Barefootdan's 280z Build

[Barefootdan]

Pulled out the Z today to break in the motor! Started right up and brought her right above 2000 rpm. She lasted about 8 minutes before I realized I didn’t hook up my radiator fans. So I turn it off and hooked those bad boys up just temporarily. Started again and continued to break in. Temp was holding in the middle of the gauge nicely! 
 

I had a vacuum leak still so keeping the idle steady was a handful. It ultimately died as I was checking timing. It looks to be running very rich as the only way to get it back up and running was to unplug injectors to clear out the fuel. Once started again, it lasted a few seconds before dying again. I pulled it back into the garage as I still have about 5-6 minutes left of break in to do. I’ll plug up my vacuum leaks in the meantime. I’m sure my idle is going to be way off this next start. I’ll need to check the FSM to get a baseline setting. 
 

My only question so far is could the vacuum leak, or wild adjustments to get it to idle, cause the rich mixture? I don’t have the cold start valve, bccd, or egr hooked up for reference.

 

I also don’t have the water temp switch hooked up because my car never came with it. I know this goes to the computer to adjust fuel as the car warms up, and this was my initial thought as the cause.  I’ll order one up in the mean time. Just seems odd it is running rich enough to flood the car. 
 

edit: looking up the temperature switch it looks hard to find. I see some options for modifying a different year. But also “Basically, if you disconnect it - circuit open - the car will run on its normal timing both when warmed up and cold. The switch is normally closed, to run off of the other, advanced 6 degrees, magnetic pickup coil (variable reluctor) when cold. I am guessing it's to increase the idle speed up a little while cold. Mine stopped working so I just disconnected it and set the timing where it should be when warm.” 
which leads me to believe that this isn’t my issue as the car was warmed up when I had the rich issue. 

Edited September 18, 2021 by Barefootdan

[siteunseen]

I'm thinking the coolant temp sensor not being in play has your ecu thinking it's cold all the time and adding more fuel.

 

[Barefootdan]

21 minutes ago, siteunseen said:

I'm thinking the coolant temp sensor not being in play has your ecu thinking it's cold all the time and adding more fuel.

 

That seems like the logical case. Ran fine until it warmed up and then it caused issues. I’ll wait to continue the remaining break in until I get that sensor plugged in 🙂 

now I know there’s two temp coolant sensors. One is for the cold start valve, the other is for the fuel mixture (or length of time the injector is open). Are we both referring to the same one, the latter? I think it is on the driver side of the thermostat housing, as opposed to the front of the housing. 

[siteunseen]

Read through this and see if it answers some questions.

I'm about to leave out for the night but will check back in the morning.

https://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

[Barefootdan]

14 hours ago, siteunseen said:

Read through this and see if it answers some questions.

I'm about to leave out for the night but will check back in the morning.

https://www.atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Thanks for that. In my previous post I was referring to the wrong sensor. Water Temperature Sensor (which you referenced) is on the bottom right of the front housing, and controls fuel amount. I was looking at the Water Temperature Switch which is timing advance/retarded related. Lastly, the Thermotime Switch drive the Cold Start Valve. 

Now that I am all cleared up (thank you Datsun for the naming conventions 😄)... What I have in my car, hooked up, is the Water Temperature Sensor. I do not have a Thermotime or Water Temperature Switch. I dont have a cold start valve, so scrap the termotime, and my car never came with the Water Temperature Switch. I'll look into sourcing one later, but this is unrelated to my fuel issues for now. 

I'll first make sure my plug is correct as I know it is common to mix up the thermotime and water temp sensor plugs. I dont think this is my issue has the thermotime plug matches the housing color of the sensor on my bench. But I will do a lead test to the ecu to be sure. From there I will test resistance of the sensor at ambient temp. If both of these check out, I will maybe start the car again and measure resistance as it warms up. Maybe it is going bad? I have a new sensor on order already...but it'd be nice to know what is going wrong. I'll report back on what I find. 

Also, as a reference, fuel pressure is good (gauge before the fuel rail), new injectors, new lines, but old injector connectors. 

[Zed Head]

Could also be the throttle valve switch.  A meter and some time spent at the ECU connection will give a good idea of what's working right.  This book has all years through 1980.  Page 59 is where the meter tests start.

 

[Barefootdan]

1 hour ago, Barefootdan said:

I'll first make sure my plug is correct as I know it is common to mix up the thermotime and water temp sensor plugs.

I swear I must have jinxed myself...Why would the orange connector go to the grey sensor?! Anyways...30 seconds at the ecu terminal lead me to no readings for the water temp sensor. I saw I chose the wrong connector 😅 Now we have accurate resistance for ambient temp! This is likely my issue but I'll need to wait a couple hours before I fire her up as I am waiting for a gasket to dry. While out there I saw your comment @Zed Head and popped open the TPS cover. I do get contact at idle with the right pin and giving slight throttle moves to the middle. Tested at the ecu terminal to be sure as well. Thanks for the tip! 

[Zed Head]

Probably fine for a short time running but you might check your oil for gasoline.  Gas-thinned oil is probably bad for new bearings.  And cylinder walls/rings.

Edited September 19, 2021 by Zed Head

[Barefootdan]

Back from another fire up. I was able to finish the 20 minute break in. So I feel much more comfortable letting the car down below 2K rpm. This time, the car smoked way less, I definitely think the water temp sensor helped. Unfortunately, this time when the car got to temp, I started to bring the idle down to 800, but it was not running smooth. It sounded okay but the engine was definitely not timed correctly or not firing on all 6. I turned it off and inspected my plugs. Dark, presumably from the previous day of running very rich, but nothing seemed wet. From here, I was not able to get the car started again. Fuel pressure was still 30-36 although I noticed a few times it was down to 20. Could low fuel be my next issue? I only recall placing about 3 gallons in since day 1 😮 I dont think the small amount of run time could go through this all, but perhaps it is intermittently grabbing air in there? I'll need to grab some starter fluid and more gas to rule this out.  I then checked my dizzy timing and oil pump shaft. I took the pump off and reinstalled about 3 times to ensure I was getting correct timing. Once I had about a "10:30" adjustment which seemed to far left. I settled on closer to the "11:30" per the handbook. Placing the dizzy back on just seems like it is not lining up with my #1 spark plug though? If it is rotating counter clockwise, it looks like it already passed #1.

 

 

The other issue could be vapor issues with the fuel? Running no heatshield in 100 degree temps, sitting at 2K rpm in the driveway, surely is getting hot in those lines. Lastly, I checked the water temp switch resistance. At this point the car was cooling down but the resistance was acting wild. Bouncing from 450 to 550 every second or so. The resistance itself seemed correct for the rough estimate of the water temp, but should it be fluctuating like this? 

I am at a bit of a loss right now. The car runs excellent from a cold start, gets to temp, dies, wont turn over. My best guesses are, in order:

• Low fuel - Car ran great, started to stumble, died. Seems like an obvious case for a low fuel symptom. But I still have pressure if I open my AFM flap long enough to build. Previously, when the car was flooding, I was able to disconnect the injectors to clear out the fuel. The car would run for a couple second a die. This time, there was no perceivable difference from injectors connected vs disconnected.
• Water Temp Sensor going bad - Resistance is fluctuating ~100ohms every second. Seems odd.
• Fuel Vapor - It was hot ambient and sitting at 2K rpm while not moving gets temps up fast.
• Dizzy timing is off - Visually looks off, but I could be wrong.

 

 

Edited September 19, 2021 by Barefootdan

[Zed Head]

1 hour ago, Barefootdan said:

Bouncing from 450 to 550 every second or so.

 

2 hours ago, Barefootdan said:

I still have pressure if I open my AFM flap long enough to build.

 

2 hours ago, Barefootdan said:

Fuel pressure was still 30-36 although I noticed a few times it was down to 20.

 

I pulled a few things out, out of order.  Fuel pressure should never get down to 20 psi.  But you can check that without the engine running.  That will tell you if the pump is running and if there's fuel in the pump.  Just disconnect the small wire at the starter solenoid and turn the key to Start.

But maybe that's what were doing with the AFM flap.  If you have to wait quite a while for pressure to build that's not right.  A good pump and clean filters and pressure will jump to 36+ in seconds.  Might be that you have a blockage or a bad pump.  There are stories about pumps that overheat and quite producing pressure and I've had one myself.  This was me just testing a pump off the car.  Started out just fine but after a minute or two of running it started making noise and pressure dropped.

The bouncing resistance I'd guess was just bubbles passing by the sensor.  I assume you tested with the engine off, so no flow other than convection through tiny holes in the thermostat.

Not sure why it doesn't start.  But once it does use a timing light to see where your timing is.

[Barefootdan]

That’s a good point. I think we’re definitely looking at fuel issue as opposed to timing (since it was running smooth before it died). 
 

I had a mini fuel filter (lawn mower style) in before the pump but took it out when I cleaned up my lines. I did notice small sediments in there. The pump is a cheap eBay special and always took about 5-10 seconds to get to full pressure. Perhaps this is just added fuel to the fire. I’ll flush the lines and tank tomorrow when I get new gas. I’ll probably disconnect the line after the fuel filter in the engine bay. I can’t imagine anything substantial getting by two filters and blocking an injector. But I also jinxed myself earlier today 😄. 
 

engine was off when testing the water temp sensor. 

 

Thanks again! Thinking out-loud and typing my thoughts helps me gather more details than just thinking in my head. 

[Barefootdan]

I was out of gas….what kind of timing is that! 
 

folks just because your fuel pressure gauge shows pressure doesn’t always mean you have enough fuel to run 😉