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Code P0340 when using CB

4K views 46 replies 10 participants last post by  gfiber 
#1 ·
I have a 97 TJ 4.0 with a Uniden 520XL CB radio and a 3' Firestik antenna. The CB has a dedicated power circuit from a Painless Wiring Fuse Block. More often then not, whenever I key The microphone, talking or not, the cel comes on and a P0340 cam position sensor code is set. Actually the cps is a pick up coil inside the distributor. It has an aftermarket CPS either advance auto or auto zone. SWR is around 1.5 on channel 1 and 40. Occasionally when driving and keying the Mike, (cel on)the Jeep will buck slightly. This one has me stumped. Could a CB's signal be enough to disrupt the CPS and set a code??? Any ideas or opinions greatly appreciated! Thanks.
 
#2 · (Edited)
Yes is some cases. even 5 watts of CB RF will be rectified by the semiconductors with in the EMU and give you false readings like you are experiencing.
Likely RF radiation on the shield of the coax or even back through the power cable.
Is the coaxial antenna connector tight onto the radio antenna connection ?
Where is the antenna mounted?
How is the coax routed to the antenna ? Sometimes relocation away from vehicle wiring is all that is needed.
Does the antenna mount have a good ground ?, best using flat metal material to accomplish it.
Many times a poor Standing Wave Ratio (SWR) will cause radiation along the coaxial cable on the shield of it and the RF will intrude into the vehicles electronics.
Have you access to a dummy load, (fake antenna) I use those to trace where the interference is coming from, either antenna which has now been replaced with the dummy load or power lead. With the dummy load most all of the RF radiation is absorbed in it and the trouble would generally disappear, if that happens then attack the grounds and SWR on the antenna system otherwise the radiation is coming down the power lead and you can get ferrite cores to wrap a few turns of the power lead around that should solve it.

I would look at your antenna connector at the radio , did you solder it on or was it factory installed? I have seen so many times on a solder type of connector folks do not solder the shield and therefore you do not have a good sold 2nd half of the antenna circuit attached. Crimp on connectors unless terrible installed you most always pick up the shield when installing them. Look at the mount and see if it really has a good ground and see if you can find a SWR meter some radios have them built in check the manual, borrow one, have a friend who owns one check the antenna SWR for you. You have any friends who are Ham Radio operators? Generally most will have the SWR or reversing power meters than can check SWR. It can get a little tedious but should not be to hard to solve, write down what you have checked and the results so you don't keep doing the same steps over and over. Hope some or all of this helps.
 
#3 ·
Reroute your antenna wire and keep it away from any factory wiring the best you can.
I have a big truck that I ran the antenna wire behind the dash and if I had the power turned up on the CB and keyed the mike the windshield wipers would start working by themselves :)

Re routed the antenna wire and no more mysterious wiper action.

Don't know if it will work for a little radio but try taking a florescent tube and holding it next to the antenna as you key up the mike, the bulb will light up, lots of power running through the antenna wire that can bleed out.

.
 
#4 ·
Great info from gfiber. I'd boil it down to thinking you've got an antenna coax grounding issue at one end or the other, or your antenna mount is not adequately grounded. Antennas and their mounts need what is called an RF ground which is far more demanding than a simple ground connection is for non-RF needs. I'd make sure your mount has a good bare-metal to bare-metal connection to whatever it's bolted to, and that the mount is assembled properly.

Also, the big nut that holds the antenna mount to the mounting bracket needs a bare metal connection so any powder coating under the bracket where the nut touches needs to be grinded off so there's a ring of bare metal for the nut to seat against.
 

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#5 ·
Thanks for all the info. The SWR is around 1.5 on channel 1 and also on channel 40 so my SWR is good. The antenna is mounted on a swing out tire carrier. I did remove the powder coat where it mounts. The cable is factory. The CB is mounted to my roll cage overhead and the wiring and cable do not run near other wiring for the most part and certainly not near the CPS circuit wiring. I'll definitely check the ground at the antenna and jump a ground from the swing out portion of the tire carrier to a more solid ground and see if that solves the problem. Thanks again for the help.
 
#7 ·
Okay, cleaned up the ground and checked with an ohmmeter. Solid. Same thing. Adjusted the swr to around 2, channel 1 is just above and channel 40 is just below and now it doesn't set the cel. At least not in the 50 times I keyed the mike on different channels. Unfortunately, not a whole lot of people on cb's around here, so not sure of how the radio will perform.
 
#9 ·
Braided ground straps aren't usually needed but when they are, they're normally to provide a better ground for things like the tailgate when the antenna mount is attached to it. The tailgate is barely/kinda grounded so when an antenna is mounted on it, a better RF ground connection is usually needed so the antenna will tune properly and work up to its potential.
 
#10 ·
Still happening. I don't think its a ground problem. I ran a jumper from the tire carrier to the neg bat terminal and the antenna shows ground when checked with an ohmmeter for continuity. I cant figure this one out. The cable is from firestik. Could the cable itself be bad? Or the antenna?
 
#11 · (Edited)
Roy,
Your SWR at 1.5:1 is fine and that usually means the antenna is working well and it is a bit unusual these RF problems will arise with the antenna working so well.

You are thinking DC ground and Jerry is saying RF Ground.

A good DC ground does not always make a good RF ground. A RF ground should be as flat of a conductor as possible. Those braided cables Jerry uploaded photos of will do. When I use those I make sure to put on a pair of gloves and put a little silicone or clean grease along both sides of the length so the cable does not corrode. Once that happens the cable becomes more of small wires since the woven points no longer contact to conduct. Just keep an eye on that ground and change it out if it corrodes. A Round Wire can be used but only in very short situations. If you must use round wire make it as big as you can since that will look flatter to RF. Round wire grounds will radiate like an antenna. Running a wire from the Tire carrier to the negative battery post will likely do nothing, BUT it is likely 1/4 wavelength long ( 8 feet ) and will act as another antenna enhancing the RF issue you are having. So what you want to do is connect a flexible ground like Jerry pictured from your swinging tire carrier to the vehicle frame. You might even have to jumper around one of the hinges of the tire carrier with the ground cables. You also try Mix 31 Ferrite beads on the coaxial cable near the antenna. Here a company sells then in a pack of 5. DX Engineering RFI Suppression Snap-On Ferrite Beads DXE-CSB-525P - Free Shipping on Orders Over $99 at DX Engineering. If you order some of these I believe they are made to fit onto RG-58 cable, you are best to give then a call before ordering. These beads snap around the coax and adding one or two will generally stop the feed-line from radiating. Another trick to try if you have lots of left over feed-line coaxial cable is to wrap as many turns as you can on, usually 5 or 6 turns, in about a 5 or 6 inch coil and tape or Ty-wrap it together. This creates a RF Choke on the shield and should help with the radiation. Some folks just tie up the cable as a "Hank" like rope and that is not correct especially in this situation. Sometimes one thing does not get rid of the RF radiation. As you I am a little surprised of the trouble since so many here do not seem to have it or just do not notice it. On my Toyota pickup I have ground straps everywhere, but I run 100 Watts RF on HF and 50 watts on VHF and UHF, 15 watts on 900 MHz and 10 Watts on 1.2 GHz. Getting the noise out of the HF was the challenge, however I did not have RF radiation causing me the issues you are experiencing. I run VHF and UHF in my Jeep, 50 watts, without noticeable RF issues.

Gary K8IZ
 
#13 ·
Okay, I was able to get 2 ferrite beads from a local Radio Shack. The salesman was useless, When I asked if they fit RG 58 A/U cable he looked at me like I was from mars. lol. They were the only 2 in stock and looked like they might fit. They don't fit tight around the cable so I'm guesing they are useless. Didn't help the problem. I put one by the ant. and one by the unit and then tried them in different spots. I had the cable routed inside the roll bar padding up to the center of my roll cage in between the seats and near the windshield. Took the cable completely out and laid it on the floor except where it had to turn up to reach the radio, thinking maybe the roll bar was making it worse. Still no change. Still lost.
 
#14 · (Edited)
Wow all of this at 5 watts of power. Did the package say what Mix the beads are? Mix 31 is best for 27 MHz and below. I would take both beads and place them as close to the base of the antenna as possible still on the coaxial cable for a test. Do you have an excess of coaxial cable, if so try doing a small coil no less than 5 inches in diameter and about 5 or 6 turns near the antenna base and see if that stops this. What I am looking for is common mode radiation. RF is a funny duck, as you are finding hard to control at times. Wish you were here in the Seattle area as I would be in a better position to assist. I looked at the Firestik web page, Tech-Docs Index and they have several write ups on installing one of their antennas. Oh they tell you not to coil the coax as I did, but I have run common mode chokes for years with no adverse effects. I also only use the length of cable I need and not coil up the excess but you would need to be able to reinstall the connector.
 
#15 ·
Looking through the thread, did you ever ground the swing out tire carrier to the vehicle frame or tub? At the back of the Jeep? Even though the tire carrier might show continuity when checking with a ohmmeter that DC ground is likely not making a RF ground. You might try connecting up a battery jumper cable if you have a set from the tire carrier to the vehicle frame. Choose a nice shiny bolt on the tire carrier to place the clamp. Yes that cable will be long but I am thinking it should be large enough for RF to ignore any radiation it might cause of it were a small round wire. If the trouble goes away then it is surely the RF ground from the tire carrier to the frame. You know this is going to turn out to be something really simple one we find it.
 
#16 ·
I tried the ground as you mentioned with no luck. I ordered a new mount and cable. The cable I have is a firestik one with the round end that a bolt passes through to secure the antenna. The end is not in the greatest of shape and where it should ground to the carrier doesn't look like I would be getting a solid ground there. The plastic of the cable is at the same depth as the grounding ring. I probably should have mentioned I had the same set up on my old warn swing out bumper and it was fine. I have a JCR bumper now. The cable and mount I ordered looks more like Jerrys picture and the cable uses PL259 attachments. I may be wrong but at least it eliminates possible problems. The saga continues........
 
#18 ·
Ok I'll keep watching here to see how this turns out when you get the new mount and antenna installed. Seems to me on my Jeep not much if any wiring goes from front to rear on the passenger side you might check your and choose that side for coax routing if you can make it work.
 
#19 ·
New mount and cable. No change. The cable has always been routed on the PS. Runs up the roll bar to the center part of the cage where the cb is mounted near the windshield. Thought that might have been part of he problem so wired it up with the cb on the center console. Still sets the code. I also have a congo cage. That's a lot of metal up high. Could that be a contributing factor? I've installed a few cbs' in different vehicles, never had this happen.
 
#20 ·
That is one of those cages that are above the vehicle roof ? Unless there are rusty joints in the cage I would not think it would be causing this. Radio Frequency interference can do lots of things, unrelated to this problem there are known issues with house roof gutters where a poor connection joint in the gutter system rectified the RF energy and caused interference in devices like televisions, stereos etc. Seems far fetched but it has happened.

Lets see trying to think of what you have tried here,
New antenna and cable routed up the passenger side away from most vehicle wiring. Though I recommended you not to do so, I wonder what would happen if you ran the antenna cable up the drivers side? Is the cable permanently installed now? Think just maybe the ECM is picking up the RF from the near by antenna cable on the passenger side. If it is easily moved I would just lay the cable on the floor up the drivers side for a test. If you have it all neat and installed it may not be worth it to take it all apart. If you do like I, my stuff is all ty-wraped in as I go with the install generally. You have relocated the radio, radio power direct to the Painless fuse block, where does this fuse block connect into the vehicle wiring?, Radio power ground is connected where? The antenna mount is grounded to vehicle, Is the Swing out tire carrier grounded to vehicle ?, Ferrite RFI beads on antenna cable. About the only thing you have not tried was a different radio. Have a buddy who has a CB you could lay in the Jeep to try a different radio to make sure yours is not transmitting any garbage? Worth a try if easily done. Any extra antenna cable coiled up in the Jeep after the install ? Isn't RF fun and this is low frequency and power RF.
 
#21 ·
RF Fun? Maybe when we figure this out I can laugh about it. lol.

Let me run through what I've done and answer your questions.

Congo cage pivots backwards placing the cage completely to the rear of the jeep and well below antenna level. No luck.

Before routing the new cable, I laid it on the floor and connected to CB. No luck. When routed, there is not much cable left that would need to be put in a figure 8 and secured. Cant run cable on DS due to the tire carrier hinge being on the PS. Cable would not be long enough (18')

Painless fuse block on DS near your left foot. about 5" from floorboard. Grounded to body panel there. wiring runs through firewall and across cowl to battery.

Tried a separate battery, hardwired to power CB. No luck.

Tried ferrite beads placed at antenna, at radio and combinations of both. No luck.

Tried with jumper cables grounding tire carrier to frame. No luck.

Have not tried another CB yet. Friend has a similar unit which I'm sure I can use. Hopefully be able to try tomorrow night.

Just a guess. The Cam sensor on a 97 is just a pick up coil which as I'm sure you know is basically a magnetic field that is broken and the ECM reads the pulses. Its a duralast which is not known to have the strongest magnetic field as compared to OEM or other aftermarket. Could the RFI be enough to disrupt the weaker magnetic field? Yes, I know I may be reaching here. But...........

Thanks for your help and patience.
 
#22 ·
I don't think your reaching, RFI can enter into a lot of device and be quite disruptive, but to send you out changing out parts that are in working order seems unreasonable. Sometimes there are devices that are quite suspectiable to RFI, this may be one of those.If the lead from that sensor was long enough you could try wrapping a turn or two around one of those ferrite beads you purchased.This one has me stumped too. I keep thinking what am I missing. Alan's page is a good read. Though mostly about Amateur Radio, 27 MHz CB is in the frequency range he describes some cures for. RFI Problems
 
#26 ·
What the heck am I missing, Just amazing 5 watts is giving this much trouble. Makes me rethink building up a 600 Watt amplifier for my mobile ham rig in the Toyota. Do you have access to an RF dummy load? Maybe have a friend who is a Ham Radio operator as many generally have RF Dummy loads available you might borrow along with a piece of cable.
 
#27 ·
I have no access to a dummy load and don't know anyone who has a ham set up.

Tried a couple more things.

Used a friends handheld portable radio that plugs into the cigarette lighter for power. No problem at all! Not sure if this matters but thought I'd let you know.

Tried a friends antenna. Same firestik. SWR channel 1 between 2.5 and 3. Channel 40 off the scale. NO CEL. The CB I have has an rf gain. When I turned the gain up, CEL came on.

After adjusting SWR to between 1.5 and 2 on both channels 1 and 40. Same problem with rf gain turned all the way down.
 
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