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Misfire after warmed up

1164 Views 2 Replies 3 Participants Last post by  GLHS60
My 92 Spirit (2.5) has developed a misfire which occurs only when the engine is really warmed up. Especially after freeway run. I really feel the miss at idle. It is hard to detect at high sppeeds other than the engine being a "little" sluggish. Things go back to normal after cool down. I have done a tune up consisting of plugs, wires, dist.cap and rotor which were needed but did not help. I am about to use a heat gun on the coil then the distributor to heat up the pick up coil. I cannot find what the resistance values should be for these. I would appreciate any suggestions.BTW- I only have the usual code 55.
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1966 Crown Coupe, 2016 200 S AWD, 1962 Lark Daytona V8.
17,292 Posts
EGR comes into play when warm (if equipped). As I remember, my '92 Federal Shadow didn't have an EGR. The valve is best removed and blown through as a leak test (the stem may be seated, but the valve still may leak if the pintle is burnt off).
Closed loop will also start the O2 sensor feedback for mixture control. Idle is also when intake manifold vacuum should be high and any vacuum leaks (PCV, booster, etc.) can raise and roughen-up idle quality.
After a freeway run could also mean that the valves aren't seating well when hot and may seal better after cooling. A hot soak 'static' compression leak-down test (not a cranking compression test) may show how well the valve seating is doing. Air hissing from the throttle body would be an intake valve and from the tailpipe would be an exhaust valve. Piston ring sealing can differ hot or cold and would be heard at the oil filler cap hole.
The distributor pick is Hall-effect (switch) and not a magnetic coil, so resistance measurement isn't really a valid test.
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