EFI Datsun Z - only runs with throttle slightly pressed

[milligan21]

1976 Datsun / Nissan Fairlady 2.0 EFI

Bought this car a year ago and been steadily working on it. The car came to me running off a fuel canister from the front. It used to run fine off that but obviously I cant drive it round like that. Once I put the pump on the back it didn’t run. And this is where the fun began. Chasing wires, relays, checking fuel pressure etc etc. All done ( for the most part following the EFI Bible )  For the last year I been tapping away at it doing this that etc.
Eventually I got it to run and this is where I am now. It starts and runs as long as I keep my foot down a bit on the throttle and have the TPS disconnected and bypassed . Fuel pressure is good at 36psi and all that. Pressure doesn’t hold but that’s because I don’t have a check valve on the pump and once shut off the pressure instantly drops to 0. I been reading a lot of things over the months and some people have this happen some don’t. Some say that its not needed as the EFI system will bring up the PSI more or less instantly anyways. I swapped out an original pump ( mine is a bosch044) and it holds pressure once shut off at 20psi but it still doesn’t keep running ( again only is the throttle is pressed it will run ) 
In my diagnostics over the year I have checked and swapped the following but still the same issue. AFM for another. Fuel pump relay ( the dual one ) pump as mentioned. Sensors to the front ( temp and thermotime) all with the same result. I checked my fuel lines, checked the AFM for ohms and voltage as per the bible. I went through the no start diagnosis as well as the start and stall diagnosis.  I checked more or less every pin on the ECM / ECU ( again through the bible or field service manual) I also adjusted the  idle screw 5 turns clockwise ( made it cut out quicker on start ) and then counterclockwise ( 5 turns and 10 ) but still the same result. 

So...now... im at a loss. Anyone come across this kind of issue before? Any ideas or help on what I can check next? Its a strange one for sure and I’m stumped 😕 but not defeated hahah 
Just to add.. as the tps is bypassed I assume its the reason when I accelerate that the rpm go up slowly. Or maybe its something else and the root of my issue? Car photo because why not 😄

[milligan21]

Oh also to add... i swapped out the ECU and coils with ones that work ( but don't change how my car is running / not running ) 

[Zed Head]

4 hours ago, milligan21 said:

I also adjusted the  idle screw 5 turns clockwise ( made it cut out quicker on start ) and then counterclockwise ( 5 turns and 10 ) but still the same result. 

Since letting a little more air in through the AFM doesn't increase idle RPM that seems like a sign that you might have a big vacuum leak in the intake system.  The engine needs a lot more air through the AFM to add more fuel.   Unmetered air leaning things out so that the engine can't run.  Do you have all of the PCV hoses properly connected and sealed?  A picture of the engine would tell more than a picture of the car.  Looks like fun.

Also possible that you're not adjusting the correct screw.

[Zed Head]

p.s. once the engine is running things like the coil and relays and fuel pressure become less significant.  Ignition timing is important though.  Have you confirmed that?

[milligan21]

Sorry Zed Head.. should have added that i done a vacuum test and was reading 15 whatever the scale is there 🙂

 

PCV pipe and the thing with the rattle ball in was replaced with new ones. 

I was adjusting the screw on the throttle body NOT the AFM ( Wasnt sure if i should touch the AFM after the calibration frol Atlantic Z)

Ignition timing.... not sure what test that would be? But if you mean the order of the spark plugs...then yes oh 100% yes they are in the right order as I checked and triple checked at this point hahah

I have read a lot of stuff on this site and always see your replys....so thanks for replying and your input. 

Regarding photos of the engine bay I am on  my way back to Italy from Ireland ( where the car is ) and i will see if i have any...if not ill get some taken 🙂

[Zed Head]

2 minutes ago, milligan21 said:

Ignition timing.... not sure what test that would be?

Using a timing light to see that the mark on the damper pulley is correct in relation to the marker on the front cover.  Sometimes timing can be so far off that the engine just won't run right.

This thing...

Picture from here.

 

[milligan21]

Thanks for the link! I will have a read

I was going to check that out but couldn't get my hands on a timing light. It's something to check for sure. 

 

Appreciate it

[milligan21]

Oh I did check that when the engine was at TDC the distributor was pointing at the right plug (1) thats more or less the same thing or no? 

[Zed Head]

No offense, but NO, not even close.  Actually, that is close, the starting point, but not close enough.  You need to finish with a timing light.

Here's a video showing how to set ignition timing.  It's very important.  This one covers the basics without a bunch of fluff.  

 

[milligan21]

Haha close but no cake 🙂 anyway... its all good info and no offence taken at all ...  I am learning so I am happy I got this far. It s enjoyable .. which is the main thing:) 

[milligan21]

But....and here comes a stupid question....  would this cause the issues that I have. Where I have to keep the throttle pressed to keep it running? 

[Zed Head]

I've never had my ignition timing off by much but I do know that when it is advanced idle RPM goes up and when it is reduced idle RPM goes down.  I did have a situation though on my first car where timing was so reduced that the engine would barely run.

Beside that though, ignition timing that is off by a lot can cause engine damage.  Reduced timing can cause overheating and advanced timing can cause detonation.  So it's very important to have it correct.

As far as your specific problem just keep in mind that, generally, the engine will rev as high as it can for the amount of air that is supplied.

A thought that just came to mind is that maybe the AFM vane is stuck or sticky, blocking air flow.  You can pop the black cover off of the side of the AFM and watch the counterweight move as air flow rate changes.  It should move easily.  You can also affect the fuel-air ratio by moving the counterweight which will move the vane.  The farther open the vane the more fuel the ECU supplies.  The cover is easily pried off it is only held on by a tight fit and maybe a few drops of sealant.

And, don't overlook the not uncommon mistake of leaving a rag or paper towel somewhere that it's not supposed to be.