Aftermarket Tach

[Preloader]

Some progress. I got the tach adaptor wired in. It wires in series to the 12v supply wire to the coil pack. Blue wire/purple stripe.

It is also grounded and has a grey wire that drives the tach or stand alone shift light.

All that is left is the wiring for the tach itself. I need to tap into a acc 12v for power and a headlight on/off source for the lighting.

Almost there.opcorn:

 

[ChrisJ]

Does this mean your engine is actually pulling strong until 7K or do you think your overshooting the peak by way too much?


The tach you picked looks good except I hate the huge shift light. Makes me think it belongs in a car running 7s not 14s. I know I know whats the difference when you're trying to shift at the right point. Its a shame there isn't a way to make the stock one more accurate or mount a better one in its place.


BTW, surprised no one said "should've got an automatic" yet.


I have to ask something regarding the waste spark system comments. I thought this was only done on systems to use half the coils as in a V6 with 3 coils which was VERY common and easily recognized by two plug wires going to each coil. Our cars have four coils, no? So why would it use a waste spark type system?

 

[DevilSonic89]

I plan my entire being around becoming a white version of Tyrese.opcorn:

then im the black version of paul walker lol

 

[Preloader]

I knew it!!!! Watch this. The stock tach is way behind realtime both on the way up and on the way down.

 

[RoXXXanne13]

how u wire tach on sonic?!!?!?! I wonder if u could possibly like customize the guage cluster so ur new monster tach will take place of the factory one n sit in there the same way

 

[tbtree55]

how to !!

 

[Preloader]

Not gonna happen. There is too much integrated systems in the tach cluster.

Like I said, after thoroughly testing the aftermarket tach behavior, I will eventually remove it and just run a shift light to supplement the stock tach.

 

[sx sonic]

wow the stock tach is WAY behind, I was not expecting it to be so far off at the lower revs and on both sweeps

 

[RoXXXanne13]

and I will copy as usual after your trial and errors lol

 

[RS Turbo]

The Tach is only late to the driver not the ECM This is due to the message being passed from modules to get to the Cluster.

 

[Preloader]

The Tach is only late to the driver not the ECM This is due to the message being passed from modules to get to the Cluster.

I wonder if the stock tach has a single input signal. If so, could use the tach adapter to drive the stock tach from the coil pulse, and do away with the AM tach.

 

[RS Turbo]

The ECM uses the 60x crank signal it is very accurate for injector timing. There are 58 indexing notches on the Crank, approx 1 every 6 degrees of crank rotation. One of them is larger then the rest, That one signals the ECM the motor is at TDC. The crank sensor is a basic holofect sensor sending voltage high and voltage low in a digital signal it is not a strong enough signal to tap for other modules. The circuit is only run on milliamps supplied by the ECM, so the signal is weak.

 

[Swordsmith]

Wow that video makes me want to plastidip over my stock tach display, just leaving holes to see the various signal lights that share the display space.

I imagine the speedometer is just as laggy? Wonder how we can check that out.

Also, how laggy are UG, Scangauge II, Torque tach displays?

 

[Preloader]

It builds a strong case for a mechanical boost gauge.

The UG RPMs are likely just an echo of the stock tach shortcomings.

As far as the speedo, I've compared mine to a GPS speed app on my phone and have not found it to be an issue.

RS Turbo, good info about how the ECM sees crank position. The complexity of the systems are increasing quickly with the advances in other technologies such as direct injection which require critical feedback for fuel timing.

The info also makes me hopeful that the stock tach is driven by a standard, albeit slow, tach signal.

If I can just find out which wire drives the stock tach, I could run it off the tach adapter and have a fully functional and accurate in dash tachometer.

Do want!

 

[RS Turbo]

The Tac signal is a message on the dataline and the IPC has a processor that reads the data and moves the gauge...

 

[RS Turbo]

Just remember this vehicle was built as an Econo box and not a Race application.

 

[Preloader]

Digital.... Figures.

I guess a stand-alone shift light in conjunction with the sloppy stock tach will have to do in the long run.

Unless an analog to digital converter surfaces. But the digital signal is probably proprietary to GM, so I doubt the aftermarket will find enough interest.

 

[ChrisJ]

How about a video of you driving and shifting the car?
I doubt the engine reacts as fast moving the car as it does in neutral and the slow drop off is meaningless.


Not suggesting the tach isn't still too slow, it must be otherwise you wouldn't have found this problem. I'm just curious how bad it really is under normal (or even drag) use.

I've shifted at 6K-6200 or so quite a few times and never hit the rev limiter.

 

[rdss]

Preload also has a light weight fly wheel which might be exaggerating the effect. Us commoners with the stock set up probably don't have as huge of a deviation even though it's probably still there.

 

[Preloader]

I'll try to take an action video soon.

But I've definitely been hitting the limiter way more often than the stock tach has warned me about.