Bullstang360

I have a 91 Cherokee and recently installed a 98 Grand Cherokee alternator. Now I have tons of static on my radio and CB but only when the Jeep is running. I went through cleaned and checked all my grounds. Also checked my antenna at the back of the dash radio. Did I miss something? Anyone else have this problem? Solution? Thanks.

moparado

I assume you got the '98 GC alternator from a boneyard.
Besides the radio noise issue, does the alternator produce a good charge voltage of 14+ volts.

I compared NAPA NEW ELECTRICAL alternators '91XJ/'98GC P/N's and they are different. Might be a good reason for the different P/N's like an EMI suppression component added internally in the '91 alternator.

Not saying thats the problem but i'll bump your tread, maybe someone else will know whats going on for sure.

I believe with later XJs the PCM controls the alternator voltage regulation but not sure about the earlier years or the GC's.

investinwaffles

What's your voltage at the battery with the engine running? Where is your radio/CB grounded to?

I had to ground my head unit to my amplifier (strong grounds) to get rid of ground loop noise, not sure if my Durango alternator caused it or not

​​​​​​Possibly weak ground to the head unit? Try using jumper cables to make sure everything is well grounded

​​​​​

Bullstang360

Thanks. I spent the day chasing it around rechecking all my grounds. I tested the voltage at the alternator and the battery both were at 14.63volts. I got my alternator from Oriley and did tons or research online before I did this and didn't see where anyone else had this problem.

Bullstang360

I grounded the cb to the fire wall and checked for continuity and impedance. I also checked impedance to ground on the head unit and it was close to zero also.

moparado

??????

Are you hearing ignition noise or random static noise?
If the only variable changed is the alternator, it could be one of four things:
-'98 GC Alternator not compatible with a '91 XJ
-Defective replacement alternator, ie. (blown diode?)
-Grounds
-EMI suppressor somewhere missing or defective

If all else fails and you're convinced none of the above 4 points are the problem.
You might want to consider installing a noise suppressor or ferrite core beads around wiring especially if its high frequency noise you're hearing.
Here's just a couple examples. Do your research though before buying suppressors.

Bullstang360

98GC alternator swap is common. It changes your max output amperage to 130 from the stock 90 for alot cheaper than a HO alternator. It is literally a direct bolt in. Connections are all the same. I did upsize my wireing though. It's a steady static, no whining and it does not change with rpm. I'm thinking I'll warranty this one out and see if it's just a bad alternator.

moparado

I suspected but didn't know for sure that the GC replacement has a higher output. The reason for the different P/N's.
However, again keep in mind the only variable changed is the new replacement alternator.

It might be a common replacement with no static for people with different HU's and different CBs (or none).
Different HU's and CB's from yours could have better noise suppression circuitry built in.

If the 2nd alternator exhibits the same problem, you might want to seriously consider looking into add-on noise suppressors such as the 2 links i provided above.
They're not that expensive to at least try if against the proverbial wall.

Bullstang360

I see what your saying. I just traced out the factory antenna line and there is what appears to be a factory splice (bare metal) that was touching the fire wall. My rig is torn apart at the moment but I wrapped it in super 33. When I get it back together I'll see if that was the issue.

moparado

Check that splice out real close and maybe re-do it.
It could all be corroded inside.
Was that splice moved or tinkered with during the tear apart?

If thats the radio antenna splice though, i don't see how it affected you CB.
Unless you're using one of those adapters that allows you to use the radio antenna with the CB.
Are you using a separate dedicated CB antenna?

Keep us posted!

Bullstang360

I have a dedicated cb antenna. I will take the splice apart and check it. I should be able to check it this week.

moparado

Now that you mention that your Jeep is torn apart, that might open a whole new bag of worms.

Is your hood off or open?
Is your Jeep in a garage?
Any other electronic devices running in the area, radios, etc?
Is the Jeep movable?

There's a slim 'remote chance' there's nothing wrong with the alternator.

It could be that if you're in a garage especially a garage with aluminum siding, the reception on the radios could be poor causing static.
And/Or
Hood open or off?...the grounded hood can act as a shield against outside EMI generated from other electronic devices running in the area causing the static. Just as important, the hood can also act as a shield from keeping any EMI generated by the ignition and alternator from reaching the outside antennas. Being in a garage with an open hood could make it even worse.

If possible, move the Jeep outside (if in a garage) and close the hood and see what happens.

Its a definite long shot but worth trying before sinking more effort and money into the problem.

Bullstang360

Haha Jeep was together till Saturday morning. I am welding in some new floor plans. They have that famous PNW patina. I have static inside and outside of the garage. I can still start an move it I only pulled out the carpet and seats.