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injectors issue


raelsmith21

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my 77 280z is not starting and it is because no fuel is reaching the cylinders. The car can be started by using starter fluid in the air intake, but not any other way. when one of the injector connections is taken off and measured for voltage as the engine turns over, 0 volts are measured. Should I be reding voltage here? and if so what should i check first?

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Hmmm They have a cut off switch when the build enough pressure when the car isn't running yet. Is there a leak in any of the lines relasing all the fuel pressure as its trying to build? As for the injectors start with the easy stuff, make sure everything on the harness is grounded. Try the connection at the ecu where the harness plugs into because I had to pull my harness off and clean it once and it solved alot of my issues why my car wasn't running.

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as for the fuel lines i have checked and they are currently leak free, i had issues with that but i replaced the lines. also after the punp runs for a minute the noise it makes begins to change (possibly due to too much pressure in the lines). and i have checked the connection at the ecu and it is clear, and if the grounds were not correct would that mess up the reading from the voltage meter?

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If your car is a 77 280Z, here's how it should work: When the key is in the start position (it's actually cranking over using the starter), power is sent directly to the fuel pump to run it. When you release the key and it is in the run position, power is no longer sent directly to the fuel pump. Instead there is a set of contacts in the Air Flow Meter that must be open to send power to the fuel pump. In this way, power is only sent to the fuel pump if the motor is actually running. It's a saftey feature in case the car is in an accident and the motor stalls but the key is left in the on position. That way the fuel system isn't pressurized and possibly damaged and starts a fire. There is a relay (or three) involved and sometimes they go bad and owners circumvent the saftey feature and directly wire the fuel pump. (not a bright idea) When the car is not running, you should not hear the fuel pump running. If you take the boot off the front side of the AFM and put the ignition switch in the on position, with the engine NOT running, you should be able to stick your finger into the AFM, raise the flap a little and hear the fuel pump kick on.

As far as the injector, get one of those little injector test light thingies, I forget what they call them, I think they call them node lights or something. They are dirt cheap (a couple bucks) go to any auto parts store and tell them what you want. Anyhow, you unplug one injector, plug the test light in the harness where it would have attached to the injector, and crank the car. The little light blinks when it gets an injector pulse. No blink, no pulse. If the injector isn't getting a pulse, most likely the ECU is bad. When the injector is fired, it is actually receiving a ground. It is powered all the time and grounded to pulse it. So it is major important that the wiring harness grounds are attached to a good ground. The fuel injection harness is a whole separate harness from the rest of the car. It has one ground terminal on the intake manifold and I think another on the fire wall. The ECU has it's own positive and negative power wires running to it as well.

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there is also a fusible link for the fuel injection harness coming off the positive terminal of the battery...i think?

I wanted to comment further on this one thing you said. Like I said in my post above, the ECU has it's own positive and negative power feed. They are somewhat larger two wires running along the top of the firewall from the drivers side to the battery. They are not as thick as battery cables but are thicker then most wires in the harness. When the battery cables are replaced during the service life of the car, often a universal type cable is used. Often these universal cables have a second smaller cable coming off the terminal and often on the posititve cable the second smaller cable includes a fusible link. I don't think the car comes stock with this fusible link in that configuration. But since the car needs a second smaller wire (for the ECU harness) that smaller wire is used for this purpose. I think the ECU is fused else where. But if that (non stock) fusable link (attached to the batttery cable) is blown, power will not reach the ECU and no joy.

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ok lets focus for a minute on the injectors, i have checked them and they are recieving power, but when the engine turns over they are not recieving the negative pulse that they should. does this mean that my ecu needs to be replaced or could it mean that the ecu is not properly grounded or is there anything else that could be causing this problem?

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The NOID that “momsZ” is talking about is an ABSOLUTE verification tool. It not only verifies power, (voltage AND current), to the injectors but also the fact that the injector is getting the pulse signal, i.e. power AND ground. It essentially takes the place of the injector itself and gives you a visual indication of what the injector is seeing from the ECU and what it should be doing.

 

Ok. So you are sure absolutely that the injectors are NOT getting their pulse and there is fuel pressure in the fuel rail? (At least 15PSI and the engine will run if the injectors are firing)..

 

1) While cranking, does the tach move, jiggle or do anything at all? It should at least slightly bounce as the engine is cranking indicating cranking speed. That is your first indication that the ECU is getting the RPM trigger from the ECU. If the ECU doesn’t know the engine is cranking, it wont trigger the injectors. (I do recall you saying that the spark plugs are firing as the engine will light off on starter fluid. Then the ECU should be getting this signal).

 

2) You fuel pump continually runs. Hmm.. sounds like the EFI relay has issues, and that very well could also be the reason the ECU is not triggering the injectors, if that indeed is the case.

 

3) Do you have a ’77 wiring diagram? If so, trace out the EFI power supply and grounds on the diagram. Verify that the connections at the ECU connector are getting the power and are grounded. You can by pass the EFI relay/s to run the engine which will let you know if it is a relay issue or ECU issue.

 

As noted before, it is rare when and ECU goes bad. Usually connections and the relay are the most common electrical issues.

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Guest Sleepy-z

Your inectors should measure resistance, but it should still run on 5 cylinders. try wiggling the harness wires, it might be corrosion, my wires going to the injectors are in bad shape and I can kill my car by moving them.

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ok so i have checked the injectors with a light and i am definately not getting a pulse. i am pretty sure that the ecu is properly powered and grounded, but still no pulse. Today i baught another ecu from a junkyard and it still doesnt work. I know the likely hood of 2 ecus being bad is almost impossible. what direction should i look in now?

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If the AFM is bad or even completely missing/unplugged, the ECU will still pulse the injectors, though at the wrong pulse width, they will still pulse. The AFM IS not the reason your injectors are not pulsing.

 

Have you verified that the dropping resistors next the clutch master cylinder are connected?

 

 

Also, you really should verify without doubt that the spark plugs are indeed sparking! Pull a spark plug, lay the plug on the valve cover with the spark plug wire attached, be sure the metal body of the spark plug is touching the valve cover. Try starting the engine. If you see that the spark plug is sparking, continue troubleshooting the EFI. If it does NOT spark, then your "injectors not pulsing" issue is ignition related. If the ECU does not get a spark signal from the ignition, the injectors will NOT pulse at all. The RPM signal is the ONLY signal the ECU uses to trigger the injectors. The base pulse width is derived off the ignition input signal. All the EFI parts and components will have power where they should, but if there is no spark, then there will be NO injector pulse either.

If the tach bounces while cranking, that is “indication” that the ECU should be getting an RPM signal. The Tach uses the same signal as the ECU.

 

In your EFI troubleshooting, you might try swapping out EFI relays. I know this has been covered in this thread already, but haven’t heard if you were able to rule out that as being the issue.

 

 

Keep us posted…

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Ah ha… Now it sounds like we are getting somewhere. If the engine runs on starter fluid, the tach should work as normal and display RPM. If your tach isn’t getting its signal, than more than likely the ECU isn’t getting that RPM trigger signal either. That would definitely cause your ECU not to pulse the injectors. (fingers crossed that we are on the right trail here…)

 

I’m going to go through my wiring diagrams and also go out and look over both of my ’77 parts cars to verify the RPM signal wire routing,(Blue wire), for you to trace and test.

 

Be back in few…

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Okie dokie.

 

In the picture below is what I refer to as the EFI Umbilical cord. This is the connector that contains the wires that communicate between the car and EFI. This connector is under the dash, just to the left of the steering column. The connector is a 6 plug connector, one of the middle ports is empty. The other middle port is the BLUE wire RPM signal.

 

1) White with black stripe is “ignition ON” signal.

2) Black with Yellow stripe is the “start” signal.

3) White with red is battery hot.

4) Green with blue stripe is Fuel pump power.

5) Blue is RPM signal.

 

It is this “blue” wire that we are currently concerned with. On the “car” side of this plug, the wires are colored as listed above. On the EFI side of that plug, the wires are all numbered and green, except for the RPM signal wire which is black and is labeled #1. (There is also a quick drawn schematic of the ignition trigger/RPM signal. Red represents the jumper wire mentioned below.)

 

Unplug this connector and verify continuity between the “blue” wire at this plug on the car side of the connector, and at the negative post on the ignition coil. If there is NO continuity, somehow or another the blue wire was cut, severed, or disconnected some where between the ignition module and the Tach/ECU under the dash. You can use a jumper wire from the negative side of the coil to this blue wire to give the ECU the RPM signal. (make sure your reconnect this plug). That may also get the tach working as well.

 

Let us know what you find.

 

UmbLarge.jpg

 

Wiring.jpg

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