stock tach w/ aftermarket ECU

[Fire67]

Just wondering who has got their stock gauges working with a standalone aftermarket ECU. All mine appear to work great... Except for the tach. At a 900ish rpm idle (verified on ECU), the tach is showing 4500. Tap the throttle and it quickly goes to 6500+

I wired the tach directly to the Points output on my FAST XFI. I thought this would work because my Harlan shift light was wired directly to the wire feeding the gage when I had the stock pcm. IIRC, the Harlan shift light should work fine with a standard points input, as long as its calibrated correctly. And it did work perfectly then.

This tells me two things, one being that I need to get out the shift light instructions and set it to come on at a low rpm to test it's response to the XFI points output. And two being that I may need a tach adapter of some sort. Anyone know what a stock 96 pcm does to the tach signal before relaying it to the gauge?

[lethal93ta]

does the 96 have a tach filter in line? the 93s have a tach filter built into the wire harness right off the coil, with out that the tach acts funny I dont have a 96 manual to check the wireing but heres a photo from my 93 manual. thats why when I put my DFI in my car I decided just to put all new gauges in there so I didnt have to deal with all of that.

http://www.streetlethal.net/pics/tachwireing.jpg
http://www.streetlethal.net/int/IMG_1874.JPG

[Blubird]

what book did you get those diagrams from ? i have a 93 and i plan on doing something kinda like what you did

[lethal93ta]

what book did you get those diagrams from ? i have a 93 and i plan on doing something kinda like what you did
thats an orignal GM service manual, there getting hard to get your hands on the real deal, I worked at a dealer when they started to put all the manuals into computers and got rid of the hard copys so I have a couple diffrent books sitting around for cars I had at the time.

[BLOWNDFIZ]

My dad and I wired it up through the MSD digital 6. I'm headed up to the shop this weekend and if I remember I'll ask if he remembers exactly how he wired it. I was working on something else wile he was hooking up the tach. We were worried it might not work but it worked great.

Funny thing is I'm working on a new gauge cluster for mine as well. Just want something different, though it appears most of us with aftermarket engine management are thinking the same way...

[Fire67]

I just want it to run for now... Aftermarket gauges are definitely on the agenda, but at the bottom of the list for now.

Lethal93ta, no inline filter on these cars... I was wondering if I could get one of those MSD tach adapters to work for me.

I'm goin out to the garage now to test the shift light... And re-ground my MSD digital 7 to the battery instead of the chassis ground on the shock tower. (Tried to avoid re-routing the wires to the back of the car).

I'll let ya'll know if the Harlan shift light still works.

[Fire67]

The Harlan light still works wonderfully, right on que without issue.

So it kinda sounds like I just need a filter. Wonder if I can get one from a 93 to work? Or just try one from MSD.