Weird misfire issue
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Weird misfire issue
So my work truck that I drive everyday is a 2008 F-350 with the 5.4 V8. We’ve got way too much weight on it, so it honestly struggles getting up hills sometimes. Especially from a stop, gas pedal is on the floor and it accelerates rather slowly. Under these extreme load conditions, it will occasionally give a misfire code (check engine light flashes). At the same time, the AC starts blowing warmer. What in the world could cause both a misfire and warm AC? Only thing I can think is that maybe a belt is slipping on the alternator and the compressor, but there’s no “belt noise,” and I’m not even sure a slipping alternator belt would cause a misfire. Any other ideas?
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If it’s the computer, would it really only do it in the case of a misfire? There are plenty of times when I have no power because of the load, but it’s not misfiring.
Fleet Mechanic
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If the check engine light is flashing then it is misfiring. It may set the code for which cylinder is the culprit. As far as ac? Most compressors will cut out on low intake vacuum and unter sever load with throttle on floor it would have low manifold vacuum. Have someone run a cylinder contribution test and see if a cylinder is not pulling its weight.
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From: Pensacola, Florida
Your truck has gone into "Limp Mode" in order to protect the engine or transmission - that's why the AC is cutting out in conjunction with the performance issue. If things get bad enough, the computer can start shutting down cylinders and pump air through them, or only engage second gear in the transmission, in order to protect the vehicle.
Years ago the computers in vehicles would completely shut the engine off as a means of protection. The manufacturers realized it may be hazardous to shut the engine down while a vehicle is on the highway, so they invented Limp Mode as a substitute. If your vehicle goes into limp mode, it needs to be pulled off of the highway as soon as possible, and towed in for repairs.
Years ago the computers in vehicles would completely shut the engine off as a means of protection. The manufacturers realized it may be hazardous to shut the engine down while a vehicle is on the highway, so they invented Limp Mode as a substitute. If your vehicle goes into limp mode, it needs to be pulled off of the highway as soon as possible, and towed in for repairs.
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Your truck has gone into "Limp Mode" in order to protect the engine or transmission - that's why the AC is cutting out in conjunction with the performance issue. If things get bad enough, the computer can start shutting down cylinders and pump air through them, or only engage second gear in the transmission, in order to protect the vehicle.
Years ago the computers in vehicles would completely shut the engine off as a means of protection. The manufacturers realized it may be hazardous to shut the engine down while a vehicle is on the highway, so they invented Limp Mode as a substitute. If your vehicle goes into limp mode, it needs to be pulled off of the highway as soon as possible, and towed in for repairs.
Years ago the computers in vehicles would completely shut the engine off as a means of protection. The manufacturers realized it may be hazardous to shut the engine down while a vehicle is on the highway, so they invented Limp Mode as a substitute. If your vehicle goes into limp mode, it needs to be pulled off of the highway as soon as possible, and towed in for repairs.
Fleet Mechanic
Joined: Jan 2016
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That’s interesting. Is there no warning or anything that it’s in limp mode? I have a check engine light obviously, because of the misfire, but the only code it gives is “random/multiple cylinder misfire” and “cylinder 3 misfire.” For the record, we’ve changed plugs and coils on every cylinder twice.
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New User
Joined: May 2019
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From: Pensacola, Florida
That’s interesting. Is there no warning or anything that it’s in limp mode? I have a check engine light obviously, because of the misfire, but the only code it gives is “random/multiple cylinder misfire” and “cylinder 3 misfire.” For the record, we’ve changed plugs and coils on every cylinder twice.
The sensors which operate your gauges are typically not the sensors that signal the engine control module. You can have a problem and all of your gauges read fine.
AC cutting out and loss of power are typical when the vehicle goes into limp mode.
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