tach bouncing, 06 f150

Need more info. Is the actual engine reving up or is just the tach needle moving? Specs power cable size, ground size, and model numbers  of the amps you have? Factory head unit or aftermarket?

xtremej wrote:

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Need more info. Is the actual engine reving up or is just the tach needle moving? Specs power cable size, ground size, and model numbers  of the amps you have? Factory head unit or aftermarket?

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no the engine is not reving its just the tach.  all the cables are #4.  the head unit is a pioneer 7700mp.  Not sure about the model numbers for the amps.  The rockford is a few years old.  the pioneer is their bottom end 300 watt amp. 

Thanks audiomaniac ill give that a try. 

any other ideas?

no the head unit has been in since i first got the truck about 10 months ago.  i did not have the problem with the pioneer amp and a kicker comp 10.  it all started when i took out the kicker sub and added the rockford amp and the type-r 10.     Will taking out the pioneer amp help?  a friend who is a professional installer is totally stumped.  The truck has a 130 amp alternator.  It is definately the system though because when i turn everything off the tach stops moving.

and you are saying that it is just the gauge moving or are the acctual RPM's of the engine going up and down as well?

Have you had someone watching the motor while the needle was moving? If you have to turn the stereo up for this to happen and you are only talking about 700rpm-1300rpm on the inside you probably would not notice if the engine was going up and down.

The thing about it is if the engine itself was not reving up and down the gauge would not bounce up and down either. "If" by some chance the gauge was bouncing up and down without the engine doing it as well, then all of your gauges would be going up and down with the tach.

01trublugt wrote:

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and you are saying that it is just the gauge moving or are the acctual RPM's of the engine going up and down as well?

Have you had someone watching the motor while the needle was moving? If you have to turn the stereo up for this to happen and you are only talking about 700rpm-1300rpm on the inside you probably would not notice if the engine was going up and down.

The thing about it is if the engine itself was not reving up and down the gauge would not bounce up and down either. "If" by some chance the gauge was bouncing up and down without the engine doing it as well, then all of your gauges would be going up and down with the tach.

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ill check the engine out today and see whats up with it.  Would my distribution blocks pay any part in this.  The ones i am using are kinda crappy, they are left overs of a buddy of mine.  would replacing these help at all.  Again im just grasping at straws here, i really cannot figure this out.

I have a feeling that the bouncing you are refering to is more like fluctuating rather than bouncing, meaning it goes down to 700 for a second or two then goes back up to 1300 then it repeats. Not knowing the details of your install but knowing Ford motors pretty well I can bet you are taxing you charging system somewhere.

The signal that feeds the tach comes straight from the PCM, if you were doing something that would affect the gauge you would be affecting everything else the PCM controls. What is happening is your engine is revving a bit to compensate for it.

Try this, with the truck at idle stereo off, turn on the a/c system full blast. You will notice the RPM's drop from the initial load of the compressor, the pcm will respond by increasing the RPM, then once the initial load is gone the RPM's will settle back down to a smooth idle. Same thing is happening when you turn the system up. Your PCM is sensing the extra electrical load, increasing RPM's to compensate.

If I had to take a guess I would say your battery is not holding enough in reserve to feed the electrical system

01trublugt wrote:

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I have a feeling that the bouncing you are refering to is more like fluctuating rather than bouncing, meaning it goes down to 700 for a second or two then goes back up to 1300 then it repeats. Not knowing the details of your install but knowing Ford motors pretty well I can bet you are taxing you charging system somewhere.

The signal that feeds the tach comes straight from the PCM, if you were doing something that would affect the gauge you would be affecting everything else the PCM controls. What is happening is your engine is revving a bit to compensate for it.

Try this, with the truck at idle stereo off, turn on the a/c system full blast. You will notice the RPM's drop from the initial load of the compressor, the pcm will respond by increasing the RPM, then once the initial load is gone the RPM's will settle back down to a smooth idle. Same thing is happening when you turn the system up. Your PCM is sensing the extra electrical load, increasing RPM's to compensate.

If I had to take a guess I would say your battery is not holding enough in reserve to feed the electrical system

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Ok so if my battery is not holding enough in reserve how do i fix it, do i take out the pioneer amp and live with the mids and highs from the head unit?  I am trying to avoid spending more money.  Id really prefer not to buy a high output alternator and a second battery. 

First thing I would do is check to make sure that I am right and that the motor is reving up and down with the tach. If this is the case then bring it to one of the "big box" auto parts stores and have them check both the battery and alt. Have them check it at idle and with the system pumping and see what kind of drop/increase you are looking at. It could be something as simple as a bad alt. or a bad battery.

I am running my car off  of an Odyssey battery, its about 1/2 the size of a normal battery

https://www.odysseybatteries.com/battery/pc680mj.htm

every other electrical connection  on my car is factory(no big 3 upgrade). I have a moddest system running maybe 500 watts RMS and the only thing my car does is the lights will dim ever so slightly, when I say ever so slightly you would have to be looking for it to notice.

Buy a batttery with more reserve capacity but 1st get your current battery tested. Second make sure you have a proper ground for the amplifiers. Third make sure all connections are perfect ie 12 volts battery and amp..

Please read above sticky on proper grounding. I would say that we see poor grounds atleast 80% of the time, resulting in electrical issues.

on my head unit there is a volt gauge and it says that my truck is going from 13.5 to 14 volts depending on the volume.  the lounder it get the more the volts jump around without the stereo it is at a constant 13.8 volts. and the engine is reving while the truck is stopped to make up for the loss in voltage.  Its a 130 amp altinator it doesnt seem right that it cant handle this.  I took out the pioneer amp and its the same thing.  Tomorrow i am going to get the battery and the altinator checked at autozone and see if that is functioning properly.