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280z 1976 stalls after startup. Throttle body switch?


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Recently (it's colder now in Holland) I suddenly had my 280z engine stall after startup. This got worse as the weather went colder (I think). My car is not road legal, so I run up and down my driveway, and have it run for some minutes now and then.

 

Startup is no issue, just after running bit, the engine just kills itself. Pressing the accelerator won't help (or just for short). 

What I did:

1. I checked the Control Unit pins according to the 280z fuel injection book. Noting special came out (water temp switch measured around 3,2kOhm, which is sort of right for 5degC I think).

2. I checked the AFM flap, which works. When the engine is about to stall, opening the flap helps a bit, but only for a short while.

3. The cleaned the connectors on the Thermotime switch, and water temp switch. Also the connectors halfway the fuel rail. They all had some corrosion on then.

I figured the car was running too rich and kills itself. Opening AFM flap helps for short time, but then also addition gas is provided, making things worse. Also the sparkplugs show dark deposit suggesting the same richness.

 

While reading other messages on this issue, I thought it might be the thermotime switch, failing to make ground after 8 seconds, causing the startupvalve to permanently dump fuel in the inlet, causing it to be rich all the time. I disconnected the Thermotime switch, no difference. Disconnected the Startupvalve also, no difference. 

So maybe the water temp sensor giving the wrong signal? and overcompensating for low temperature. Therefore I also disconnected this sensor and started up. result was the same. 

 

4. I also checked the air temperature sensor, and measures 4.2kOhm at around 5 degC. Also this is within spec according to EF-52  as it stated for 10 degC 3.25 - 4.15 kOhm and -10 degC  7.6 - 10.8 kOhm

 

I put all the sensors and switches back in, and removed the plug to the Throttle body switch. I started it up and it run like a charm.

 

Even though it is nice, I found something that has effect on the engine not killing out, this obviously is not the solution. 

Does anyone have a clue what is going on and what the action is i should take?

 

I feel by removing the plug, the throttle switch does not send "near idle" and full throttle (which are both Enrichment modes) information to Control unit anymore as it simulates the middle contact not connecting to any, and providing non riched fuel mixture therefore.

image.png.44136ad9a15ee6598b1b5d6016b5a4a2.png

 

 

 

I need help (once this issue is solved, I will also post the solution also).

 

Hope to get a reply,

 

Joost

Edited by Sjoost
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5 hours ago, Sjoost said:

 

1. I checked the Control Unit pins according to the 280z fuel injection book. Noting special came out (water temp switch measured around 3,2kOhm, which is sort of right for 5degC I think).

 

 

Did you check the throttle valve switch pins?  There's a procedure.  Sometimes they do get stuck on full throttle, they get dirty.  That adds 27% extra fuel.

 

image.png.b1a06578ef4074c29ae5adcfaef24a0d.png

image.png.a91bf19093f96411b4558cd8be489c33.png

image.png.6b5ab09b412733e3665061b3b80496c3.png

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Hi NewZed,

 

Yes I did also check whether it was stuck. Which was not the case. And the middle needle makes contact with the idle needle, when the throttle is not touched. So by removing the connection of this throttle valve, there is no signal, which joins the middle with either the " idle"  or the " full enrichment". Both these add extra fuel. So the reason why my engine was running better with the throttle valve connector off, was because the fuel mixture then is leaner (from the fuel graph, (2) is then not there, making overall fuel amount less). 

 

In the mean time i have also removed the startup valve (which is in fact an extra injector). I was suspecting the Thermotime switch to be faulty and not closing this startup valve anymore. Also with the signals to the injector removed, it was still way too rich and killing itself. 

So I was suspecting this valve to leak-open all the time. Removed it (with fuel line still connected), tested it with 12volts, which showed it functioned open/close. Then removed solenoid connection to starter, cranked the engine (making the fuel pump to run, which all worked) so there would be pressure on the valve. Nothing, no leakage. Dropped it in an jar, 12volts on the connectors, and i had a nice spray. So the startup valve is not leaking. 

 

All the sensors seem to be within the resistance range for the temperature, so how come it is too rich?

 

Could it be something with the Control Unit? I read in EF-8, that if the ignition coil, negative terminal has issued to the CU, the mapping is also off.

image.png.23485390b6813cb18af0b4266b65b301.png

But I also tested this 

image.png.02638f58fe1f143bc5ad11e9f6b9082e.png

 

So still without a clue, only that the sum of all fuel portions is too high, making it too rich.

 

Hope to hear some possible leads.

 

Regards,

Joost

 

 

 

 

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15 minutes ago, Sjoost said:

Hi NewZed,

 

Yes I did also check whether it was stuck. Which was not the case. And the middle needle makes contact with the idle needle, when the throttle is not touched. So by removing the connection of this throttle valve, there is no signal, which joins the middle with either the " idle"  or the " full enrichment". Both these add extra fuel. So the reason why my engine was running better with the throttle valve connector off, was because the fuel mixture then is leaner (from the fuel graph, (2) is then not there, making overall fuel amount less). 

 

 

You seem to be saying that the idle circuit is causing the ECU to provide too much fuel.  That the switch tested correctly but when you disconnected it, disabling the idle enrichment, it ran better.  Disconnecting the switch would be like opening the throttle, but without actually opening the throttle.  It might be that something else is causing it to run rich and disconnecting the switch makes things better but is not the true cause.

 

Running very rich is one of the signs of the ECU going bad.  Sometimes people find that it's actually the connections at the plug.  They tap or beat on the side of the ECU or wiggle the cable to the plug and the problem gets better.  The source is broken solder joints at the ECU connection.  Try beating on the side of the ECU and wiggling the cable while it's running.  Nothing should happen, if there's a change that's not right.

 

image.png.8c82d9971fc6b2f34f468c88105b39fd.png

Edited by NewZed
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Indeed NewZed,

 

That was my point, That it is not the throttle valve switch, but something else.

2 minutes ago, NewZed said:

You seem to be saying that the idle circuit is causing the ECU to provide too much fuel.  That the switch tested correctly but when you disconnected it, disabling the idle enrichment, it ran better.  Disconnecting the switch would be like opening the throttle, but without actually opening the throttle.  It might be that something else is causing it to run rich and disconnecting the switch makes things better but is no the true cause.

 

The issue is elsewhere, but this does show that when the CU is fooled, that it is not in " idle" mode (and the mixture is leaner) the motor does not die and runs nice (but higher rpm).

 

I will take out the CU tomorrow, and check it a bit. As testing the cable to the CU gave no issues, it indeed still might be in the CU.

 

Thanks for thinking along.

 

Joost

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7 hours ago, Sjoost said:

1. I checked the Control Unit pins according to the 280z fuel injection book. Noting special came out (water temp switch measured around 3,2kOhm, which is sort of right for 5degC I think).

 

So maybe the water temp sensor giving the wrong signal? and overcompensating for low temperature. Therefore I also disconnected this sensor and started up. result was the same. 

 

There have been discussions about what, exactly, goes bad in the ECU when they do go bad.  The fact that disconnecting the water temperature switch has no effect suggests that that circuit is broken inside the ECU or at the ECU connection.  You got the proper resistance measurement but the ECU did not respond when you disconnected it, suggesting that the ECU didn't "see" it.  It should have had an immediate effect.  If you can get it running, maybe try disconnecting the sensor at the engine while it's running to be sure there's no effect.  If it works correctly it should go super-rich right away as soon as you disconnect it.  Like you're in the Arctic.

 

Good luck.  The simple check is to swap in a spare ECU if you can borrow one.

Edited by NewZed
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I agree to check the ECU. But your point on the water temp sensor I can not follow. Lower temp means higher resistance, meaning ECU gives richer fuel mix. But disconnecting it make it even worse, as the resistance becomes infinite. So as my engine was already rich with the sensor in, disconnecting it should have made it worse. But indeed, this i would not notice, as it was already way rich.

But i have close to rules out all the rest, so ECU might be the one left. This before I would think about changing AFM less rich.

 

One other thing, I changes the fuel pump for an aftermarket one, could it be that the pressure is way to high, causing excessive fuel release when injectors open? I thought the fuel pressure regulator would solve that, but maybe that one is toast?

 

Spare ECU is not easy in Holland. Do they need to be very time period specific?

 

regards,

 

Joost

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1 hour ago, Sjoost said:

But disconnecting it make it even worse, as the resistance becomes infinite. So as my engine was already rich with the sensor in, disconnecting it should have made it worse. But indeed, this i would not notice, as it was already way rich.

But i have close to rules out all the rest, so ECU might be the one left. This before I would think about changing AFM less rich.

 

One other thing, I changes the fuel pump for an aftermarket one, could it be that the pressure is way to high, causing excessive fuel release when injectors open? I thought the fuel pressure regulator would solve that, but maybe that one is toast?

 

Spare ECU is not easy in Holland. Do they need to be very time period specific?

 

 

You said the engine runs but it runs poorly.  Removing the water temperature sensor should make it so rich that it won't run at all.  Different levels - runs well, runs poorly, doesn't run at all.  You should at least hear a difference in the way it runs when you disconnect it.

 

Which aftermarket pump?  Some of them are high volume and might overpower the regulator.  Did the problem occur immediately after changing fuel pumps?  Basic troubleshooting rule is to undo what you just did if a problem appears.

 

I found that any of the 1975 - 1978 ECU's would run my 76 engine.  I had many spares that I had collected and tried them all.  Whatever differences there are must be minor. 

 

I also had one ECU that went bad.  First it just died while I was driving, it restarted a couple of times so I could get closer to home, then, apparently, it also started dumping fuel when I was trying to restart it and wouldn't start again.  I replaced it with one of my spares and everything was back to normal.  I never really figured out what was wrong with it.  I changed a transistor in it and it worked correctly again but I never trusted it enough to leave it in.

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Hi NewZed,

 

I might not have been to clear indeed. I changed out the pump last year, and never had an issue. However it is not street legal, so it is more  only idle running and driving up and down my driveway :-).

 

This issue on the engine dying during idle/warmup, has only recently popped up. One thing which is different, is the outside temperature. Even though I had the impression it always ran rich, I feel now the stack up of all enrichment due to cold weather, at startup/idle, make it stall after the initial start-up. If the Fuel pressure is too high, it will only make it worse if the ECU is indeed correcting for cold weather.

Tomorrow I will start looking at the ECU as I have the impression all signals going into the ECU are accurate.

 

I have ordered an inline fuel pressure gauge, but will take some time before it comes in.

 

What would normal "correct" fuel pressure be?

 

regards,

 

Joost

 

 

 

 

 

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I was reading a related post (trying to sort this issue). While reading I noticed something

-I wrote earlier that i tested the startup valve (if it was leaking/if there was fuel pumping), by removing the starter solenoid and cranking the engine. The fuel pump started to run, and I had fuel at the injectors as I wrote earlier.

BUT, is it not the case that the fuel pump will not start running, UNLESS the AFM flap is triggering the pump due to the revolution the engine is making???? I recall testing the fuel pump by putting a screwdriver in it to keep it open when I installed a new fuel pump a year ago...

 

If that is the case, and my AFM was not opening, but pump was running, there must be a issue with the information the AFM is sending. I will need to revisit the AFM again i think.

 

Would help if someone could confirm my assumption on the AFM flap needed to move for pump to run.

 

Regards,

 

joost

Edited by Sjoost
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  • 2 weeks later...

Hi all,

 

Just update. Installed fuel pressure gauge today, and I had a nice 2.5-2.6 bar. So I am ruling fuel pressure out for now.

I managed to find 1,5 ecu's which I hope to get in soon. I will try those.

Today I cleaned the sparkplugs also. All were dry, but black. I think that is the sign for too rich (but correct me if I am wrong). From the fact that they were all dark, in similar shape, I would also rule out one of the injectores not closing (as the richness would not be to all 6). And I have already inspected and tested the cold start injector. Noting found there.

I noticed my AFM adjustment screw was all the way in (turned right, clockwise). I think that means less air passes. Therefore I turned it out (counterclock) completely.

 

Hope these measures will help, but any suggestion is welcome.

 

Take care!

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Hi ETI2K,

 

Thank for your thoughts. I did operate the AFM flap, and would indeed get changes in the engine sounds.

But eventually I ruled out the AFM as I was of the assumption that my issue was the engine running too rich and stalling. All the EFI sensors seem to work in a way that you can easily adjust it to make it richer, but making it run leaner seems to bit harder.

 

Anyway, I think I did make good progress today. I was changing out some other things so I did not actually run the engine when testing the fuel pressure. After I finalized all those works, today I cranked it and had it running again. Starts right up, with nice 2,5-2,6 bar fuel pressure when I turn the starter to ignition (start). Somehow my starter switch has always functioned very bad, and i really need to put pressure on the key to get the pump running at ignition/start. Well after the ignition, the key turn to ON, and in the past all was fine. But now I noticed fuel pressure completely dropped to 0!. So I now thing there is a issue with my ignition switch (I did already try another ignition relay so feel that is not the issue). All that time, the issue was not that it stalled due to richness, but more to the fact that the fuel supply is cut out...

 

I have had issued before with this ignition switch but thought I fixed them. So now first I need to get the fuel supply to remain running after start.

 

Or is there another system that could cut out the fuel supply at start?

 

Cheers,

 

Joost

 

 

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hhm did some study of FMS and injection manual,

Could also be the pump contacts on AFM or, the throttle switch idle contact not being closed. In both cases, pump will stop running in the "ON' position (safety measures when engine stalls due to crash, fuel pump should stop also).

Well I have some work to do this Christmas. Corona helps keeping you working on your Datsun!

 

Merry Xmas Z lovers.

 

 

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If you are able to start the engine everytime and after it's running it then shuts down, it doesn't seem to indicate a problem with the ignition switch.  Though recalcitrant, it works.

If the fuel supply is cutting out after the switch returns from START to ON, then I'm with @sjoost.  The problem sounds like it's related to a condition needing to be satisfied after start - the condition being a matter of safety.

If you an ammeter, look at the current to the pump compared to time.  When is it on, when is it off.  If it's repeatable, then it is under control, and suggests something is telling the ECU to shut it down. 

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Today's followup,

 

Issue was, that somehow my pump would stop running after START (and a very rich fuel mixture).

I checked the ignition relays. I wanted to check that after START (so in ON position), the relay was working to supply power to the AFM and Pump. I also checked the fuses in that line. All fine.

I screwed back in, the Idle/flap bypass screw on the AFM. So it would force more flow through the main flap. BAM! the pump would not die anymore from START to ON. Apparently the bypass was too big, not closing the pump switch in the AFM (which only happens when the flap is forced a bit open by airflow to the engine). So that is fixed now.

 

However, that still did not fix my suspected RICH running issue and engine stall after running for a bit (its still around 4-6 degC here, and humid). I found 2 alternative ECU's, because I wanted to rule out any issue with those. No change, car still running rich and stalling after while.

 

So finally, I adjusted the AFM flap resistance (obviously marking it's original points). I tightened the flap, so less opening at airflow, making the mixture less rich (as I understood from my research).

Started like a charm, and the engine kept running for a nice time. However, after maybe 10 minutes, and some runway driving, I was feeling misfire, and bit rough idle again. I also thought I heard a electrical discharge /spark sound...

Exhaust fumes, still smelling rich. And again, it would stall (however this was definitely longer than before).

After bit of cooling, engine would run again, but not for long, and only bit rough.

 

Then, while engine was running, I saw some discharge sparks from the Ignition coil center to the - terminal. Figured that could also have been the spark sound I heard earlier.

 

Reading online, and also the Ignition troubleshooting guide, I discovered that the thing I had not checked was the functionality Ignition coil in relating to fuel mixture. As I have now understood, if the ignition coil is bad, this can cause (among others):

1. rich fuel mixture

2. wobbly engine, especially at low rev's and hard accelerations

The Ignition coil influences the frequency of injection (engine RPM).

Also, once the coil could warmup, making things worse. Cooling down would improve the functionality.

 

So I tested the Ballast Resister at the coil. 1.3 Ohm

I tested the Coil alone: 1.8 Ohm

 

What I have seen online that 1.8 Ohm for the ignition coil would be too high (should be around 0.6 Ohm primary winding, and 8.5-12.5 kOhm secondary (I get 13.7kOhm)). It would lead to rich mixture, and misfire I understand. Is my assumption correct?

I am on the lookout for a <=0.6 Ohm ignition coil, but before I buy it, some feedback would help me.

 

Cheers,

 

 

 

 

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