D-Jetronic

Common Faults: On the older version

Now with the technology in fine micro processing, things look a bit different:

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Common Faults: On the later version

GROUPED INJECTION

Grouped injection is more commonly known as D-Jetronic. D-Jetronic was the first of the Bosch pulsed injection systems. The most recent cars with Bosch D-Jetronic were the 1975 Volvo 164e and the 1975 Mercedes 450. In 1976, both changed to K-Jetronic. It's most interesting to see how L-Jetronic evolved from D-Jetronic. At the 1967 introduction, Bosch called it ECGI, Electronically Controlled Gasoline Injection, contrasting this new electronic system with a long background of mechanically-driven injection pumps. In 1968..69, VW square back's, fast back's and the Kharman Ghia 911E also had this type of injection system. Based on a cross-licensing of the Bendix Electrojector system, which was briefly used in the U.S., D-Jetronic depends on sensing manifold pressure as an indication of engine load.

You can refer to the L-Jetronic section for details concerning most of D-Jetronic.

The major differences are:-
1. Manifold-pressure sensor, senses engine load.
2. Trigger-contacts in the distributor synchronise injection pulses.
3. Injectors are operated in two groups:- ----- 4-cylinder, 2 groups of 2:
VW, Porsche, Saab, Volvo -----
6-cylinder, 2 groups of 3: Mercedes, Volvo -----
8-cylinder, 2 groups of 4: Mercedes.

Although MAP sensors in vehicles have become popular again, due to less malfunctions, it was regarded by Bosch that manifold-pressure sensing was a less accurate measure of load, and measuring air flow as in L-Jetronic, and in K-Jetronic, or measuring air mass as in LH-Jetronic was more accurate.

For certain Bosch racing applications, however, manifold-pressure sensing is sometimes used. Manifold-pressure sensing is widely used by GM, Ford, Chrysler, AMC, and some Toyota’s.
For years after the initial introduction of D-Jetronic, the trend has been away from manifold-pressure sensing. ( But not quite read on below)

Common Faults:
The diaphragm (Metal Disk mainly copper material) in those large manifold pressure sensor splits around the moving channel causing an extremely rich mixture and high fuel consumption.
This is noticeable when it is at its extreme, that the exhaust tailpipe is wet or oily and the oil level in the engine is higher than normal.

A split vacuum hose on the sensor or on the manifold will to the same thing and is cheaper to replace the hose then this sensor.

Now with the technology in fine micro processing, things look a bit different:

MANIFOLD ABSOLUTE PRESSURE OR MAP SENSOR

Conveys information on manifold pressure versus atmospheric pressure.
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A kinked or perished hose, or leak in the hose to the MAP sensor may cause rich running, rough idling and poor performance.
Note: Carbon build up in intake valve area do the same.
Service every car with the INTER-JECT LB-291/2F servicing technique and keep the fuel conditioned with INTER-JECTRON.

FAULT SYMPTOMS:-
Hesitation on acceleration. Poor idle. High fuel consumption. Stalling.

TESTS:- With key on engine off at SEA LEVEL an EEC 4 should show 5 volts. With engine running the voltage will vary from 1 to 5 volts depending on load. May be checked using a tachometer or scope. The MAP sensor readings can be out of calibration due carbon build up on the back of the inlet valves. By using the INTER-JECT servicing equipment, the MAP sensor restores its reading automatically to normal

Common Faults:
An extremely lean mixture, what ever the cause maybe, will load up the Ignition Spark capacity which destroys the Coil pack's Distributor cap, rotor, ignition leads and the next is deadly to your MAP sensor, which is a backfire into the inlet manifold.

The sensing plate pushing onto the crystal will be bend into the negative way into the lean segment. The result is then a hunting engine idle, hesitations, poor idle characteristics.

F O R T H E I M P E R I A L I S T S
Say the engine is idling at 16 inches of mercury or say 8 psi vacuum.
It should have that (minus) - 8 PLUS 40 psi = 32 psi fuel pressure.
When the FPRCSV (FUEL PRESSURE REGULATOR CONTROL SOLENOID VALVE)
is open it will have atmospheric pressure which is 14.7 psi absolute or zero, plus the 40 psi making 40 psi. When the engine is under wide open throttle it will have that reading too because there is no vacuum then either.

F O R T H E M E T R I C I Z E D
Say the engine is idling at 50 kpa absolute pressure.
It should have 50 plus 250 = 300 kpa absolute pressure.
When the FPRCSV (FUEL PRESSURE REGULATOR CONTROL SOLENOID VALVE)
is open, it will have atmospheric pressure which is 100 kpa plus 250 kpa or 300 kpa absolute.
Your gauge probably reads atmospheric pressure as ZERO, so it will read 250 kpa. Below 98 C
at idle your gauge would read 200 kpa or 300 kpa absolute.
Fuel injected cars always have a circulating fuel system. That is, the fuel goes in a circle, up to the injectors and back to the tank all the time the engine is running. This prevents vapour lock.
EXCEPT of course when a hot engine is left standing. In this event the problem soon rectifies itself as cold fuel cycles through the system as soon as the key is turned.

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