1973 Porsche 1.7 D-Jet, No power to two injectors Options

[crodog]

I have power to #3 and #4 injectors but not #1 and #2. The car will run but it is missing on 1 & 2. I have spark but when I pull the wires off the injectors nothing happens. After testing more I found I have no power to both of them. Where does the power come from? Do I need to look at the releasing contacts at the base of the distributor?

[larss]

No1 and 2 have a common spade connector fort earth on top of the case not far from the plenum...right side...at the back.
If that connector comes loose you will have no pulsing in no1 and 2.
Power to the injectors comes from the ECU but there is no constant power just pulses about 4-5 Volts DC.
No I would not look into the trigger contacts in the dizzy since those contacts controls no1/4 and 2/3 respectively.

/Lars S

[crodog]

Thx for the info. I will hunt down the grounds. Maybe my way of checking for that was not so good. I used an Ohms meter and removed the plug from the injector, put one lead into the plug and the other to a good ground. I got 0 when I touched the lead to a good ground. Maybe this is not a good test for that.

[larss]

Thx for the info. I will hunt down the grounds. Maybe my way of checking for that was not so good. I used an Ohms meter and removed the plug from the injector, put one lead into the plug and the other to a good ground. I got 0 when I touched the lead to a good ground. Maybe this is not a good test for that.

Well not so bad test! You should get 0 ohms (or close to yo 0) on one of the two terminals in each plug meaning that the ground is OK.

/Lars S

[CatDaddy60]

I agree that most likely it is a ground issue as this happened to me years ago. You can check the function of the contacts of the distributor with your ohm meter by touching the center pin and one of the outer pins by rotating the distributor you will see the contacts open and close. The other pin controls the other two.

[Dave_Darling]

Power to the injectors comes from the ECU. The trigger points in the base of the distributor tell the ECU when to send power to the injectors. They do that in two "batches", but those are #1/#3, and #2/#4. They are diagonally across the engine from each other, not on the same side.

If the trigger points are to blame, something is funky with your wiring.

I would start by re-checking that you are actually getting pulses of power to those two injectors while the engine is cranking over. If not, then I would suspect the wiring.

--DD

[crodog]

Power to the injectors comes from the ECU. The trigger points in the base of the distributor tell the ECU when to send power to the injectors. They do that in two "batches", but those are #1/#3, and #2/#4. They are diagonally across the engine from each other, not on the same side.

If the trigger points are to blame, something is funky with your wiring.

I would start by re-checking that you are actually getting pulses of power to those two injectors while the engine is cranking over. If not, then I would suspect the wiring.

--DD

How do I go about checking for pulses at the injectors? With a test light?

[bdstone914]

Power to the injectors comes from the ECU. The trigger points in the base of the distributor tell the ECU when to send power to the injectors. They do that in two "batches", but those are #1/#3, and #2/#4. They are diagonally across the engine from each other, not on the same side.

If the trigger points are to blame, something is funky with your wiring.

I would start by re-checking that you are actually getting pulses of power to those two injectors while the engine is cranking over. If not, then I would suspect the wiring.

--DD

How do I go about checking for pulses at the injectors? With a test light?

Get a set of Noid lights. They plug into the connector and will flash when sent a signal. Do check the injector grounds first. No ground no signal.

[larss]

Power to the injectors comes from the ECU. The trigger points in the base of the distributor tell the ECU when to send power to the injectors. They do that in two "batches", but those are #1/#3, and #2/#4. They are diagonally across the engine from each other, not on the same side.
.......

--DD

Dave,
Not sure here bud looking at the electronic diagram below it seems like terminal 3 and 4 (upper right corner) in the ECU share the same output transistor.
Terminal 3 and 4 should be for injectors 1 and 4 respectively (see öower wiring diagram) and if I am right in this they are forced to fire simultaneously.


Lars S


(IMG:http://www.914world.com/bbs2/uploads_offsite/www.pelicanparts.com-10787-1493614597.1.jpg)


(IMG:http://www.914world.com/bbs2/uploads_offsite/www.pelicanparts.com-10787-1493614598.2.jpg)

[JeffBowlsby]

Actually the injector groups as the ECU see them are:
1&4, 2&3, diagonally across the engine. Their shared transistor would only see a 1 fuel injector load at a time when one of them fires as controlled by the trigger points, making most efficient use of that transistor, but the ECUs rarely are a problem.

Injector pairs 1&2 and 3&4 share a common ground.

So depending on which pairs of injectors goes down, suggests a look at either the grounds or trigger points.

[larss]

Actually the injector groups as the ECU see them are:
1&4, 2&3, diagonally across the engine. Their shared transistor would only see a 1 fuel injector load at a time when one of them fires as controlled by the trigger points, making most efficient use of that transistor, but the ECUs rarely are a problem.
.....

Just curious how that could work since each injector in a pair is electrically tied to the other (only a 6 ohm resistor divides them)? I can not see the triggers, as how they are connected to the circuit, being able to divide the signal to reach just one of the injectors in a pair.

My theory is that both injectors in a pair are activated at the same time and this is not optimal since they not ignite at the same time - a compromise. They have chosen the pair 1-4 and not 1-3 since 1-4 are closer in the fireing order (1-4-3-2) making it a better compromise.

Pls correct me if Im wrong!

/Lars S

[JeffBowlsby]

I could be wrong, its been years since I read these but for the theory and how these things work, see here:

http://bowlsby.net/914/Classic/zTN_Man04.pdf

http://bowlsby.net/914/Classic/zTN_Man06.pdf

http://bowlsby.net/914/Classic/zTN_Man14.pdf

http://bowlsby.net/914/Classic/zTN_Man16.pdf

[larss]

Below from the Robert Bosch 914 D-jet manual.
The injector pairs fires at the wery same time and the pairs are 1-4 and 2-3.

/Lars S

(IMG:http://www.914world.com/bbs2/uploads_offsite/www.lsmteknik.se-10787-1493648486.1.jpg)

[Dave_Darling]

Yes, the injectors are opened in two batches. I had the cylinder numbers wrong, but the idea correct--the pairs are diagonally across the engine from each other. If the injectors on one side of the engine aren't opening, then the major suspect is the ground part of the circuit, not the power side. (Or, on the 1/2 side, suspect debris in the fuel clogging up the injectors--those tend to clog up first as they are closer to the pump.)

Verify that the injectors are getting power when the starter is cranking. A test light probably will work for that. Check all four injectors so you can compare the injectors that aren't working to those that are.

--DD

[larss]

Agree Dave, I just used a cheap test lamp with LEDs for the same purpose, worked great!

Lars S