76 no start problem

[darom]

The lead path from pin 4 goes to the T300 transistor (C1833 L281) on the 'daughter' card circuit.

Does anybody have a circuit board diagram for a 1976 ECU? Thanks!

[alhbln]

Spend a bit of time with the fuel injection book and found some helpful information:

• The cold start valve is activated by the ignition key in position start, the opening time is then controlled by the thermotime switch (which acts as a variable timer based on the engine temperature) (page 17). If the engine is hot, the thermotime switch does not activate, e.g. you start with the fuel injectors only.
  
• The start signal to pin 4 of the ECU prolongs the opening time of the fuel injectors (page 15), but seems to control nothing else within the ECU
  

So, if the input driver of pin 4 is defective, you should still have standard fuel injector activity. Question, if you start the engine with your current setup, can you measure a voltage on the two connectors of an injector?

Regarding the thermotime switch, could you do a quick test: connect a wire to ground and pin 46 of the cold start valve and try to start the engine. The wire will keep the cold start valve open as long as you run the starter. If the engine now starts, your cold start valve is broken.

[darom]

Adrian, I will run those 2 tests (voltage at CSV and pin 46 ground) tonight after work.

Thanks!

[darom]

Update: no voltage is registered on the CSV connector, neither in the case when 46 is grounded, no voltage shows up on the other CSV plug.

The ECU is definitely fried.

Edited March 2, 2010 by darom

[alhbln]

Not necessarily, the CSV is not controlled by the ECU but the thermotime switch, it just reports its state via line 4 to the ECU. There is no indicator yet that the ECU really has a fault

Trace and check the wire marked red in the attachment, it connects the fuel relay pin 86 to pin 47 (original CSV connector) of the CSV. I bet this connection is broken, so you need to fix it first. If the thermotime switch itself is ok, we we might be quite close to a running engine.

[darom]

Excellent, thanks - I will trace the wire (my 2 fuel inj. relays are out, should be a pretty straight forward operation).

[darom]

Another update:

- Ignition switch's START wire to 86a/76 (ign. relay) -> continuity

- Ign. relay 4/47/86 to ECU's 4 pin -> continuity

- CSV pin 47 to the ign. relay 4/47/86 pin -> continuity

- CSV pin 47 shows 12V when the key is in START (it is alive!)

- When the thermotime switch's 46 pin is grounded -> CSV squirts fuel (I took it out)

Installed the CSV back into the intake, the engine just cranks. I can't hear the injectors clicking at all. Fuel pump runs.

I am guessing the ECU doesn't pulse the injectors on pins 33, 32, 31, 30, 15 and 14. I wish I had a circuit board diagram to see which part of the ECU is managing the injectors. My replacement ECU is going to be here in a few days.

Thanks!

[alhbln]

Good, so the +12V supply for the CSV is ok, and the thermotime switch supplies ground when the engine is cold, correct? Just want to be sure as it sounds like you manually applied ground to the thermotime switch for testing. (In post #16 you mentioned that there is no voltage at the CSV, did you change something?)

With the amount of fuel supplied by the CSV the engine should nearly be able to start, just cranking sounds like there is no spark present.

Quick question, have you pressed the throttle pedal when starting, or did you just turn the starter?

The fuel injectors are triggered by the ECU supplying ground to the injectors when a ignition impulse is registered at pin 1 of the ECU. The length of the opening time (ground supply) then depends on the external sensors such as the throttle switch, air & water temperature and air flow.

1. You need to make sure that the injectors get +12V to the resistor pack via relay terminal 88B. A quick check is to switch on the ignition and then manually provide ground to the ground pin of the injector coming from the ECU (pin 15, 33, 32, 14, 30, 31), you should then hear the injector clicking.

2. Next the ignition should be checked, do you get a spark when starting? Is the wire between coil terminal 1 and the ECU pin 1 ok? You should be able to measure +12V on pin 1 of the ECU if the ignition is switched on to check the coil to ecu wiring.

3. If the voltage supply in 1. is ok, and the ignition does work/ignition signal is available at pin 1 of the ECU, we then need to take a look at the sensors, as a faulty sensor can confuse the ECU enough to not activate the injectors.

The most important sensor for the ECU is the air flow sensor, if the variable resistor in the air flow meter delivers wrong values, the ECU might not trigger the injectors at all.

You can test the air flow meter by measuring the resistance between ECU connector pin 7 and 8, it should vary when you move the flap manually.

The next important sensor is the engine temperature (water temperature in your setup). Measure the resistance of ECU connector pin 13 against ground, you should see around 2000-3000Ω at room temperature.

Air temperature is the third sensor to check, the principle is the same as with the water temperature sensor, measure the resistance between ECU connector pin 6 and 27, you should also see around 2000-3000Ω.

Edited March 3, 2010 by alhbln
added sensor info to 3.

[darom]

Adrian,

I think my thermotime switch is faulty - I will need to run some tests on it per the FSM. I grounded the thermotime pin while cranking the engine. The amount of fuel it sprays should be enough. I was actually afraid to flood it.

Nothing has changed, I was testing the wrong leads back to the cabin for 12V (user error).

There is voltage at the coil and there is continuity between the coil (-) and the ECU's pin 1.

I will run some tests on AFM per the Fuel Inj. book.

Can a bad TPS cause the engine _not_ to start? I removed the intake while changing the studs/gasket - maybe the TPS sensor finally decided to quit? I will re-check its connector settings as well.

Thanks for your help!!!

[alhbln]

If your thermotime switch is faulty, bridging it for continuing the tests is quite ok - just don't forget to exchange it eventually.

There is no real TPS on the 280Z as it seems, you have a an AFS for the air flow (e.g. engine load), and two throttle switches (idle and full throttle). The AFS is important to check (see sensor check in my last post), you might also want to check the two throttle switches while you are at it.

Good luck and looking forward to your test results

[darom]

A few more tests done:

1. I made each injector click when the corresponding pins were grounded (15, 33, 32, 14, 30, 31) and the ignition switch in ON position.

2. There is battery voltage at the coil, and spark at the leading coil wire to the distributor (when held close to ground while cranking the engine)

3. AFM passed all the tests, 9 and 8 pin - 103 Ohm

6 & 8 - 180 Ohm

27 & 6 air temp sensor - 26.8 kOhm

Potentiometer is good with flap door being gradually opened. The voltage went down in incremental steps on pins 8 and 7 (EF-51)

4. Water temp sensor shows 2700-2800 Ohm

I also hooked up the fuel pressure gauge - 37 psi at START.

I appreciate any advice on making the ECU ground the injectors now :-)

Thanks!

[alhbln]

Ok, so we know that the ignition works as expected, the injectors itself are functional and get their +12V supply and the air flow meter is ok.

You have measured the resistance of the sensors at the ECU connector so we know that the wiring itself is ok?

Are you sure about the air temperature sensor having a 26.8 kOhm resistance (that's -22F), or did you mean 2.68 kOhm (that would be ok).

Optional: i would like to make double sure that the coil kickback signal is available at pin 1 of the ECU as the symptoms sound like the ECU does not receive the trigger input. if you have a multimeter with a voltage range up to 400-600 volts, then you can measure ECU pin 1 against battery (+), while starting the multimeter should show peaks up to 400 volts.

Assuming now that all sensors are ok and their resistance/signal is available at the ECUs connector as measured, it is quite likely that there is a defect in the ECU. The possible defects sorted after probability:

1. Defect of the output stage transistor. I would guess that this is the large round TO-3 package transistor mounted at the side of the ECU. What is the number/type printed on the outside of the transistor?

Could you trace the injector output pins (15, 33, 32, 14, 30, 31) on the PCB to which component they lead? Are the output pins internally connected?

The large output stage transistor will have a smaller (probably TO-92 package, half round black plastic) driver transistor in front. This one could also have failed but both are easy to replace.

2. Defect of the incoming signal stage for the coil kickback (pin 1). Please trace the first two or three components after pin 1, it should be a resistor, a capacitor and then a small (TO-92) signal transistor.

3. Defect of the incoming signal stage for the air flow meter pot, air and water temperature. Same procedure as for 2., but we can ignore these for now until we are sure that 1. and 2. are ok.

4. Defect of the internal injector time regulation circuit. Not so likely so we ignore this for now.

If you are ok with delving into the ECUs internals, i am happy to guide you here. If not, a replacement of the ECU has a high probability to fix the issues you have encountered.

Do you have a multimeter which has a "hFE" setting? This setting is for measuring the function and amplification of a transistor. You would also need a decent soldering iron with a fine tip to replace component. A scope would be quite a time saver, so if you can borrow one it will really help

Let me know how you want to proceed.