GPS speedometer issue

[Sixpactogo]

I am starting to think my Charger has a Demon....................
I have a 6.1 Hemi in my 68 Charger with the factory computer and a Hotwire engine management system running the engine and 545RFE system. I have a GPS speedo that works intermittently. It seems to get a good signal as the GPS clock fires up and is accurate. I thought my antenna was weak so purchased another but my problem is elsewhere. I have taken my gauge cluster out of the car and hooked it up to a 12v portable battery in my daily driver and it tests out fine. I even put the antenna sensor under the seat and it monitored my speed without interruption. I put it back in my Charger and the speedo will only register the speed once in a while for like a block or so the drop to zero. I have tested my source to the speedo and it is 12.4V (battery voltage) without the engine running. 14.4 with engine running. (same as the rest of the system) My cluster is properly grounded. My plan now is to hook my 12V portable battery to the speedo and test it again thinking maybe the speedo doesn't like the 14.4 volts my system is sending to it. I did unhook the alternator but that didn't help so it must be getting some interference from from my system that it doesn't like.
Anyone experience this before or is my car possessed?
Here is a pic of the speedo. I have driven the car close to 100 miles and most of the 20 miles on the odometer are from my daily driver.

 

[67 coronet]

if you drove it while pluged into a diff source of power and it was fine,then it is the connection to the car.either your source power or ground is comming loose somehow or,as you stated,the voltage is too much.
1)call the guage manufacturer and check on the voltage thing.
2)check for any loose connection in power or ground to the system.try reading the power output and ground continuity while wiggling all wires involved.could be a bad pigtail connection.

 

[Sixpactogo]

I am not losing power to the unit itself. If I were losing the ground or power source, I would lose the display. The clock / odometer display is built into the speedo unit and does not flutter or fluctuate. That by itself, tells me the signal is not being lost. The speedo is manufactured by Speed Hut. I spoke with their tech guy and he is baffled as I am. He says it is made to work with 12 - 14.8 Volts. When I first got my car put together, the computer was asking for 16 volts from the alternator. I never drove it until I got the 16 volt issue fixed but I suppose I could have taxed the system with the 16 volts a few times. I was worried about my battery getting cooked so never ran it for more that a few minutes at a time. Maybe the high volts did something to hurt the speedo but you would think it would have affected the display so it wouldn't work at all. All of my connections are either soldered or have the proper crimped ends. I plan on calling Speed Hut again and ask them about the possibility of the 16 volt issue as I did not think to bring it to his attention since it works perfect in my daily driver. It is getting to be the only thing possibly causing the issue is the high voltage thing from early on or else it is getting some interference from something else.

 

[kiwigtx]

Is the sender unit running a 'screened' cable to protect from electrical interference? Or does that not affect the way the speed sensor transmits to the gauge?
I installed a Hall Effect driven speedo years ago in a Hot Rod, and that cable we were supplied with was regular auto cable - got loads of interference from the coil etc....ran a screened cable, and nailed the problem.

 

[Sixpactogo]

Is the sender unit running a 'screened' cable to protect from electrical interference? Or does that not affect the way the speed sensor transmits to the gauge?
I installed a Hall Effect driven speedo years ago in a Hot Rod, and that cable we were supplied with was regular auto cable - got loads of interference from the coil etc....ran a screened cable, and nailed the problem.

No screened cable. That was one of the concerns I asked the Speed Hut tech guy about. He said there has been some interference problems from some of the older race engines with High output coils and distributors but none with the newer style coil packs. That could be my problem though as he did mention that if my tach pulse wire was too near the antenna wire it could cause an issue. I have the wires separated as much as possible but the gauges are right next to each other. I plan on trying a different battery source. If it works with a different battery, I may need to get a different cable like you did. Thanks for the input.

 

[67 coronet]

wait a sec.i thought gps speedos dont need senders.electronic speedos need senders.the point of a true gps speedo is that you dont need a sender.if your speedo has a sender,then i would guess your prob would be in that wiring or the sender itself.

 

[Sixpactogo]

wait a sec.i thought gps speedos dont need senders.electronic speedos need senders.the point of a true gps speedo is that you dont need a sender.if your speedo has a sender,then i would guess your prob would be in that wiring or the sender itself.

Maybe sender is a wrong term. The Antenna gets a position signal from the satellites and communicates it to the speedo. My antenna seems to be getting the signal from the satellites because the clock is run from the GPS as well and has a constant signal & keeps accurate time but the speedo part is what is intermittent. It is confusing because it seems like the clock should be intermittent as well.

 

[Sixpactogo]

I still have not figured out what the problem is but I did verify that the problem is caused by my engine causing interference somehow. Today I drove the car a while. No speedo. I put the car in neutral and shut off the engine while cruising about 45 mph. Turned the ignition back on and the speedo immediately started registering speed. As soon as I started the engine again, it immediately went to zero. That tells me I have interference from somewhere. Speed Hut tells me they don''t have an antenna that has a shield wire so I guess I am going to have to trade the GPS for an electronic unit. Gotta love it! Leave it to me to find a problem that no one can fix. Shannon at Redline tells me he has done hundreds of these conversions without an issue like this with a modern engine.

 

[kiwigtx]

The rotating assembly of your engine causes interference.
I know this, as when my wife and I were touring Europe in our 1987 Range Rover V8, we used a compass to check our map reading skills. It was only after a few days that I realised we were always heading North. I guess placing the compass on top of the centre console was not the best idea after all. Your engine will create a fluctuating magnetic field which can an effect on many items in the car. Just another spanner to be thrown in the works.....

 

[Sixpactogo]

The rotating assembly of your engine causes interference.
I know this, as when my wife and I were touring Europe in our 1987 Range Rover V8, we used a compass to check our map reading skills. It was only after a few days that I realised we were always heading North. I guess placing the compass on top of the centre console was not the best idea after all. Your engine will create a fluctuating magnetic field which can an effect on many items in the car. Just another spanner to be thrown in the works.....

Yeah Kiwi, I have been exposed to plenty of electrical phenomenons during my career with the power company. What is frustrating is knowing that retiring from that career hasn't stopped them from showing up at my front door.

 

[kiwigtx]

Yeah Kiwi, I have been exposed to plenty of electrical phenomenons during my career with the power company. What is frustrating is knowing that retiring from that career hasn't stopped them from showing up at my front door.

I hear you....I've been working with elastictrickery myself for 34 years now.

 

[kb67mopar]

I run a late model hemi and a speedhut gps speedo without issue. Also my alternator puts out 15 volts. So Not sure where your issue could be coming from. I have my antenna on the dash and the extra coiled up underneath and zip tied.

 

[Sixpactogo]

I run a late model hemi and a speedhut gps speedo without issue. Also my alternator puts out 15 volts. So Not sure where your issue could be coming from. I have my antenna on the dash and the extra coiled up underneath and zip tied.

That is exactly what I did! I'm sure we are not the only ones either. Do you also have the Speed Hut tach? I tapped into the #8 coil pack for a pulse for my tach. The Speed Hut tech said I may be getting some interference from that. Are you running the 5.7 or 6.1?

 

[kb67mopar]

That is exactly what I did! I'm sure we are not the only ones either. Do you also have the Speed Hut tach? I tapped into the #8 coil pack for a pulse for my tach. The Speed Hut tech said I may be getting some interference from that. Are you running the 5.7 or 6.1?

Yes I did the exact same thing for the tach. I have never had any issues with either of mine. My GPS speedo works fine and the tach works great too. Have you tried running a new power and ground dedicated from the battery? I wonder if there is something dropping your power out minutely or something? It is very strange what you describe and I don't see how you would get interference from the engine on the GPS antenna.

 

[5.7 hemi]

Are you using the msd tach adapter?

 

[747mopar]

I'm running a complete Autometer GPS and speedo with no issues, I've got my antenna mounted in the rear package tray. I'd try (like mentioned) running a battery feed directly from the battery then the ground, next move the antenna and then check the speedo connections?

 

[Sixpactogo]

Are you using the msd tach adapter?

no adapter for the tach. I runs off directly off of the .5 pulses from the engine coil pack.

 

[Sixpactogo]

I'm running a complete Autometer GPS and speedo with no issues, I've got my antenna mounted in the rear package tray. I'd try (like mentioned) running a battery feed directly from the battery then the ground, next move the antenna and then check the speedo connections?

I have tried a different battery 12 Volt source and it works fine. I have not tried running another feed from my battery since it is trunk mounted. Plus I do not want to add a designated switch for the speedo source as the display would be lit all the time. The source I have now is off of the fuse box "ignition on" source. The reason I believe it is getting interference from the engine is because it registers speed just fine without the engine running. The built in GPS clock does not lose it's signal with the engine running so maybe my problem is in the speedo itself. When I first put this system together, the computer was sending 16 volts to the system. I am wondering if the 16 volts did something to the reception for the speedo but didn't affect the clock or anything else. I thought maybe the speedo didn't like the 14.4 volts with the engine running so I unplugged the alternator and test drove it at the 12.5 battery voltage but it still won't work with the engine running. Crazy!
Dev, I was looking at the time of your post. When do you sleep?

 

[747mopar]

I have tried a different battery 12 Volt source and it works fine. I have not tried running another feed from my battery since it is trunk mounted. Plus I do not want to add a designated switch for the speedo source as the display would be lit all the time. The source I have now is off of the fuse box "ignition on" source. The reason I believe it is getting interference from the engine is because it registers speed just fine without the engine running. The built in GPS clock does not lose it's signal with the engine running so maybe my problem is in the speedo itself. When I first put this system together, the computer was sending 16 volts to the system. I am wondering if the 16 volts did something to the reception for the speedo but didn't affect the clock or anything else. I thought maybe the speedo didn't like the 14.4 volts with the engine running so I unplugged the alternator and test drove it at the 12.5 battery voltage but it still won't work with the engine running. Crazy!
Dev, I was looking at the time of your tpost. When do you sleep?

Haha, When you have a list a mile long that you want done and have kids that sleep until 9:00-10:00 working late in the garage grantees you'll be left alone! Still get 6-8 hrs of sleep too, what can I say I've always been a night person. Last night was unusually late though, B.S ing with a friend till midnight put me behind......

I was thinking the same thing about it being the speedo and not the GPS.

 

[747mopar]

I think you jinxed me, after saying mines worked perfectly it quit yesterday!!!!! I dug around last night and found the signal wire terminal had come out of the connector that plugs into the GPS unit. Still need to get it out and test it but I'm pretty sure I got it.