1990 VW Vanagon Westfalia Engine Shuts Down When Transmitting on 2 Meters

[W6LDX]

I have tried everything and an out of ideas. The antenna is mounted to the steel top and is perfectly matched. I have put ferrite Chokes on most of the suspect wiring that would cause fuel starvation and still no change. The radio is powered from the auxiliary battery and all other wiring from that battery have been disconnected and still no change. I have shielded the computer under the back seat and installed extra grounds on it.
There has to be other hams who have had this problem, if so please help. I can run 5 watts and all is well, but when I go to 45 watts the engine starts to starve for fuel. I have talked with experts on Westfalia campers and none have any ideas; I have even talked with a man that re-builds the computers and he is stumped. UHF doesn't effect the engine. There has to be a way to shield or chocked RF from getting into the fuel management system or some sensor. I have the maintenance manual and schematics and have run into a dead end. Even tried ferrite chokes on the antenna feed line. Anyone have this happen to their VW Van?
Thomas W6LDX

[K0BG]

Sounds like you have the bases covered, but I didn't see any mention of a common mode choke. Assuming the coax connections are robust, and the antenna is properly installed (so that there is a good contact between the NMO mount,, and the sheet metal), then the next step is a common mode choke. On 2 meters, mix 31 is still a good choice, and if you're careful, you can get 7 turns of RG8X through a 3/4 inch ID bead. The choke needs to be as close to the antenna as you can.

By the way, powering the radio via a separate battery is typically an act of frustration, and may actually cause more problems, not less.

[W6LDX]

Alan,
I have tried common mode choke, but not as large and with as many turns as you indicated, will give that a try. Also will try going straight to the vehicle battery. But I think it is RF getting into the fuel control system; hope this works out. Thanks for the input. Any others?

[KB4QAA]

I would try bonding all the doors, trunk, etc.

[K0BG]

I'll bet it is not the fuel system, per se. It is the engine CPU. Circa 1990s VW products use Bosch's third generation fuel injection electronics. They're much more susceptible to RFI than the later model units. You also want to make sure the engine grounds are still intact. Twenty plus years can cause a lot of things to come loose,corrode, etc.

[K9ASE]

Where are you grounding the radio? Most engine management systems work by controlling the ground side of the sensors and actuators.

[K8ERV]

Twenty plus years can cause a lot of things to come loose,corrode, etc.

That's what my wife says.

TOM K8ERV Montrose Colo

[W6LDX]

Everything that I have tried has failed. The engine's fuel control system just keeps shutting down. I did put a dummy load on the nmo mount and everything work well so it must be RF getting into the computer which is next to impossible to put chokes on. There has to be somone who has had the same problem, if so HELP!
73, W6LDX

[K0RGR]

Does the vehicle use a tailpipe sensor to adjust the mixture? Perhaps RF is getting on the line to that sensor?

[K0BG]

I have a few questions, and you can e-mail me directly if you wish. My e-mail is on my web site's front page, and here on QRZ.

One thing to keep in mind about ferrite chokes. You want to pick a material that works well at the frequency in question. In this case, mix 31 or mix 43 are good choices. Wound correctly, the reactance will be primarily resistive, and that is exactly what you want. You stated you used a common mode choke, but didn't describe it. Home many turns is it?

One turn chokes are nearly worthless, even at 450 MHz., so clamping them over leads to and from the CPU is about as effective as covering it with aluminum foil!

I haven't seen the installation, and I don't know how well the coax connections are. However, in most of the cases I've seen with similar problems, were traced to loose coax connections. The SWR notwithstanding.

[K4KWH]

This a wild shot, but have you tried grounding the exhaust pipe just shy of the engine and right as the tailpipe exits the car? Also run your power and any other necessary wires as far from the computer as you can. IOW, if the computer is on the right side of the car, take wires to the LEFT, then across to the battery or vice versa. If you are using 50 watts or less, I have also run RG8 as a power lead, grounding the shield at each end to the radio AND at the battery (altho this usually is to quell spark plug noise, etc. Don't laugh! I've found other solutions that people mocked, too, but they worked! :) Like screen door grid in tail lights to stop ignition noise! Gud luck.

Jerry

[K0BG]

Using RG8 as a power cable is ill advised for several reasons. Folks do so because they think RF can easily flow on the power cable. About the only way that can occur is to have an inordinate amount of common mode current. Some further state that the capacitance of the coax shorts the RF to ground. At ≈25 pF per foot, the reactance isn't very effective. And lastly, coax has a relatively low temperature rating.

[K4KWH]

Using RG8 as a power cable is ill advised for several reasons. Folks do so because they think RF can easily flow on the power cable. About the only way that can occur is to have an inordinate amount of common mode current. Some further state that the capacitance of the coax shorts the RF to ground. At ≈25 pF per foot, the reactance isn't very effective. And lastly, coax has a relatively low temperature rating.

This is the very reason I am reluctant to help anybody, for everytime I do, sooner or later you will find fault! Everybody is NOT 'stupid', Alan, and I had tried many things chasing ignition noise, computer issues--like the screen door wire in the tail lights that STOPPED ignition noise in its tracks in my '68 Chevy. I am fully aware that coax is NOT THE "best" power wire, but ignition noise often has some mysterious characteristics. It can keep a fella searching for WEEKS--even months---trying to figure a cause. Desparation can lead to "strange" solutions. Sometimes they work, sometimes they don't. I have certainly used RG8 and it worked. Sometimes it annulled the noise, sometimes it reduced it, sometimes it made no difference. I'll try anything once! But don't worry, Alan! I won't say another word or horn in on your perfect world of knowledge.
After all. I've only had a mobile since 1966! ;)

J

[K0BG]

One of the problems Jerry, is that folks quite often flow advice from us old timers, even when it isn't such a good idea.

RG8 has a 11 gauge center conductor, and the shield is roughly the same size. Thus, a 10 foot run (typical for a mobile) of it, powering a 100 watt transceiver, will have a peak voltage drop of ≈.75. The accepted standard is less than .5 volts.

And, I will still stand behind the idea, that if shielding the power cable cured, or reduced, RFI from whatever cause, then something else in the installation wasn't right.

[K4KWH]

One of the problems Jerry, is that folks quite often flow advice from us old timers, even when it isn't such a good idea.

RG8 has a 11 gauge center conductor, and the shield is roughly the same size. Thus, a 10 foot run (typical for a mobile) of it, powering a 100 watt transceiver, will have a peak voltage drop of ≈.75. The accepted standard is less than .5 volts.

And, I will still stand behind the idea, that if shielding the power cable cured, or reduced, RFI from whatever cause, then something else in the installation wasn't right.

I think that we were talking about a 50 watt, 2M in the original thread. Surely, using coax for anything other than feedline is "iffy". I've even used it to hold a trailer in place out in the garage!

RFI is a funny animal. It will do some really strange things. I've had some situations that were easy to cure, and others that I NEVER was able to chase down. Really ticked me off!! :)It was one of the reasons, in the early days, I swore off Ford cars. Chryslers could be a booger, too!!!

I would never recommend coax or attempting to shield the power wire in that way as a matter of course. But, faced with a stubborn case, I'll try anything once. Sometimes the oddest things DO work, even contradicting conventional wisdom! :)

73

[WA7KKP]

If the CPU is not well bypassed/shielded for RF, take it to your dealer. If he can't deal with it, you might be up that proverbial creek.

This is one of the reasons I prefer a diesel engine with mechanical fuel injection.

Gary WA7KKP

[VK2KC]

Thomas, I had this problem with a V6 GM engine, all it took to cure the engine shut down was to re-route the coax away from the vicinity of the ECM (computer). Previously, I had tried the chokes etc, but in the end the fix was simple. You could try reducing the transmit power and see if that fixes the problem like it did mine.
John
VK2KC

[K0BG]

While I'll agree that rerouting coaxial cable can reduce or eliminate an RFI issue, it is best to look at the real reason that it so.

If the current flow through the coax is balanced, there will be no common mode current. Hence, the coax will not radiate. However, there is always some level of common mode in a mobile. It is exacerbated by poor mounting methods (mag and clip mount, to low on the vehicle, etc.), as they increase ground losses. Common mode increases as the frequency is decreased, again due to increasing ground losses.

If the antenna is mounted correctly (which almost always requires drilling a hole), and the coax is properly (common mode) choked, it shouldn't matter where or how the coax is run. And, there is another aspect.

The interior of a modern vehicle is almost as RF noisy as it is under the hood. If there is common mode, not only can the RF get out, it can get in too! If it does, the level of received hash we all have to endure, will be increased. Put another way, proper common mode chokes are a mobile prerequisite.