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V8 overfuelling on one side


sotal
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Hope nobody minds me posting in here, tried posting in the relevant section but had no answers and hopefully it's generic enough to be the same for any land rover!

Basically I have a Gems 4.6 V8,

I bought it with blown head gaskets. I rebuilt it and it started straight up and I've had no problems on the cooling side of things but I'm having problems with the fuelling.

It idles nicely with no smoke, and it drives fine with no signs of smoke - although it does feel down on power.

However if you rev it in Netural on the Drive it gives out big clouds of smelly smoke (smells like petrol) This only starts above 2000rpm

It seems to be the drivers side of the engine which is overfuelling. The third from the front was black and wet, the other three were all black but not quite as bad.

The lamda sensor on the drivers side is ranging between 0v and 5v on idle, the passenger side is ranging between 0v and 0.3v on idle and 0v and 1v when revved a little.

I've tried with and without the MAF with no differences, and have cleaned the MAF and replaced.

I've used a generic OBDII scanner which reported no faults, and the engine light doesn't come on.

I'm trying to get as much info so I can spend the weekend on it, and I currently can't pass the MOT with it like this!

So far I'm going to try swapping the lamda sensors round, and I'm going to have a play with moving HT leads and plugs round to see if I can move the fault.

Any other suggestions?

THANK YOU!!!

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Check for stuck/leaking injectors. If it's overfuelling massively it may be clogging the lambda element and giving a false lean reading, or it may be that the lambda is dead and giving a false lean, leading to massive overfuelling.

You can clean the lambda element by heating it up with a blowlamp, cherry red for a few seconds. Just wait for it to cool down before picking it up & refitting :P

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before removing injectors remove its plug and check for resistance - i cant remember whether they are around 1 Ohm, or 4 Ohms. compare the injectors on the faulty bank for a noticeable differance (1 or more Ohms is enough to indicate a problem with an injector) - it would be wise to also check the resistance back at the ECU but you will need to know what pin outs to check etc.

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I've been running some OBDII software today which monitors the lamda sensors and it says both are working fine so I think they are OK.

I think for some reason a cylinder isn't firing or has low compression etc. So the fuel is just getting pushed out, just trying to figure out why now

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I managed to move the fault from one bank to the other by swapping Bank 1 spark plugs to bank 2 and vice versa. Ran on the drive and bank 2 appeared to be over fuelling from the short term fuel trims.

Bought new plugs and replaced them all, completley fixed, idle increased from 650rpm to 750rpm, fuel trims moved up and down no more than 5% each way, settled at 0 some of the time.

Took it for a drive and it felt to have much more power, turned round in an empty car park and revved it to 2500rpm - no smoke, drove back home happy. On returning I revved it on the drive to 2500rpm and the smoke started again, checked idle and it was back to 650rpm. Fuel trims were now sowing that Bank 1 was over fuelling again. Pulled the plugs to find cylinder 3 was wet (it was wet in the morning when I swapped them).

Just don't know why it's wet now. It appears to be oil to me.

Compression test for that cylinder gave 160 psi on the first test, then 150 psi after. If you remove the oil filler cap whilst running it doesn't chuff.

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Could it possibly be a small leak on an injector on that bank? new plugs coped with the over rich mix but then fouled up, see if the fuel rail pressure drops after switching off the ign, I know they are bank fired but you might get lucky and find its the injector closest to cylinder number 3 thats at fault, move to other bank and see if the fault moves.

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Suppose it could be? if it is oil getting in somewhere the new plugs would fix it for a short period of time.. But usually it is possible to recognize the two from eachother. If it is oil on the plug it never "dries up" and will have shiney surface, whereas petrol usually vapourises leaving only a mat black color. That is if you take it out and leave it on the table for a while.

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I've had a look on google images for pictures of wet spark plugs from fuel and it does look the same as mine. Mine was still wet after a couple of days on the kitchen table.

I would instantly say it was oil, but I'm running out of quick fixes for oil, the only possibilities seem to be major engine work - so I'm hoping it's fuel and I'm going to investigate the injectors a little further - I'll probably try and swap a couple round to see if that makes a difference.

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Defo seems to be oil, oil has dropped about a cm on the dipstick.

I unplugged the injector on Cyl 3 and ran the car at idle for a few minutes - the plug was then wet again. I cleaned the plug off again and left it out for a minute with a peice of paper outside the hole, it sprayed the paper with light brown splatters. I then put the spark plug back and ran it again for a few mins, again it was wet.

Fuel pressure doesn't seem to drop (fuel pump runs for a short amount of time when it hasn't been run for a long time - otherwise I don't notice it run). So I don't think it has a leaky injector.

Cyl 3 doesn't smell at all of fuel since disconnecting the injector.

Just don't like the thought of where that much oil is coming from!

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well theres only really a couple of options, its a valve guide/stem seal, or the rings. Or perhaps the engines breather vents very close to the inlet to the bad cylinder?

If you pop the inlet manifold, you can sometimes see the back of the valves and if its a stemseal or guide it can usually be seen from there.

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I think part of the PCV is close to that cylinder but I don't really understand how it works.

paul.adshead.pcv_pipes.jpg

The above picture from another forum shows the two pipes used, pipe 1 is very close to being above the cylinder. How would that get to it?

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Ah, it connects to the inlet at the throttle body, so one would assume the air would disribute it round all the cylinders evenly.

Some engines have the pipe connected directly to the plenum chamber, meaning an especially heavy breather can end up throwing a lot of oil directly at one particular inlet runner.

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