Ditron 812D D-Jetronic Tester, Searching for instruction Options

[nordfisch]

Hi,
this forum was recommended to me... and this is really a great place for guys like me, interested in the D-Jetronic system.
We have a forum in Germany, German and English language "oldtimer.tips", too.
We are more conservative than you are, mostly just trying to find out everything about the system and how to repair the components. We are hobbyists mostly MB, but also BMW, VW, Opel, Porsche, Renault, Citroen, Lancia... all the car brands D-Jetronic was installed in.
I by myself designed a tool for re-adjusting the trigger points to the original values. Simple to be rebuilded if you have a lathe - I will send you a figure on request.

Now my own request:

Does anyone here own a Ditron 812D tester, too?





I own such a device, but without any instruction.
It once came to Europe with the instruction, but it got lost.
I bought the Ditron some months ago on ebay from switzerland - the seller told me he had bought it many years ago at ebay USA.

It's no problem for me to understand and use the basic testing functions, but this tester is not only a testing - but an ECU-simulating device.

I don't really need the Ditron 812D to diagnose or optimize my car - I own some other testers.
But because the D-Jetronic-system is my hobby, I would like to understand the additional function, i.e. what the manufacturer intended the user to test / adjust with it.

Hope that someone still has the instruction for the tester...
My tester has serial #119 - don't know how many were built at all.

P.B. "Brad" Anders described the tester: D-Jetronic Testers as being similar to the Janbo Model 112 he described more detailed.

Does anyone own the tester / the instruction?

Please help...

Regards
Norbert

[pbanders]

OK, I just went and looked, and like you, I don't have any instruction manual for it. However, it shouldn't be too hard to figure out how it all works. Mind you, what follows below is from my experience with such testers, I have not used it on my car personally. I have a somewhat similar tester from Kent-Moore that has similar features, but it has a guide in the lid (will post pic below), some of my interpretations come from that guide.

Note that the car is assumed to have been run prior to the test and is at operating temperature. This is important for a number of the tests that follow.

My unit is serial number 128.

The first thing to notice is that this tester plugs into the wiring harness, but NOT into the ECU. Many D-Jet testers connect to the system with an interposer, so that they can test both the ECU and the other D-Jetronic components (e.g. VW1218). The Ditron 812D does no ECU testing, and in fact, substitutes for the ECU in some functions.

The unit has a switch on the RH side for 4,6 and 8 cyl operation. This switch determines the injector groups used. The ECU fuel pump control, which is normally 1.5 sec when switched on, then constantly on when the car is running, is replaced by a simple fuel pump switch which toggles the pump on or off.

There are various indicator lights. The early throttle switches (1968-1969) had an idle switch, and there was an additional vacuum-controlled pressure switch. When the throttle is closed, the "THTLE. SW." light should be on, and should go off when the throttle is opened by more than 4 degrees. When more than 1 or 2 inHg of vacuum is present at the pressure switch, the "PRES. SW." indicator should turn off.

The later throttle switches (1970) have an idle switch (THTLE. SW.), and two inter-digitated switches for fuel enrichment (F/E) injection pulses (F/E 1, F/E 2). The throttle is taken from closed to fully open to show the operation of the idle switch, and 10 flashes on each of the F/E lights.

There are also lights that show the starter signal (when the key is turned to the start position), and battery voltage.

There are four knobs on the tester and an analog gauge, as well as a push button. The central knob on the top of the unit has settings for "AIR TEMP. SENSOR", "ENG. TEMP. SENSOR", "TRIGGER POINTS", "FUEL INJECTORS", "PRESS. SENSOR", and "RUN/DWELL". Each of these settings are described as follows.

"AIR TEMP. SENSOR": The air temp sensor is switched in to the meter to indicate its resistance as a function of air temperature. The meter range is marked, and it covers the operating range of air temperatures expected. Readings outside of this range indicate a problem with the sensor.

"ENG. TEMP. SENSOR": The engine temp sensor is switched in to the meter to indicate its resistance as a function of engine temperature. The meter range is marked, and shows ranges for water-cooled engines and air-cooled engines at operating temperature. Readings outside of the associated ranges indicate a problem with the sensor.

"TRIGGER POINTS": The Ditron 812D and the Kent-Moore tester differ in operation with this test. The Kent-Moore tester has a "START" push button that substitutes for the start signal from turning the key to the start position. On the Ditron 812D it is necessary for an assistant to turn the key to start during this test. Depending on the D-Jetronic application (4, 6, or 8 cyl), either 2 or 4 injector groups are used. These injector groups are selected using the top left knob, and turning it to positions I, II, III, or IV. At each of these positions an assistant turns the key while the meter is observed. The reading should switch between "OPEN" and "CLOSED". The dwell is tested later. Note there is also a knob setting for "INJ. FLOW". In this setting, when the "ACT. INJ." push button is pressed, all injectors will be opened and fuel will flow. This setting can be used to verify injector fuel flow and spray pattern.

"FUEL INJECTORS": Operation of this function is unclear to me and will require testing on a car to verify. If this setting is similar to the Kent-Moore tester, it may be a way to determine if each of the injectors flow the same amount of fuel. I cannot comment further until some testing is done.

"PRES. SENSOR": If this function operates as it does with the Kent-Moore tester, then it indicates the response of the manifold pressure sensor over a range of vacuum from 0 inHg to 15 inHg. Disconnect the hose to the manifold pressure sensor and connect the sensor vacuum port to a hand vacuum pump with a gauge calibrated to inHg. At 0 inHg, the meter should be at the far right of the range labeled "PRESSURE SENSOR". Pump the sensor down to 15 inHg, the gauge should move to the far left of the range.

"RUN/DWELL": In this setting the 812D substitutes for both the ECU and the MPS in the operation of the engine. Set the upper right knob to "RUN DWELL", set the "TRIGGER POINTS" knob to I, and detach the hose from the manifold pressure sensor and plug the hose. Set the "MIXTURE CONTROL" knob to mid-range if the engine is still warm, and further to the right (rich) if the engine has cooled off significantly. Turn the "FUEL PUMP" switch to on, and have an assistant turn the key and start the engine, some throttle opening and adjustment to the "MIXTURE CONTROL" knob may be required for best results. In this mode, the dwell of the trigger control points can be measured and compared for each injector group. Turn the "TRIGGER POINTS" knob to each injector group and compare the reading in the "DWELL" zone of the meter, all of the groups should be the same.

That's my best take on how this tester works, it should be easy enough to connect it to a car equipped with D-Jetronic and verify these tests, or figure out what they really do. Experiment always trumps theory, as they say. Let me know what you find out.

My Ditron 812D Tester



My Kent-Moore 112D Tester



Kent-Moore 112D Test Checklist (inside lid of tester)