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Author Topic: When I transmit my oil pressure gauge drops to 0  (Read 8785 times)
KG5AEN
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« on: May 14, 2015, 08:46:11 AM »

I have a 2007 Suburban.  I have installed an NMO mount on the roof about a year ago when I bought my ICOM IC-2820H.  Power is run directly to the battery.  In March 2015 I swapped out the ICOM for the Yaesu FTM400DR.  Everything has been fine.  Then this past Sunday we had a tornado and I was out spotting for the local SkyWarn group.  I noticed that my oil pressure gauge was dropping to 0 every so often.  I thought well its just a bad gauge or sending unit, and didn't worry about it.  For the last two days I have had the radio off.  Well last night we had some flooding going on and the local EOC asked for some volunteers.  So I went out.  To my amazement the issue returned.  However this time things were a little calmer.  I began to notice that every time it happened was when I was transmitting.  I was on high power and the needle would drop to 0 in about 3 seconds.  So I reduced power to low, same thing would happen but the time it took it to get to 0 was about 15 seconds.  I do not know if this could be a grounding issue, an RFI issue or a power issue.  I am hoping that I am not posting in the wrong forum.  Any ideas would be much appreciated.  As I have only been licensed for a year I am still learning a lot!
 Huh

73,

Chris / KG5AEN
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HFCRUSR
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« Reply #1 on: May 14, 2015, 09:02:02 AM »

For starters I would check the engine ground strap for tightness.
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Not a ham, but an avid hobbyist in HF world. All things, short of transmit happen in this shack.
KG5AEN
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« Reply #2 on: May 14, 2015, 09:06:12 AM »

Okay I will give that a shot!
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KD0REQ
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« Reply #3 on: May 15, 2015, 12:24:42 PM »

most light truck "gauges" are fake now... the oil pressure sender is a short circuit just like idiot-light cars, and otherwise the gauge is rigged to show mid-scale.  so don't be afraid to put a .01 disc cap from the terminal to ground on both sides of the line, or if that looks to take more time than you have today, slap a couple of clip-over ferrites on the cable where it goes into the protection wrap.
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KG5AEN
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« Reply #4 on: May 15, 2015, 01:38:06 PM »

Do you thin RF is getting into it?
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KG5AEN
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« Reply #5 on: May 15, 2015, 01:39:46 PM »

The bigger issue is that it's crammed between the engine block and firewall.
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SOFAR
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« Reply #6 on: May 15, 2015, 02:08:55 PM »

Maybe key up a 5 watt talkie, right by the gauge, and under the hood, by the wiring to check for RFI. .... Also check if any of the install wires/cables are running parallel to the stock truck wires.
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KG5AEN
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« Reply #7 on: May 15, 2015, 02:16:42 PM »

Thanks that's a good idea.  I'll check it this evening or tomorrow.
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KG5AEN
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« Reply #8 on: May 15, 2015, 02:22:32 PM »

Went ahead and did it now.  Sure enough with the HT in the driver seat it did it too.
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WB4M
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« Reply #9 on: May 29, 2015, 04:48:43 PM »

My old Honda Passports tach gauge would peg the needle during transmit.  Just some rf getting into the computer, no harm done.
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KG5AEN
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« Reply #10 on: May 29, 2015, 04:53:17 PM »

The only problem is the constant dinging from the alarm of the low pressure.
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ND8M
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« Reply #11 on: December 15, 2016, 07:00:20 PM »

Sorry to bump the old topic, but I just ran into this exact same issue.  I've got a 2005 Chevy Avalanche, pretty much the exact same truck as the OP's Suburban.  I run a Kenwood V71A to a NMO antenna in the roof.  I never had any issue with RFI. Eventually the oil pressure sensor went bad, and was replaced.  As soon as I got it back from the shop I started getting intermittent drops in oil pressure, and quickly realized it happened when I keyed the mic. Mine only drops to zero when transmitting with 50W.  Mid power causes the gauge to drop about halfway, and low power has no effect.  So far I've just been keeping the power down since the sensor isn't very easy to reach.  Next time I have a warm garage available I'll see if I can do something with a ferrite bead or two. 
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KG5AEN
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« Reply #12 on: December 16, 2016, 06:12:00 AM »

Thanks for the info. It's interesting that this only happens after replacing the sensor. My suspicion has always been in the quality of the after market sensors vs OEM. I never tried doing anything else with mine. I am planning to trade it in after the first of the year now that it has 240k miles on it.

However I am curious to know if you do that and if it fixes it.

Chris
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AC7CW
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« Reply #13 on: December 16, 2016, 06:57:10 AM »

Thanks for the info. It's interesting that this only happens after replacing the sensor. My suspicion has always been in the quality of the after market sensors vs OEM. I never tried doing anything else with mine. I am planning to trade it in after the first of the year now that it has 240k miles on it.

However I am curious to know if you do that and if it fixes it.

Chris

I've found that aftermarket quality car parts are hard to find. I go to NAPA nowadays. Never, ever do I waste money in any of the cheesy name brand auto parts places, it's all junk. NAPA's catalogs are amazing, they could get me parts for a 1975 IHC  Travelall when the rest of the stores didn't even have it listed...
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Novice 1958, 20WPM Extra now... (and get off my lawn)
KH6AQ
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« Reply #14 on: December 16, 2016, 07:42:26 AM »

The Chevy technical service bulletins can be checked for this problem. There are over 300 of them.
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