Injectors Not Spraying

[Srwilliams]

Okay in fault checking my no-start issue I have traced it down to my injectors not spraying. I have new injectors. Also I have fuel going to the injector rails. None of the injectors however are spraying letting me know that I have no power going to the injector rails. I have being doing my forum SEARCH as required and found the below post. Can you guys break the below down further (more elementary) so i can follow its lead to find out why I have no power going to the injectors. Any further suggestions will be greatly appreciated.

"It should be easy to test the wiring. All 6 injectors fire from a common signal. One place that is suspect is the connector on the rear firewall. A large connector that can get loose/dirty/-disconnected? The Bentley manual has a test to ground one pin of the ecu connector - 14 or 15 iirc - while ignition is on and the injectors should click/fire. If they do then the wiring is good. If not, then when the ignition is on, one side of the injector plug should read 12V. The other side should have continuity to pin 14/15 of the ecu connector (ignition off)."

[Targalid]

It will help if you reveal what year car you have, fuel system you are diagnosing, what you have done so far, etc.

[Srwilliams]

Originally Posted by Targalid

It will help if you reveal what year car you have, fuel system you are diagnosing, what you have done so far, etc.

Sorry, I have a 87 911 Carrera, 3.2 liter engine.

I have no power going to the injectors in that they are not spraying. I checked the big plug on the back firewall as suggested and it is connected. I have good ground at the ground strap. Made sure my reference and speed sensors are not mixed up. Also, I have 12volt at the coil when the engine is turned on. Fuel is being pumped to the fuel rails and so my fuel pump is working. But still no power to injectors because they are not being commanded to spray.

I have no idea what has caused this because I did not have this problem before taking the top part of my engine a part to customize. Everything was running fine before I dismantled the top part.

On another note my research tells me that there is supposed to be a ground point at the battery in the front trunk area. But I cannot see it. On my negative battery cable there is no separate ground wire, although I do see a black wire bundles with the wires on my positive post.

Any suggestions would be greatly appreciated.

[pete3799]

Originally Posted by Srwilliams

I have no idea what has caused this because I did not have this problem before taking the top part of my engine a part to customize. Everything was running fine before I dismantled the top part.

What exactly did you "customize"?

[Srwilliams]

Originally Posted by pete3799

What exactly did you "customize"?

Had my engine cover painted as well as the valve covers. Had other parts powder coated. All cosmetic stuff. the entire engine remains stock. All I did was powder coat paices like the fan, shroud, etc

[bazar01]

Originally Posted by Srwilliams

"It should be easy to test the wiring. All 6 injectors fire from a common signal. One place that is suspect is the connector on the rear firewall. A large connector that can get loose/dirty/-disconnected? The Bentley manual has a test to ground one pin of the ecu connector - 14 or 15 iirc - while ignition is on and the injectors should click/fire. If they do then the wiring is good. If not, then when the ignition is on, one side of the injector plug should read 12V. The other side should have continuity to pin 14/15 of the ecu connector (ignition off)."

The above means that all six injectors are fired all at the same time by the DME computer providing the ground path for all 6 injectors provided all 6 injectors have 12V power on one pin of the plug with ignition ON.

To test the injector, you must pull one of the injector plugs, turn ignition ON, (do not start) and probe the pin with a multimeter. One pin should have 12V with ignition switch ON.

If you don't get the 12V power to injector plug to begin with it will not fire even if your DME is good. Then you need to find out why it is not getting 12V to the injector plugs.

But if you have 12V to the injector plug, then you need to test the ground path from the injector plug's other pin. You need to check continuity of the ground wire from the injector plug to the firewall connector and from the firewall connector to the DME.

Good luck.

[HawgRyder]

If you had a lot of things powder coated...be advised...you may have lifted the ground for the injectors!!
I'm not sure where the individual injectors are grounded...but...if it was running before the powder coating...and is not afterwards...then by logic...the coating IS the problem!
Bob

[SchnellSchweitz]

Do you have noid lights? You can get a set for around $40 from Harbor "Fright". These can help you trace the issue. Without them you'll be looking for a needle in the haystack in the dark.

[E Sully]

The ground point for it is the wires connected to the intake runner. Yellow circle in picture, under blower motor. This ground is carried to the chassis through the ground strap on the transmission. The DME supplies 12V to the injector when the engine is running. By switching the ground connection the DME pulses the injectors to deliver the correct amount of fuel.

[Srwilliams]

Originally Posted by bazar01

The above means that all six injectors are fired all at the same time by the DME computer providing the ground path for all 6 injectors provided all 6 injectors have 12V power on one pin of the plug with ignition ON.

To test the injector, you must pull one of the injector plugs, turn ignition ON, (do not start) and probe the pin with a multimeter. One pin should have 12V with ignition switch ON.

If you don't get the 12V power to injector plug to begin with it will not fire even if your DME is good. Then you need to find out why it is not getting 12V to the injector plugs.

But if you have 12V to the injector plug, then you need to test the ground path from the injector plug's other pin. You need to check continuity of the ground wire from the injector plug to the firewall connector and from the firewall connector to the DME.

Good luck.

Bob:

I believe the connector plug is the big square plug in the back of the engine wall, on the drivers side, correct?

Will I be able to detect the ground wire from the injector plug to the firewall as you suggest. Will that be readily apparent to me?


Also, my other fellow poster stated I need to check the grounds for the injectors given the powder coating I have done. Where would that ground point be for the injectors. Because it is correct that everything was running fine until I had the powder coating done and tried to reassemble

[bazar01]

Originally Posted by SchnellSchweitz

Do you have noid lights? You can get a set for around $40 from Harbor Fright. These can help you trace the issue. Without them you'll be looking for a needle in haystack in the dark.

I agree with you on using a noid light as a quick way to find out if the injectors are firing.

But after finding they do not fire, he still has to find out why they are not firing. So he will still end up doing the test I suggested above. If he already has a multimeter, he can easily test for 12V power and perform ground circuit continuity test at the injector plug level. A noid light will not do that.

[E Sully]

Pins 14 and 15 are the ground wires, one to each set of injectors, switched by the DME. Power is supplied to the 2 injector banks when key is on. You should get voltage from the Red wire at the chassis side of the big square connector by the shock tower to the engine ground point with the key on. You will not get a ground reading on the injecor plug when the engine is not running. The DME breaks that connection till it is running.

[bazar01]

Originally Posted by Srwilliams

Bob:

Also, my other fellow poster stated I need to check the grounds for the injectors given the powder coating I have done. Where would that ground point be for the injectors. Because it is correct that everything was running fine until I had the powder coating done and tried to reassemble

You have to keep in mind that the injectors are not directly grounded. They are grounded by the DME computer internal circuitry. That grounding point in the picture is for other electrical components in the intake manifold that need +12V and a ground to work.

check first for 12V at the plug then move to the ground circuit as I mentioned above testing the 2 pins on the injector plug.

[E Sully]

If you powder coated the intake runner, then that could cause the problem. You need to strip the connection I showed circled in yellow to allow the wires to contact bare metal.

[Srwilliams]

"check first for 12V at the plug then move to the ground circuit as I mentioned above testing the 2 pins on the injector plug."

Bazaar:

I am going to do as you say, but you loose me when you say move to the ground circuit. I can test for the 12 volts at the plug, but where do I find the ground circuit you reference. Remember I am a novice and so you really have to give me an elemantary vision

[HawgRyder]

Logic...if something goes wrong...always look to the thing you did last.
In the electronics industry...when you replace a component...and all of a sudden the equipment stops doing what it is supposed to do...it's a no brainer.
Many an hour has been spent running around the bush looking for other problems...when all the time it was the last thing YOU did!
Don't worry...it's not the last mistake you will make...but learn from all mistakes...and become a person we can all look to for help.
Bob

[bazar01]

Originally Posted by Srwilliams

"check first for 12V at the plug then move to the ground circuit as I mentioned above testing the 2 pins on the injector plug."

Bazaar:

I am going to do as you say, but you loose me when you say move to the ground circuit. I can test for the 12 volts at the plug, but where do I find the ground circuit you reference. Remember I am a novice and so you really have to give me an elemantary vision

If you pull one injector plug, you will see two pin connectors. One pin must have 12V with ignition ON. Put one probe of the multimeter on one pin and the other probe to ground, you should have 12V.
The other pin goes to the DME. How many connection points in the firewall? I do not know and I do not know where. According to E.Sully's diagram, the grounding pin goes to the DME pins 14 and 15 depending on which bank.

To test ground circuit continuity, set your meter to continuity, then you need to put one meter probe to the other pin on the plug for cyl #1 and the other meter probe on pin # 14 of the DME plug (Ignition OFF). If it beeps, you have connection. If it does not beep, you have a break in the connection somewhere maybe on the firewall plug, who knows. You have to find out.

[E Sully]

Here are the pin outs and tests for the DME connector.

[Srwilliams]

Sully:

I sent you a message asking for how to check if 12 volts is going into the ECU and if 12 volts is being distributed from the ECU to the back of the car. The printout you provided above is what I needed and I will begin to test from there

[bazar01]

Originally Posted by Srwilliams

Sully:

I sent you a message asking for how to check if 12 volts is going into the ECU and if 12 volts is being distributed from the ECU to the back of the car. The printout you provided above is what I needed and I will begin to test from there

12V is not coming from the DME (ECU). 12V must be coming from the DME relay pin 87.

Do you have 12V or do you have missing ground circuit from the injector plug?