I have a '91 Mercury Capri ( Base - Non Turbo ) , automatic transmission .
The car runs fantastic until it reaches operating temp , then Just won't hardly run at all . I have replaced - Alternator & belt , Battery , Distributor Cap & Rotor , Spark Plugs & Wires , Ignition Coil , and Engine Coolant Temp Sensor . I tested my Throttle Position Sensor , checked good . I Removed and cleaned the throttle body .
Could this be the Ignition Module or Distributor Pick up Coil ? And if so , Anybody know how to check these with an Ohm Meter ?? I'm at my wit's end !!
Hi! My name is Loni, I’m an ASE master tech with 29 years of experience. I haven’t seen a Capri from that era in almost 20 years! Ok, time to stop throwing parts at this problem. I hope your car needed all those parts, because none of those could have been the source of your problem. There are still lots of possible causes for your issue, fuel pump, mass air flow sensor, computer, oxygen sensor, etc. old fuel injected engines like yours run in ‘open loop’ until they warmed up, engine coolant temp comes up and oxygen sensor heats up, then they go into ‘closed loop’. In open loop, the computer ignores most of the sensor inputs and adds fuel and timing based on minimal inputs, just trying to get the engine to warm up. Old engines spewed harmful emissions out the tailpipe at this time. Once warmed up and in closed loop, the computer adjusts fuel trim and timing based on all the sensor inputs. I believe this is when your problem occurs. If this were a newer car you could plug in a high quality scan tool and read the data from the computer, but computers weren’t very tech friendly and lacked the ability. It would still be worthwhile to have your computer checked for any codes that won’t necessarily turn on the check engine light. To further duagnise your car, you will need a lab scope, as your ohm meter just won’t do the job. I would scope the oxygen sensor signal to see what’s going on. From that data, you can tell if the engine is running lean ( I Suspect) or rich, or if you have a bad oxygen sensor. You could also try disconnecting your mass air flow sensor after the engine is warm and is acting up. With the MAF disconnected, the computer calculates how much air ‘should’ be passing the sensor rather than how much is actually passing the sensor. If it runs ok with the sensor disconnected, you could have a bad sensor or you could also have a vacuum leak. To check for vacuum leaks, you’ll need a smoke machine. I hope this helps you a little trying to understand your problem, and regrettably you are going to need more tools to diagnose it
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