Distortion problem - Jeep Grand Cherokee & JVC KD-TD71BT head unit

[blueribb]

I'm a 70 year old retired TV and Computer Tech. I own a mint condition 1998 Jeep Grand Cherokee and decided to treat myself to a new head unit. I ordered a JVC KD-TD71BT from Crutchfield along with a pre-made wiring harness adapter. Installation was a breeze and now I can stream Pandora music via bluetooth from my cellphone. After 6 months of use with no issues, I now have bad intermittent distortion when the engine is running. The distortion is not static but sounds like blown speakers. It affects Pandora streaming, playing a CD and FM equally. All 4 door speakers were replaced a few years ago.

With the engine shut off, the audio is fine.

My Jeep came with the upgraded Infinity System. There's an amplifier under the back seats. My hookup allows that amplifier to work with the new JVC head unit.

Since the distortion is only heard when the engine is running, can I assume the problem is not the new JVC head unit ?

Any suggestions would be appreciated.

Glenn

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[dragon.breath 10+ year member]

several different things could cause that.
1.A broken wire grounding to the body,
2. A bad factory amplifier,
3. A bad adapter between the jvc and the factory amplifier,
4. The jvc is going bad.
5. The ground for the jvc is loose.

probably my first move would be to disconnect the jvc from the adapter and connect it directly to a speaker. ( any speaker, old speaker? House speaker, etc.) if the noise goes away you know the jvc ands it’s wiring is fine.

 

[blueribb]

several different things could cause that.
1.A broken wire grounding to the body,
2. A bad factory amplifier,
3. A bad adapter between the jvc and the factory amplifier,
4. The jvc is going bad.
5. The ground for the jvc is loose.

probably my first move would be to disconnect the jvc from the adapter and connect it directly to a speaker. ( any speaker, old speaker? House speaker, etc.) if the noise goes away you know the jvc ands it’s wiring is fine.

Thanks for the quick response. I don't see how it could be #2 or #4 since the audio is just fine with the engine not running, even for extended times. When this first started, I though maybe a bad alternator but the distortion is not a "whine" and does not change with RPMs. I suspect a bad ground but it could literally be almost anywhere. I just might remove the JVC and reinstall the original OEM factory radio temporarily to see if the distortion is there.

 

[dragon.breath 10+ year member]

It could be 2 or 4 if the ground side of either started to go bad. Basically if the ground circuit stopped being able to isolate electrical noise from your car.

 

[hispls 5,000+ posts]

I don't see how it could be #2 or #4 since the audio is just fine with the engine not running, even for extended times.

Internal fault in head unit or amplifier can absolutely cause intermittent noise issues. JVC is among the top reliable brand head units so it's likely not that, but you really never know.

Honestly my first suspect would be the 25 year old factory amp, but it really could be anything. If you're an electronics guy you probably have an idea of the life expectancy of any of that sort of stuff (particularly electrolytic capacitors) and 24 years old is definitely running on borrowed time at best.

I think the best suggestion is to try to bypass the factory amp with whatever speaker you have handy run direct to the back of the head unit into one channel and see if the problem shows up in that when your issue comes up in other channels. I'd guess that a modern head unit may well output as much power as those old factory amps and you may not even notice the difference just deleting it entirely and either running fresh wire or buying whatever bypass adapter Metra sells if you don't like popping panels and pulling seats.

My big audio build is a 97 grand cherokee and I bypassed the factory amp and ran all new wire to my fronts right out the gate. It's my second Jeep this model and I've had really good luck with them. It'll **** when I finally have to retire it because I know they don't make them like that anymore and I'm sure nice condition ones are going to be pretty well dried up or project/restoration pieces these days.

As an aside, my dad is a little older than you and I got him into using modern head units a couple years back and he really gets into the flexibility of USB or bluetooth for MP3 and streaming from his phone. The moral of the story is you can teach an old dog new tricks.

Good luck.

 

[blueribb]

Internal fault in head unit or amplifier can absolutely cause intermittent noise issues. JVC is among the top reliable brand head units so it's likely not that, but you really never know.

Honestly my first suspect would be the 25 year old factory amp, but it really could be anything. If you're an electronics guy you probably have an idea of the life expectancy of any of that sort of stuff (particularly electrolytic capacitors) and 24 years old is definitely running on borrowed time at best.

I think the best suggestion is to try to bypass the factory amp with whatever speaker you have handy run direct to the back of the head unit into one channel and see if the problem shows up in that when your issue comes up in other channels. I'd guess that a modern head unit may well output as much power as those old factory amps and you may not even notice the difference just deleting it entirely and either running fresh wire or buying whatever bypass adapter Metra sells if you don't like popping panels and pulling seats.

My big audio build is a 97 grand cherokee and I bypassed the factory amp and ran all new wire to my fronts right out the gate. It's my second Jeep this model and I've had really good luck with them. It'll **** when I finally have to retire it because I know they don't make them like that anymore and I'm sure nice condition ones are going to be pretty well dried up or project/restoration pieces these days.

As an aside, my dad is a little older than you and I got him into using modern head units a couple years back and he really gets into the flexibility of USB or bluetooth for MP3 and streaming from his phone. The moral of the story is you can teach an old dog new tricks.

Good luck.

I tried to order the Infinity Amp bypass harness from Xscorpion but they are no longer available. There is a YouTube video showing this adapter and how it just plugs in to bypass the Jeep's Infinity amp. As soon as the weather here (PA) starts to warm up, I'll probably remove the JVC and reinstall the factory Infinity head unit temporarily to see if the noise continues. I know all about failing electrolytics and yes - 24 years makes the Infinity amp a suspect. I will update this thread when I solve this mystery. Thanks for the suggestions.

 

[blueribb]

Here is the Infinity Amp Bypass harness that I need. Can anyone locate one for sale ?
- Xscorpion CHR-5622

 

[hispls 5,000+ posts]

Here is the Infinity Amp Bypass harness that I need. Can anyone locate one for sale ?
- Xscorpion CHR-5622

Crutchfield or installer.com would be my two top stops for wiring and adaptors and such. Best Buy may well have that sort of thing either though it would likely be a special order I'd imagine there's some left in some warehouse or stockroom somewhere out of all their locations.

 

[Firewalker]

The black & grey is typical jeep wiring harness as I have a few of those laying around. That is a metra 70-1817. Metra makes one but it is a lot longer then that, never seen one like that before with them going into each other. Metra # is a 70-6505 if you are going to use an aftermarket amplifier.

Metra 70-6505 Amplifier Bypass Harness for 1997-04 Jeep Cherokee/Dodge Dakota | eBay

Amplifier Bypass Harness for select 1997-2001 vehicles from Dodge, Jeep. 204" Long factory amplifier bypass harness. Compatible with select 1997-2001 vehicles from Dodge, Jeep. See Below for the Vehicle Compatibility List.

ebay.to

And I think Metra online is gone. Website won't even come up anymore.

 

[blueribb]

I was in contact with Metra today. They do not make an Amp Bypass Harness Kit for the 98 Jeeps. Xscorpion USA has no stock and may have closed since they no longer answer emails. I did manage to locate some in stock at Xscorpion Mexico, but they might not ship to the US. When I emailed them this morning, they responded by mentioning Xscorpion USA. If I can't locate the jumpers, I will just insert wires into the molex plugs, bypassing the amp

just to see if the noise goes away. Here is a picture of the Infinity Amp jumpers that I need.

 

[Firewalker]

.

 

[blueribb]

YouTube video showing Xscorpion Amp Bypass Jumpers

Go to 32:35 of the video above

 

[Firewalker]

Just do the jumpers instead if you have to easy to do and takes a few mins to see if it is the cause.

 

[blueribb]

Okay how is the aftermarket amplifier hooked up to the speakers in the vehicle? Is it separate speaker wire or did they use 9 wire Stinger/Metra Wire? Kinda curious on this.

Just do the jumpers instead if you have to easy to do and takes a few mins to see if it is the cause.

There is no aftermarket amplifier. My Jeep came with the upgraded Infinity Audio system which included a separate power amp under the rear seats. The video above shows someone installing the amplifier bypass jumpers to eliminate the factory Infinity Amp and utilize the head units built-in amplifier. I am only doing this to see if the factory Infinity Amp is the cause of the engine noise I experience.

 

[Firewalker]

Okay I mis-read the 1st post that is on me.

Just use the jumpers then. The head units built in amplifier is only going to be maybe 20 watts if that. It isn't going to see that 50 watts they claim peak.

I would personally just dump the stock amplifier and go with a 4 channel aftermarket since you replaced speakers depending on the brand of speakers you used unless you went back to stock.

I would also run a separate ground from the head unit to a bolt in the area behind the head unit. I have done that multiple times with the Kenwood/JVC branded head units as they are the same company because of the issues you are talking about.