RPM erratic on Vapour gauge

I bought a vapour gauge a while ago after I fried the factory gauge and got the big E. I'm having trouble getting the RPM to read properly. Where is the best place to tap into and get the most accurate reading? Pics would be a bonus please.

Where did you connect the tach wire ?

Trailtech has 4 different options for the install

http://gallery.trailtech.net/media/instructions/computers/vapor/010-ELV-07.pdf

Also make sure all your grounds are good.

I went with option 1 and tried the 5 wraps first. Got erratic RPM and reduced wraps all the way down to 1 wrap. Still the same result. Then for shits and giggles tried more than 5 and same results. I checked the ground and it's good, I've got .6 ohms between the ground wire and the neg at battery. Wondering if option 2 would be a better way to go but I don't know which wire to tap into.

Bump. Looking for some helps boys. Anybody know which wire to tap into instead of wrapping around the coil wire?

STEVE!!!!

Lol. I was hoping Steve would chime in. He seems like our electrical guru around here.

it would be one of the coil wires i would think....STEVE!!!...lol

That's what I'm thinking but don't know which one.

Tech Man wrote:

I went with option 1 and tried the 5 wraps first. Got erratic RPM and reduced wraps all the way down to 1 wrap. Still the same result. Then for shits and giggles tried more than 5 and same results. I checked the ground and it's good, I've got .6 ohms between the ground wire and the neg at battery. Wondering if option 2 would be a better way to go but I don't know which wire to tap into.

Hi there guys. Did somebody call my name?

Tech, is that 0.6 ohms an accurate measurement?  That equates to 240 feet of 14 gauge wire. That is a lot! That resistance is likely to be putting a lot of noise into the tach signal. Have you 'improved' the grounding system on your machine? If not look over this thread: https://hotrodrhinoforums.forumotion.com/t1104-improve-your-grounding

Try moving your tach ground around: At the battery negative, at the engine case, at the coil ground wire (out of the harness at the rear), at the same frame member as the coil is mounted to (a part of the frame that is welded to the part that the coil is bolted to). Ensure that your grounds are scraped free of paint and clean ( use dielectric grease to make sure that they stay that way). You might want to try (temporarily) having your tach back by the coil to reduce the 'antenna effect' of long sense wires.

Just a starting point, I'm suspicous of your ground quality. Go back to the number of wraps that was recommended by the tach people to get a fresh start. Good luck, it might be simple.

Great! Thanks Steve. I'll give the ground a good look over and let you what I find. Right now, I'm grounded to an engine bolt. I thought that would be as good as any place but maybe not. While I'm there and checking, I'll Read and improve the grounding. 

Let you know what I find.

Just read the topic and the last sentence hit me in the face like a cheep Yankee beer:

The factory setup does not deliberately electrically connect the engine to the frame anywhere. The above suggested 'low road' approach does address this failure mode.

I'll do the upgrade and let you know my findings with the tach. 


Thanks Steve and sorry boys for the beer comment. Lol


Troy

Tech Man wrote:

Just read the topic and the last sentence hit me in the face like a cheep Yankee beer:.......and sorry boys for the beer comment. Lol

And here I thought that you had to put up with the taste, in order to get the buzzz

I was just looking at the 660 service manual schematic. It looks like the coil is grounded 2 different ways simultaneously. The coil is supposedly grounded to the frame back there (presumably through the coil laminations being bolted to the frame) AND though a black wire connection to the wire harness. If this is so, it might deserve a look see if you have any corrosion or poor electrical connection in either of those pathways to ground. Get that ohmmeter out and poke around back there with it.

Is it the same as a 700? Ive got a fluke meter so I'm guessing it's accurate but I've also got a snap-on as well so I'll double check when my clutch parts get here from James.

Tech Man wrote:

Is it the same as a 700? Ive got a fluke meter so I'm guessing it's accurate but I've also got a snap-on as well so I'll double check when my clutch parts get here from James.

Good point. No they are rather different in that on the 660 the CDI pulses the coil which is grounded on the far end and on the700 the coil is ignition hot and the far side is sinked to ground by the ECU.

The grounding of the tachometer itself will still be important and generally you want short leads to minimize inductive pickup of noise. Hopefully the tach is provided with a shielded cable leading to that length of wire that you wrap around the spark plug cable? If so, the shield in that cable needs to be well grounded to be effective (that 0.6 ohms might be the killer there). When you measure resistance (or voltage drop) of your ground connection, you will want to use the battery negative terminal itself as your point of reference, for the most accurate measurement.  

I think that I can see now why everyone has problems with direct connection of the tach to the coil wires on the 700 now. Generally tachs like a short positive pulse with each spark. With the 700 it would seem that you would have a long positive signal with short gaps in the voltage instead.

Why don't I tap into the wire that's feeding the ECM the signal? Run my ground to the mounting bolts for the coil?

Tech Man wrote:

Why don't I tap into the wire that's feeding the ECM the signal? Run my ground to the mounting bolts for the coil?

Hang tough on taking that route. From what I can see, the signal will be inverted if you run directly to the ignition coil terminal. You could try that but I would be a bit worried about overloading the tachometer itself ????

I did go to the TrailTech website and looked at a few of their documents. Is this the same as what you should have gotten with the computer?
http://gallery.trailtech.net/media/instructions/computers/vapor/010-ELV-07.pdf

I snipped a few portions of the document and annotated some things that I thought important. One thing that is not spelled out is the direction of wind. From the pictures, it would seem that the sense wire is wound over the spark plug lead with the red wire toward the coil and the tip of the red wire ending up toward the spark plug. That might make a difference as to the electrical polarity of the signal going to the tachometer. Did you try going to the full 12 turns of wrap? You mentioned 'intermittent' operation and the instructions mentioned using more turns in that case. They say less turns if the tach 'bounces', I'm not clear as to what 'intermittent' and 'bounces' exactly means. Apparently, the sensor 'wire' is a red/black 'zip cord' that you peel apart to get individual red and black wires? If so, then you need to seperate them and wrap the red and ground the black. I hope this helps?

That's what I got for instructions. I guess I could have been more clear, my rpm "bounces". I'm guessing they're talking if its intermittent then the tach is either zero or a value of some kind. Bounces meaning a difference in rpm +-100 rpm. That what I've got. Sitting at idle I'll get anything from 600 to 1500. I've tried 1 all the way to 12 wraps for shits and giggles. I can't remember which way I'm wound on the coil wire.

Tech Man wrote:

That's what I got for instructions. I guess I could have been more clear, my rpm "bounces". I'm guessing they're talking if its intermittent then the tach is either zero or a value of some kind. Bounces meaning a difference in rpm +-100 rpm. That what I've got. Sitting at idle I'll get anything from 600 to 1500. I've tried 1 all the way to 12 wraps for shits and giggles. I can't remember which way I'm wound on the coil wire.

Yeah, I'm not sure what the diff between a bounce and an intermit is either, HaHa. So, you did find seperate red and black wires to wrap and ground then? Wrap direction could make a difference in the polarity of the pulse, so double check that when you get a chance. That is another thing that you could try both ways just to make sure.

Well, perhaps we are back to the grounding of the frame to the battery negative terminal. Have you had a chance to scope that out yet?

Oh, another thing that I found puzzling. Apparently the power cable and the sense cable are identical. This would mean that they can be swapped where they plug into the computer module. It is internal battery operated from what they say. Any chance that things are swapped around backwards? Also, is the internal battery good?