4.9 has miss
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4.9 has miss
Ok, this is my first post. Tried to look at other post, have found no solution to problem. 1990 f-150 300 6 auto. 4x2 short bed. Just bought truck. Has 79,250 miles (actual). Has a dead miss at all speeds & at idle. Not continuous, but constant. Compression at 148 to 150 on all cylinders. Replaced so far, injectors, fuel filter, plugs, wires, rotor, cap, stator assembly, and coil. Think that’s everything. Tried the egr plug fix, no good. Thanks, any help appreciated. <O
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Tuned
Joined: May 2005
Posts: 436
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From: MI
check over plugs on harness for loss of connection. Could be the coil's power isn't making good contact. More recent, I had an injector plug not make good connection. It actually melted the plug and started shorting out.
Have you tried reading the trouble codes?
Have you tried reading the trouble codes?
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Ok, checked connections, seemed good. Check engine light has never come on. But, I unhooked map sensor. (Not vacuum) just electric plug. As soon as I did, it ran great. Ran down road great, so I replaced map sensor. Didn't help it one bit, but I unhooked new map sensor, truck ran great. Not a single miss. Drove it about 15 miles, ran great whole time (never ran like it before) pulled in driveway, hooked up sensor, started missing immediately. Check engine light on as long as unhooked, re-hooked, check engine light goes off. Only problem when map sensor unhooked, truck shifts really, really hard. I don’t have a clue. 
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