Weird-erference

[Scipio Kid]

Hey all, haven't been around much lately. Been swamped with work and mostly out of town in remote areas with no cell phone or internet coverage. I tried to log on a few times in the past months & the site was down. I thought, "That's weird" maybe it's interference".

We often talk about and find remedies for interference in vehicles such as ignition, alternator, barking dog in the back seat, chatty friend in the front seat etc. There are always good remedies for these problems and lots of good ideas here on the forum.

I drive a variety of vehicles and several different trucks. In our little business, we've set up several radios on the old slide brackets for quick in and out of various vehicles. The truck I typically drive back and forth to jobsites is an old (1997) Ford diesel. Now with a diesel engine, you don't have the typical problem with ignition and / or spark plug noise, but you still have to deal with noisy alternators and electronic fuel injectors that give interference very similar to spark plugs.

But I've got a new and weird interference problem now. A while back, I was sitting at a long red light and the diesel engine (in the 97 Ford) suddenly died. It never does that. I started it back up and all was well, (yes, this is a CB issue, not a truck issue but sort of both). The next day, I was idling in a parking lot and the truck shuddered, then went back to normal. It interrupted a conversation I was having on the CB. I watched the tachometer and it looked normal and the engine seemed normal. I started talking again and noticed the problem again. Then I realized it was the CB! I just hadn't put it together. Whenever I keyed the mic, the engine speed would drop considerably and even die. My buddy said the radio (a modified Cobra 29 NW) sounded great and nothing seemed weird about the way it was working. I took it out of the truck and tested it and all was well. I bought it with some mods (more watts, echo, talkback etc.) and wondered if they might be screwed up so, I put a different radio in the truck and got the same thing. Tried 5 different radios with the same result. Doesn't matter which radio or frequency I choose, it still does it. When I'm driving and the engine speed is up, it's not noticeable but if I watch close, the engine still struggles a little when I'm broadcasting.

I'm thinking maybe my coax is too close to the engine computer or something but ... Another mystery here, we've had a radio in that truck for years with no trouble and suddenly this starts up.

It's really annoying. The other day we were hauling materials out of a jobisite in rough terrain so I had the truck in 4-low winding down a steep grade with a heavy trailer behind me. I was yacking with my operator back up at the rig when the truck started freewheeling down the hill. I was using the diesel engine compression to control the speed and when I was transmitting, it killed the engine and the automatic tranny just let it roll away. I lost the power steering too so it was scary for a second or two. After screaming hysterically for a while, I realized what had happened, hit the brakes and started the engine back up. I keyed the mic and it died again. It's just really weird.

Anyone every heard of such a thing and any remedy for it?

Thanks,

Scipio

[51]

most likely poor ground, poor bonding, and rf getting into the computer. a cb radio cant kill a motor from amperage draw (standard radio). you gotta go thru the whole setup section by section and do the install right, no shortcuts. wheres the antenna? how is it mounted? how is your radio connected to dc + and ground? how are the wires and coax routed?

[Scipio Kid]

Hey You're right. It could be a ground problem ... and more than right that the radio can't pull enough current (it only runs about 10 watts and won't blow a 4 amp fuse) to lug the engine, especially a diesel with huge dual batteries. I didn't check anything before I posted the story. It's a typical installation (I've done a lot of them) but its not run directly off the batteries. I pulled power and ground under the dash and mounted the radio on the ceiling, between the sun visors. The coax is routed to the right side with the extra stashed under the dash and the antenna on the RH mirror bracket. It's always been a good setup with a near perfect SWR match. But ... it's a couple years old and the truck spends a lot of time on rough roads so something might be loose or worn. I think the coax is pretty close to the computer on that right side (not 100% sure, never had to deal with it).

I'll check the coax and power connections and run some tests and see if that fixes it.

Thanks for the good advice.

[Scipio Kid]

Did a quick check and found no bad connection but need to be more thorough. Pulled the Uniden and put in my Galaxy 979 for the sideband for a while. sheeesh! Forgot it puts out about 30 watts maybe more! Kills the engine as soon as I key up even if it's at high idle. Works good on the road though. I'm going to go straight to the battery ground with the power supply and see what happens.

Weird thing came to mind when that happened, I had a super high powered Connex 3300 in there for a short while about 6 months ago. (Sadly, sold it when someone offered me 5 times what I paid for it, what a jerk!) Never had a problem with it.

[TNT1450]

Yeah, I always run radio power leads directly to the battery. Sounds like there might be a problem from wherever you're drawing power from, or else the truck's computer is really susceptible to 27 MHZ RF.

[Scipio Kid]

My wife suggested it is I who am susceptible to RF interference and not the truck, that the truck is running fine and I'm the one who's been shutting down. Now, I don't need a CB radio to do that, but the thought is intriguing.

I'm working on a newer, bigger tin foil hat.

[jessejamesdallas]

Your the second person in as many months that has posted this problem with a Ford Truck that I have read...(other was on a different forum)

Another guy had a Ford truck and when he would key the radio, he noticed a voltage drop from 12.5v down to 10-11 volts at idle...Plus truck tried to die...Come to find out his truck had BMS (battery management system) which apparently didn't like CB Radios....He found a way to disable the BMS and after that everything was fine....

I've never herd of "BMS", but then again I don't own a FORD either...guess that's just another one of Fords "Better Ideas?"

[Scipio Kid]

Well, I have heard of it but, I thought it was something only the women had to deal with. That's what I get for letting my wife drive the truck I guess. Dang.

I'll have to hook up the ol' VOM to the thing and see if that's actually what's happening. Dang, if it is.

I guess it wouldn't be too hard to take off the antenna and slide a Dodge under it.

[51]

why dont you first try to do a quick power lead hookup directly to the battery? then check for proper operation. could be as simple as that for a fix. plus, any electronic accessories should be made direct to the battery bank to eliminate problems, never use the fuse block.

[Scipio Kid]

I agree ... But still, I often use a good circuit under the dash, usually a main, un-fused circuit if I can find one, I never come off the ignition switch (well unless it's a radio with a memory lead like a Cobra 18 WX ST, I think that's the one), they have 2 hots, one for the memory and another to light it up off the ignition. I've got a little Chevy 1/2 Ton with one of those in it and it's a great little radio. It's mounted on the hump rather than the roof so the front facing speaker is nice. It's not wired to the battery either but works good.

I am going to go directly to the batts on that Diesel. Just so busy I probably won't get to it until next year.

[MDYoungblood]

Just to add to what JJD was saying about the "BMS" system on newer Fords. Ford's idea was to help prevent dead batteries in the event you left the lights on, a control tuned the battery connector off when the voltage dropped.A lot of radio ops were thinking this was a good connection for the radio and ran the positive to it being it was a terminal lug connection, problem was it actually backfired on them and they have been paying for it. If you own such a vehicle go to the dealer and they will flash the computer with a better program.

3's

Greg