1993 Discovery High fuel consumption

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Originally Posted by bee utey

The fuel pressure regulator has a vacuum hose attached to it and sometimes this falls off the connection at the back of the idle stepper motor. Sometimes the regulator leaks fuel via this vacuum hose into the manifold, check the hose for drips of fuel. Fuel pressure should be able to be checked at the Schrader valve on the fuel rail. I don't have specs, a workshop manual (available from the "shop" tag above) should have those.

The MAF adjustment is a try-it-and-see thing, or you probe one of the connectors and see which one's voltage varies with adjustment. I did one that way, can't remember the numbers.

Also check the 2 wire plug on the temp sender at the front of the inlet manifold, this should read around 300 ohms with a warm engine. Note that this isn't the 1 wire sender for the dash gauge, that's next to the 2 wire one.

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Thanks for the steer! The fuel reg seems ok, but the Vacuum advance does nothing. the mechanical advance moves the timing, but the vacuum (with my mouth attached) just sucks like an open straw. so no vac advance and effectively creating a vacuum leak.
Then I tested the coolant temp sender. reads as an open circuit at hot. I assume the sender works by decreasing resistance as it heats, thus the computer now thinks it's at cold and increases the time the injector is open for.

Do you think adding a resistor between the pins trick the computer into adding less petrol? then I would use one that's about 300 ohms?

So if I fix the Vacuum advance, that will help with LPG, and the Temp Sender fix will help petrol.

The spark plug gap was set to the .8mm but LPG should be .7mm?

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Originally Posted by Redfoxie

Thanks for the steer! The fuel reg seems ok, but the Vacuum advance does nothing. the mechanical advance moves the timing, but the vacuum (with my mouth attached) just sucks like an open straw. so no vac advance and effectively creating a vacuum leak.
Then I tested the coolant temp sender. reads as an open circuit at hot. I assume the sender works by decreasing resistance as it heats, thus the computer now thinks it's at cold and increases the time the injector is open for.

Do you think adding a resistor between the pins trick the computer into adding less petrol? then I would use one that's about 300 ohms?

So if I fix the Vacuum advance, that will help with LPG, and the Temp Sender fix will help petrol.

The spark plug gap was set to the .8mm but LPG should be .7mm?

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You could try the resistor, I've never done that myself. I just keep a spare sender on hand.

Vacuum advance is not too hard to change, does not require major distributor dismantling. I get mine from the UK, not too dear.

Land Rover Discovery Defender V8 replacement vacuum unit Powerspark RTC3201 | eBay

0.8mm should be fine, providing the plug gaps are straight and unworn.

[table]
[TR]
[TD]The Coolant Temperature Sensor should change resistance with heat, per the following specs:

- 10 c ....................9,100 - 9,300 ohms
[/TD]
[/TR]
[/table]
0 c.........................5,700 - 5,900 0hms
20 c.......................2,400 - 2,600 ohms
40 c.......................1,100 - 1,300 ohms
60 c........................500 - 700 ohms
80 c........................300 - 400 ohms
100 c.......................150 - 200 ohms


The Coolant Temperature sensor is used to enrich the fuel mixture whenthe engine is cold. These devices almost always fail open-circuit, which makesthe injection system believe that the engine is at somewhere around–40 degrees Centigrade. The system will always detect this as a faultcondition, and use a substitute value of 30 degrees Centigrade whilstsetting a fault code in the ECU. In practice, thismeans that the car will be difficult to start when cold (too lean), andwill be too rich when warmed up. However, it will usually get home!
.................................................. .....................................
These sensors are still available and not expensive. p/n: ETC8496. If a faulty sensor is replaced it will be necessary to clear the fault in the ECU either by unplugging it, or disconnecting the battery for a few seconds.

So I went shopping on the net for a new temp sender and discovered I was testing the wrong thing.
I was testing the Thermo fan switch (it has 2 wires next to the single wire). I have found and tested the actual sender and it fits the table from Old Farang (thank you very much for that info!)

So now I am back square 1 ( surely vacuum advance alone wouldn't cause my problem)

You may be suprised with the vac advance.
My 300k old 3.5L auto with bull bar winch lights roof rack will still get 15-16L/100

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Originally Posted by Rick1970

You may be suprised with the vac advance.
My 300k old 3.5L auto with bull bar winch lights roof rack will still get 15-16L/100

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that's the sort of consumption I would expect. My 1996 4.0l Jeep used 9-11 L per 100 on the highway and 13-16L per 100 in town. (that was a rubbish motor vehicle)

After cleaning the MAF and replacing every Vacuum hose I am getting better economy (with the Vacuum advance still capped off while I await the new part)

I am still convinced I would get better performance if it was fitting with working O2 sensors, and the computer was capable/ programmed to use them.

O2's are a cruel master,, ( and I havent miss-used the word master.....)
I'd love not to have any on mine and just run a dedicated fuel map.

Just got 170km out of the 35l petrol tank. better, but still 20.5l per 100kms. I should be getting over 200kms per tank yeah?

Had to read about the '93...

I found th same issue was with my '98 disco... Same fuel injection/computer 14 cux... anyway I found the idle had been tampered with and once reset, that made huge changes then the last change, was correct size tyres...

I was lucky to get 300 k's out of 75 litres on a gentle long run... Now I get around 450 - 500, depending if town or long distance... Oh and towing a trailer makes bugger all difference now...

Tyres are first and foremost I recon, but check if idle screw is missing its cap or looks like its been out... If so then it needs a double check...Mine was idling at 2,000 rpm when the computer had no control...

Not sure if your engine is set up the same, but you could find how to adjust idle, then go from there...

Ok it's been a mission but I solved it.
The silver bullet was the vacuum advance unit. It just took me a few shots:

3 faulty vacuum advance units later... the one on the dizzy was busted so replaced with recommended eBay job. Seemed to run better at first but after 80 kms of driving it proved no better so went hunting again, nothing obvious so I sucked on the vacuum advance line and it had failed!!
got it replaced free of charge from the UK supplier, new unit went on. Ran better, fuel gauge dropped slower first 30 litres took me 160kms better but not the best fix. Next 30litres got me only 130 kms again, went straight to the vacuum advance unit... failed!!!!

I took to the spare first failure with a tin opener and discovered that in the process of making these items, the diaphragm was crimped too tight on one side and made the joint too thin... so the vacuum just tore it....
out with the silicone, clamped it up installed it and hey presto my little 30litre tank gets me 200kms... even towing a trailer.

So if you have fuel consumption of 20l per 100 kms, check the Vacuum advance unit. An instant fix (if you buy a good replacement) down to 15l per 100kms.

talk about a simple thing made hard.