Question about 1998 Jaguar XJ8L

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Restricted performance under load

Jag dealer cleaned injectors & replaced fuel filter twice
reset computer. after driving a few miles restricted performance lite comes on???????

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I had the same problem on my 1998 XJ8. My dealer told me it was the Mass Airflow Meter, which needed replacing to the tune of around $500. After a second opinion at my local Jag mechanic, it turned out to be a hose that was broken on the lower part of the front of the engine. Check the vacuum hoses for breaks or loose fittings.

Posted on Mar 16, 2009

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Some times, it only takes a good cleaning of the Mass Air Flow Meter to get it working again. Also clean out the full air intake and down the throttle body, especially the butterfly flap. There are special cleaners for both the Mass Air Flow Meter, and the Throttle Body. Be sure to use the correct ones as there are special coatings that can be damaged by the wrong cleaners.

Posted on Apr 01, 2009

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I have a 2001 Ford Escape w/ loss in fuel economy


Your tires as they wear will affect milage. Maybe an alignment check is do, All it takes is a couple PSI difference in the tire to loose a few miles per gallon.

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Slight apparent misfire under load (small hill). Significant loss of power. Checked injectors, plugs, wiring, no trouble light. Runs fine on straight and level. 350 cid never been opened up. 98,000 miles....


If only under a load, it is possible that the fuel filter is mostly clogged. Also check air cleaner (you probably already did). The concept is that under a load, your throttle body is mostly open, requiring high volume of air and fuel flow. Restrictions in either of these will make it run bad.

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2 Answers

Hard start on cold mornings; replaced plugs but did not fix; fuel filter?


If the vehicle runs normally otherwise, your fuel filter is likely not the problem. A plugged fuel filter would likely cause misfiring under load, such as when going uphill.

Make sure, by the way, that you do not touch the gas pedal when starting. That could make it hard to start.

Old fashioned cars used a choke to feed it more fuel for a cold start. Modern cars use a computer to feed the fuel injectors more fuel on a cold start, and rely on a sensor or two to know that it's cold.

Couple of possibilities here:

a) Has the check engine light been on? If you have a bad sensor, such as oxygen, throttle position, or coolant temp sensor, the computer may have an error code stored in it's memory about this.

b) How many miles on the vehicle? Some other problems could be leaky injectors, leaky injector 0-rings, or intake manifold air leaks, all making it difficult to start when cold.

A fuel pressure gauge on the fuel rail would tell you if a leaky injector is causing the fuel pressure to drop....then a cold start would be difficult if there is no pressure in the system.

If there is a leaky o-ring or intake manifold, the vehicle will typically misfire and/or light a check engine light.

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^ Fuel Vapor Canister saturated with fuel.

IMPORTANT:
If the front oxygen reading voltage is above 600 mV and the rear HO2S is above 600 mV all the time, the O2 sensors are probably not
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god bless you for serving our country!!!

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