Discovery 1 V8 Fuel Consumption






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  1. #1
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    Default V8 Fuel Consumption

    Ok ok, for the billionth time here we go with the consumption thing again. I have been driving my D1 V8 auto around a bit this weekend and worked out the fuel consumption. It equates to about 3 km/l which is mainly highway driving. Now i know they heavy but this is crazy.

    So fiddling in the engine bay there is 2 lambda sensor plugs, the sensors have been unplugged at some stage in the vehicles life when a new exhaust was being installed and then just done away with. Has anyone unplugged there sensors? How does the ecu know they no longer applicable?

    What do i need to check in order to understand the high consumption? by no means do i "race" the disco.

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    Keen, 3km/l is insane to say the least. My D1 V8 in town i'm getting 5km/l. I was getting 4km/l and thought something had to be wrong. If i was you i'd call Jack with regards and ask if he wouldn't mind checking the items possibly contributing to the high consumption.
    I went to him after thinking i could of had a faulty MAF, he connect up his laptop diagnostics machine, confirmed all was OK and cleared the remaining faults.
    You wont know untill you get it checked...
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  3. #3
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    Ajay, the issue at the moment is that i need to get some mileage on the thing so that i can take it back to him for a service after the engine work done. He was having an issue connecting to the ECU last time i was there. There must be something i can look for though.

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    Wow, and I thought 5km/L is bad.

    I didn't think Lambda’s were fitted to D1's in this country.

    I have a 97 Range Rover and the Lambda plugs are just sitting each side of the sump. Only the North American model actually had them fitted. I could be wrong but I think the wiring exists but the sensors were never fitted.

    However if you are supposed to have sensors fitted and the CPU is not getting a reading then it may consider this to be a very lean mixture and pump all the fuel it can into the motor to compensate.

    If it is a little smarter then it would have gone into a limp home function which would probably still give you at least 5km/litre on the highway.

    Personally I don't think the lambda’s are your problem. Again I could be wrong but the D1 had a lot of vacuum pipes which if perished could have a major influence on fuel consumption.

    You don’t mention what speed you travel at on the Highway. I recently drove to Durban and back with 5 people and luggage, returned 13L/100 on the way down from JHB and 15L/100 on the way back with the Cruise Control set at 110 on the GPS and that's the 4.6L motor.
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    unplug the MAF and check if there is any difference in the idling, pulling or general driving. if not, the MAF is shot.
    i would take it back to Jack and check the MAF in any event.
    check the timing as well.
    5 is more or less what you should be aiming for around town if you don't drag race and 7 on the highway.
    i know the motor has been redone and should still be stiff but those figures are crazy.

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    OK, if you can take a photo of where the lambda’s plug in and a breif discription i could check for you on mine. I've still got stock std branches and pipe. Then i'd follow LL's instructions about checking the MAF. Other problem if not the MAF could be a lifter problem. No point guessing though...
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    there is a way the lambda sensors can be disabled from the ECU.
    the same ECU was used on vehicles fitted with and without Lamda sensors. Jack should be able to do that.

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    I agree, MAF is the most likely cause if the wiring to the CPU is ok. As you mention the mechanic had problems wiring it up.
    Godzilla - 1997 Range Rover 4.6 HSE
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    MAF is ok, Jack confirmed that it was fine. There must be something else i can check. My highway speeds are between 90 and 110kmh so no low flying. Can vacume hoses really have that much odf an effect?
    How can i check the coil? And plug leads? There is no mifiring but maybe there is an issue with that?

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    Does your cruise control work? If so i'd say your vacuum pipes are OK. All the soft rubber pipes around the engine bay are mostly vacuum pipes, comes from the the masterbrake cyl up the firewall (top) across the top to behind the water bottle (into a T piece) then distributes to accel and to the front left headlight area.
    I'm sure Jack would of set the timing correctly, unless it wasn't tightend and has come lose? No missfire would be an indication of tiing being good. Hell bud i don't know. I'm getting 5km/l, but i don't think i'd be a happy camper with getting 3.
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    Quote Originally Posted by Keenfish View Post

    So fiddling in the engine bay there is 2 lambda sensor plugs, the sensors have been unplugged at some stage in the vehicles life when a new exhaust was being installed and then just done away with. Has anyone unplugged there sensors? How does the ecu know they no longer applicable?
    AFAIK, the Disco 1 sold in this country did not have lambdas but a lot had them fitted aftermarket. Mine does.

    You need to check what tune resistor is fitted. You will find it in the loom going to the ECU which is in the footwell fitted to the rhs of the vehicle. You need to remove the cover just about above your shins. It is taped in to the loom and quite hard to find. It will have a blue connector and a resistor inside clear plastic. You can tell the value of the resistor by the colour of the wires. If it is a white one then it is (I think 3900 ohms) then it is expecting to see lambdas. If it is red or blue your lambdas will be ignored.

    What do i need to check in order to understand the high consumption? by no means do i "race" the disco.
    The usual culprits are the MAF, the coolant temp sensor and the lambdas (if fitted). These are quite easy to test with a multimeter. If you are happy to diy I can give you more info.

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    Hi Ancient, i'm more than happy to DIY, please send me the info.

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    Rub your finger around the inside of the exhaust, is it black sooty and smells of petrol?

    Remove each spark plug and see if they all look the same or if any are sooty or dark to light grey. If any are not like the majority, make a note of what cylinders and then let us know
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    Don't forget the vacuum advance. This is easily missed and makes a huge difference to fuel consumption. A common problem on the D1.
    camelman
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    Ok, let me give you a bit more backround. The disco was heavy on fuel, then i found out the head gasket was leaking. We sorted the head gasket, rebuilt the motor and now the consumption is still heavy. So Estee i don't think we will be able to pinpoint it to a cylinder, it would have to be something pre existing. The throttle body was really dirt so i tried giving it a clean with some carb cleaner. Maybe that will help the consumption.

    Vacuum advance seems fine. Tried to clean MAF again but haven't had time to take it for a drive.

    AncientGeek mentioned the resistor, i had a look and it's green so the ecu is not looking for the lambda sensors. This issue has me a bit foxed.

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    Quote Originally Posted by camelman View Post
    Don't forget the vacuum advance. This is easily missed and makes a huge difference to fuel consumption. A common problem on the D1.
    Just out of curiousity, the vacuum advance pump? Where is it located on a D1?
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  17. #17
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    You need to disassemble the MAF to clean it properly. It comes apart quite easily with a torx key. Be careful with the gaskets. On the left you will see a separate passage with 2 wires in it. Give it a good spray with an electronic cleaner that leaves no residue. If its very dirty use carb cleaner first. Let wel I have heard the Bosch maf on the disco 2 does not like being cleaned.

    To check the MAF you need some way of tapping into the wires going into it. I made up an intermediate connector with male and female spade plugs that I could clamp a multimeter into. The red/black wire is ground. You should measure 12v between this and the brown/orange wire. The blue green should be about .5v volts with the ignition on and engine not running, and about 1.7 v at idle. While you have the maf apart blow into the passage with the wires and you should see the voltage increase. Hardly rocket science but a good test. The blue-red is the CO trim, it should be between 1 and 1.5 volts. You can adjust this with a screwdriver inserted into the tube facing backwards which has a potentiometer inside. It might have an anti-tamper plug but the chances are someone has already removed it. Accurate setting requires a CO analyser but you could use the lean drop method provided your idle is good (and the IAC disconnected). This has a big effect on idle mixture pretty much like the mixture screw in a carburetor.

    The 3.9 engine has 3 temp sensors! If you look behind the distributor you will see one the on left one at a strange angle on the thermostat housing. This is the over-temp switch that turns on the AC fans if the engine is too hot. Measure the resistance across the 2 connectors. It should be an open circuit on a cold engine. If its shorted your fans will come on all the time.

    To the right is the temp sensor positioned vertically in or above the thermostat housing. Pull the plug off and measure the resistance on the sensor. It should be about 5000 ohms with a cold engine. The resistance decreases with temp so you can test it again with the engine hot or remove it and test it in near-boiling water. It should go down to about 200 ohms when hot. If your temp sensor is faulty you will probably have a very poor idle when hot. Behind the temp sensor is another one with a single wire which is the one used for the dashboard.

    Here are some good reads:
    http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm
    http://www.g33.co.uk/fuel_injection.htm

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    Quote Originally Posted by AjayDisco View Post
    Just out of curiousity, the vacuum advance pump? Where is it located on a D1?
    Theres no vacuum pump you only get those on diesels. But above the throttle there is a nipple that has a pipe going to the vacuum advance on the distributor. It is easily blocked. You can prise out the nipple to clean it properly.

    Its a strange design in that the gaaitjie for the vacuum is just upstream of the throttle so there is no vacuum at idle, only at part throttle. I've yet to see an explanation of why they did this.

  19. #19
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    Ajay, The vacuum advance is on the distrubutor.

  20. #20
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    Quote Originally Posted by AncientGeek View Post
    You need to disassemble the MAF to clean it properly. It comes apart quite easily with a torx key. Be careful with the gaskets. On the left you will see a separate passage with 2 wires in it. Give it a good spray with an electronic cleaner that leaves no residue. If its very dirty use carb cleaner first. Let wel I have heard the Bosch maf on the disco 2 does not like being cleaned.

    To check the MAF you need some way of tapping into the wires going into it. I made up an intermediate connector with male and female spade plugs that I could clamp a multimeter into. The red/black wire is ground. You should measure 12v between this and the brown/orange wire. The blue green should be about .5v volts with the ignition on and engine not running, and about 1.7 v at idle. While you have the maf apart blow into the passage with the wires and you should see the voltage increase. Hardly rocket science but a good test. The blue-red is the CO trim, it should be between 1 and 1.5 volts. You can adjust this with a screwdriver inserted into the tube facing backwards which has a potentiometer inside. It might have an anti-tamper plug but the chances are someone has already removed it. Accurate setting requires a CO analyser but you could use the lean drop method provided your idle is good (and the IAC disconnected). This has a big effect on idle mixture pretty much like the mixture screw in a carburetor.

    The 3.9 engine has 3 temp sensors! If you look behind the distributor you will see one the on left one at a strange angle on the thermostat housing. This is the over-temp switch that turns on the AC fans if the engine is too hot. Measure the resistance across the 2 connectors. It should be an open circuit on a cold engine. If its shorted your fans will come on all the time.

    To the right is the temp sensor positioned vertically in or above the thermostat housing. Pull the plug off and measure the resistance on the sensor. It should be about 5000 ohms with a cold engine. The resistance decreases with temp so you can test it again with the engine hot or remove it and test it in near-boiling water. It should go down to about 200 ohms when hot. If your temp sensor is faulty you will probably have a very poor idle when hot. Behind the temp sensor is another one with a single wire which is the one used for the dashboard.

    Here are some good reads:
    http://www.britishv8.org/Articles/Rover-14CUX-EFI.htm
    http://www.g33.co.uk/fuel_injection.htm
    AG - Just out of concern, i do understand the voltage tests as well as the cleaning of the MAF. But i've been strongly advised by LR Indies that the screw which is blocked off on the MAF where you make adjustments up or down what ever the case should never be adjusted. Its blocked off for a reason. Unless you have had success with regards?
    I'm still at a dead end about vacuum. I'm going to check this area on the distributor since i've been having endless troublshooting of the cruise control. Sorry off of the subject, but its just been something i've not been sure of and will check there now...
    Platkar driver...
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    Challenger Bundu Basher - SOLD
    I will drive a Land Rover again...

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