Injectors not pulsing.

[Carter2350]

Hello, friends.

I am having a similar problem to a few ive seen on these forums but am having a lot of difficulties starting this 1987 924s that has been sitting for many years.

The injectors are not getting the signal to pulse. They have 12v power to both ends. but do not pulse. Here is a little information.

New injectors (tested good)
tach bounces when cranking
DME relay tested good (fuel pump works and bench tested ohms)
12v to each side of injector connector

I am doing my best to problem solve this issue here are some questions I am having difficutly finding answers too.

What tells the DME that the car is now cranking and ready to start? Could this message not be getting to the ecu?

The car is one owner and only has 17k miles if that influences anyone response on what to do. he was an old man tho and does not remember any work that he has done on the car (of course i have already gone through the timing components)

[kdjones2000]

You will probably get a better response if you post in the 944 (NA) forum. This one is a 944 Turbo specific one, which doesn't see the same traffic.

To briefly answer your question, DME relay goes through and tells the computer to start. If you jumped it out and still not good, then you are looking at a new DME computer, or a rebuild.

Cheers, Keith

[uathanna67]

The crank position sensor provides the DME (Digital Motor Electronics) with information about the engine's position and speed. If this sensor is malfunctioning or not sending the correct signals, it could prevent the DME from pulsing the injectors. Check the crank position sensor's wiring and connections, and consider testing or replacing the sensor if necessary. Check the connections between the ECU (Engine Control Unit) and other relevant components. Loose or corroded connections could lead to communication issues between different parts of the system. screen mirroring

[nize]

moving this thread to the N/A forum.

[walfreyydo]

Originally Posted by uathanna67

The crank position sensor provides the DME (Digital Motor Electronics) with information about the engine's position and speed. If this sensor is malfunctioning or not sending the correct signals, it could prevent the DME from pulsing the injectors. Check the crank position sensor's wiring and connections, and consider testing or replacing the sensor if necessary. Check the connections between the ECU (Engine Control Unit) and other relevant components. Loose or corroded connections could lead to communication issues between different parts of the system.

More on the above here (and I recommend OP reads through clarks garage) - Also check the section about engine cranking/running signals:
Troubleshooting Fuel Supply Problems

For the fuel pump to start and remain running, for the ignition coil to develop secondary voltage, and for the injectors to fire, the DME computer must see an engine start signal or an engine running signal (greater than 200 RPM). When it does, it completes the circuit for the Fuel Pump / DME Relay secondary coil and the fuel pump starts. It also provides a ground or current flow path for the ignition coil primary and secondary coils. As a result, the current flow through the primary coil induces a voltage in the secondary coil. The voltage across the secondary coil is what is seen at the distributor. The engine cranking / running signal also goes to the injector drivers (2) which provide a ground or current flow path for the fuel injectors to open. The injectors are batch fired which means that all four injectors are fired together. On 944s, injectors 1 and 2 are wired together and injectors 3 and 4 are wired together. However, they are all powered from one injector driver inside the DME computer.
The engine start signal is normally generated by a combination of voltage from the ignition switch to the starter solenoid and a signal from the reference sensor. However, if the starter solenoid signal is not present, an engine cranking signal can be generated by the combination of the speed sensor and reference sensor signals.

"Other related fuel problems - see Injector Firing Signal not Present" - ie: speed/reference sensors