EFI Datsun Z - only runs with throttle slightly pressed

[milligan21]

20 minutes ago, Racer X said:

As mentioned, I have limited experience with the system on the Z, but quite a bit with domestic, and some other import brands.

You commented about the crankcase vent allowing the carbon buildup behind the throttle plate. This is common, I've "fixed" lots of cars for poeple by simply removing the throttle body, cleaning the carbon, and reassembling.

Cost?

My time and some carburetor cleaner.

So it might be something to look at, and insure the idle air bypass is clear too.

 

Regarding the timing.

I would set the engine to number one TDC (the positive stop method is perfect), then ensure the timing mark is at zero. If not, correct it, then set the static timing, start the car and set the timing after warming the engine and attaining a stable idle. 

Also, while looking at the initial timing, have a good look at the damper rubber. When it fails, bits begin to come out. If there is any doubt, replace it.

 

Sound! I have my list for the morning to do 😉 Thanks again

[milligan21]

19 hours ago, milligan21 said:

Sound! I have my list for the morning to do 😉 Thanks again

Well I done and that ..mostly cleaning stuff today. Anyway...  what I did try was .. I disconnected the CSV and cranked it... didn't even fire up. Now I'm thinking that maybe my injectors are blocked?

The reason being is that if I press the throttle it would force more fuel in and pass the injectors and run a bit. That little bit is only a little bit and won't allow more past the injectors hence why it won't revv up. 

This is my thinking because surely it should fire a bit if the injectors were firing. The csv makes it fire differently  .. so what ye think? 😛

[Zed Head]

You should read the Engine Fuel chapter in the FSM so that you understand how things work.

And, for whatever reason, you don't use the advice you get and do something completely different instead.  Nothing wrong with experimenting but people will lose interest if their advice is ignored.  Good luck.

 

Edited March 6, 2023 by Zed Head

[Racer X]

27 minutes ago, milligan21 said:

Well I done and that ..mostly cleaning stuff today. Anyway...  what I did try was .. I disconnected the CSV and cranked it... didn't even fire up. Now I'm thinking that maybe my injectors are blocked?

If your injectors were blocked, it would't run, or it would run very poorly.

27 minutes ago, milligan21 said:

The reason being is that if I press the throttle it would force more fuel in and pass the injectors and run a bit. That little bit is only a little bit and won't allow more past the injectors hence why it won't revv up. 

 

Pressing on the throttle in of itself doesn't directly cause more fuel to be injected. That's why I mentioned earlier about not touching the accelerator pedal when cranking the engine to start it. The system is designed to start without accelerator input, and will automatically provide the correct amount of air and fuel for startup, and provide a slightly higher idle with an enriched mixture for cold starting.

The control module looks at many parameters. engine speed and load, coolant temperature, ignition, then processes the information and sends a signal to the injectors causing them to pulse at a given frequency. The higher the frequency, the more fuel is injected.

I admit I didn't read through the entire thread, but in the recent posts your description of symptoms indicates inadequate air getting into the engine at idle. I've already commented on solutions there.

Now you mention it won't rev up. That might indicate a fuel pump that is failing, and cannot keep up with the fuel system demands. You mentioned that there was a problem with fuel pressure, and that you corrected that.  Have you done a flow test?

 

 

 

[Zed Head]

There's a gauge on the adjustable FPR.  Watch the gauge after you prop open the throttle blade so that the engine will stay running.  Once the engine is running, many things can be learned and understood.  Fuel pressure, ignition timing,  throttle response. vacuum leaks, etc.

[milligan21]

Ok so…

There doesn’t seem to be an air leak as when I done a reading it checked out to be normal or close to what its supposed to be ( I think it was 13 or something )

My CSV idea was just an idea and I wasn’t straying from what you both wrote about. I checked some things like the timing ( as I said already ) at BTDC it was at 20 on the harmonic balancer. I then twisted the distributor by loosening the screw but it made 0 difference.

 

Throttle blade looked relatively clean as I took off the AFM pipe to check.. cleaned it a bit anyway .. but was mostly just black so not gunked up

The main problem is that it wont start without the throttle pressed slightly…

I noticed today that all the gauges move slightly or to where they should be on key turn EXCEPT the water temp gauge ( also noticed my dash lights are out and also my dip / running light – so maybe I have a broken wire or dodgy connection somewhere) was super cold today and the shed isn’t ideal that kinda weather

 

I wasn’t ignoring your advice  far from it.. I was just saying.. would ya look at that 😄 or … this is interesting isn’t it haha

I will try prop the throttle open and get it to run and leave it run if I can tomorrow and then maybe I can shake wires and spray stuff to check for leaks etc etc

I see your point in having a running engine being easier to diagnose 😊

[siteunseen]

Normally efi isn't effected by the gas pedal on start up. Not like a carbed car. I wonder if the light gas peddle push is enough to open the throttle blade allowing more air? I'm not sure how ported/nonported effects starting.

If it had already been talked about you need to try opening the big phillips head bypass screw in front of the dashpot. It's got a spring around the threads.

[milligan21]

"you need to try opening the big phillips head bypass screw in front of "

 

thats been screwed ahahah both ways everyway and no difference 

[milligan21]

Also came back to mind today when I was trying to crank it. When it started ( off the CSV & NO throttle pressed ) the rev counter went up to 1500 approx rpm then it just shuts down. Maybe thats something maybe not 🙂 

[Zed Head]

It's not really clear if the engine starts and will continue to run if you keep your foot on the gas pedal.  Or if it only starts then dies.

If you sit in the driver's seat and hold the gas pedal partly open can you get the engine to start and continue to run?

[milligan21]

8 minutes ago, Zed Head said:

It's not really clear if the engine starts and will continue to run if you keep your foot on the gas pedal.  Or if it only starts then dies.

--- yes I can keep it running if I keep my foot just a touch on the pedal. If I press further down it boggs down / stalls.  If I press down any further than that sweet spot then not only does it cut out but it does not revv up. 

So yes... Once its at that perfect point of pressing the throttle 

[Zed Head]

48 minutes ago, milligan21 said:

Also came back to mind today when I was trying to crank it. When it started ( off the CSV & NO throttle pressed ) the rev counter went up to 1500 approx rpm then it just shuts down. Maybe thats something maybe not 🙂 

Does the tachometer needle go to zero while the engine is still running?  Not clear if you're saying the tach shuts down or the engine shuts down.  " it just shuts down"

You might be noticing that some of us are having a hard time figuring out what you're trying to communicate.

Could be a bad ignition module.  Could be a bad AFM.  Could be clogged fuel injectors.

Edited March 6, 2023 by Zed Head