What a miss
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What a miss
Well, here's the story. I got an '88 F-150 with the 4.9L six about 18 months ago and when I first got it, it would start and idle fine, but now sometimes when I start it it wont idle unless I rev it up a few times and it has a nasty little miss a idle and a really bad one from 1500 RPM to 2500 RPM. Last week i replaced the cap, rotor, plugs, wires and coil; a few months earlier I replaced the ignition control module on the distributer because, it went south. I also cleaned out the idle air valve. When I started it back up, it ran smooth with no miss for about 15 minutes then started again. I've run out of trouble shooting ideas and don't want to throw money at it unitl I fix it by chance. Any help would be great.
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Joined: Jul 2004
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From: Northern Virginia, USA
I have the same truck, and it has a near miss. Runs fine until it warms up, then it develops a "tick", and a near miss. I can hear it in the exhaust note as well. I suspect they might be the original injectors. 112k mi. Worst at around 1200-1500RPM, then smooths out beyond 2000. When the weather gets warmish, and I get motivated, I'll replace the injectors. Don't feel like unbolting that upper intake...
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BigBlue88, thats is the exact same thing as with my truck, so you think that it is your injectors? I'll have to look into that. Could someone please explain to me how a bad injector would cause the miss?
Elder User
Joined: Jul 2004
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From: Northern Virginia, USA
Camino-
An injector spraying too little fuel, no fuel at all, or the solid stream from a clogged nozzle would cause a miss. The computer would detect the excess oxygen from the missing cylinder, think the engine was lean and try to dump in more fuel to compensate, running the other cylinders rich (ruining gas mileage and fouling your cat). The clogged nozzle would dump a stream, not a spray of gas into the cylinder, which woulnd't all combust, leaving excess oxygen that the computer would interpret as lean, just like too little/no fuel. Either way, that one cylinder wouldn't be operating at the same power level as the others, and you'd feel a miss.
Also, an injector spraying too much fuel would quench the spark/flame and cause a miss as well.
The "tick" on my truck distinctly comes from the injector side of the engine, and an exhaust leak would only make a sound, not feel like a miss.
I've checked the ignition. Since it runs fine after first startup, and especially starts instantly in this cold weather, I'm not concerned about compression or burned valves or anything serious like that.
An injector spraying too little fuel, no fuel at all, or the solid stream from a clogged nozzle would cause a miss. The computer would detect the excess oxygen from the missing cylinder, think the engine was lean and try to dump in more fuel to compensate, running the other cylinders rich (ruining gas mileage and fouling your cat). The clogged nozzle would dump a stream, not a spray of gas into the cylinder, which woulnd't all combust, leaving excess oxygen that the computer would interpret as lean, just like too little/no fuel. Either way, that one cylinder wouldn't be operating at the same power level as the others, and you'd feel a miss.
Also, an injector spraying too much fuel would quench the spark/flame and cause a miss as well.
The "tick" on my truck distinctly comes from the injector side of the engine, and an exhaust leak would only make a sound, not feel like a miss.
I've checked the ignition. Since it runs fine after first startup, and especially starts instantly in this cold weather, I'm not concerned about compression or burned valves or anything serious like that.
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agryphon
1983 - 2012 Ranger & B-Series
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Oct 31, 2006 10:10 AM
