1989 Ford Aerostar Hesitating - Engine

Question: Hi - I have a 3.0 liter with 5 speed. runs perfectly when cold, but as soon as it warms up it misses and hesitates under light throttle. also misses at idle once warm. under heavier throttle the misses and hesitation goes away. Any help appreciated.

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Technican: A bad plug wire can do that, or one not installed properly. If your wires are new, check that they are plugged in both ends firmly. Look for burns where they may have touched the exhaust. Check for ends pulled loose from the wire. If the tuneup was done recently, check for cracked electrodes on the spark plugs. The difficulty installing plugs on this van has caused plugs to get cracked in the process. If no tuneup has been done recently, it may be time to replace the wires.

Owner: hi - I'll check all that, but I have a question. Would bad wires explain why it runs great when cold, but lousy when warm? thnx Mike

Technican: I had a Chevy with the same symptoms. Could not figure it out, but it ran great after the wires were changed. The spark plug require the highest voltage when the mixture is the leanest=warm and light to moderate load. When the engine is cold, the mixture is richer, under heavy load it is richer and will fire easier than when it is lean. You may want to check the plug wire resistance. Should be approximately 7000 ohm/foot.

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