Injectors Not Spraying
 

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)."

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.

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

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.

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

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.

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.
http://forums.pelicanparts.com/uploa...1367955235.jpg

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

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.

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.
http://forums.pelicanparts.com/uploa...1367956708.jpg

http://forums.pelicanparts.com/uploa...1367956723.jpg

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.

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.

"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

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

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.

Here are the pin outs and tests for the DME connector.
http://forums.pelicanparts.com/uploa...1367962605.jpg
http://forums.pelicanparts.com/uploa...1367962618.jpg

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?

Behind the pictured ground are three connectors. They are for the speed, reference, and cyl head temp sensors. Did you have these unplugged? Any chance you mixed two of them up? You would not be the first guy this happened to . The speed and ref sensor wires should have markings on them on little tags, make sure they match.

Fastredracing:

Yep I had them disconnected but I was very meticulous about making sure I did not mix them up. I have always had them tagged when I myself replaced all three sensors a year ago. So, I know they are correct.

P.S> That was the very first thing I checked anyway when I suffered the recent no start

This is a good post. Also, I would begin to suspect the reference sensor if you fail to get ground pulses and can find no break in the ground wires. Especially if you get 12 v at all of the injectors.

Rusnak:

I know the reference and the the speed sensors are good because I replaced them months ago and never drove the car. But the car was running fine, that is until I decided to dismantle and do powder coating.

Tomorrow I am going to check the injectors and see if I am getting 12 volts like everyone is telling me before I go to the ground aspect. I am still confused on how to check the ground to the injectors, assuming I have 12 volts

If you are confused on how to do continuity test on the ground, this diagram might help. It shows the volt meter set up to check presence of 12V with ignition ON and ohm meter set up to check the ground wire from the injector to the ECM with ignition OFF.
If still confused, time to get an automotive electrician help.




http://forums.pelicanparts.com/uploa...1367982739.jpg

Lookin at my 87, pull injector connection from injector and it will have a scooped out, half moon, part on one side of the connector. With the scooped out part facing up, the right side should should have 12v+ and the left will be the ground. Take meter, set on volts and put 1 lead in the right side of the injector connector and other lead of meter to a ground, with key, ignition all the way to the right, engine not started. There is a ground on the body behind fuel filter. Try that ground to check for volts. If that works, try the ground on the left intake. To check for ground, set meter to ohms, key off and put one lead in the left side of connector and other to a ground. Use ground behind fuel filter and then the ground on the intake. Provided your ground strap is good from tranny to body. My 87 has 1 ground coming from neg. side of battery to the front fender. Pull the battery and its right there. Ground from battery might be 8 inches long. When I checked the ground, ohms, on injector connection, my meter was around 14k ohms. Hope this helps.

Good point on the 12V power check.

On the injector plug ground wire, we are looking for zero to 1 ohm to verify good wire continuity from the injector plug to the ECM plug (both plugs removed). If the resistance is very high to infinity, there is a break in the wire or connector somewhere in between.

First I want to sincerely thank everyone for pitching in and trying to assist me, but more importantly thanking all of you for the time you took to educate me on the workings of my car. AGAIN THANK YOU!!!

Well, I took everyone's posts to heart and really studied them before going back out to my car at a local storage unit I am renting. Remember, my initial concerns were that my injectors were not spraying and I did not have 12 volts going to the injectors, although i had plenty of fuel going to the fuel rails. You guys spent a lot of time breaking down in a super elementary fashion ways for me to check if I am getting voltage to the injectors as well as if I am getting proper ground at the injectors. And I mean you guys painstakenly broke things down to the level that even a 11 year old could follow. Well having been properly educated by y'all here is what i found:

1. First, pulled the injector plug as y'all instructed and put a voltage meter on the right prong. Surprisingly, I was getting 12 volts on all of the injectors with car turned on.

2. Went to left prong of each injector and was getting ground signal on each injector with car off.

3. As yall instructed I then moved to test all of my ground points. Found the one behind the fuel filter on the drivers side wall of engine and it was properly grounded, as well as the ground strap on the front of the intake manifold (hope that is what it is called---But trust me I found that strap that you guys posted for me). One poster said on his 87 he had a ground point at the negative side of the battery (8 inches long). On my 87 Carerra, 3.2, I could not find that front ground wire.) Me and a friend mechanic looked all over by the battery---could'nt find.

3. Here is where the problems kick in. Although I was getting 12 volts to the injector, they still were not pulsing. I got noid lights as you guys instructed and I and the mechanic put them on the injectors---no pulsing.

4. Went to check for spark. No spark or fire at the distributor.

5. Checked coil. With engine off, got negative on both wires and postiive on both wires when the engine is on (this may be reversed but you get the idea. Power was going to the coil, as well as ground. But coil was not sending pulse to the distributor to cause arc, fire, or spark (one of them is correct). Everything completely dead at distributor. We pulled a spark plug and put it in the ignition wire that goes either from the coil to the distributor or to the coil and nothing (mechanic did this test so I am ignorant here)

5. Sully sent me a diagram of the readout of the DME. I went to the interior of the car and checked the output of the DME (brain) to the coil (Pins 1&19). The brain was sending out a pulse to the coil as the diagram said it should. HOWEVER, the pulse that is sent by the brain is not being read by the coil and then sent to the distributor (hence no spark).

6. Also, using Sully's diagram I checked the read out of the reference and speed sensors and I was right in the correct readout range.

7. I had Specialized repair my ECU once because it was the board controlling the pulsation of the injectors was malfunctioning. I called them and they asked that i send them back the ECU for them to recheck that board. So, I am feeling pretty good about that being addressed. But what has me stumped is why isn't the pulse being sent out by the brain not being read by the coil and distributed to the distributor to create a spark or fire. there is no fire getting to the plugs. Isn't it interesting that I m not getting a ground pulse in either the injectors or the coil. My voltage side is working well, but everywhere I am supposed to get ground pulse it ain't happening
.

WELL, that is where i am at. I hope you see from the above I took everyone's guidance and instructions to heart and really tried to work my way thru this. So, trust me all of your efforts have been paying off. SO DON"T QUIT ON ME YET!!!!

the DME sends ground pulses, not 12v pulses. 12v should be there with the key on, as noted by bazar, and vmax. You might try a noid light while cranking since they are very cheap at O'Reily and the like. You can use either an assistant or a remote starter switch to jumper the starter solenoid to kick out the starter gear. The reason to check ground continuity is to eliminate bad connections. I suspect the reference sensor, so you might check continuity there as well. It's time to ohm the reference and speed sensors.

I would think that the actual signal from the DME (to fire the injectors) really needs to be looked at with an O-scope.....I like to look at the slopes/waveform to check true firing integrity.

Aside, couldn't your coil (or coil wire) be bad? Or did I miss something? (your mention: """5. Sully sent me a diagram of the readout of the DME. I went to the interior of the car and checked the output of the DME (brain) to the coil (Pins 1&19). The brain was sending out a pulse to the coil as the diagram said it should. HOWEVER, the pulse that is sent by the brain is not being read by the coil and then sent to the distributor (hence no spark). """". I assume that means the coil has no output..


Best to your efforts!

Doyle

Rusnak:

In my long diatribe and I apologize about that I said we used a noid light after I saw that I had 12 volts to the injectors. the noid light was let me know there was no pulse at the injectors.

Also, when you say it is time to ohm the reference and speed sensors, isn't that what i did when I located the pins at the DME harness and made sure I was within the appropriate readout provided in the charts in this thread. Did I not check the ohms by doing that

Doyle:

You read correct. the pulse is going to the coil, but there is no output of the pulse from there. There are two wires to the coil. When the car is off they both read negative and when the car is on they both read positive (or vice versa). Doesn't the fact that these wires are reading positive and alternatively negative mean that they are good. What do you mean by a possible bad coil wire---could you direct me?

No apologies necc'y there, I would think, in making use of the noid light. Having 12 volts, it's just like you (and Rusnak) stated: it is a ground-fired circuit topology. Ground continuity through each connection (back to the DME) is quite important.

Best,

Doyle

I assume by your comment: """""5. Sully sent me a diagram of the readout of the DME. I went to the interior of the car and checked the output of the DME (brain) to the coil (Pins 1&19). The brain was sending out a pulse to the coil as the diagram said it should. HOWEVER, the pulse that is sent by the brain is not being read by the coil and then sent to the distributor (hence no spark).""""" that you mean the coil input signal is seen at the primary, yet the secondary has no output (that is, the coil output signal is not there (AT the coil output, that is). One could test the coil's output (and it's associated cable connection TO the distributor) through simple spark testing of the feed wire to Distributor from the coil. Of course, one has to gauge the spark "qualities" (as to health), but you get the drift, I'm sure.

As well, there exists some resistance measurements/specs within the Bentley that will give you a static resistive read of both primary and secondary coil condition. Of course, sometimes, when heat is expended, things change: still, a good check.

Best!

Doyle

Sorry, I missed that. Did you also say that you filed any powercoat off of the DME ground at the intake manifold? You might have a defective DME, but the timing of the failure would suggest not.

"One could test the coil's output (and it's associated cable connection TO the distributor) through simple spark testing of the feed wire to Distributor from the coil. Of course, one has to gauge the spark "qualities" (as to health), but you get the drift, I'm sure."

Doyle:
In my earlier listed points I mentioned that me and the mechanic did the test you reference above.

Rustac:

DId not have to scape powder coat off of the ground point on the intake manifold because there was no coating there. I had good ground there

Yes there are 2 wires to the ignition coil. First wire is the 12V power feed when ignition is ON. Second wire should also read 12V or less due to voltage drop from primary winding of the coil with ignition ON. When you crank the car, if the ECM is good, you will see the pulse on the second wire as 12V and 0V but your voltmeter may or may not be able to display this change depending on the model of your voltmeter. But a scope or graphing type meter will.

I suspect you have a loose speed or reference sensor connector or might have been accidentally switched when you put the intake back together since both the injectors and spark ignition circuit do not work.

Bazaar:

You are correct. When I turned the engine on both wires to the coil read 12 volts.

We connected and reconnected the speed and reference sensors and so they are not loose. Also, I switched the sensors around just to make sure I had not crossed them up. But I know that did not happen because I have the ires labeled so as to prevent this. But, your surmise is on point because I too feel this way given that i am not getting a ground pulse both at the the injectors and spark ignition circuit. this is really perplexing me becuase i have pulse going into the coil from the brain

You are doing great. Having 12V at the coil and injectors are good. If you label the connectors, I believe you did not get them mixed up.

12V feed to ignition coil comes from the ignition switch if I am not mistaken. You confirmed 12V was present.
12V to injectors are fed from the DME relay. You confirmed this too.
12V to ECM is also fed from DME relay. You need to test if ECM is getting power at terminals 18 and 35. If it is not, DME relay is suspect. Do you have a new DME relay?

Bazaar:

You know I never checked the DME relay because since the car was running great before I powder coated I assume that the DME relay was good. But I am a little confused. I thought the relay next to the DME (brain) was the fuel relay and if it was no good your fuel pump would not have power to work. Since my fuel pump is powered and spraying its butt off I assumed that the relay was good. If that relay was not good my fuel pump would not engage, correct? Could that DME relay prevent the spark that I am missing. Here, I am trying to educate myself