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2004 Silverado Ham Install Question

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Brts96

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For several years, I've had a Yaesu FT-2800 installed in my pickup, a 2004 Silverado. The radio has fallen into disuse over the last couple years, due to the radio intermittently causing my oil pressure to drop to zero when the microphone is keyed.

The issue isn't easily replicated, though. My oil pressure doesn't always drop every time I transmit, and doesn't do it on the same channels.

I've had a Motorola shop look at it, as well as the shop that installed the radio originally. Both came up with dead ends for the cause.

The radio is run on a relay, switched with the ignition, and the antenna (1/4 wave) is a permanent mount NMO on the roof. The antenna cable is run between the roof and headliner, down the passenger side A pillar and under the dash.

What am I missing, folks? Is it maybe something blatantly obvious that I'm looking right at and is an easy fix? What would the risks be with running the radio as is? The truck has 214,000 miles on it, so I'm not going to spend a ton of time or money on it.

It sure would be nice to have it fixed, though. Otherwise, think I'd be further ahead using it as a scanner or removing it?

Any ideas or help are greatly appreciated. Sorry for the long post.
 

OhSixTJ

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Are you sure the TX isn't just causing the gauge to freak out? Kinda hard to see how it would cause an actual drop in pressure in the engine.


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jonwienke

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There's no way your oil pressure is actually dripping. It's some kind of interference between your TX and the gauge circuitry. The most likely cause is the coax running next to wiring associated with the gauge.

I would try temporarily pulling the coax out from under the dash, and see if that eliminates the problem.

Make sure the antenna mount is grounded to the roof panel (properly weather sealed, no corrosion, etc), and that the coax is properly connected to the mount. If it isn't, the shielding of the coax can radiate, which will raise your SWR and make this sort of interference far more likely.

If all your connections are good, try coiling up ALL of your excess coax in a loop right next to the antenna mount inside the headliner (See http://www.k3dav.com/rfchokecoil.htm for examples and an brief explanation of why this works) to form a choke coil. Use zip ties to hold the loop together. The coax choke coil will not interfere with your RF signal going to the antenna, but will prevent the coax shield from radiating RF between the radio and the coil, and reduce or eliminate any RF interference with your vehicle's gauges.

I have a very similar installation in my 2001 Silverado, and can TX 80 watts without any interference to any gauges.
 

mmckenna

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Since it's inconsistent, it's hard to know for sure, but here's what I'd try:

Reroute the coaxial cable to come down the "B" pillar. Running it along with the wiring that runs down the "A" pillar might be your issue. I've always avoided running coax under the dash any further than necessary. Also, make sure the coax is well separated from all the other wiring. Ideally it should only cross existing harnesses at 90º angles, but this is sometimes hard.

Check SWR and all your connections. High SWR can cause some of the signal to radiate along the coax. If the coax is too close to existing wiring under the dash, this can be an issue. Faulty connections in your RF connectors can wreak all kinds of problems.

Ground the radio chassis. Do not rely on the negative power lead or the coaxial shield for the radio ground. Run a short strap from the radio body to the nearest chassis ground. I had an older Yaesu FT-2500 that would randomly restart. Tracked it down to static electricity with me and the truck seat (radio was mounted on the front edge of the seat). Adding a chassis ground fixed the issue. Even though the radio had a good power ground and good coaxial ground, it wasn't enough.

Back in the 90's I had a GMC 3/4 ton truck with the 350ci V8. Oil pressure gauge was always a bit wonky and would wander all over the place. Double check for a good connection on the oil pressure sensor. Could be corrosion on the connection. Since its in the engine bay and exposed to the environment, and no doubt has seen a lot of "environment" in 12 years and 214,000 miles, something simple like corrosion on the connector is a real possibility.
 

Brts96

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Thanks for the advice, everyone. I will look at how my antenna cable is routed on my next day off, which will be Monday.

I appreciate the tips and ideas, and might need to buy an SWR meter, but may borrow one long enough to check my measurements.

The issue has caused me to not operate from the mobile very much, and miss out on some good discussion.

Thanks again, and I'll try to report back soon! Hopefully, this will fix the problem.
 

clbsquared

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My 03 Silverado does the same thing. I have a 50 watt VHF mobile. It's not physically dropping the oil pressure. It's just interference. My power and antenna cable comes from behind the backseat and runs under the carpet next to the center hump and isn't near any factory wire harness. It was never an issue until I had to replace the gauge cluster at 286,000 miles. I just attributed it to an aftermarket gauge cluster.
 

Brts96

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I rerouted the cable to the B pillar, and under the passenger seat temporarily. So far, it seems to have eliminated the issue.

Everything looked good as far as visual connection to the roof, but I'll have to get an SWR meter to verify that it's working correctly.

I'm also going to verify that there are good grounds, but will need to get a bit more time and a better garage.

I'm not sure if I'll be able to coil the wire between the headliner and roof, but if there's enough cable, I'll do it.


I also replaced my instrument panel, with a replacement from Dorman, and they both have done it.

Thanks for all the input, everyone! I think you all just cleared up a major source of headaches.
 

jonwienke

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Making the choke coil with your excess coax is extremely important because it will prevent stray RF from radiating from the coax, which is most likely what is causing your interference problem.If you lay the coil flat, you should have plenty of room in the headliner.
 

cmdrwill

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Making the choke coil with your excess coax is extremely important because it will prevent stray RF from radiating from the coax, which is most likely what is causing your interference problem.If you lay the coil flat, you should have plenty of room in the headliner.

If the antenna IS properly tuned and has the required groundplane area, the there would be NO RF radiation back down the coax cable from the antenna.
 

jonwienke

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Neither of those conditions are completely met in the real world. No antenna has an infinitely large, superconducting ground plane, and no antenna is perfectly tuned to every TX frequency. And the cable connectors and antenna wiring always cause some degree of impedance mismatch to the coax. So there's always some tendency for the antenna system to radiate RF off the coax.

With a well-tuned and properly installed antenna, the amount of stray RF on the coax is small. But it doesn't necessarily take much to cause undesirable interference. Forming the surplus coax into a choke coil costs nothing, and drastically reduces any stray RF. There's no downside, and several potential benefits.
 

HummerMike

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Make sure your Antenna mount is grounded good and the coax is grounded good at the antenna mount. I also agree with "jonwienke". A choke or ferrite snap on choke will help decouple any RF from getting down your coax.
 

Brts96

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Thanks for the good replies and ideas, everyone! It still is happening, but less than it was.

On my next day off, I will try to go and get the SWR checked. If need be, I'll replace the antenna and cable.

The ferrite chokes are also a good idea, and I may install those, even if I put a new antenna cable in.

The reason I said I'm not sure if I'll be able to coil the cable is that once I get the cable run to the radio from the B pillar, there's not much left to coil. My fault for not explaining that part.

I checked with a couple shops that install squad radios, any can't believe what they charge these days. May need to just go with a portable after this one.

It would be nice to get it fixed, but I don't want to spend a pile of cash on a hundred dollar radio in a thirteen year old truck, either.

Hope it can get figured out soon, though.
 
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GM oil pressure gauges are notorious for bouncing all over the place. My 04 trailblazer did it, my 2013 sierra does it. Unless you have a true analog gauge on the vehicle, I wouldn't chock it up to it being an actual problem.


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Rred

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AFAIK all modern auto/light truck oil pumps are mechanically driven off the engine, so it would be physically impossible for your transmitter to cause the pump to stop. And that's the only way your oil pressure would drop to zero.

Which means the problem is the damned computer controls or the gauge itself. Disconcerting, but ignorable. Any competent mechanic would check that out in ten minutes by attaching a mechanical oil pressure gauge to the engine ("T" on the sender on the block" and verifying it. The industry doesn't use simple mechanical gauges because when and if they fail--that' a real problem, and they do fail.

So as others have said, you check for grounding, check for EMI/RFI, and also contact Chevy directly. The dealer is supposed to do this but sometimes doesn't. See if there is a technical service bulletin ("TSB") about radio transmitters and the gauges, odds are that Chevy has information about remediating this since there are commercial radio installations in their trucks all the time.

The other asset would be a commercial radio shop, which has done these installations and probably done them on Silverado's as well. One of your local Chevy dealers may have sold a number of them for fleet or municipal service and know which radio shop is familiar with them.

Oil pressure warnings are something to be concerned with, you're 100% right on that. They just cry "WOLF!" too often, and then you've got to outsmart them.
 

Brts96

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I'll have a mechanic check it out, and see if there are any TSB's about transmitters, as well. Figured that it wouldn't actually drop the oil pressure, but never hurts to be safe, right?

Lot of projects to do with this one concern, got to check the antenna and cable, verify SWR, coil any excess cable, add a ferrite choke or two, get the oil pressure checked with a mechanical gauge, verify grounds are good, and double check for any known issues on TSB's.

Hopefully, something will yield a fix to the issue. Out of all that stuff, the cause has to be in there someplace.

Thanks to the members of the forum for all the great ideas, I greatly appreciate them. It's good to have this kind of knowledge on tap.
 

wx5uif

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No way TX is causing oil pressure drop. Oil pump is driven mechanically of the crankshaft on that engine.
 
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No way TX is causing oil pressure drop. Oil pump is driven mechanically of the crankshaft on that engine.


But the gauge in the cluster is driven electronically like all the other gauges in the cluster.


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Brts96

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Fair enough, I'll still try to mitigate any RFI issues, though.
 
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