Julian B
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| posted on 16/3/04 at 12:00 PM |
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V8 petrol EFI Range Rover misfire
Hi all
I have a friend who has a V8 3.9 efi Range Rover. It has a misfire fault when pulling a load or when overtaking at about 75ish mph.
Trying to track the problem down is a bit difficult and it has been suggested that the first thing to replace is the ECU
Apparently this is a stock fault on a lot of EFI rangies but no one can identify exactly which sensor or part is at fault
Does anyone have an ecu that my friend could try/borrow?
His name is Nick and his email address is Nick@tritechuk.com
Thanks for your help on this not strictly kit car topic
Cheers
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Graceland
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| posted on 16/3/04 at 12:57 PM |
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i'd be tempted to change the throttle position sensor - does it do it at the same revs in every gear (if manual) or hesitate when pedal reaches
a certain position? and then once pressed further drives right thru it?
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blueshift
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| posted on 16/3/04 at 02:40 PM |
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There's an EFI rangie in a scrapyard near me (hemel hempstead), probably a bit far for you unless your friend is down here. We've been
raiding it for bits but it may still have the ECU in it. it does have the throttle potentiometer still on, and the rest of the EFI loom and devices.
It's flapper-type rather than hotwire type.
We have a vitesse engine with flapper EFI and ECU for that, not got it running yet so not 100% sure the ECU works, but if he's nearby he's
welcome to try that, assuming his is a flapper system. Would let us know if the thing works, too.
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britishtrident
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| posted on 16/3/04 at 03:15 PM |
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Start with the simple things that cause misfire under load --- fuel flow from the pump (fuel filter choked ?), plugs, plug leads.
The flapper type airflow meters on rangies are prone to sticking, but this usually first apears when pulling away at low speed usually cured by a
good blast with carb cleaner.worked in with a stiff paint brush to clear the carbon.
After that do a compression test before looking at anything else the injection system. and then the first thing to check is if the manifold
connections (including to the MAP sensor) are all air tight and the ecu is earthing properly., then check the outputs from the coolant sensors the
throttle sensor needs connected to an oscilloscope to check for glitches.
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blueshift
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| posted on 16/3/04 at 04:59 PM |
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Interesting comment about earthing the ECU there. I was wondering if it needed an earth.. thanks. I'll make sure ours has one for the bench
test, saves one of the many things to tear my hair out over.
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britishtrident
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| posted on 16/3/04 at 06:58 PM |
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Its unlikely to be an ecu board fault --- MAP sensor perhaps which is fitted to the ECU board in on most (but not all) Rover systems. To test the
map sensor you really need a vacum pump -- some people have used a bike pump with the washer reversed.
A while back a guy in one of the Rover 800 groups had a misfire -- he change everything in sight , ECU (twice), crank pick-up, tps coolant and
ambient sensor, coil, injectors, cylinder head and cams and what was the cause ? very simple but it took him 6 months to find --- the rotor arm.
Simple things first.
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Fatboy Dave
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| posted on 16/3/04 at 09:59 PM |
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Indeed, simple things first.
Also, remember, the 3.9 has the Lucas Hotwire, not the earlier flapper air flow meter system. The two systems are wholly incompatible.
Common favourites with the RR (from bitter, bitter) experiance, are ignition amps, TPS, and coolant temperature sensors.
Start with simple things like sparks/coil/leads fuel etc. first though. Costs less on the Rangey :-)
Dave
Stop the planet, I want to get off
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britishtrident
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| posted on 17/3/04 at 08:38 AM |
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Ignition modules tend to go with age -- then the main power transistor fails and you get total loss of spark.
Hot wire airflow meters -- The hot wire (actually hot film) type only tend to fail when the output voltage at idle creeps up giving an over rich
mixture and MOT failure., I have never seen any other problems with them
The throttle postion sensor was also fitted to some 1988 to 90ish Montego Efi and 820Si &SLi models with Lucas 14CU injection. (the Range
Rover is Lucas 14CUX), these models are a potential source of minor spares but as Rover injection systems have changed several times finding the
right model in a scrapie might be difficult. Many parts from the earlier Lucas CU11 system should also fit.
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