Stereo only works with engine not running

[budman k20]

I spent a good part of my weekend wiring up my stereo and sub feeling pretty good thinking I'm done wiring up my truck so now I can finally enjoy tunes...Wrong!! I was so bummed on my maiden run when the radio started cutting in and out like someone was turning the volume up and down every second or two. Then the engine stalled as I was leaving and what do you know... my stereo played normal! So with the ignition switch on but the engine NOT running or with the key in the accessory position my radio plays fine only when the engine is running do I have the problem! I have a good ground to the radio and I'm using the radio feed from the fuse block to power it up. The truck has all new wiring in the cab and I have a HEI ignition. My thoughts are I need some sort of filter but I have never had a problem like this before. Anyone else have this happen? Or more importantly does anyone have a cure for me?

[tubbedII]

It sounds more like a loose wire/connection if you ask me. Did you run an amplifier as well or just a stereo that powers speakers? I'd grab the wiring and jiggle it with the engine off to see if you can duplicate the sound you were hearing with it running.

[budman k20]

Yesterday I started my truck and the sound was normal for the first 30 seconds then it started going up and down with the engine running. Turned off the engine and everything is normal at low and high volumes. I read that the alternator could have a one bad diode and still charge the battery. So I measured AC volts on the power feed to the radio and with the truck running I get .18 AC volts and not running I get zero AC volts. With the truck running I get 14.4 DC volts and 12.0 DC volts not running. Everything I read for AC issues describes the noise matching engine speeds. This is not my problem it doesnt change with engine speed its the same cadience when the engine is running fast or slow. I gues I'm going to buy a new head unit to trouble shoot it next.

[kieth]

Try running a seperate power supply via a relay to the stereo/what ever else you have tied into the system. Just may not me enough power available. As a test power it directly from the battery with the engine running. If it functions correctly run the new relay power supply. JMO Kieth

[Special-Ed]

i would say bad wire connections somewhere.

how did you splice the wires together?

make sure you have the body,frame and engine grounded properly.

if you are running aftermarket radio and amp... the little factory radio power wire will not be enough.
and are you having 2 problems? is there a whine in the radio?

its hard to help when you dont give enough detail or what parts you are using.

its like saying i have a car and it wont go over 60....

[budman k20]

I figured it was something that others have experience before? I have a separate 8ga wire wired directly to the positive post on the battery with a 30 amp fuse to an 8in powered sub under my pass bucket seat. The ground wire is less than 1 ft long and it’s a seat bolt screwed up from the bottom with star washers on clean metal on both sides. The sub is driven by the rear pre outs and the front speakers are wired to the head unit wires. I have filters on the smaller front speakers to cut out the low freq. since my sub does not have a crossover network. The truck has a brand new American auto?? wiring harness. Like I said everything works fine at high and low volumes when the engine is not running. So my thinking is it’s not the wiring otherwise how can it work so well with the engine not running. I'm going to try putting a cap on my head unit power line to see if it that makes any difference. Now after driving it a little more sometimes it works fine with the engine running and sometimes it doesn’t! It's either some interference from the ignition or my new JVC head unit is defective. It could also be an intermittent connection in my ignition switch since that is the only other thing that I have not replaced? I suppose it is worth trying a separate wire from the battery to the head unit that will confirm if my ignition switch or wiring harness is the culprit.

[Special-Ed]

do you actually have a ground wire from engine to body and to the frame?

the ground for the amp sounds ok. but what about ground to radio.

i can think of 5 reasons off the top of my head without thinking why it would work with the engine off and not running... they all indicate, poor splice, bad wire,crushed wire, screw thru wire, improper wiring, bad ground.

it is very possible its the head unit... but that is not where i would start...

do you see a pattern yet? the pattern is something wrong with the wiring.

[budman k20]

Yes I have 2 engine grounds to the body and I have 3 body to frame grounds not counting the large one that goes to the battery. The head unit is also grounded to the body. Please explain how a bad ground is not bad when the engine is not running, explain to me how a bad splice isnt bad when the engine is not running, so on and so forth...do you see a pattern here?

[tubbedII]

Originally Posted by kieth

Try running a seperate power supply via a relay to the stereo/what ever else you have tied into the system. Just may not me enough power available. As a test power it directly from the battery with the engine running. If it functions correctly run the new relay power supply. JMO Kieth

I'd try this...or even put a volt meter to the power wire and check with engine off and then on to see if there's a difference.

[Special-Ed]

Originally Posted by budman k20

Yes I have 2 engine grounds to the body and I have 3 body to frame grounds not counting the large one that goes to the battery. The head unit is also grounded to the body. Please explain how a bad ground is not bad when the engine is not running, explain to me how a bad splice isn't bad when the engine is not running, so on and so forth...do you see a pattern here?

Look i'm not trying to be a doucher! My schooling is automotive engineering and I have been doing electronics engineering for the last 20 years professionally.

i cant tell you how many problems are caused by damaged, improper wiring or bad grounds... almost all of my problems have been created by wiring issues of some kind and not a failure of a mass market piece of equipment...

and just because the wire is bolted doesnt actually mean the connection is good. remove all grounds clean and reinstall.

did you solder and heat shrink all wires or did you just twist and electric tape.

you must isolate before you can trouble shoot... otherwise you are just shot gunning a solution.

the problem is this forum is a combination of DIY, professional, shade tree and the clueless... and as a professional i cant assume everyone else is.

[jb9281]

Has anyone found a solution, I have this same problem. I have tried everything. It has happened with three different radios.

[Andy4639]

What wire do you use to feed the radio? Try a straight wire off the battery and see if that works while the engine is running if so then it's at the feeder wire. The hot wire.