HELP---Strange Engine Noise is very puzzling

[raythomas]

9 hours ago, 1001001SOS said:

Check out this thread, had some good things to check (clutch safety switch and battery terminal jankiness):

https://www.nissanforums.com/threads/hot-no-start-problem-on-86-5.168820/

 

Regarding getting 35mpg, how accurate is your speedo? Tire size?

 

 

I read that. Never knew a fuseable link could do such a thing. 

Thanks

Ray

[1001001SOS]

3 hours ago, raythomas said:

 

 

I read that. Never knew a fuseable link could do such a thing. 

Thanks

Ray

I was honestly more interested in the clutch switch, it sounded like the guy messed with it and the fusible link at the same time. Made a lot of sense and is really easy to bypass to see what happens.

[raythomas]

57 minutes ago, 1001001SOS said:

I was honestly more interested in the clutch switch, it sounded like the guy messed with it and the fusible link at the same time. Made a lot of sense and is really easy to bypass to see what happens.

 

So if the clutch switch is bad, the engine won't fire while starting?

Ray

[raythomas]

Also, how would the engine being warm or hot have anything to do with the clutch switch?  It's mounted in the cab away from the engine heat. Don't think its neutral safety switch either, if it was the truck would have issues cranking cold as much as when hot. This only seems to happen when truck has been driven already and has warmed up.  To the best of you fellows knowledge, is there anything that might turn off, or disengage or fail when heated under the hood that would prevent fuel flow or spark? Fuseable links do that? Wig out when hot? Couldn't be coils failing when warm cause it has 2, what are the odds that both quit at the same time and then start again later?

Ray

[1001001SOS]

22 minutes ago, raythomas said:

 

So if the clutch switch is bad, the engine won't fire while starting?

Ray

Oh yep youre right, was mixing up symptoms.

[datzenmike]

Test for spark when hot and won't start.

 

IF... no spark when hot, could be the ignition module in the distributor that fires the coils.

 

There may be a clutch interlock switch that prevents starting in gear and/or neutral transmission switch. Try starting in neutral.

[Stoffregen Motorsports]

If it won't start unless you floor the pedal, it's running too rich. Unfortunately, that knowledge only tells you that there's a problem.

[raythomas]

7 hours ago, datzenmike said:

Test for spark when hot and won't start.

 

IF... no spark when hot, could be the ignition module in the distributor that fires the coils.

 

There may be a clutch interlock switch that prevents starting in gear and/or neutral transmission switch. Try starting in neutral.

 

I'll have to check for spark when hot. Don't think neutral switch is problem. It will always "turn over" when hot, just doesn't seem to want to fire up. 

Ignition module, is that the same thing some were calling the crankshaft sensor?

Thanks

Ray

[datzenmike]

Yeah... no. Sorry was thinking 720 Z24i. I think the spark signal to the coils is sent by the EFI's ECU.

[raythomas]

New info----- Worked on truck after work. Run it until it was fully warmed up. Killed it and it didn't want to start back. 
Checked spark, and it HAS spark. Looked down inside top of TB and couldn't  see if any fuel was spraying out of injectors when it was being turned over trying

to restart. I poured a tiny amount of gas down TB and tried to start. Had to hold throttle to the floor and then it started. I check fuel pressure regulator to see if the diaphragm held pressure or had fuel seeping past it. It was not seeping and held vacuum according to the gauge. Anybody got any other ideas on what to check now?

Thanks
Ray

Edited September 30, 2023 by raythomas

[raythomas]

Could this have anything to do with the engine temp sensor? Not the sensor in the intake that goes to the temp gauge in the dash. The one that goes to the ECU.

Ray

[Stoffregen Motorsports]

Have you checked the fuel pressure? How about fuel flow. Remove the schrader valve when cranking and see if fuel pumps out. Be sure to have a fire extinguisher handy...

[raythomas]

12 minutes ago, Stoffregen Motorsports said:

" the schrader valve "

 

Does an 87 D21 with a Z24 TBI engine have one of these? Where is it located?

Thanks

Ray

[raythomas]

Thought it might help if I included a picture from the manual and put a red "X" on the things this truck "DOESN'T" have on it anymore. Hope it give you fellows a tiny bit of insite on your diagnosis.

Thanks
Ray

Edited September 30, 2023 by raythomas

[datzenmike]

How does this even run like that?

[Stoffregen Motorsports]

I don't know if it has a schrader valve or not. If it does, it will probably have a black plastic capo covering it. If it does not have the valve, you can simply crack a fuel fitting to see if it has pressure while cranking. Again, be careful. Fuel will spray out. Wear goggles or face shield.

[raythomas]

1 hour ago, datzenmike said:

How does this even run like that?

 

I been trying to tell you guys the ECU codes would be all over the place on this thing. 
And to answer your question, I have no idea but it does and has for years. 

How long should the fuel pump run in the tank each time the key is turned forward but the engine is not started?

When it primes the very first time, should it run each time you turn the key off and back on again?

Is it loosing prime at the TB?

Ray

[datzenmike]

I should imaging there is a timer turned on by the ignition in the ON position to prime the pump for starting. How much? Well generally as soon as the ignition is turned on we start the engine more or less right away. Lets say a 5 seconds*. However the starter also has an input likely so as soon as the starter engages the timer is reset and held on till the starter operation stops and there is a 5 second wait till it shuts off, but by then the engine has probably started and something such as oil pressure maintains the fuel pump on till the engine stops.

 

If we turn the ignition on but wait 20 min the pump has long shut off. When the starter is engaged the pump starts but it may take an extra couple of seconds to build pressure so the actual start may be slightly longer than if started right away.

 

*I say 5 seconds (could be less) because you don't want the fuel pump running too long on a timer. Lets say you have an accident and are incapable of turning the ignition off, and there's an engine fire. You want the fuel pump to NOT be on, feeding the fire. So as soon as the oil pressure drops below 8 PSI, say 2 seconds the timer begins counting down and in well under 10 seconds the pump stops.  

 

I said at the beginning I imagine. I don't know but it seems likely to me.

[raythomas]

Okay, that all makes sense. If when the truck does start, it runs until I shut it off. So this should mean the fuel pump is working normally?

In everyone's best guess, what would cause no fuel to be at the TB when it's first trying to start after being shut off and hot? I am assuming this but I'll ask anyway. When the engine is being started, should I be able to see fuel spraying from the injectors if I'm looking down the top with the air cleaner removed?

And when It won't start, I can hold the throttle to the floor and it will start after a few seconds of spinning over, blubbers a little and then catches its breath and idles fine. What has the throttle wide open got to do with that? 
I'm thinking I just need to test the fuel pressure coming from the tank. Should I check it before or after the fuel filter mounted on the passenger side inner fenderwell? The filter is new if that matters. 

thanks

Ray

[datzenmike]

Idle doesn't take much gas so you might not see anything at the injectors.

 

You would have to put a pressure gauge on the fuel rail to be sure there is none on hot restart. Can you hear the in tank fuel pump on the hot restart? No pump... no pressure.

 

[raythomas]

36 minutes ago, datzenmike said:

Idle doesn't take much gas so you might not see anything at the injectors.

 

You would have to put a pressure gauge on the fuel rail to be sure there is none on hot restart. Can you hear the in tank fuel pump on the hot restart? No pump... no pressure.

 

 

There is NO fuel rail. Its lines coming from the tank straight to the fuel filter then to the TB.

No sir, I CAN hear the fuel pump each time. My luck its putting out just enough pressure to run sorta normally and then not hot restart. 
What actually has changed between a cold start and a hot start? Nothing except the temp of the engine. What would it do to by-pass all those coolant lines that run from the intake up to the TB? It has two that go to the TB, I've been told to help warm the fuel for colder climates. Then there is the coolant line that goes to the "wax" something or nother that comes in to play with high idle when the truck is cold and then idles down when it warms up. .

 

Ray 

[datzenmike]

Cold start is richer than warm start and the O₂ feedback loop is open. When cold there is an idle air control that lets extra air in and the engine revs up slightly with the richer air mix to speed warm up. There is a coolant temperature sensor (NOT for the gauge) that tells the ECU if engine up to temperature. When warmed it switches to closed loop operation and the mixture richness is monitored and reduced much closer to stochiometric and the idle air control is now closed. The idle air control is warmed electrically somewhat like an electric choke.

[raythomas]

1 hour ago, datzenmike said:

Cold start is richer than warm start and the O₂ feedback loop is open. When cold there is an idle air control that lets extra air in and the engine revs up slightly with the richer air mix to speed warm up. There is a coolant temperature sensor (NOT for the gauge) that tells the ECU if engine up to temperature. When warmed it switches to closed loop operation and the mixture richness is monitored and reduced much closer to stochiometric and the idle air control is now closed. The idle air control is warmed electrically somewhat like an electric choke.

 

 

Is there an easy way to test that temp sensor? Could any of this have anything to do with low fuel pressure?

Ray

Edited October 1, 2023 by raythomas

[datzenmike]

Would be better to test the fuel pressure rather than assuming.

[Stoffregen Motorsports]

You may have to rig up an in-line block or tee to test pressure, if there is no schrader valve (I can't believe that there wouldn't be one somewhere...)

 

Generally, the pump primes with key0on, but it will  not always cycle if sufficient pressure exists.  So turning the key on and off then on again, you may not hear it cycle, because it already has enough pressure.

 

Many EFI setups use a cold start injector. If this system uses one, then you may not see fuel spray from the main injectors on start up.