Massive AM radio interference, maddening (1 Viewer)

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Scota4570

Scota4570

Joined
Mar 6, 2019
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Location
Salinas, CA
92 Land Cruiser, Original radio. I normally only listen to AM. I am not interested in a new head unit or modern digital solutions.

The radio works great with engine off. It is very sensitive and receives distant AM stations well. When running there is a loud ignition type noise. It seems to have started with a recent "tune up", new wires, new plugs (NGK BPR5EGP), New cap, new rotor.

So far:
-Checked all the wires, pulled them out one at a time and started the engine, no change. Reseated all with dielectric grease
-Pulled a plug to determine what was used
-Pulled cap, rotor and cap are clean and nice looking
-replaced the antenna, the new antenna worked good with the wire from the radio out the window with the engine running, Once permanently installed the interference was the same as the old antenna.
-Used a separate chassis ground jumper to the radio case, no change.
-I see no sparks when viewing in the dark.
-Poking/moving the ignition wires with a stick changes nothing.
-I changed the coil with a backup that is known to be good

Any ideas? Did they use the wrong plugs? Is there something other than ignition that ruins AM radio in these vehicles?
 
No LEDs.

I will check the battery and alternator grounds.

The frequency of the noise is about like a chainsaw, or model airplane engine. At 2000 RPM and six cylinders, that makes 12K sparkplug firings per minuet. That is the RPM of those little engines. I wonder if they installed the wrong sparkplugs, wires, cap or rotor?
 
Wow. Blast from the past. Your description sounds like ignition noise. Alternators make more of a high pitch whine.
When I use to diagnose this it was normally unsuppressed plug wires. Considering the issue started with a tune, that's where I would start.

Things I would see beside plug wires are, issues with the antenna cable, alternator whine, plug wires laying against a power wire (this can transmit noise into a power wire) plugs rarely and radio filtering having issues. Some of the aftermarket ignition systems were horrable for noise. If yours is stock, thats not an issue.
There are filters you can install on the power side but they only really help if the issue is coming in from the alternator. A good way to test that is unplug the alternator and see if it goes away.
I've seen poor connections on antenna cables, normally the outer shield side. They need a good connection to the body at the antenna end as well as the radio. I dont remember if you can get filters for the antenna end.

Other than that, good body ground and radio ground.
Wish I had more to give you.
 
I did some things that helped. I identified that it is being radiated into the antenna. It it is not in the power system. I shielded the antenna cable with aluminum tape and grounded the shield to the body. The taped covers the cable and sticks it to the firewall. That helped. Then shielded the plug wire that goes form the coil to the distributor with tinned copper mesh tube. That is grounded. That helped more.

It seem weird to me that the ignition system is pouring out such massive RFI.
 
I found a big issue. The main ground cable that goes to the block from the battery was not connected at all. The connector that the bolt goes through was shiny. I had only a smaller chassis ground making the truck operate. It appears to have been deliberately disconnected by the last guys who worked on the truck.

That shop broke my antenna on this vehicle and refused to admit it. They also overfilled my 4-runner by two quarts of extra oil. They told me that the overfill was not a problem. They appear to be crooks and incompetent.

It is pretty tight in there. Can anyone tell me exactly where the primary ground is supposed to bolt to? Is any old place on the block OK?
 
Been there for sure. The jabronies at my ex place broke my radiator nipple and jb welded it back on without saying a word.

The main ground from battery to block runs in the harness from the battery then splits off the harness and bolts to the block right to the rear of the oil filter. Also attaches to the lift bracket via the ground below the ignition coil.
 
Holy s***, you listen to AM radio? :rofl:
 
Scota4570 said:
92 Land Cruiser, Original radio. I normally only listen to AM. I am not interested in a new head unit or modern digital solutions.

The radio works great with engine off. It is very sensitive and receives distant AM stations well. When running there is a loud ignition type noise. It seems to have started with a recent "tune up", new wires, new plugs (NGK BPR5EGP), New cap, new rotor.

So far:
-Checked all the wires, pulled them out one at a time and started the engine, no change. Reseated all with dielectric grease
-Pulled a plug to determine what was used
-Pulled cap, rotor and cap are clean and nice looking
-replaced the antenna, the new antenna worked good with the wire from the radio out the window with the engine running, Once permanently installed the interference was the same as the old antenna.
-Used a separate chassis ground jumper to the radio case, no change.
-I see no sparks when viewing in the dark.
-Poking/moving the ignition wires with a stick changes nothing.
-I changed the coil with a backup that is known to be good

Any ideas? Did they use the wrong plugs? Is there something other than ignition that ruins AM radio in these vehicles?
Click to expand...
Plug in a known similar radio and see if problem still persists. Could be radio.
 
My radio's display is no longer working. It plays fine though. I would like a replacement. Mine is just like the picture.

Does anyone have a working OEM radio they might consider selling?

I'd like to avoid cutting up the radio wiring harness. The original radio was totally satisfactory to me.

I do listen to AM almost exclusively. I like talk radio. FM coverage is limited in my area. For a variety of reasons I do not want a modern head unit. I have been down the rabbit hole already on an '04 Sequoia it was a total mess and very expensive. The final sound system was no better than the original. The AM reception was very poor on the modern head unit.


radio.jpg
 
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Not sure if it helps but the old radios use to require a condenser attached to the alternator which somewhat mellowed charge output readings. I guess something like a mini reg for the radio. I remember in my old bj40 it had a little condenser , approx. 1cm x 1.5cm canister bolted to the alternator. Once I forgot to put it back on the alternator and the radio made all sorts of whirring static sounds in synchronicity with revs. No idea where to get one other looking up on an epc.
 
Scota4570 said:
My radio's display is no longer working. It plays fine though. I would like a replacement. Mine is just like the picture.

Does anyone have a working OEM radio they might consider selling?

I'd like to avoid cutting up the radio wiring harness. The original radio was totally satisfactory to me.

I do listen to AM almost exclusively. I like talk radio. FM coverage is limited in my area. For a variety of reasons I do not want a modern head unit. I have been down the rabbit hole already on an '04 Sequoia it was a total mess and very expensive. The final sound system was no better than the original. The AM reception was very poor on the modern head unit.


View attachment 3468000
Click to expand...

Modern head units can have good AM reception, but many modern head units have poor radio reception in general with focus on digital features like bluetooth and carplay integration taking priority. If you can't find a working used OEM radio, it is possible to get a good modern, receiver but some homework is necessary.

When I was looking for a replacement head unit, Sony and Alpine had the best AM receivers available at 26uV-20dB S/N. Kenwood used to be at the top, but all of the current Kenwood and JVC receivers are using the same AM receiver (Kenwood merged with JVC) at 28.2uV-20dB S/N (lower uV is better). I ended up with a JVC unit, but I wasn't very concerned about AM radio reception, and the JVC I chose has a very good FM receiver. It appears to me that both Sony and Alpine are using the same AM receiver since the specs are identical between those brands. I'll try the AM receiver in mine, I've never actually put it on AM since I installed it.

There are wiring harness adapters that plug into the 80 series harness so that you can install anything you want without cutting wires, in general you should never have to cut wires in any car to install a stereo. Something like a Sony DSX-700 is a good basic double DIN sized radio receiver with knobs and buttons, bluetooth to connect your phone if you want, but no tape or CD player, and they are also cheap (like $139).
 
WOW!!!!

I tried to pull the new antenna wire through the original grommet. That is simply impossible. So I figured I take the fender off to get better access. That is crazy stupid complicated. I am going to put it back together and put up with some radio interference. It is not worth the time and risk of breaking something to route the antenna properly. Shame on Mr T.
 
I suspect a diode in the alternator may be goiung south on you.

Had a similar issue in my 2010 F150. New alternator solved all the lousy AM reception issues I had.
 
I have traced it down, it is ignition noise. It is a ~10K cycle popping type noise. It varies with RPM. The pops are caused by the rotor, apparently.

The alternator makes a steady static type of noise, it is different.

The root cause is that the previous owner cut the original antenna wire. That wire was routed through the fender to avoid close proximity to the coil.

The coil ignition wire that goes to the distributor is the source of the RFI. I shielded it and the noise got 90% less.

I will look for some braided copper shielding to encase the antenna wire.

facepalm.jpg
 
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