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MikeD', Technician
Category: Car
Satisfied Customers: 696
Experience:  ASE Cert, AS Degree in Automotive Diagnostics
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I have a 1997 Land Rover Discovery with a V8 4.00 liter engine

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I have a 1997 Land Rover Discovery with a V8 4.00 liter engine in it (approx. 125000 miles); it has a rather curious power problem that is becoming more pronounced over time: i.e. when I first start off driving (engine and related parts are still relatively cool) power is good to excellent as things warm up - it almost feels as if the timing has been retarded as the engine runs more sluggish. I have new plug wires, plugs) O2 sensors are only 18 months old, MAF is good, ETC sensor is new, IAT is new, air filter is top notch, I run it on 94 premium octane fuel. The engine uses next to no oil for her age (i.e., less than half a liter/quart in 4349.8 miles or 7000 kliks), new exhaust with headers, good air-flow from an ARB Snorkel intake. The engine does not run rough and has a very smooth idle as well. The only thing that I have noticed amiss is the fact that the starter is old and has trouble starting at times - almost does not start; the battery is a new Optima and I have a new aux Optima as well.

Hi, I am a Land Rover Technician, Sounds like you do some off-roading, good for you just remember to "tread lightly". We have had problems with aftermarket O2 sensors robbing power, If you have these installed you may want to have them replaced with OEM. They will not set a code but you will get reduced power and fuel economy. I do not believe it to be an electrical problem because you would hear the alternator whine if it was running full field and supporting a large drain. I noticed that you were using and aftermarket air delivery system (snorkel ect) Another problem we have seen is when people use K&N filters (or a similar oil base filter) The oil used on these reusable filters contaminates the mass air flow meter and caused a multitude of drivability concerns. It will kill a new sensor and as you know these sensors are very expensive. These also must be factory, these vehicles do not like aftermarket parts. These are really the only thing I can think of that will rob power but not set a fault code in the system.

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