The V8 Owners Forum -

Hi,
3.9 V8 LPG single point using a Lambda control
And the ignition is Mega jolt
Engine has a mild tune (stage 2 heads etc but prob not relevant at the mo)
OK
Started over-fuelling like crazy have replaced plugs, leads, and coolant temp sensor.
Discovered loads of petrol in the oil, changed the oil.
Still runs like a bag of spanners
Disconnected the fuel pump and the injectors so it runs LPG only (thought I might have a dual fuel thing going on)
still runs like a bag of spanners,rough tick over, on a spin mid range is OK ish once its cleared its throat but no real top end.
pulled the plugs... R/H set spot on (1357 ) L/H set (2468) all wet but don't smell of petrol (oil?)

Ive been at this on and off for a few days now, was getting stressed as I need it for work tomorrow, (am going in on the motorbike now !!)

would appreciate some ideas I'm quite sick of the bloody thing now and am so close to breaking it and selling off the bits, Ive always enjoyed working on my motor but now I just hate the thing

Andy
(Very cold been working in the snow on his damn Disco again)

andy2986 wrote:Disconnected the fuel pump and the injectors so it runs LPG only (thought I might have a dual fuel thing going on)
still runs like a bag of spanners,rough tick over, on a spin mid range is OK ish once its cleared its throat but no real top end.
pulled the plugs... R/H set spot on (1357 ) L/H set (2468) all wet but don't smell of petrol (oil?)

Hello Andy, I'm not an LPG, single point or mega J person, but just this passage alone make me think is would be an ECU fault. affecting just one bank of cylinders with over fuelling whilst the other bank is behaving OK.

If it's a single point LPG, and the two cylinder banks are running differently, then it must be an ignition problem......

However, if you are using EDIS-8, then you have four coil packs, connected:
1&6, 2&3, 4&7,5&8, and they fire together..

If it's a 3.9, presumably it's a Hotwire fuel injection?

Could it be running on both fuels?, thus making it very rich? Does it change if you unplug the petrol pump supply (pull the fuse, not sure how it's wired)

Does hotwire have a diagnostic port?

Does the LPG take it's lambda reading from the hotwire?, could that be a common cause of a fault?

Just some musings.

Chris.

"L/H set (2468) all wet but don't smell of petrol (oil?) "

Surley this points to something other than over fueling, for instance valve guides, and then failed plugs through carbon build up.
I would drop off the exhaust manifold on the even bank and have a look back up the exhaust port to see if there is heavy carbon build up there. I must confess I suspect valve recession following burning of the seats due to running it on LPG without enough compression.
Best of luck
Mike

Hiya guys and thanks for all your comments and thoughts so far.
when I posted yesterday I was very stressed and beyond cold !!
I have calmed down now and have had a good think about the order of things etc...

So it is a 3.9 EFI Hotwire

It is EDIS 8

The coil packs are all in good nick and I have spark at the all the plugs.

It has a small petrol tank in the rear wing and two LPG tanks where the original petrol tank would be.

Thinking again about the order of things

There was a LOT of petrol in the oil

The last time I pulled the plugs they "might" have had petrol on them not oil but I was so cold by then I was full of snot !! (sorry!!)

I did get it running well on LPG by the end of the day and noticed then that the petrol tank was empty, so after changing the oil I took it to the petrol station to re fuel both LPG and petrol.

I had been starting it on LPG ( it wouldn't run on petrol at all)

because it had run so well after fuelling I tried to start it on petrol (as usual) and straight away back to bag of spanners. so I then removed the fuel pump fuse thinking it was duel fuelling. but it still ran badly.

after that I got it home and ran out of light to work.

Could it be the Fuel Pressure Regulator ? if the diaphragm has split would it not pull fuel into the plenum? (explaining where all my petrol went and the petrol in my oil)
It ran well on gas because it had run out of petrol so none could come through the FPR diaphragm.

I may be clutching at straws here but the reason the L/H bank was wet and not the R/H bank could be because the Disco is parked on a camber and the L/H side is lower ???

Ive just got in from work and am freezing ( had to use the motorbike ) so will have another go tomorrow

Andy

So, it can run on LPG OK if the petrol tank is empty. Yet if there is petrol in the tank, it runs badly.

Interesting.

Does the Hotwire have the gadget that alters fuel delivery pressure with manifold vacuum? As you say, a duff diaphragm could allow neat fuel into the inlet manifold. You could prove this by unplugging the vac feed to the fuel pressure regulator.

I think I would try things like unplugging the fuel pump, crimping off the delivery pipe, unplugging injectors etc, to try to somehow prove that it is excess petrol getting in when it shouldn't be.

Chris.

If there was lots of petrol in the oil you may have washed it out and starved bearings of oil??

ChrisJC wrote:So, it can run on LPG OK if the petrol tank is empty. Yet if there is petrol in the tank, it runs badly.

Yes !

ChrisJC wrote:
Does the Hotwire have the gadget that alters fuel delivery pressure with manifold vacuum? As you say, a duff diaphragm could allow neat fuel into the inlet manifold. You could prove this by unplugging the vac feed to the fuel pressure regulator.

I believe that the fuel Pressure regulator is "driven" by vacuum from the plenum.

will look into this tomorrow rather than chase my tail trying to prove an ignition fault !!

mgbv8 wrote:If there was lots of petrol in the oil you may have washed it out and starved bearings of oil??

Yes, this may well be the case, will check and change the oil again tomorrow
and see how it goes if I can get it running.

OK an update,

I have removed the fuel pressure regulator, blocked the vacuum tube that fed it, removed the fuel pump relay, and disabled the injectors (they can be turned off by two relays as part of the LPG system)
cleaned up the plugs and tried to start it on LPG only and BINGO fired first time perfect tick over. let it warm up and took it for a gentle run round the block and it runs great.

Im not sure how to test the FPR so might just bang a new one in there and see...

Andy

Now it seems logical to start reconnecting stuff until it plays up again.

Chris.

Hi Chris, thats the plan.

Ive ordered a new FPR from Rimmers. on the basis that when replaced with a new one I can discount it.

some one else has said it could be leaking injectors... but one step at a time!
Im feeling a little more positive now, its good to hear the motor running properly a last, as I was starting to think it was a more sinister problem.

Hopefully all this fuel in the oil hasn't knackered the bearings, its not been driven really since this fault showed itself so I'm hopping !!!

Andy

FPR are easy to test, just rig up an airline and it should 'leak' at whatever pressure it's set to, probabbly 37ish psi.

When tuining my engine my plugs easily get wetted in fuel then stop 'sparking'. Then the engine runs like a bag of spanners, usually only one or two plugs is enough. To locate the plugs which aren't sparking I check which exhaust header is not as hot as the others then clean that plug and it runs fine.

The plugs don't seem to like getting wet too much as my previous engine wouldn't start due to an electrical problem, when fixed it still wouldn't start even after cleaning the plugs (which were new). Brought new plugs and ran perfect.

Tom.

Tom Great idea with the airline.
Using the compressor on the disco ( for the lockers) I rigged up an air line to the fuel in on the FPR when I squirt air in it defiantly blows out of the vacuum pipe. I put the pipe in some water and was getting bubbles !!
I guess if that was on the car and the air was petrol then it would be blowing petrol into the plenum...