Amp cuts only when engine is running

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Hello, I have 4 ch amp which has 1000w max. and i believe it delivers about 70 rms from each channel. I think bridge gives around 170 rms. I have connected my sub into 3th and 4th channel. When i have my car engine running, red protection light starts to blink and sub cuts, it blinks every time bass wave hits from the song. But when i turn off the engine ( only battery supplies ) red light goes off and it doesn't cut. When engine switched off i can get gain to the max, and it doesnt light, but if i try to start the engine on about 10% of gain it already showing protection lights and cutting. With this i want to understand how is it possible when the engine turned off Amp works and when engine is on it doesnt? Where should i look for my problem?
 
So some research ive done today, i found out that it goes to protection mode when sub is connected to bridged channels, after i took sub wires out of amp, protection mode turned off. So what i can see its not the problem in HU or RCAs cables. It should be sub? Just i didnt think sub could be bad... because last guy didnt mention that something is wrong with this one.
Tomorrow i have asked my friend if i can borrow his sub and connect to my amp to see if the reason is my sub

hmm, but why on ACC it works perfectly... and on engine running it doesnt? See no logic
 
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Don´t know what is HU..but you now have a wire going from car stereo to amp remote. Remove that and install jump wire straight from amp´s B+ to REM.....for test purpose.

I wondered that if the car stereo remote voltage is a lot different than the B+ voltage on terminal.....that could cause something.
 
Maybe something not so complicated: running engine causes loose connection or short circuit
When i was installing i have double checked everything before hiding wires and connections.

If it's playing loudly, then it's probably the sub is too low impedance for the amp in bridged mode and the over current protection is coming on.
Have checked impedance is 4ohm :) same as amp
 
well guys dont forget when engine switched off everything works without any protection light, and when engine is on so it starts to cut. I think it somehow must be a reason. Also alternator looks that its fine, because when engine runs i have 13,7V and it stays stable, when i turn engine off voltage goes slowly from 13.7V to 12V but not under 12V!! Im not a mechanic, i dont know if it normal that when u switch ignition off it not jumps right away to 12V but goes slowly down from 13,7V
I have asked all my friends who have installed stereo have read a lot of info from internet, have checked everything what could cause this.
Well maybe the problem is simple, sub or amp... Which was running fine before i put them into my vehicle.
Iam not that guy who ready to pay many K and take car to the people who works with audio so they could do everything working. I prefer do something by my own, and so i get experience after i solved the problem
 
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