John-Ellis

John-Ellis

New Member
Hi All,

I have a couple of issues with my 1998 Disco 1 3.9 V8 Auto with LPG conversion.

ON PETROL

Whilst driving on petrol, the engine idles ok, but the revs suddenly drop for a second then come back, this also happens whilst I am driving it could be any speed and it does not matter how high the revs are it drops then comes back as if my foot has slipped off the accelerator. It is also suffering from a misfire.

ON LPG

Whilst driving on LPG the revs do NOT drop that problem disappears however if I try and drive above 40mph I get a bad misfire but not bad enough yet to cause the engine to backfire.

WHAT HAS BEEN DONE SO FAR

So far it has had a new dizzy cap, plugs and the HT lead from the coil to dizzy cap was replaced as it was damaged.

This cured the problem with the LPG for a short wile but it has come back worse.

I have also put some injector cleaner through with the petrol.

Thinking it might be a fuel blockage on the petrol issue but nothing has changed.

Last night my dad put his spark tester thingy on each HT lead and plug and before I started scolding my fingers on the manifold I got to test 6 of the plugs and leads and all gave a good strong consistent spark. I plan on doing the others as soon as.

I have ordered a Fuel Pressure Test Kit off ebay to test the pressure from the fuel pump. I have also ordered a fuel filter for how much they cost.

So I have taken it off the road for the moment.

Has anyone got any idea's as to where to look next.

I plan on changing the air bypass valve (I think it's called) that screws into the back of the plenum chamber.

As I say if anyone has anymore idea's I would be really greatful.

Cheers

John
 
I know you say LPG is running fine but change the lpg fuel filter put ssome IC12 injector cleaner threw the lpg jets, then change the leads LPG has to have above average leads you say yours ar fine but I would recommend a change Lpg I a filthy fuel for the engine even tho it kicks out H2O mine gets the same probs every now and then going too chsnge filter and ic12 clean out on Monday as mine has started too run lumpy
 
Hi chaps,

Thanks for the replies, the leads that are on are heavy duty leads it was only one lead that failed and as I say it ran fine for a while as for the lpg system, it is a first generation system so it does not have injectors for the lpg it gets mixed in with the air.

Ive been working all weekend so far so i havent had chance to look i dont think today is going to be any better.

I will post an update as soon as i can.

Cheers

John
 
compression test as I suspect you may have hgf between 2 cylinders
 
John-Ellis said:
Silly question, what is a hgf.

Thanks

John
Click to expand...

head gasket fail between 2 cylinders-- petrol a slight hgf won't show- gas it will.

Compression tester saves hours chasing tail and if it isn't rules out issues
 
Well the bad news is that the disco has had a small leak at the rear of the engine for years but the leak was always external so i just kept topping up with antifreeze.

The good news is, whilst the old girl is off the road the head gaskets are going to be changed and the heads themselves are going to be tested.

Thanks for the advise though its much appreciated.

John
 
Ok, I did the fuel pressure test and found that when I turned the key to position 2 I got 2.4 bar, then I started the engine and it dropped to just over 2.1 bar.

So whilst looking round the vac pipes and having a poke round I noticed a crack in the exhaust manifold.

So most of the morning Me and my dad have been removing the manifold bolts, putting copperslip on them and putting them back in.

Regarding the fuel pressure test, I dont think the pressure is supposed to drop like that or am i wrong can anyone confirm, i did the test from the Schraeder valve on the fuel injector rail.

I have just picked a set of exhaust manifolds i got cheap off ebay a couple of years ago (dont ask i was drunk), I plan on getting a gasket set and fitting them.

Thats the update so far.

If anyone could confirm the pressure readings i would be most grateful.

Thanks

John
 
Update......

This afternoon finished changing the front passenger door spring that had gone, i give my dad full credit on that one no way in hells chance i would have done that job. Started at 7pm last night til 9pm then another 2 hours this afternoon, not a two minute job.

Im ordering a gasket set for the engine, that way I get head gaskets as well as exhaust manifold gaskets.

There is one more bolt to get out of the manifold but it looks like someone has tried before and rounded it slightly so that will be fun.

Ive got to look into the pressure test results, im going to change the fuel filter, do a re test, if they are the same then I will get a new fuel pump.

All good fun but my baby aint going to be on the road for a while yet.

John
 
Update.....

So I finally found what the fuel pressure should be and it is 2.4 bar, but im not sure it should drop like it does when the engine is started.

Wait and see what happens with the new filter in place.
 
Update.......

After two days hard graft we finally got the cracked exhaust manifold off, two rounded bolts made the job hard work.

However there is a good chance that this is what was causing the running issues.

See the pictures

ImageUploadedByTapatalk1409507371.107661.jpgImageUploadedByTapatalk1409507406.242624.jpgImageUploadedByTapatalk1409507441.328445.jpg

Even though we got this sorted out, we decided whilst we got this far we are going to change the head gaskets.

Does anyone know how I can re set the long term fuel trim, could taking the battery off for a few days work?
 
To put this one to bed.

It was the cracked exhaust manifold that caused both issues.

The old girl passed the MOT today and is back on the road with a massive smile on my face.
 
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