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Old 11-08-2005, 21:01   #1 (permalink)
Anthony
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Check engine light illuminated on 95 disco

Hey guys. I've posted once or twice on this forum before for my
fiancee's '95 Disco with the 3.9 V8. Responses seem helpful. I'm no
stranger to working on cars, but I am somewhat in the dark regarding
Land Rovers. I have a question for you guys:

Her check engine light decided to illuminate tonight. Background:
recently, the car has stalled out on me several times. Once right
after starting it, once while I was making a turn at a slow speed from
a light (so the engine was idling, essentially -- it's an auto tranny).
We decided to run some Techron fuel system cleaner through the tank
right before her last oil change. Not sure if it had much effect
besides a slight improvement in throttle response.

I have been very suspicious that the plug wires need to be changed. Is
there a possibility that bad plug wires would trigger a check engine
light? It's not flashing, just remaining illuminated. Correct me if
I'm wrong, but OBD II diagnostics came about for the '95 model and this
means we need a tech to turn off the light, pull the codes. Of course,
if he comes up with a P0300 (I think?) it's a misfire which would mean
bad plugs or possibly a screwed up crankshaft/camshaft (don't know
which these cars use) position sensor? Maybe the distributor?

What other things could cause the car to occasionally stall, idle a
little rough and turn on the check engine light?

We just replaced the air filter about two months ago, as well.

Thanks for any help. Oh, the car seems to running OK, minus the above
problems. Fuel mileage seems normal, so I'm not suspecting emissions
related problems (catylist, O2 sensors, etc)

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Old 11-09-2005, 02:01   #2 (permalink)
Badger
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Re: Check engine light illuminated on 95 disco


"Anthony" <ant9983@yahoo.com> wrote in message
news:1131511529.171580.45960@g14g2000cwa.googlegroups.com...
> Hey guys. I've posted once or twice on this forum before for my
> fiancee's '95 Disco with the 3.9 V8. Responses seem helpful. I'm no
> stranger to working on cars, but I am somewhat in the dark regarding
> Land Rovers. I have a question for you guys:
>
> Her check engine light decided to illuminate tonight. Background:
> recently, the car has stalled out on me several times. Once right
> after starting it, once while I was making a turn at a slow speed from
> a light (so the engine was idling, essentially -- it's an auto tranny).
> We decided to run some Techron fuel system cleaner through the tank
> right before her last oil change. Not sure if it had much effect
> besides a slight improvement in throttle response.
>
> I have been very suspicious that the plug wires need to be changed. Is
> there a possibility that bad plug wires would trigger a check engine
> light? It's not flashing, just remaining illuminated. Correct me if
> I'm wrong, but OBD II diagnostics came about for the '95 model and this
> means we need a tech to turn off the light, pull the codes. Of course,
> if he comes up with a P0300 (I think?) it's a misfire which would mean
> bad plugs or possibly a screwed up crankshaft/camshaft (don't know
> which these cars use) position sensor? Maybe the distributor?
>
> What other things could cause the car to occasionally stall, idle a
> little rough and turn on the check engine light?
>
> We just replaced the air filter about two months ago, as well.
>
> Thanks for any help. Oh, the car seems to running OK, minus the above
> problems. Fuel mileage seems normal, so I'm not suspecting emissions
> related problems (catylist, O2 sensors, etc)


Personally, I'd be looking at the idle speed control stepper motor on the
rear of the inlet manifold as a first port of call. Unscrew it and clean
with carb cleaner and see if that makes any improvement.
Badger.


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Old 11-09-2005, 07:01   #3 (permalink)
Anthony
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Re: Check engine light illuminated on 95 disco

Thanks Badger. How does the idle speed control stepper motor work?

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Old 11-09-2005, 09:02   #4 (permalink)
MDH
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Re: Check engine light illuminated on 95 disco

Anthony wrote:
> Thanks Badger. How does the idle speed control stepper motor work?
>


Anthony,

I had my Disco II in the shop last week for a check engine light. How
many miles on the vehicle? Has the truck been maintained, are these the
original plugs and wires?

Bad plugs and or wires will cause a check engine light. The vehicle
possibly misfired which would trigger the light.
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Old 11-09-2005, 09:02   #5 (permalink)
Badger
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Re: Check engine light illuminated on 95 disco


"MDH" <matt-at-matthosford.com> wrote in message
news:prGdnaqLzKhqgu_enZ2dnUVZ_vidnZ2d@britsys.net...
> Anthony wrote:
>> Thanks Badger. How does the idle speed control stepper motor work?
>>

>
> Anthony,
>
> I had my Disco II in the shop last week for a check engine light. How
> many miles on the vehicle? Has the truck been maintained, are these the
> original plugs and wires?
>
> Bad plugs and or wires will cause a check engine light. The vehicle
> possibly misfired which would trigger the light.


Matt, the misfire detection system and assosciated fault codes are only
applicable to the Disco II, not Disco 1. The D1 has the Lucas 14CUX
fuel-only management system, which is relatively basic in terms of fault
monitoring, whereas the D II has full Motronic engine management and a lot
more fault code info. FWIW, UK spec D II vehicles do not have the fault
light activated within the ecu software, only US spec models.

Anthony, the idle stepper motor is just that, a stepper motor controlled by
the ecu. ECU see's an rpm value, decides if it is correct, low or high. If
correct, it does nothing. If low, it opens a given number of steps. If high,
it closes a given number of steps. In all cases, it constantly monitors rpm
and when the target rpm is achieved it remains stationary. it's basically a
stepper motor connected via a screw thread to a tapered port valve, but the
whole gubbins can get gummed up with oily carbon residue, quite a common
failure.

Badger.


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Old 11-09-2005, 10:01   #6 (permalink)
Anthony
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Re: Check engine light illuminated on 95 disco


Badger wrote:
> "MDH" <matt-at-matthosford.com> wrote in message
> news:prGdnaqLzKhqgu_enZ2dnUVZ_vidnZ2d@britsys.net...
> > Anthony wrote:
> >> Thanks Badger. How does the idle speed control stepper motor work?
> >>

> >
> > Anthony,
> >
> > I had my Disco II in the shop last week for a check engine light. How
> > many miles on the vehicle? Has the truck been maintained, are these the
> > original plugs and wires?
> >
> > Bad plugs and or wires will cause a check engine light. The vehicle
> > possibly misfired which would trigger the light.

>
> Matt, the misfire detection system and assosciated fault codes are only
> applicable to the Disco II, not Disco 1. The D1 has the Lucas 14CUX
> fuel-only management system, which is relatively basic in terms of fault
> monitoring, whereas the D II has full Motronic engine management and a lot
> more fault code info. FWIW, UK spec D II vehicles do not have the fault
> light activated within the ecu software, only US spec models.
>
> Anthony, the idle stepper motor is just that, a stepper motor controlled by
> the ecu. ECU see's an rpm value, decides if it is correct, low or high. If
> correct, it does nothing. If low, it opens a given number of steps. If high,
> it closes a given number of steps. In all cases, it constantly monitors rpm
> and when the target rpm is achieved it remains stationary. it's basically a
> stepper motor connected via a screw thread to a tapered port valve, but the
> whole gubbins can get gummed up with oily carbon residue, quite a common
> failure.
>
> Badger.


The truck has around 157,000 miles on it and I seriously hope the plug
wires are not the originals but I don't know. Oil and filter changed
every 3000 miles but I really don't know the rest of maintenance
history. I will check out the stepper motor condition and vacuum lines
and stuff. Thanks so far

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