CB Radio causes oil gauge to drop when keyed

[Creo]

Anyone one have a problem with their CB radio causing the oil pressure gauge to drop when you key the radio?
Installation was checked with a multi meter for good ground connections and to make sure I didn't create a short when soldering on the PL259 connector. Antenna tuned so SWR is < 1.5 on channels 1, 20, and 40. During the antenna tuning is when I noticed the oil pressure gauge would drop when keying the radio. If keyed long enough, truck will chime and give a low oil pressure warning.

Specifics:
Cobra 29LX.
4' Firefly Firestik on truck bed stake hole mount.
Positive and negative wires for CB radio come from distribution blocks I already had in the truck for an aftermarket stereo amplifier and power inverter. Large gauge wire straight from the battery to the positive distribution block and the negative distribution block is grounded to the same point a large cable on the rear seat is grounded to.
Radio is mounted under dash, center of vehicle. Coax runs straight down to hump then under carpet right in front of driver seat to channel in running board, then to back of vehicle where it exits out the driver side vent on the back of the cab then up to the front driver side stake hole.

A user posted in another thread that he was having the same issue AFTER he replaced his dead oil pressure sending unit with a "standard one", whatever standard means. I replaced mine for the same reason about a year before installing the two-way radio with one from O'Reilly so I am going to get a GM sending unit to swap out and see if that fixes it and also run a large ground from the frame to the antenna mount but was wondering if anyone else has had and solved this issue.

Or, if someone can tell me that it won't hurt anything, I won't bother trying to solve the issue....just don't want to damage the PCM or gauge to where I can't monitor the pressure.

Thanks

 

[littleblazer]

On my boat the VHF messes with the tach signal... I would guess it is interference with the signal? If it is otherwise fine I wouldn't worry about it. It's not actually causing the oil pressure to drop or anything. Where by chance do you have antenna mounted and also, it may not be the ground for the radio but rather the one for the sender or sensor. Or the block.

 

[djthumper]

Where is the antenna mounted at? You may want to create a bond to the frame for the antenna. You seem to be getting into the system due to lack of bonding.

 

[Creo]

Mounted on the front driver side stake hole in the bed rail.
So, last night I removed the antenna mount and added a ground wire down to the frame....no go, still messing with oil pressure gauge.
I know it isn't actually causing the oil pressure from my mechanical fuel pump to drop but my concern is that if I keep the radio keyed long enough, if it might damage either the PCM or the gauge to where the gauge stops to function and I can't tell what my oil pressure is. If it was messing with something else not extremely critical, like a tachometer, I probably wouldn't worry about it.
I have to place an order with RockAuto, I am going to go ahead and get an AC Delco oil sending unit to try and will check grounds to sensor and block when I swap sensors.
Only other forum I can find the issue in is jeep forums. Ferrite cores are suggested in those threads and I will get some to try if the sensor swap doesn't do the trick.

 

[mrrsm]

The biggest indicator of the problem you are having ....also offers the easiest solution as well...and that comes right there in your hand... as the Microphone Switch. Each time that you press and release the switch... the sudden break in the circuit can create Radio Frequency Interference that can range all the way up the RF scale to (VHF) Very High Frequency.

And unless the Oil Pressure Gauge responds by dropping out for the entire duration when you are keying the Mike and speaking-transmitting... then perhaps these "Circuit fixes" for dealing with this issue listed on the link below might help eliminate this problem... even though the issues posted there is actually "reversed" to keep the Marine Transmitter-Receiver "Static Free". Nonetheless.. You might see the issue you are facing as the exact same problem here as being "Mirrored" RFI. ;>)

But if this does not work... perhaps using a "Mini-Mesh Copper Faraday Cage" mounted as an RF Shield around the Oil Pressure Sensor positioned to cover at least 120 Degrees of arc around it ...and pointing back towards the Firewall that would protect the OP Sensor from the vector from your powerful RF from the 4 Watt Antenna.

Hope this Helps...

http://www.dieselduck.info/machine/03 electricity/radio_interference.htm

 

[littleblazer]

Maybe try using another battery to the radio and seeing if it still interferes with the gauge? If still its RFI and if not its dropping something into the grounding system then. It's got to be a grounding issue though I would think.

I mean my boat system is a bit different being 25 watts, it actually loads the motor up as well lol. Just saying.

 

[djthumper]

You are having an issue with it not bonding properly or a problem in your feed line. Is that a fire stick? If so it should be top loaded and hopefully clearing your cab. At this point you are getting too much RF into the cab. If you are not bonded to the frame and body properly this will cause this. Placing a ferrite core in line will cut down on the RF which also cuts down your out put. I run 3 VHF/UHF radios in both of my rigs and do not have a problem. The CB only puts out 5-watts of power. If you have the length of Coax you can try the rear pocket so you are not bouncing directly into the cab.

 

[Creo]

And unless the Oil Pressure Gauge responds by dropping out for the entire duration when you are keying the Mike and speaking-transmitting...

Yes, gauge begins to drop when you key the mic and stays at zero until the PTT is released. I don't have to speak, just pressing PTT causes it.

But if this does not work... perhaps using a "Mini-Mesh Copper Faraday Cage" mounted as an RF Shield around the Oil Pressure Sensor positioned to cover at least 120 Degrees of arc around it ...and pointing back towards the Firewall that would protect the OP Sensor from the vector from your powerful RF from the 4 Watt Antenna.

I was thinking about trying this but the link you sent mentioned that it won't work if any wires to the culprit device are outside the cage(they say metal can) but it may take this and some kind of noise filter/suppressor on the oil pressure transducer wires to fix.

Maybe try using another battery to the radio and seeing if it still interferes with the gauge? If still its RFI and if not its dropping something into the grounding system then. It's got to be a grounding issue though I would think.

This is the first thing I am going to try with my boat battery while I wait for the GM sensor to come in the mail. I added a wire from the antenna mount to the frame last Thursday but it may need to be bigger than 12 gauge.

Is that a fire stick? If so it should be top loaded and hopefully clearing your cab.

Yes. Hopefully, that was the intention with this antenna/mount combo.

Placing a ferrite core in line will cut down on the RF which also cuts down your out put. I run 3 VHF/UHF radios in both of my rigs and do not have a problem. The CB only puts out 5-watts of power. If you have the length of Coax you can try the rear pocket so you are not bouncing directly into the cab.

Ferrite bead would be used on the wires for the oil pressure transducer, not coax. Ferrite bead shouldn't bother the DC output of the transducer but should cut back on any RF induced voltage as it will be AC. An electrical engineer I work with suggests using a capacitor either with or without the ferrite bead on the oil pressure transducer. He said that if my issue is voltage induced in the sensor wire by the RF, the capacitor alone would be better than a ferrite bead.
I will have to see if I have enough coax to reach there.

I had to much to do this past weekend to mess with it but hopefully I can try to pinpoint the issue this weekend and will post outcomes.

Thanks all!

 

[Creo]

No luck yet.
Powered CB from battery not connected to truck, no difference.
Firefly says 12GA wire is OK for antenna mount ground.

Sensor won't be in until Feb 7th.

 

[Creo]

Bingo! After my hand looks it lost a fight with a feral cat, a genuine AC Delco sensor fixed the issue.
GM part #12616646, AC Delco #D1846A

Thanks for all the suggestions!

 

[Chickenhawk]

LOL. Well, I sympathize with you. I have a GPS plugged in to my cigarette lighter. If my GPS is off, it turns on when I release the PTT of my walkie. If it is on, the 12 volt power supply dies when I key the mic.

 

[Creo]

LOL. Well, I sympathize with you. I have a GPS plugged in to my cigarette lighter. If my GPS is off, it turns on when I release the PTT of my walkie. If it is on, the 12 volt power supply dies when I key the mic.

Is the walkie running off batteries? If so, your issue is probably RF induced voltages on the power wires to the GPS. Have you checked the output of the cigarette lighter port with a multi-meter? If you still have 12V at the port when keyed up, a ferrite bead might solve it. Capacitor would work better but a snap-on ferrite bead would be a much simpler/easier installation.

 

[Chickenhawk]

That sounds exactly like the issue. I am not all that worried because I rarely use it inside my car anyway.