EFI Datsun Z - only runs with throttle slightly pressed

[milligan21]

Just now, Zed Head said:

Does the tachometer needle go to zero while the engine is still running?

If I'm pressing the throttle then no it holds at about 12 - 1400rpm. 

If I try to start it without the throttle pressed then it fires off the csv > dies > and the tach drops at the same time as its almost like its not firing up the AFM control for the pump ( the 76 safety cut off nonsense ) . But.. that all checks out as I checked ...  twice or maybe e times as i thought from start to ok it was cutting the fuel but its not. Obviously pressing the throttle confirms its not that either ( surely );

[Zed Head]

Kind of sounds like the AFM is either disconnected electrically or the vane is stuck or the spring is too tight.  The ECU is not getting the signal to open the injectors for longer periods of time.

Have you tried putting the other AMF on and do you get the exact same results?  Can you see the counterweight move when the engine starts?  It should move when the engine is cranking and even more when the engine starts.

Have you checked the AFM results at the ECU connector?  Do you see the 180 ohms, and the 100?

 

[milligan21]

10 minutes ago, Zed Head said:

Kind of sounds like the AFM is either disconnected electrically or the vane is stuck or the spring is too tight.  The ECU is not getting the signal to open the injectors for longer periods of time.

Have you tried putting the other AMF on and do you get the exact same results?  Can you see the counterweight move when the engine starts?  It should move when the engine is cranking and even more when the engine starts.

Have you checked the AFM results at the ECU connector?  Do you see the 180 ohms, and the 100?

 

Yes i see the vane moving as i have the cover off.

I got the ohm readings and they check out as they say in the EFI Bible which I have been through twice on both the non start issues and crank and die issues. 

 

Everything I tested as per the manual checks out. 

 

The AFM is definitely not disconnected as its operating when I crank and also with the pedal pushed it works 

[milligan21]

Also it cant be too tight as I calibrated it as per the AtlanticZ reset of the AFM. The flap is free moving 

[milligan21]

and also also.. I had a loan of a non molested AFM and another one that I wasnt sure about and NEITHER of them worked .. as in they done the same thing 😄 POX

[Zed Head]

1 hour ago, Zed Head said:

Have you checked the AFM results at the ECU connector?  Do you see the 180 ohms, and the 100?

Still not clear where, exactly, you took your measurements.

 

Maybe you have a bad ECU.

[milligan21]

29 minutes ago, Zed Head said:

Still not clear where, exactly, you took your measurements.

 

Maybe you have a bad ECU.

Where? On the AFM. While connected and also disconnected. Also through the ECU tests. Alllllllll of the tests I done have checked out and are OK. I also done every pin test on the ECU as per the bible & manuals.  When I say I done the tests ... I done them. 

I done some of them twice to make sure the reading voltage or ohms was correct. 

I been through the bible and the wiring and I even tested the dual relay off the car and in the car. I swapped the AFM...the ECU the dual relay ( efi one under the dash left side ) also swapped fuel pumps and thermotime switch , water temperature switch.

I even got a new ignition switch as the one that came with the car was from a skoda so had to change it. 

 

Anyways... that's where I'm at. I have spark , fuel pressure is good and air pressure is also good. It just seems to trip out when the key goes from start to on unless I press the throttle.  Simple no? Haha

[Zed Head]

1 minute ago, milligan21 said:

Also through the ECU tests

This is the most important one.  It shouldn't be an also, it should be the first thing.

Have you checked for injector activation using the lights?  Over here we call them "Noid" lights for some reason.

[milligan21]

8 hours ago, Zed Head said:

This is the most important one.  It shouldn't be an also, it should be the first thing.

Have you checked for injector activation using the lights?  Over here we call them "Noid" lights for some reason.

Yes I checked using a Christmas tree light 

[ckurtz2]

Ok, so I read through this whole forum and it sure seems like you have a disaster on your hands. I myself was in your position a few years ago and it honestly took up to a few months ago to really figure these EFI systems out. They are primitive, annoying, but man once you have toiled enough it's super easy to diagnose and fix. I will do my best here to help you, but often times these problems will just take persistence and time to figure out. Even the smallest hiccup in these systems can make the whole system seem like it is failing.

I am going to assume your spark is good, and from what is sounds like, it is. Anyways. Make sure the distributor rotor is clean, and please please clean the spark plugs, it actually makes a huge difference. While you are chasing this problem continue to clean them regularly, even new ones can foul quick and can cause all types of poor running/misfires.

Don't have the "it's fine" mentality, it will bite you in the arse, it has many times for me.

I am not sure if your tank is rusty or not, but I recommend a clear fuel filter before the fuel pump. It will give that extra assurance that rust isn't ruining your fuel pump, as well as you can physically see how the fuel is moving in the system. 

Now the car runs with the pedal partially pushed. Now from what I have read it doesn't rev, just dies. Now it is possible that it is from running stupid rich, but I count this more than unlikely unless you see black smoke out the tailpipe. Which narrows things down a little bit.

When the pedal is partially pushed, the engine vacuum is more centered on the AFM vane, thus opening the vane more (electrically sending a signal to add more fuel) thus making your engine run, however it sounds like it is running stupid lean if it won't rev/ start on it's own. My advice would to get a buddy to help you and get the car running. Now attempt to rev the car, but when you push the pedal further, and the same time have your friend push the AFM sweeper more (or completely) rich, This will allow the injectors to open more and rev. Another way (I did this, but wouldn't recommend) is to just loosen the AFM till its almost completely loose. This will allow it to significantly richen under throttle, but of course the motor still won't run right. Just kinda hints at the fact that the motor is running lean, injectors work, fuel system is fine, etc, if the engine revs with some help. Then we can do some real diagnosis.

        In my opinion this is what I would do. #1 I know it sucks, but either clean every single electrical connection in the engine bay, or replace it entirely. This may help you in the future for quick disconnecting electrical connections with quick disconnects. #2 do the test I mentioned. #3 I know you said your vacuum seemed fine at 15in/hg (which is low by the way) or so, but I really feel like this is the classic case of the elusive vacuum leak. My motor had your exact symptoms and it turned out to be a series of vacuum leaks. There are a lot of other possibilities, but I want you to focus on these things first. Judging by how old the motor looks, a vacuum leak wouldn't surprise me. 

I am no official mechanic, but I hope this helps. I don't think your issue is going to be anything crazy or out of the box.

[dutchzcarguy]

6 hours ago, ckurtz2 said:

a clear fuel filter

You could use a piece of clear fuel line though.. 😉 

[Patcon]

A clear fuel filter before the fuel pump will be fine. No high pressure at that point in the system