318 EFI conversion - tachometer fix?

[adamgraves]

Need some advice on how to get my tachometer to work again... Converted to EFI using all 1984 318 parts including the ECU.  Had to make a bastardized distributor with parts from both 2002 and 318 distributor, so now there's no points on my distributor... Whats an easy fix to get my stock tach back working? 

[jimk]

You need a spike pulse generator.  The 318 stuff puts out a square wave that is not at all what the points system generates.  Try a MSD tack adapter or similar.  A simple relay, a transistor and resistor can be configured to do the same thing.

[xr4tic]

Doesn't it just use a normal single coil?  Connect the tach to the negative terminal of the ignition coil like it should be.

 

 

['76mintgrün'02]

13 hours ago, adamgraves said:

Had to make a bastardized distributor with parts from both 2002 and 318 distributor, so now there's no points on my distributor...

 

I'd like more details on this bastardization.  Is your current distributor spinning clockwise, like on the 2002, or ccw, like the '84 distributor?

 

There must be more to having the advance mechanism work than simply changing gears and camshafts.  Especially if you are running points (which you're not, apparently).

 

Interesting topic, but a tangent I suppose.

Tom

[adamgraves]

Trying to remember but... Bastardized distributor is the lower gear from the 2002 onto the lower shaft of the 2002 distributor. Then the mech advance plate/weights from the 2002 distributor lower shaft (these parts are pressed together so really just the whole lower shaft) which spins correctly, is mated to the upper shaft of the 318, which its little fins that fit into the mech advance pieces doesn't fit right (reversed) so you have to grind them a little to fit right. Then the pointless distributor guts from the 318 fit back onto the upper shaft. All of this goes into the 318 distributor casing. The vac advance on the distributor does nothing any longer as it's on the wrong side and would retard vs advance if hooked up...   

 

Will try the MSD tach adapter, or possibly the inline transistor stuff... Saw that option but wasn't sure if it would work with the 318 dizzy.

[pato2002]

Try the negative terminal on the coil first. Easy check. 

[xr4tic]

20 minutes ago, adamgraves said:

Will try the MSD tach adapter, or possibly the inline transistor stuff... Saw that option but wasn't sure if it would work with the 318 dizzy.

 

It's not the dizzy that drives the tach, it's the flyback voltage generated when the coil triggers.

 

Doesn't matter how you trigger the coil, as long as it's one trigger per firing (MSD does multiple sparks, requiring an adapter)

 

Tune123 doesn't have points, tach works just fine.

['76mintgrün'02]

Thank you for the explanation.  I think I sort of understand what you did.  I have never been inside a 318 distributor though and I don't understand how their electronix werk.  (glad I don't need to know.  points and condenser mindset here).

 

35 minutes ago, adamgraves said:

The vac advance on the distributor does nothing any longer as it's on the wrong side and would retard vs advance if hooked up

 

I wonder if you could use a dual-action advance/retard pod, flipped upside down and installed on the (retard side of the) body and then using what would be the vacuum retard side to provide advance.  Follow me?  The back side of the pod would pull vac retard in the original configuration, but vac advance in yours.  You would possibly have to add another hole (or two) to the flange on the pod to have it fit, but that's easy.  I guess with EFI the pod might not be necessary anyway.

 

Another concern is whether you could provide a ported vacuum signal to the pod with your EFI system.  I tend to doubt it, but I don't know anything about those new-fangled systems either.  (downdraft jets and floats mindset here).

 

Tweaking distributors is my kind of fun, but I'll go back to minding my own business now.   

 

Tom

[jimk]

43 minutes ago, xr4tic said:

It's not the dizzy that drives the tach, it's the flyback voltage generated when the coil triggers

That's right, I didn't consider the coil.

My head was locked onto smart coils.

 

Edited September 24, 2019 by jimk

[Geoff Raynak]

when we were doing our electric conversion ... we needed to boost the controllers RPM output in order to match the 'flyback voltage'

 

once we did this ... the silver dollar tach was 100% perfect.

 

we used this part: "TachMatch Voltage Boost Module"

https://www.technoversions.com/TachMatchHome.html

 

 

AND ... Adams also has a BMW specific version ... which may be even better ...

https://adamsautosport.com/product/bmw-2002-tachometer-adapter-for-engine-swaps/

 

we just had previous VDO+controller experience with the tachmatch ... so just knew it would work

 

YMMV

 

g

 

 

[Dudeland]

Dude I have just the device for you.  I got it and don't need it as I went trigger wheel.  PM me if you are interested. 

 

$30 plus shipping and it is yours. 

 

 

https://www.ebay.ca/itm/UNIVERSAL-TACH-ADAPTER-CONVERTER-COP-1-2-3-4-5-6-8-10-cyl-to-any-4-6-8-Tach/141931549970?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

 

[adamgraves]

PM'd you for that little thing...