member

Saint.V8

Dyed-in-the-wool 100% RR Junkie

merlinpjl

Active Member

Datatek

Well-Known Member

Saint.V8

Dyed-in-the-wool 100% RR Junkie

merlinpjl

Active Member

jerrytlr

New Member

merlinpjl

Active Member

merlinpjl

Active Member

Similar threads