Zemco Fuel Computers

[Keyair]

Wanted to start a discussion, and resource page for these cool little units.

Long been a fan of these, and had one on my Mini in the mid 80s and loved it.

I have bought a bunch of them over the years(maybe 5 or 6 of em!).
I have begun to set up a ZT4 unit in the Motorhome, and installed the fuel flow sensor in the carb feed line.
They came in a variety of units, from a dash top mounted unit(ZT1 and 4), to a DIN style(DCS).

As stock, they are only suitable for carburetored vehicles.
The fuel flow sensor installs in the feed line to the carb.
The unit senses speed and distance by some magnets and a sensor on the driveshaft.
Some units have a cruise control integrated.

However, I knew that Zemco built a optional add on box that replaced the flow sensor for Fuel injection vehicles, but they are rare and have proved elusive for years.

That changed this week, because a Zemco unit (DCS 310 EFI) that is a DIN style head unit, popped up on Ebay this week. I didnt hesitate, and bought it.

It has the EFI box.... and whilst it has not arrived yet, just looking at the box there is more info there than I have ever been able to glean before!

I will begin adding more info, and pics of the units I soon.

[Keyair]

So, this is a ZT4.
This one is mine and it’s an unmolested, NOS unit.
Box.
You can still find these, like this, on Ebay and the like.



Instruction manuals.


This is how it came packed.


This is the fuel flow sensor.


I have several of these.
I have a later unit, looks like the ZT4, but has an LCD display, and that is the one I am planning on installing in the MH.

[Keyair]

This is a DCS 310 EFI unit.
This one has the EFI add-on box, and the cruise control module which is vacuum powered.
I also have a DCS 310 without it.

[Keyair]

Contents of the box...

[Keyair]

What intrigues me is this elusive "EFI box".
I have been looking for one, for years!

This info says that the box connects to "TBI and Bosch Electronic" injector with two wires, that sense the fuel injection pulses and provide accurate fuel consumption readings.

There was a guy on another forum, years ago that replicated this box and had a diagram.... but its a long dead trail, and his email address is dead too.

[Keyair]

Unit arrived, and I wasted no time to examine the EFI box.

Note the date code!


I’m glad I’m staying period correct! [emoji3]

So, I examined the box, and it seemed to be held together by a strip of electrical tape....


And so, throwing caution to the wind, and without a care about voiding the warrantee, I pulled off the tape to find it’s secrets......




I have no idea what I’m looking at, but it’s 1983 technology, so..... [emoji16]

[Keyair]

And so, im digging around today and I find this thread from 2008...

https://ecomodder.com/forum/showthre...-box-5369.html

And there is a diagram, Post #18, by Racprops...

Apparently it has some errors, but this is what he posted...

[bkahler]

Originally Posted by Keyair

And so, im digging around today and I find this thread from 2008...

https://ecomodder.com/forum/showthre...-box-5369.html

And there is a diagram, Post #18, by Racprops...

Apparently it has some errors, but this is what he posted...

Makes me think you should have a conversation with Wayne about reverse engineering the board and then having him make some new ones.

One of the reasons I gave up on using a Zemco was the scarce availability of the EFI support module. I've got either four or five of the Zemco units sitting on the shelf and can't use them. At one time I was going to use one in my Argosy and one in my TR6. Now that the Argosy is fuel injected and my TR6 is getting the same treatment the Zemco units are useless to me.

[Keyair]

I’m sure Wayne will pipe in when he gets a minute. Magnet18 was interested too, and I sent him some pics of the board yesterday and he seemed to think it was pretty straightforward.
Me, I’m clueless on electronics, and not ashamed to admit it!

[Magnet18]

Originally Posted by bkahler

Makes me think you should have a conversation with Wayne about reverse engineering the board and then having him make some new ones.

One of the reasons I gave up on using a Zemco was the scarce availability of the EFI support module. I've got either four or five of the Zemco units sitting on the shelf and can't use them. At one time I was going to use one in my Argosy and one in my TR6. Now that the Argosy is fuel injected and my TR6 is getting the same treatment the Zemco units are useless to me.

I'm already halfway done reverse engineering it!

Raw costs should be about $8 per board plus a couple bucks in parts, whoever has a TBI unit and volunteers first to test it gets a free one

[Magnet18]

One of the mistakes the other guy made was that those 1Megs from the injectors pull up, not down

Maybe Wayne can chime in with how he thinks the injector sense lines are wired. I can't decide if it's one line to ground at an injector, and one to the coil, or one line to each of the 2 injector coils.

The signal is measured differentially, and it's intentionally designed to be bipolar, but I can't tell if that's for counting both injectors with just 2 wires, or if it's just to idiot-proof it and make it less prone to noise

[bkahler]

Originally Posted by Keyair

I’m sure Wayne will pipe in when he gets a minute. Magnet18 was interested too, and I sent him some pics of the board yesterday and he seemed to think it was pretty straightforward.
Me, I’m clueless on electronics, and not ashamed to admit it!

Myself, I know just enough to be really dangerous

[bkahler]

Originally Posted by Magnet18

I'm already halfway done reverse engineering it!

Raw costs should be about $8 per board plus a couple bucks in parts, whoever has a TBI unit and volunteers first to test it gets a free one

I don't mind volunteering. It looks like in about 2 maybe 3 weeks I'll be able to drive mine out of the shop for the first time under it's own power

Steve, can you post a complete list of components (with pics!) used in an EFI version of the Zemco ZT-4? I have several NOS ZT-4 units but I don't know what extra bits and pieces are needed for the EFI version.

Brad

[Keyair]

Brad, my understanding is that this EFI module replaces the Fuel Flow Sensor, as it plugs into the same wires, and replicates the input to the Head unit.
I did not receive a manual with this unit.

There are 5 wires coming out of the EFI unit.
They are labeled on the circuit board as follows:
Orange, Labeled ACS.
Grey, Labeled OUT.
Grey/Black, Labeled GND.
Two Black wires Labeled IN, which I assume means Injector.

My research tells me that TBI and Bosch EFI injectors run on two wires: A battery + wire, and another wire that goes to the ECU/PCM, which is a Ground.
We believe the two black wires go to one injector only.
I believe that this feedback is then calibrated like the fuel flow unit via the Head Unit. I have added the fuel calibration page from a ZT4.
See the attached pics.

[bkahler]

I tend to agree that the two wires go to one injector only. If it was one wire per injector then it would only be good for throttle body injection and not multi port injection.

What I believe happens is the system counts the number of pulses and uses that to help determine fuel usage. Kinda of a crude way to to it but it should be in the ball park.

Do you have any instructions on what settings and/or parameters that you have to enter when you set things up? I.e. number of injectors, etc.

Brad

[Keyair]

Brad,
I have no info, but, my guess is:
1/ The EFI unit is set up to replicate the input from the flow meter that you normally get in the kits.
2/ The Head unit has the logic capability to be adjusted/calibrated for fuel discrepancies.
3/ So, my assumption is that the the EFI module converts the Injector pulses, and pulse widths, into a simple analog signal, that roughly replicated the fuel flow sensor, and the Head unit is calibrated by the user to smooth and refine the differences.
4/ The Head unit wiring incorporates a simple battery backup that retains the calibration in case of power loss.

[bkahler]

Converting the injector signal to replicate the flow meter does make sense and would explain why you don't need any changes in the head unit.

The one thing I didn't like about the flow unit was the ports were 5/16" when 3/8" was really needed. This EFI unit eliminates that issue completely.

[Keyair]

Scanned a copy of the ZT4 Instalation Manual...

Took it apart and tried to get the scanner to do it so it would print as a 2 sided doc... not sure if I was successful, but its all there!

See Attached.

[Keyair]

And the Zemco ZT4 Operation Manual.

See attached.

[Keyair]

Wow, its been strange... the Zemco godfather must be smiling at me!

Picked up a used ZT4 a while back for $20, and it was just the head unit and fuel flow sensor... Figured it might work for an idea I had to watch the fuel consumption of the onboard genset... or dissection or something...

Anyway, with Magnet18 working on duplicating the EFI Module, I figured I would mail it to him to mess with, test or something... but there was no wiring harness or speed sensor, etc. He said cool, he could figure it out.

Then another popped up... used but looked complete.
Made the guy a cheap offer which he accepted.


That is heading your way next week Magnet18.

The surprise was hiding in the box...
An opened, but seemingly unused "P/N 4792 Fuel Return Kit".
Probably means nothing to 99.999% of people... but to me, having seen it mentioned in the install manual, I always wondered what it was, how it worked, and if I needed it...

Drum roll.....