This is a weird one. All I did was replace the plugs, wires, dizzy cap and rotor on a gen 1 SBC. Now, when the engine is off, the speakers sound fine. After the engine starts, the speakers start distorting or cutting in and out erratically. Doesn't matter if it's the radio, a cd, aux device, etc., it doesn't change anything. It progressively gets worse as I drive but as soon as I let off the pedal, it comes back in crystal clear for just a few seconds then progressively gets worse again. Cut the engine off, and it sounds perfect. Throttle position seems to have a direct effect on the problem.
Don't know if replacing the cap and stuff was just a coincidence and is unrelated or not. I looked for wires I may have damaged while in the engine bay during the repairs but couldn't find anything. Any ideas?
take a look at the rotor to cap terminals for excesive distance for one thing, take a look at your old plugs and wires ,were they resistor plugs or wires? the car makers used them to reduce ignition noise in their radios. Also I believe it is mandated by the FCC to cut down on radio and tv interference.
If you still have your old wires try just putting your old coil wire back on and see if it makes a difference
Depending on the quality of the spark plug wires, that might be your problem. Put the old ones back on and see if the problem goes away, cheap wires has a lot to do with their quality.
Thanks guys. The MSD rotor and cap I used came with 2 different types of the little pin that is under the coil. They say one is OEM and the other is for specific types of electronic ignitions that I don't have. Supposedly there can be interference if the wrong combo is used here. I used the correct one but swapped in the one from my old cap. Now the radio sounds much better but the interference is still there. I also cut a couple wire ties where I had the plug wires bundled up so don't know if that helped some too. Guess I'll shop for a better set of wires. The ones I used were a $25 set of Taylor wires from Summit.
I don't know that it's the wires yet. I did buy the cheapest set of wires they make but I know Taylor is a respected maker of ignition parts. It may not help but I'll have to swap them and see. All I know is when I turn the engine off, all problems go away immediately. When I'm cruising at regular highway speeds, it sounds bad then I lift my foot all the way off the gas and it clears up instantly but just for a few seconds. When at idle, I can fluctuate engine rpm and the sound of the speakers changes with engine speed.
I don't know much about car audio but there are probably several ways to wire in an aftermarket head unit to the electrical system that encourages less potential interference, I don't know. I'm just considering the fact that the problem started after I changed the wires, rotor and cap. I might try to route the plug wires different to see if that changes anything. I hate to waste a set of new wires but it may come down to that.
"Hardwork" has given you the best advice; give it a try. Without a resistance plug wire set, your going to be chasing engine noise........Also, you haven't mentioned the type of vehicle the Gen 1 SBC is installed in.
Some suggestions:
1. If an older vehicle, get a GND location diagram for the car, then lift, & clean all GND wire contact points, re-attaching with star-washers, if none are present. Most importantly, make sure that your battery GND wire isn't corroded, (at the battery, and at the chassis connection point), and that the chassis connection point is good & solid.
2. With your aftermarket stereo head unit, make sure that its supplied GND wire is properly connected to the original factory harness GND connection. As an alternative, try grounding the head unit GND wire to a different point on the body/chassis, not using the factory GND connection. (Sometimes this will lesson the ignition noise.)
3. If an external amp has been installed, make sure that it has a solid, unpainted, star-washer GND connection to the vehicle body/chassis.
Like many large companies, Taylor makes varying quality plug wires. If you go to their higher quality wires, your problem will probably go away. I like the Moroso Ultra 40 plug wires myself. They're about $70 a set, but have a lot of nice features that are only found on wires over $100 a set. The ends are sleeved with shrink tube to strengthen them, and they are numbered on both ends. They're also larger diameter insulation, so your MSD system wont fire through to ground, or other plus wires.
Thanks for all the information guys. I believe I have enough to go off of this afternoon as I begin more troubleshooting. To fill in the gaps of info I left out, the cap and rotor is genuine MSD brand. The ignition coil is the same one I had, not an aftermarket high output. I just swapped it into the new cap. The vehicle is an 85 Chevrolet truck. The engine is a 290 hp GM crate engine. Unfortunately I tossed the old wires before I realized this issue. All I remember is they were AC Delco brand. I don't have a spark plug type coil wire. The power wire to the coil is regular wire that connects with a female butt connector to the male connector in the dist cap.
I don't quite understand about the excessive distance between the rotor and cap terminals. I thought they were all fixed and not adjustable? Maybe I don't understand what Hardwork meant in that post.
If the CD player is being effected ? In my opinion its not wires or plugs, Resistor plugs and wires only work to stop disruption in radio waves, But once you put in a CD or tape deck in a radio, there are no radio waves to disrupt! you can disconnect the antenna and the CD or tape will still play good, unless your power to the radio is also feeding the power to the coil or the distributor ground is in the same wire as the radio ground!! They both should be on completely different circuits! Radio ground should go directly to the battery ground circuit and radio power should be on the accessory circuit of the fuse box or ignition !! That would be my guess on were your problem is? I do not run resister plugs or wires and all my radios play perfect in my cars with MSDs and multi discharge MSD BOXES but my neighbors TVs and Home radios Go crazy LOL
There is a condenser on the gen 1s heater and the distributor circuits that if not hooked up or blown will transfer electrical pulses and you will hear the heater fan or distributor in your radio speakers !! That may be your problem also ? Just a few more things you can check!
Yeah, man it's crazy. It does it with a CD or if I'm listening to Pandora through my iPhone when it's plugged in the aux port on the CD player. The only thing that's not affected are the subwoofers. The PO had subs behind the seat and an amp under the seat. They will still play the bass notes as usual. The audio from the door and side speakers is what's affected unless the engine is off.
There are a lot and I do mean a lot of wires/connectors bundled up behind the motor on the fire wall. There has been a lot of things removed/bypassed. For one, the original 700R4 has been replaced with a TH350 and all the smog stuff is gone. The AC is half hooked up because the compressor and reserviour tank Is gone. I'm not sure what it all goes to but I'm in the driveway now removing all the electrical tape and separating everything so I can see what's what. There is a ground wire with a big loop that's always been suspended. I think it originally connected to one of the bell housing bolts.
The wiring has always been hacked up like this since I bought it last spring. The problem started after I changed the wires and stuff but I started thinking that maybe I upset some of this rat nest in the process and it's what is causing it. I don't want to rip it all out because I may need it down the road. I need to find a way to have it out of the way without causing interference if in fact it is.
You have probably learned a lesson that I learned years ago...... never throw out old plugs/wires/cap until you verify all is working well...... that way you can swap in the old parts etc..... the distance between the rotor and cap terminals is a fixed distance, but if the part was manufactured incorrectly it might be out-of-round so to speak.
If it were mine I'd disconnect the radio from the hot feed it's currently connected to, then run some temp jumpers directly from the battery to the radio and see if the issue goes away.... if it does ..... you might have to dive into that rats nest......
"There is a ground wire with a big loop that's always been suspended. I think it originally connected to one of the bell housing bolts." I'd start by re-attaching that GND wire to the block ASAP! Without that GND wire connected, (unless the engine is grounded by another strong braided GND wire elsewhere), you're leaving yourself open for a myriad of other future electrical problems, the least of which is head-unit static.
Read this; it's lengthy, but gives a great overview of proper grounding procedure, & the potential problems with incomplete/bad grounds:
I can't stress any more on how important that engine-to-body GND strap is; I'd re-connect it BEFORE you fasten other wires/bundles back in place. Consider it a main foundation electrical circuit grounding point, with every other GND indirectly tied back to it. You are fortunate that you've not had starter, ignition, or alternator problems up to now........
Just finished checking all grounds under the hood and cleaned up all the loose wires at the fire wall. I used a wire wheel to polish all ground connections to the body and frame. Still no change. Next weekend I'm going behind the dash to see how the head unit is wired in. If it's wired in to another circuit, I'll rewire it. If it's not then I guess I'll try a different set of plugs.
The woofers are the key they are not effected so the radio signal and out put to the woofers is not whats effected its in the other Speaker hook up probably the grounds, the Amp and woofers would be grounded separately, with a power source not the same as the radio!!
While I agree grounds are important, if the only thing you changed was the cap and wires....... odds are it's not a ground. Try running the temp jumpers (jumper cables work well but insulate the pos clamp so it won't short on any thing, and see if the noise is still there.
Inspect the cap and make sure it isn't cracked, a cracked cap will produce all kinds of weird things.
Take a look at the back of your hood where it meets the cowl. There should be either a serrated contact strip (piece of steel with sharp teeth that makes contact with the hood when it's closed) or a grounding wire from the hood to the body. In other words ground your hood. Yeah I know it sounds goofy but a un-grounded hood can become a large antenna. Hoods are grounded from the factory.
It will do it with the radio or the CD player, as the interference is affecting the speakers. They don't care where they get their signal from, radio or CD.
To elaborate on this!
AM and FM is a radio signal caused by a specific wanted and produced radio wave, unwanted noise is from an unwanted radio wave caused by energy fields its not a sent signal! That confuses a lot of untrained people!
I stated the RADIO signal was not effected because the woofers played good it was in the front speakers circuit? When listening to the radio The radio signal is detected by the antenna and any magnetic wave can disrupt the antennas signal to the radio and cause unwanted noise, but when switched to CD player the antenna is out of the picture because the CDs infrared signal is produced by a laser ( you can pull the antenna right out of the radio and the CD will still play) so if radio plays with disruptive magnetic field noise like plugs or plug wires the CD will still play good ! If the disruptive noise is in just the speakers or speaker you can sometimes shut off the radio and unplug the speaker or speakers from the radio ( it must be disconnected at the radio!!) and you will still hear disruptive noise coming through the speaker! or the speaker disruption is in the radio case not through the antenna.
A RADIO Signal is sent on purpose by man from a transmitter!! A radio wave can be produced by any type of energy release or collapse even a solar flare ! like if your antenna cable is too close to any electrical or magnetic field or speaker wires are to close to other wires or motors or engine components! or if the radio frame is not grounded good even though the speakers are grounded! Say a distributor cap is ion saturated and not venting it will cause magnetic pulses and spark scatter in the cap and if the radio is too close to the cap even right through the fire wall it will create radio unwanted noise ( a small hole drilled at the base of the distributor cap can cure that!)or insulate the radio housing, Corvettes used a metal cover over the cap and plug wires because of just that problem! Radio wires and antenna or antenna cable should not run alongside or even close to any other wires or anything that can produce a magnetic or electrical field, all, heaters , the dash board, fenders , doors, alternator, engine , hood, frame need good external grounds completing the circuit back to the battery (Like BB and crdnblu mentioned)!! Power Windows if not grounded good will disrupt door speakers and when you hit the button up or down you will hear the motor through the speaker! if a dash or column is not grounded good you will hear the turn signals through the speakers, ETC,ETC, Too small a gauge wire is also a bad ground and the longer the wire the larger the gauge has to be!!
This isn't aimed at anybody in particular, and the use of "you" is plural !
And if you read it you will understand more of what I'm telling you! This noise suppression guide works with old or new systems! http://www.termpro.com/asp/pubs.asp?ID=121
I know you didn't change anything with it but you could also be experiencing noise from a bad diode in the alternator. I would try unplugging the alternator to see if the noise goes away.
you could also try twisting the power and ground wires for the radio or adding a capacitor.
My guess is the noise is coming from the ground circuit or the power circuit for the radio but it is hard to tell. One other test would be to power the radio and amp from a separate battery not connected to the cars system in any way and see if the problem persists.
I have also seen someone add a ground strap to teh fire wall right be the distributor to kill RFI
Finally got time to mess with this issue more today. I checked all the things mentioned in the last few posts and none rid the issue. I pulled the radio out and cleaned up the splices. Both the constant power and key on power wires terminate at the fuse panel. The ground was connected to a piece of sheet metal behind the radio. I ran a new ground wire out to the primary ground connection under the hood. The battery negative has a pig tail that goes over and connects here on the frame also. Still have the interference. I guess tomorrow I'm changing plugs. If that doesn't do it, I'll put the old cap and rotor back on to see what happens. Either way, I feel like I ruled out having a bad ground connection. Still sounds clear if the engine is off.
What about those plug wires? My money is still on them as the culprit.
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