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CB radio turns on my fuel pump??

G

goodluckchuck

NAXJA Forum User
Location
iowa
Hey guys new to the forum, I am a 6 year vet of the offroading world but just bought my first xj last week. My jeep is a 96 4.0. The guy that had it before me had a cb wired into it already and didn't want to remove it for the sale, day 1 it worked fine no issues. He had a tiny antenna on the roof rack. I put a 102" whip (let me explain) on it which is mounted to a mount on the pass side rear fender and tied up to the roof rack so it isn't sticking up in the air and swinging everywhere. The wire, antenna base, antenna, and spring are all isolated. When I installed the antenna I had to try it out which cause this peculiar issue. With the ignition on only and I key the mic it doesn't do anything until I start talking, when I talk into it it makes my fuel pump run. Now with the jeep running it will make the engine spit and sputter and throws a P0340 code which is camshaft position sensor. As long as I am not using the cb the jeep runs fine. I figured maybe he had something wired wrong, so I wired the cb DIRECTLY to the batter, positive wire to positive post, negative wire to negative post, still does the same exact thing. That is what confuses me. The cb is a cheapy cobra 19 DX IV from walmart. Any input is appreciated and appologize in advance for the brief introduction, thanks guys!
 
Welcome.
Do a quick search. I recall somebody else here with the exact same issue.
I have no suggestions, but please keep us updated on this.!
 
I did a search just couldn't find any helpful information. I have heard that on a rare occasion something with the frequency in the cb can interfere with the vehicle's computer, just looking for some advice before I run out and buy another cb.
 
Double triple checked all wiring, antenna, wire, base all isolated I made double sure of that. Would the interference with the cps also cause the fuel pump to run when the mic is used?
 
I would try routing the coax differently, as far away as possible from any wiring, especially those headed toward the computer and from its sensors.
If necessary, cross wires at 90 degrees and do not run the coax parallel with any wiring, to prevent any coupling.
RF can do funny things.
 
With my Galaxy and a Wilson mag mount in the back i have never had a problem. I have the CB wired right to the battery hot all the time for nice clean power. The Coax runs under the center console to a 600 watt kicker and then follows the hump back to under the rear seats. It then runs over to the drivers side wall and follows that to the back and out the hatch to the roof. Running a Astatic D-104 power mic with a Galaxy 959 at 2.5-3 watts going into a 600watt booster.. USB and LSB have been fine as well. Even with the roger beep that is %100 full modulation i still have never had a problem with the Jeep. I can however set off some car alarms and motion lights as well as open some garage doors. haha
 
For my two cents worth, take a good look at the coax as well as the antenna mount. Even an inexpensive radio has to meet Federal standards for spurious RFI.

Radio Frequency Interference for those wondering. It is possible that the carrier is causing the issue which indicates a need to revisit the installation. A proper installation should preclude any FRI issues.

As for the 102" antenna, that would be close to correct for the wavelength involved.

You can determine the proper length of an antenna by using a formula:
Wavelength (in feet) = 984 / frequency (in megahertz)

The CB portion of the spectrum begins at 25.01 megahertz, so a full wavelength antenna would be a bit more than 39.34 feet (472.08") long. A quarter wave antenna then would ideally be 118.02" long.

All sorts of arguments will come of this but, 1/4 wave is the most common length used. Just be sure to check/adjust the SWR (Standing Wave Ratio) to be as close to 1:1 as possible. Some radios come with a SWR meter in them but they are an inexpensive bit of kit to purchase.

Also for those that do not know, the shape of the transmission envelope will be determined by where on the vehicle the antenna is mounted. The ideal (an least practical) location for the antenna is dead center of the vehicle on the roof. Not the center of the roof, but the center of the vehicle.

CB radio transmits using a ground plane. The shape of the plane is important. With the antenna mounted on a quarter panel, the radio will be biased to throw the signal towards the opposite corner of the vehicle. For those that mount the antenna on the front fender, the shape is biased towards the rear of the vehicle.

IMO that is...

I ran 2 mobile 2 meter back in the '70s along with stationary HAM radio. Was a member of the ARRL as far back as 1968. Was into CB until the FCC removed the need for a license...

Amateur
Radio
Relay
League

http://www.arrl.org/about-arrl
 
Thanks for the input guys, checked the grounds everything looks fine there, moved back to my smaller antenna on the roof rack and it works fine, not sure why the body mount is causing my issues. I tried just using the insulator washers on the bracket, isolating the brachet itself from the body, hard mounting the antenna to the bracket without insulation just out of curiosity, which obviously the radio didn't transmit in this case but it also didn't cause the issue. I'm not too affluent on the science behind radios I've always had a cb in my vehicle for hunting and offroading never had this issue. I'm going to wait for my rear bumper to come in and see if mouting it on that works. I have a 6.5" iro lift in my garage that is begging to be installed so that project precedes the cb for now. Thanks again for your information guys!
 
I agree, it sounds like your signal is rectifying on your wiring harness inside the vehicle body because of a crappy coax cable or a bad electrical bond between antenna mount and the vehicle body (ground plane)

To be sure.. the antenna ground connector, spring, mount and coax connector at the mount should all be electrically bonded together and to the vehicle body at that location.

If that assembly is isolated from the body where it is mounted then the signal will counterpoise on the coax cable between the radio and the antenna instead. This would explain the interference on your wiring harnesses and/or the slight odor of cooking flesh and your eyeballs feeling "hot" (hehe)

Make sure you remove that direct battery connection ASAP. Even if you fuse both leads, which is a must, your starter or electrical systems could return through the radio if you rip off a grounding strap. This in turn could burn up the traces on the CB circuit board before the fuse has time to blow. Out of curiosity is the radio case bonded to vehicle ground?
 
goodluckchuck said:
it worked fine no issues. He had a tiny antenna on the roof rack. I put a 102" whip (let me explain) on it which is mounted to a mount on the pass side rear fender and tied up to the roof rack so it isn't sticking up in the air and swinging everywhere.
Click to expand...
A 102" whip (yes, that is the right length), is meant to stick straight up.
Mounting it to the side of your Jeep is not optimal as 3-4 feet of antenna is within inches of the body. However, folding the antenna over and tying it to the roof rack hosed you completely. Essentially, you made a 102" loop, and that is causing your coax to radiate as if it was the antenna.

The wire, antenna base, antenna, and spring are all isolated.
Click to expand...

Make sure the coax is 52 ohm Coax. It is printed on the cable.

Coax length for a 1/4 wave antenna can be any length, but for a 5/8 wave, like a Firestick it needs to be 18' as it is part of the antenna.

The Coax needs to be connected at the radio, the center conductor to the antenna, and the braid to the body ground at the antenna.

The Coax needs to be routed so it does not run parallel to the vehicle wiring to avoid the vehicle wiring picking up the signal from the CB.

I recommend that the radio power (Ground) be attached to the electrical ground by the shortest length, and the power (Positive) can be taken from the accy fuse box or the battery.

Get a SWR meter. You can get one at your local truck stop, They are inexpensive. Or find someone in your area who can help you with your installation that has one. A SWR Meter will assist you in tuning your installation by telling you the ratio of outgoing power vs reflected power. The ideal number is 1:1, but some antenna systems won't get below 1.5:1, my bet is your system is really, really bad.

Lastly, if you don't actually NEED a 102" whip, get rid of it.
Most Off-road parks won't even let you in the gate with that thing swinging about as it is a hazard. A well tuned 5/8 wave will perform well on the trail and not get hung up on everything in sight.

-Ron
 
Ok guys sorry to dig up an old thread but this really has me baffeled still. I tried several different antenna lengths, checked and cleaned all of my grounds, checked my wiring to the cb which is directly to the battery, tried a different radio altogether, tried a different coax, tried different mounting points, took the antenna off the jeep completely, hooked the cb to an entirely separate power source, nothing seems to change or fix my issue.
 
Have you had the cb tuned up at all. I would at this point think that if it has been tweaked at all it could be spraying a lot of rf that it's not ment to. Therefore interfering with other electronics in the jeep.

Either that or try another cb. They are very cheap.
 
Well, let's revisit the basics...

Try this and we'll get to the heart of the matter pretty quick.
Take a pre-built mag mount antenna, stick it to the hood,and run the coax to the radio though the door window.

Now try it. Did that solve the problem?

Ron
 
Last edited:
It was in the jeep when I bought it but as far as tuned I doubt it has been. Its nothing fancy just a cheap Cobra from walmart. And I did try another cb as well that I know hasn't been tuned up and it gives the same results.
 
Those symptoms are typically associated with excessively high SWR. Have you tested the SWR ? High SWR can be from an improperly tuned antenna, old or damaged coax cable, or an improperly installed antenna mounting system. As suggested, if a different antenna in a different location does not cause the same symptoms, you need to suspect the antenna set-up that creates the symptoms.

Pictures of the antenna mount ?
 
O-Gauge Steamer said:
For my two cents worth, take a good look at the coax as well as the antenna mount. Even an inexpensive radio has to meet Federal standards for spurious RFI.

Radio Frequency Interference for those wondering. It is possible that the carrier is causing the issue which indicates a need to revisit the installation. A proper installation should preclude any FRI issues.

As for the 102" antenna, that would be close to correct for the wavelength involved.

You can determine the proper length of an antenna by using a formula:
Wavelength (in feet) = 984 / frequency (in megahertz)

The CB portion of the spectrum begins at 25.01 megahertz, so a full wavelength antenna would be a bit more than 39.34 feet (472.08") long. A quarter wave antenna then would ideally be 118.02" long.

All sorts of arguments will come of this but, 1/4 wave is the most common length used. Just be sure to check/adjust the SWR (Standing Wave Ratio) to be as close to 1:1 as possible. Some radios come with a SWR meter in them but they are an inexpensive bit of kit to purchase.

Also for those that do not know, the shape of the transmission envelope will be determined by where on the vehicle the antenna is mounted. The ideal (an least practical) location for the antenna is dead center of the vehicle on the roof. Not the center of the roof, but the center of the vehicle.

CB radio transmits using a ground plane. The shape of the plane is important. With the antenna mounted on a quarter panel, the radio will be biased to throw the signal towards the opposite corner of the vehicle. For those that mount the antenna on the front fender, the shape is biased towards the rear of the vehicle.

IMO that is...

I ran 2 mobile 2 meter back in the '70s along with stationary HAM radio. Was a member of the ARRL as far back as 1968. Was into CB until the FCC removed the need for a license...

Amateur
Radio
Relay
League

http://www.arrl.org/about-arrl
Click to expand...

Exactly! :thumbup:
 
Please Don't repost bad information, and endorse it with a thumbs up. You do everyone a disservice by doing so.

-Ron
 
Last edited:
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