I had to get one of these damn things because for the life of me, I can't find an 18 tooth driven gear. I have the SGI-5E. I'm a bit less than impressed. It took all day to install because every power tap I found caused the speedo to bounce with engine revs, and at idle it would just sit there bouncing all over the gauge. I ended up settling on one in the fuse box. Other than that, wiring it was easy. However, it does not read until I get up to 20 kph. The needle jumps from 0 and starts at 20. Same with deceleration. Soon as I get down low it just drops off to zero. I also caught it bouncing again now and then. This isn't a part I wanted, the fact I had to get it, and it seems rather erratic really ticks me off. Wondering what your experience is with it.

 

Mine does it too,... digital speedo shows I'm doing 80+ @ start-up and it the speed reading gets lower a little as the idle begins to drop off after initial start-up. As soon as I start driving, the speedo begins to show the actual speed. Here's what DD has to say about it:


I figure it's #2 because the 2 speedo sending unit wires are run parallel with each other that this is causing the speed reading while in park. I just never got around to separating those 2 wires to see if it would correct the problem.

 

I have an SGI-5c and am using "Output 4" with all the dip switches set to OFF. Speedometer works well with T56 trans in a 1989 Firebird.

If you really think you need some protection from electro-magnetic interference, then put the speed signal wires in a twisted pair. There are guidelines for how many twists per inch (Google it for more info).

There is a part of me that wonders if you didn't wire it correctly and are getting noise from the original speedometer buffer. Make sure it has a very good ground. And the buffer box should be completely disconnected (mine is laying on a shelf in the garage). The link below shows how I wired in my SGI-5c.

https://www.thirdgen.org/forums/ltx-...ml#post5969849

 

My 5E is connected to the buffer box. I cut the yellow and purple wire. Purple wire comes from trans to the 5E and the yellow one goes to sensor ground on the 5E. The purple then goes from the 5E to the buffer box and the yellow does nothing seeing as it's grounded by the 5E. That's all as per my discussion with Dakota tech support. My speedo works. Just starts at 20 and occasionally has a little jitter around 100 kph

 

You talking about the same purple wire that came from the transmission? That doesn't make any sense at all.

Describe every connection you make to the SGI-5.

 

Purple and yellow are the speed sensor wires. According to my manual and I have the actual GM book for the year. Purple is signal and yellow is ground from the speed sensor. Those plug into the speed buffer via a 2 pin connector. I cut that connector. The sensor side of the purple goes to signal in. The sensor side of the yellow goes to sensor ground. Out 3 goes to the purple in on the speed buffer. The yellow on the speed buffer is just taped off. That's how I was told by tech to wire it. Basically the 5E sits in between the speed sensor and the speed buffer. Like I said, it's all working aside from the odd jitter. I have no more bouncing needle at idl . That was corrected when I moved the power tap to a different source.

 

That makes more sense.

The only reason I see to keep the buffer box is if your car uses the output from Pin F, otherwise the buffer box is redundant. Ya, I know it is kind of like catsup versus ketchup, but fewer devices are usually a better thing. Just something to keep in the back of your mind if you keep having problems with the speedometer.

FYI - You could have tapped power from Pin H (pink wire) of the buffer box. That is the switched 12V supply.

 

Sorry, I forgot to say that it is normal for the speedo to not read anything at very low speed. The T56 transmission has a magnetic pickup speed sensor that doesn't register a speed signal until an adequate magnetic field is achieved. This might be up to 5 mph on most cars. You could be making this worse if there is excessive voltage drop in the B+ power circuit (including connections) that you ran to the SGI-5. Too much voltage drop in the ground circuit (including connections) will do the same thing. And voltage drop in your transmission signal wires will do the same thing.

 

I thought I had to keep the buffer so the odometer and cruise control would work. Are the wires that come from the buffer not for those purposes?

 

Yes, they are for that purpose but the SGI-5 has the same outputs. "OUT 4" is the 4000 ppm signal that your speedometer needs, and "OUT 5" is the 2000 ppm signal that your cruise control needs.

You used "OUT 3" which is an AC waveform that the buffer box understands. All the buffer box does is change that to a 4000 PPM and 2000 PPM signal for speedo and cruise, respectively.

 

My 84 had the Factory Buffer Assembly removed and the SGI was installed in it's place. I've got speed output to the original Cluster as well as an aftermarket Speedo,... I wired the cruise control too when the car was still running a Carb, but then converted to LT1 and deleted it.


The odometer is part of the cluster function ( if the Odometer isn't working it's almost certainly a cluster issue.)

 

Ahhh, so the buffer is redundant. I can go right to the ECM and move the signal to Out 4 as the manual suggests? I guess the reason tech told me to use Out 3 was due to me keeping the buffer. Would removing it smooth out the operation? Where then would the Out 3 wire attach too?

 

ECM? Your buffer box is connected to an ECM? In that case just leave the buffer box in place.

What you can do is change the wiring a bit so the SGI-5 is driving the speedo but the buffer box still retains all other functions. That way you're not screwing up something else unwittingly. Leave all your existing wiring in place except remove the wire from Pin C at the buffer box. That is the wire that runs the speedometer. Connect that wire to OUT 4 of the SGI-5.

You might have to play with the dip switches to calibrate the speedo but you'll be able to see if bypassing the buffer box makes the speedo run any smoother. I think dip switch 3 changes the characteristics of OUT 4. I have dip switch 3 set to OFF to make my speedo run right.

 

Its connected to the ecm to shut off after whatever speed it was, 110mph maybe? Either way I pulled my factory buffer. After some troubleshooting I have a smooth speedo from 0 to jail time.

 

What year is your car and how exactly did you wire in? It's my understanding that 1989 and up had no buffer. I'm not opposed to bypassing it. Just didn't think it needed to be.

QWK, I may have it wired differently than you guys. Doesn't mean it's right. Personally I'd like it to operate as if it wasn't even there so I'll change it up if need be.

 

You don't need to copy us by throwing away the buffer. You already have things wired and at this point the easiest thing for you to do is follow my advice by moving the 1 wire. That way you keep the buffer in tact for all the other functions it serves but bypass it just for the speedometer.

My '89 still had a buffer. The buffer exists because neither the speedometer or the engine ECM can understand the speed signal from the transmission speed sensor. Eventually the buffer was no longer needed when somebody had the bright idea to change the ECM so it can understand the trans speed signal and also run the speedometer.