Zemco Fuel Computers

[bkahler]

Originally Posted by Keyair

Looking good Brad, altho the sensor might need to be closer to the magnets.

No, right on spec. Per the instructions the head of the sensor is supposed to be 5/8" from the drive shaft. The magnets supposedly are 3/8" overall which leaves a gap of 1/8" to the drive shaft.

[Keyair]

Ok, I stand corrected. Seems my memory is failing!

Here is my collection, and I am sure I have a couple more, even tho I sent one or two to Magnet!
4x ZT4’s, and 2x DCS320’s, one of which is the EFI version that I sent the EFI unit to Magnet to copy.


I also have a ZT5, which is similar to the ZT4, but has an LCD display. That’s the one I am installing in my Motorhome

In the non EFI box, there it is.... the installation manual with the EFI installation!

[FrankGRUN]

OK, Rob, time for a bit of a data transfer. I'm enclosing several traces from the Fuel Injector signal from a 1996 Jeep 4.0L. Engine control provides OBDII data and no check engine light is triggered wiring these measurements. Since I didn't think you needed really close profiles of the signal waveform, I'm including scans 10V per division on the y-axis and from 1 to 50 ms. per division on the x-axis. If you need other scales, let me know.

But as always, following data there is more data and a question. After I tapped the Fuel Injector circuit, I add several different 12V LED diode bulbs (contained purpose built drivers) in parallel with the Fuel Injector Solenoid, much as we will be doing with the adapter. All functioned, but the higher output ones triggered the check engine light. Both OBDI (the system delivered with our target injected vehicles) and the current OBDII systems have check engine lights and depending on the triggered code, there may be a response of the engine ECU changing the operating parameters of the engine tune. I think it's important to make certain that the addition of the adapter box have no impact on the PCM operating the injectors.

In my LED experiments, I tried 3 different LEDs all compatible with 12V. The first and most powerful (61 lumens) had a measured DC resistance of 198 K Ohms and drew 39 milliamps when connected to 14.5 V. When connected across the fuel injector, this bulb triggered the check engine light.

The second trial used a multiple SMD LEDs, indicated 9 M Ohm and drew 60 milliamps connected to the 14.5V source. It also triggered the Check Engine Light.

The third LED was a single SMD chip, with embedded driver I could not measure the cross-terminal resistance, only that it was in excess of 25 M Ohms. It drew 14 milliamps connected across 14.5V. This one and several other instrument lights I had on hand did NOT trigger the Check Engine light! I conclude that current draw is the important parameter (less than 0.014 amps and resistance/impedance must be greater than 10 M Ohms.

Hope this helps!

[Magnet18]

Thanks for posting the instructions Steve!

Thanks for the scope traces Frank

Your resistance and current values don't pass the V=IR giggle test, 14.5/198000 should be 73 microamps, 3 orders of magnitude less than your measured current. Reversing it, 14.5/.039= 371 ohms, the actual resistance of your first LED when turned on in situ

LEDs have much higher turn on voltages than normal diodes, so you probably measured it in it's off state as a normal DMM won't turn it on

Your jeep 4.0 injector should be 10.8 ohms minimum. Anything more than 10K resistance should be completely within the noise of the injector resistance measurement (10K would be 1.45mA, and 10K in parallel with 10.8 makes.... 10.79)

[FrankGRUN]

As suggested by Rob, I connected a series of different fixed resistances in parallel with the Jeep fuel injector and looked for the triggering of the check engine light. Started with 47K Ohms and continued through 10K Ohms down to 47 Ohms. None of these triggered the check engine light. I then tested (wired in parallel) a series of LED bulbs that were not polarity sensitive (assume they have imbedded driver circuits) and all triggered the check engine light. I then tested a set of LEDs that consisted of an LED diode and a dropping resistor (package is polarity sensitive) for use at 12V. None of these triggered the check engine light. It appears the issue is in the driver circuit of the more powerful LED's as the 47 Ohm resistor draws more current than any of the LEDs tested.

[Keyair]

This is the Zemco unit I’m planning to install on my Motorhome. I called it a ZT5 but not sure that’s correct. Either way, it’s the only one like it I’ve ever seen.

[FrankGRUN]

I have never seen one like that before. I'm mounting the ZT-3, and I just picked up another old stock NIB unit complete for $20.54, shipped! So now several additional spares. Wish I could find one like yours. Must be one of the very last designs!

[Bgibbs]

It’s been years since I have thought of Zemco. I used to own an auto shop and we actually sold Zemco computers. I installed one on my Jeep Cherokee and it was a fun toy, but actually pretty accurate. I say pretty accurate only because my faith in its accuracy left my family and I stranded between Capulin and Raton, NM in the dead of winter. My wife wanted to stop in Dalhart to get gas, but I insisted that we could make it to Raton with 20 miles to spare according to the trusty Zemco. WRONG! This is one of the most desolate stretches of highway anywhere in the lower 48. We could see Raton as we sat beside the highway, but I was in a bit of a quandary. I didn’t feel it was safe to leave my wife and 3year old son in the car while I went for gas and it was too cold for our son to be in the elements. Luckily, it wasn’t too long before some guys in a stakebed truck came along looking for the driveshaft they had lost the day before. And, they had a full gas can on their truck. MORAL: The wife is almost always right!

[Magnet18]

I recieved notification the boards have shipped!
I've gotten distracted by homework and other projects, so I haven't ordered the BOM yet. I'll try to sit down and do that tonight. I also recently finished dropping the engine into my 86 4runner but haven't turned it over yet, and I'm itching to do that, so no promises.

[FrankGRUN]

The engine for the 4Runner, original or? Fuel injected??

[Keyair]

Confirmed it was called a ZT5!
Here is the box.

[Magnet18]

Originally Posted by FrankGRUN

The engine for the 4Runner, original or? Fuel injected??

Both! They switched to efi in 85

Yes, putting a Zemco in has crossed my mind!

[FrankGRUN]

Just adding the FiTech Street 400 today. I have tapped the fuel injectors in heady anticipation!

[Magnet18]

I haven't forgotten about this! Currently digging my way through a couple other piles of work (literally, physical piles of paper)

In the meantime, the circuit boards came in!

[Magnet18]

Aforementioned circuit boards

[bkahler]

Originally Posted by Magnet18

I haven't forgotten about this! Currently digging my way through a couple other piles of work (literally, physical piles of paper)

In the meantime, the circuit boards came in!

I haven't either but I've also not had a chance to continue working on the installation. I'm not giving up and with luck I'll still be ready when you are....

Brad

[FrankGRUN]

I just finished installing the FiTech EFI system and wiring up the Zemco ZT-3. I built it on to the nominal center dash speaker port and it fits cleanly. The tapping of the fuel injector wires on injector #4 went very cleanly using the pin type piercing taps. I wrapped the conductor pair coming from the injector in a copper foil tape with conductive adhesive to shield the cable on to the Zemco wiring cluster in anticipation of the rapidly evolving boards! Fingers are getting less useful for fine work ... must be the miles!

[Magnet18]

Still not forgotten!
Now that it's light later I find myself going days at a time without sitting down at the computer

Hopefully some crappy weather later this week coupled with the fact that I'm not weeks behind in school will give me an afternoon sitting inside to work on this

[Magnet18]

Mkay, my current class wraps up Saturday, this is in my sights for Sunday

[Magnet18]

Sorry for the delays, life and stuff

Finally sat down and made a BOM this morning and ordered the parts!

I ordered enough parts for all the boards (parts are like $5.00/board)

When they arrive I will build a prototype and test it on the bench, and build up the other two and mail them out (Brad and Frank still willing to test?)

I've also attached the BOM for those following along. It won't let me upload a .csv, but the .txt is a .csv file