EFI Datsun Z - only runs with throttle slightly pressed

[milligan21]

Thanks again 🙂 Well, I had the AFM open to calibrate it because I thought that was my initial issue. But .... now this is a big but. it probably was not the issue to begin with. 

I am that far in now I lost track of things I changed etc but I think I am close ( hopefully without a rag 😄 ) Next time I am at it I will check the timing for sure. My dad ( mechanic - mostly diesel trucks etc ) moved the distributor cap slightly one way then the other and there wasn't much change really. It was then put back to where it was originally. If it was running ok before we investigated to why it wouldnt run from the fuel pump in the original position then  ( my thinking ) is I messed with the AFM too much. Then I THOUGHT by calibrating it with the weights that it would make it all ok again. 

 

Who knows.... its a mystery 😄 for now

 

[Zed Head]

Try to find the glue blob marks and put it back exactly where it was.  The only reason to adjust the AFM is to fix the last guy's adjustment.

I assume by calibrating with weights you mean the atlanticz procedure?

http://www.atlanticz.ca/zclub/techtips/afm/index.html

[siteunseen]

Will they run without the TPS? I can't remember reading anyone bypassing the switch, too lazy to go downstairs and try. Maybe this weekend...

[siteunseen]

Oh yeah. You said the fuel tank was bypassed when you bought the car. What's the reason if you know? The metal fuel filer up front could be horribly clogged starving it for fuel at higher rpm. Pressurize the system and try pinching the fuel line coming out the top of the filter. It should be really hard to pinch. If it's soft and squishy the filtet is probably clogged.

[Zed Head]

10 hours ago, milligan21 said:

The car came to me running off a fuel canister from the front. It used to run fine off that

 

10 hours ago, milligan21 said:

. 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.

 

38 minutes ago, siteunseen said:

Will they run without the TPS?

That's a good point Cliff.  I glossed over the fact that the TPS was connected before but is not now.  Having the TPS disconnected would be like having the throttle pedal partially open.  No idle enrichment and no full throttle enrichment.  According to the FSM.  Not clear what "bypassed " means though, above.

Another switch that might be disconnected is the AFM plug.  Not uncommon for it to fall off as you're trying to get the AFM plugged in and back in its hole.

Really at this point it would be a good idea to go through the electrical tests in the EFI Guide Book.  Lots of other stuff that could be unplugged and affecting things.  Coolant temperature sensor, for example.

Electrical tests here.  Good practice with the meter.  

Nissan has some weird formatting in the FSM.

 

Edited January 27, 2023 by Zed Head

[milligan21]

13 hours ago, Zed Head said:

Try to find the glue blob marks and put it back exactly where it was.  The only reason to adjust the AFM is to fix the last guy's adjustment.

I assume by calibrating with weights you mean the atlanticz procedure?

http://www.atlanticz.ca/zclub/techtips/afm/index.html

yes that calibration 🙂

[milligan21]

13 hours ago, siteunseen said:

Will they run without the TPS? I can't remember reading anyone bypassing the switch, too lazy to go downstairs and try. Maybe this weekend...

it will run but the revs arent right or its slow when i push the  pedal.. probably from bypassing it? 

Regarding the fuel filter.. never checked it 😮 Could be a possibility for sure but then the pressure gauge still reads at 36 until I shut it off and it drops instantly. I have no idea why the fuel tank was disconnected but when I disconnect the fuel infeed pipe it flows very good into a bottle.. i say very good as I didnt time the flow but as the pressure is up I thought well its normal ( but still the filter might be worth a check ) 

The way I have it now ( and not sure if it is what is making the difference  ) is with the TPS disconnected. I guess that having it disconnected ( and by that I mean that i have a wire running from the WOT to Idle on the connector ) means that it wont give full throttle enrichment. Maybe I will try it with it reconnected. I am not too sure if it will start though but worth a shot for sure. 

AFM is connected for sure. 

I done most if not all the electrical tests in the manuals and all came back fine. By that I mean I tested the ones for injectors, sensors etc etc .. believe me.. i been through them twice at this stage 😄 I didnt write my readings down but they all checked out fine. 

At this point ( when I am back in Ireland ) I will check 1. the timing 2. the fuel filter at the front 3. the TPS reconnected and see what it does if started 

 

Thanks for all the info again.. I came to a roadblock mentally with it. Just remembered . I think that when I had the TPS connected that it didnt run even with my foot down slightly and that is why I disconnected it in the first place. I also adjusted that as per a video I seen on youtube. 

[siteunseen]

This is a good place for those mental roadblocks. These guys sure have helped me. 

[Zed Head]

3 hours ago, milligan21 said:

i have a wire running from the WOT to Idle on the connector

According to the FSM there are three states for the switch.  Idle contact (2) connected to 18, full throttle contact (3) connected to 18, and none of the contacts connected to anything (inside the switch).  There is no state where 2 is connected to 3.  So what you described is an odd thing.

 

[Zed Head]

Your fuel pressure should drop when the engine is running, to somewhere around 30 psi.  If it doesn't it could be because the vacuum hose is disconnected or because intake vacuum is very low.

People have reported problems with rotten EGR passages causing big vacuum leaks.  It's hard to see them because the holes are inside the EGR passages.

[milligan21]

4 hours ago, Zed Head said:

I think that the pressure stays at 36 when running. Pretty sure anyway 😄

The EGR is currently blocked off as the pipe was broken 😞 so.. Cant be leaking is my guess 😄 I only discovered that last week by chance as the pipe was butted up against the broken bit and was hard to spot but it was snapped for sure. 

Regarding the TPS bypass i thought that by connecting a wire between full throttle and idle it would give me neither and therefore bypassing it. I think I seen / read somewhere someone doing that but.. now looking at the diagram above that wouldnt do anything to anything haha I think I am gonna have to go back over that then and see if it makes a difference to anything at all 

 

 

 

 

 

[Zed Head]

6 minutes ago, milligan21 said:

I think that the pressure stays at 36 when running

 

6 minutes ago, milligan21 said:

The EGR is currently blocked off as the pipe was broken 😞 so.. Cant be leaking is my guess

 

6 minutes ago, milligan21 said:

Regarding the TPS bypass i thought that by connecting a wire between full throttle and idle it would give me neither and therefore bypassing it

36 psi while running is not right.

The EGR can leak internally, within the ports on the intake manifold itself.  Even with the a plate on the top.  You'd have to block the bottom hole too to be certain.

You said that you tested the TPS (actually TVS).  Did you test at the ECU connector?  Best to do all tests at the ECU connector as described in the 1980 EFI Book I linked above.

On 1/26/2023 at 6:05 AM, milligan21 said:

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.

Did the fuel canister on the front have a pump that gave proper pressure at the rail?  Not really clear how things were when it ran for you.  Might be that the PO "tuned" the system around a bunch of wrongness and you'll have to undo all of that wrongness.