Dave Carney

First off I'm not an electrical engineer. But I thought I'd try here since TechEdge is no help. I have their new wbo2 wideband and cannot log rpm using the tach feed wire to the pcm. I ran a wire from there to the rpm feed on my wideband. My voltmeter just shows 4.53 volts all the time, I even tried using a data Q to read it but I just get a flat line voltage with tiny spikes and certain intervals.

Harlan has managed to design a device (shift light) that can clearly see rpm from this wire. Whats the scoop on this regarding wave form etc? I'd like to forward the info to TechEdge to see what they can do. They are swamped right now with complaints similar to mine. The only ones logging RPM are using a 12 volt coil signal. I jumpered my wideband unit according to the TechEdge directions to capture a <5 volt PCM signal.

Dave Carney

Looks like this will be a dead thread, anyway, just in case one of the readers is interested....

The Haynes manual states to test the tachometer, you use a tool they reference and set it to 54mph (60 Hz) the tool is connected to ground and the tach lead, the tach is supposed to read 1900 rpm given this input (60 Hz).

So, I guess the tach reads frequency some how

red ws6 99

I never could not use the direct rpm wire option (FJO wideband) to the pcm. I belief its a digital signal. In the dash there is a digital to analog converter just before the tach. Well at least thats what it looks like. I ended up just using the current clamp. Although should be just a matter of finding the right wire.

Gary

HumpinSS

iTrader: (1)

Well I hooked a tach up in my car to replace the factory tach and used pcm wire number 10, if you are curious as to the placement of this wire visit www.autometer.com and look at their instructions for hooking up a tach in a 4th gen F-body

Dave Carney

Wire number and color are model year specific, what are you driving?

I have a '98 and used the white wire in the upper pcm block, number 35 I think(?),... the one Harlan shift lights use.

Dave Carney

This from the autometer sight (scroll down towards the end for LS1 info):


The newest addition to late model ignition systems...C.O.P. (coil on plug).
We are getting more and more requests for tach signal wires and connection points on all kinds of new vehicles, and virtually every new vehicle has at least a DIS (distributorless ignition systems, or coil pack as it is more commonly referred to). The days of the "old distributor and coil" are gone, friends. This is a whole new ball of wax. The automotive industry appears to be shifting toward an even newer ignition system - C.O.P. This stands for coil on plug ignition system, which consists of attaching a coil atop each cylinder's spark plug, eliminating any coil pack, distributor, or plug wires. The computer for the vehicle controls the targeting for firing the plug when needed, supplies the voltage to the coil to discharge, and has a "monitor" to ensure that the coil did fire and at the appropriate time.

Ok, now you're asking your self, "What does this mean to me?" The answer: if you have a late model vehicle (most '99 and newer models) with C.O.P. ignition, it has everything to do with you.

We have not had much, if any, success installing any of our engine RPM devices (tach, shift light, RPM activating module, etc.) on this type of ignition system. This is due to each cylinder seeing a portion of the entire motor's firing order. First, say for instance you have an 8 (eight)-cylinder motor, such as a Ford Mustang, for example, and it is a '99 or newer model. You have eight cylinders, and that means you have eight coils now, too. Trying to splice into one of the eight coils seems like the first thing to do, but it IS NOT! You see if you were to do that, you would only see 1/8 of the engine's true RPM signal. This is far too spaced out or sporadic for our tachs to register correctly off of. Also, we have seen on some of these late models that there is multiple spark discharge at lower engine RPM, which causes severe pointer bounce (which makes the tach pointer swing wildly from 1k-3k) usually within the 0-2k RPM range. You say to yourself, "combine the signals". This won't work either, because you would first to have to find two opposing cylinders in the firing order, and then build an inline adapter or circuit to prevent crossfire, or potentially damaging cancellation of both cylinders firing. This situation could allow fuel to load up in the cylinder tubes, then when it does fire, BOOM.

This leads us to the next point and question, "Why can't I just splice into the wire(s) that goes to the tach in the cluster?" This sounds like a viable option, but the signal to the cluster tach is not the same signal as what our tach needs to see (12v square wave). This is commonly referred to as Multiplexing, which is the process of communicating several messages over the same signal path or wiring. In most cases, the wire that has the tach signal also has the signal for any of the following:

Tachometer
LOW FUEL level indicator
Speedometer
The standard gauges; oil, water, fuel level and volts
Odometer
Brake warning light
Seat belt
And so on...
As you can see, for this example '99 Mustang there is a lot more than just the tach's engine RPM signal going up to the cluster and our tach cannot derive the signal needed to operate, nor is it the correct signal. We have also found that the rate of refresh is very low, so it does not give as accurate readings as our tach needs to see.

Now, this dark cloud looming is not all a lost cause. Some vehicles, even to the day this article was written, had the new C.O.P. ignition system and also a devoted "tach signal" from which to work from. A few examples of such applications are:

Ford Triton V-10
GM LS1(used in the Camaro, Firebird, Corvette, Silverado)
'01 Honda Civics
As stated above, 1) the Ford Triton V-10 motor, which has what they refer to as a CTO (clean tach output) which our products, after some modification, are capable of working on. Also, 2) the new LS1 motors found in such vehicle platforms as the Pontiac Firebird, the Chevy Camaro, and the Chevy Corvette. And lastly, 3) '01 Honda Civics, one of the latest additions to this listing, but they too have a tach wire to work off of. These vehicles have the C.O.P. ignition, yet the factory cluster tach has a wire that uses a signal our tachs can work off of from the computer that you can splice into to obtain the engine RPM signal from.

So with all this in mind, we are trying to do everything we can to stay compatible with the later model ignition systems, but don't always have the answer. We STRONGLY urge you if you are looking to purchase one of our products that you check the ignition system first, to see what you have to work with, then step two should be to call us and inquire about the compatibility with your specific vehicle.

Dave Carney

Ok, found the Autometer tach 4th gen install instructions, they say to use the same wire that I used...

HumpinSS

iTrader: (1)

I drove a 2000 SS anbd used the white #10 wire IIRC

Flyin'Brian

hook the Tach signal wire up to the 12v logging input of the WB.
IT's a pulsed signal @ 4 pulses per revolution.
So set up your logging software for 4 pulses per rev.
I think this will work for you.

Dave Carney

Thanks everyone, I've got it resolved. The answer does not appear in this thread. I'll post later on solution.

Smoke_Ford

The tach wire reads a varying voltage.

Dave Carney

You sure about that? Shows constant voltage regarless of rpm, on a mulitmeter and on a data q. I believe it reads frequency.

mikey_ls1

Ok Guys i know this thread been dead for couple months but i really need some help here..

I'm hooking up a silver 5' tach in my 2000 TA now autometer says i need to buy the distributless adaper kit (9117)9117 Link now i am confused with this and it is killing me, i finally located a pink wire at the harness on the drivers side before the coil packs, i hooked it up the the red/green wire out of the 9117 and the red i hooked up to the 12v+ and the black to ground and the grey to the green tach wire comming from my tach. now before i clipped any wires on the tach to support the right pulse. it was a low rpm reading then i cut the blue and it is just under the stock rpm reading. now it kinda jitters when idling like apulse jitter, is there anyways to hook this up in a better way perhaps without the 9117 adapter kit from autometer? i read something about the #10 wire(white) in the thread but where is it i have no electrical schematics on the harness or anything and im fairly new to ls1 engines. please help!!!! i would greatly appreciate it.. and where else can i use a pos+ connection for the ignition wire under the hood.. thanks alot guys in advance!!

mikey_ls1

I tried to locate the white #10 on the pcm but there are a few.. man im so lost!!!

exstanger

iTrader: (4)

I think that tou might could use the installuniversity.com website. They have a good article on installing a shift light and I used the same info to install my autometer tach. Just remember to cut both wires like for a 4 cyl. engine.

mikey_ls1

when i cut both wires the rpm was reading higher... but am i suposed to?

if im using the pink wire in the coil harness etc...

mikey_ls1

Found this artlicle.... seems very intresting!!!!!

ARTICLE

mikey_ls1

ok i figured this part out.. its the LOWER PCM block(RED) FOR 99+MODELS) and is the #10(white) the 98 model is a #35(white) UPPER PCM block(blue) so i guess there is a difrence with year afterall.. so anyways i hooked it up. and itworks... now i can dispose this dman kit adapter 9117(autometer)


And i don't even have to send it back to re calibrate it..

MrDude_1

iTrader: (4)

for anyone curious, this is what the LS1 tach signal looks like:


its a just shy of 5v square wave, 4 pulses per every TWO revs.

that is, 2 pulses per rev. like a 4 cyl car.


it is not a varying voltage... the frequency (how close the little bumps in the pic are to each other) is what changes.

on a volt meter, it cant read that, so it averages the pluses together and gives the only thing it can.... a voltage reading.

dieselgeek

Here's a quick fix for making that tach signal work with devices that won't pick up it's signal - you need a 12v "pullup circuit". We had problems getting our MEgasquirt to trigger, we got it working by combining a 12v source through a 13,000 ohm resistor, and BAM you get a nice 12v pulse that will work with most equipment that needs a tach signal.

The only real issue is that this is a pulse for a four cylinder engine, so you have to config your tach/box/whatever for a four cylinder.

But anyways, a "pullup circuit" is all you need to make the signal compatible with most devices that require a tach signal...