Radio noise only when ignition power is on & engine is OFF

I have a strange radio static noise issue.

87 Jeep, 4X4, stock wagoneer ltd. with an after market, recent vintage, new, cassette/AM/FM stereo with a new internal (indoor) electronic amplified radio antenna, also no stock aftermarket. I have a seperate power toggle switch (custom) that allows me to run the radio with out the keys in the ignition (I recently by passed the igntion switch for the blower fan, and radio power).

The stereo sound is great, no static, great signal with just the radio turned on. Once I turn the ignition to the run position (but with the engine off) I start getting noise like I would if I was too far away from the radio station, or like I would with the engine running with the wrong spark plugs and wrong plug wires, except the engine is OFF!!! WTF? Anyone ever run into and slve this problem before? Is the Renix ECU or TCU be throwing off RF noise that the radio or antenna is picking up, or is it a ground issue?

Noise from the fuel pump or maybe blower motor? I'd be tempted to start pulling fuses until the noise went away.

A lot of Renix ECU's sent out nasty RF, and I think there even was an upgrade though not a recall. My 87 did this. I never found the solution except for stronger stations. It was not a grounding issue in this case, but grounding might cause additional problems, and so might poor wiring to the hot side. I passed the vehicle on before I got around to trying to figure out whether it was coming through the power supply or in the air, but did find that it varied with what radio you have.

The ECU interference was a kind of high-pitched whine with a little white noise on the top. A strong enough station would mask it out, but it made fringe stations unusable.

If the problem were the fuel pump, it would go away after a few seconds with ignition on and engine off. Blower fan is a good possibility, easily tested by disconnecting the fan.

As an experiment it might be worthwhile to try running a dedicated positive power lead to the battery and see if bypassing the under-dash wiring might help.

lawsoncl said:

Noise from the fuel pump or maybe blower motor? I'd be tempted to start pulling fuses until the noise went away.

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Neather one was running at the time, so scratch those two and the igntion system and igniton system parts like the CPS.

Does it sound like crappy reception or are you getting a buzz? If it's static, is your antenna powered? If so I would guess there's probably something funny with your wiring. Where is it getting power from? Try a different antenna if you've got one.

Static is hard to troubleshoot, I've found it's mostly trial and error. In line filters for the ignition (power) wire to the ECU and the main power from the fusible link may be helpful, RF may be generated backwards into the system and/or through the ground. Try your the AC mode on your voltage tester or better yet a tester with AC-DC LED's on some of the red and yellow wires in the harness. Red (wire) is usually current straight from the battery through a fusible link, yellow (wire) is usually switched current from the ignition switch. You may get some RF in the DC power side no matter what you do, but if possible you can compare with another XJ and see if yours seems excessive and possibly where it's being generated.
Many after market amplifiers come with filters installed in the power in line, so this is likely a common problem. The only real problem is finding a filter in the proper range (they often only filter a fairly narrow frequency, like ignition and/or alternator noise).
Don't discount the 5 volt supply for the MAP sensor, the TPS and the cam position sensor. You can measure this circuit with your meter in A/C mode and possibly pick up a problem. High voltage in the 5 volt circuit can be a sure tipoff of a power supply failing, this can likely generate noise also.
Sometimes disconnecting a ground helps, sometimes adding shielding helps. I've had some success with aluminum foil and a couple of alligator clips (for ground), when troubleshooting CB noise problems.
You may also try and disconnecting the alternator, if the regulator circuit is acting up, it can also generate noise. Try disconnecting the small single wire (yellow I think) plug at the back, this disables the regulator.
Like I said trial and error.
Almost forgot, the noise may be radiated and not in the power lines. If you have added a coil of extra wire anyplace in the system recently, this is a good place to start looking. I've had noise disappear or reduced, just by uncoiling wiring and/or rerouting cables.

Well I went back in there and grounded the radio case (it was not directly grounded yet). That may have done the trick, at least for the FM stations. If it acts up anymore I will dig into your list.

Thanks!

Ecomike said:

Well I went back in there and grounded the radio case (it was not directly grounded yet). That may have done the trick, at least for the FM stations. If it acts up anymore I will dig into your list.

Thanks!

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I probably should have read your post a little closer. Most radios ground through the black ground wire (also grounded to the case) and through the antenna wire shielding through the antenna mount (swivel clamp). On yours the black ground wire may not include a case ground (possible), it may have only a single case ground that is supposed to ground through the antenna cable shielding.
It crossed my mind (late last night) that your antenna mounting clamp was loose and might not have a good ground. I believe this is the the first step in troubleshooting radio noise on most lists. I tend to look for the exotic, thinking "if it was simple, it would already be fixed".
In fact, my tool box has that written on top "If it was simple, somebody else would have already fixed it" .
Mine gets an ignition pop, only through the right front door speaker and only when the stereo is off.

The OEM antenna was gone. I aquired a special ampliefied indoor antenna from Crutchfield (online) that saved me the hassel of running a new anttenna and wire and tearing up half the jeep just to run it. It was not a standard grounded antenna system so it did not ground the radio case and the antenna gound depended on the radio case ground (which was not there). May explain why grounding the radio case helped kill most (if not all the noise). I can no longer tell the difference between having the ignition ECU powered up, versus off when the radio is tunned into a good FM station.

So I am calling the problem solved now.

Thanks!