Check engine light illuminated on 95 disco

Nov 09, 2005 5 Replies
A

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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B

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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A

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

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M

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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B

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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A

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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