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6.5 MPG Disco V8


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Hello folks, happy new year!

nice forum, first of all, i must apologize for my bad english, i am slovenian and it's hard to me to write and much easyer to read, so i'll try the best i can.


So, i got myself a 1996 Disco 3.9 EFI hotwire, auto and LPG. It's a nice Landy and I love it, but..........6.5mpg??

it seems also not all cylinders working sometimes, when cold starts ok, when hot and after a half stopped i have to crank it for 15 seconds to start.

Sometimes i smell petrol but can't locate from where then. The idle is not smooth and the engine will shake/vibrate when stepping the throttle.

The sound isn't also smooth when driving, sounds like an Audi with 5 cylinders and feeling some vibrations from the engine.

Checked the coolant sensor, resistance is falling when warming up, ok, changed MAF, ECU, dizzy cap, rotor arm, cables, ignition module and coil ...all from another, wich was working fine.

Changed the sparkplugs also with new ones (NGK BPR6ES), set ignition on 6° without vacuum hose.....

no vacuum leaks present, stepper works fine (cleaned), TPS setting is ok too....

the behevor on petrol or lpg is the same, no leaks anywhere

cats are removed, lambdas still on, but not checked yet

also i'll try to check all again on the ecu connector, maybe the gremlin is somewhere in the wires

i think the compression is ok, no oil consumtion, no blue smoke, however, the exoust gas smells more like there still cats are present or maybe can smell petrol....or like sweet smell, it's hard to describe

mpg on lpg is very low too

the sparkplugs looked like this: (it's in the same order like in the engine)


need help, tips, advices, ......please

after lots of googling and using search functions on forums leads me only to confusions, on the other hand, i leraned a lot smile.gif

yesterday i read something about cleaning them and adjusting, adjusted it, set it on 1.8V on the first wire from the right on the connector (it was set to 3V and something) while engine was ideling

did i do correct?

also did disconected the ecu connector i noticed some bad contacts


on the other side, there are two smoked wires (ground)


fixed the contacts and measured the wires, it's still ok

checked the signal from coolant temp sensor, ok fuel temp sensor, ok, then we go to lambdas.

Using two multimeters, black cables to ground, red cables to pin 23 and 24.Starting the engine and left bank pending between 0 and 0,85V, rihgt bank between 1,096 and 1,227V....first i think something wrong with the multimeters, so i swiched them and the same come up for the banks....the rihgtone is faulty somehow.

Ok, so what does this mean?

Is it running to rich on the right bank?

Or is this a faulty O2 sensor?

here is a short video i made, it's shows the behavor of the multimeters during the lambda test:


another thing is, the disco had cats, but not any more, only lambdas left, so i changed the tune resistor from 3900 ohm to 470 ohm...did i do that correct or should i put the white resistor back?

i think, im a little bit closer, but still far from solving my problem,

all best from the sunny side of the alps

ps: in other posts i read something obout "tick over", what does this meen?


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hey, thanks for reply

so "tickover" meens idling, idle? (if i understand right, it's only another word ?)

ok, this morning i located the smells of petrol; when engine cold, i can smell petrol in the exaust gases, when engine is warm and is hard to start, i can smell petrol in the MAF when i remove the filter housing...

i noticed also in the dizzy the axles has a very little play, something between 0.05 and 0.1mm -- does this afect anything?

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i got same vehicle on gas. so you getting 6.5mpg on gas and petrol? how have you arrived at this figure? what tests have you done? its a low return to the gallon it has to be said. what concerning the most from what you have said is you appear to be lookin for an electrical problem causing this? yet you say it appears to be running on not all cyliders. have you considered that engine is way past its best days.

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You have lambdas, so leave the resistor as is. OTOH with the 470 ohm the lambdas will be ignored so that can be a useful debugging tool.

1.8 is correct for a lambda motor, should be 1.4 with the 470 ohm if memory serves.

If somebody has set it to 3.x I would look for a piggyback chip spliced into the ECU wiring.

Some of those plugs look much blacker than others so I would suggest cleaning the injectors and checking them for leaks.

Nice work so far.

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First thing to do is to check that the vacuum pipe from the plenum chamber to the fuel pressure regulator is connected and not leaking vacuum.

Then, there is enough evidence that when a V8 goes that heavy on fuel, it is most likely the MAF (air flow sensor) that is not reading correctly. Replace it with one you know is good and then check your fuel consumption. They can be adjusted (if they still work) by turning the adjusting screw closed off behind an aluminium plug. This is best done with a wideband oxygen sensor like the Innovate LC-1. AFR at idle should be around 13.5. CO meters are junk (IMHO)

If that does not improve your fuel consumption (and power) then you need to investigate the coolant temperature sensor. If that goes open loop the ECU will think your engine is ice cold and will enrich the fuel mixture as for a very cold engine. This is the sensor with two pins. It should read around 300 Ohm when hot. Also make sure the connector is plugged in properly.

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Oh, I should have added that you should also check that the diaphragm of the distributor is still OK. Pull the pipe off the top of the throttle body and suck on it hard as you can. You should then be able to block the pipe with your tongue and then it should hold the vacuum. This will only save you fuel on light throttle and it also assumes that the internal bits of the distributor is OK.

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AFM shoul be ok, measured it......fi i disconnect, the engine will die or almost die

red/black wire is ground on AFM, then we have a feed (brown/something 12V), a blue/purple (i think), that's set to 1.8V and another (blue/green) gives some voltage (0.3V i think), and when i blow in the AFM, the voltage rizes.

Coolant temp sensor is ok, checked even the wiring all the way to ECU, fuel temp, too.

Dizzy changed, pickup coil too, cap and rotor are lucas, they all ok, no changes.

The vacuum for before is ok too, checked that also.

No vacuum leaks anywhere

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Hi guys and girls happy new year to you all. I got an Endoscope for xmas, it cost £89.99 from that well known auction site !, and very useful it has been up to now [for working on the Disco of course].It makes it so easy to see where you normally cant, why didnt i get one years ago ?.If anybody needs specific details on where to get one from i can supply you with the company details. Sorry to hijack this post.

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