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1975 Datsun 280Z Running rich

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Please excuse the specific title and non issue.

I'm hoping if I post this on a forum, and somebody else is having the same issue they're googling, they can avoid my headaches.


This is also a cautionary tale on why it's good to have a new set of eyes after you've developed tunnel vision...


My 75 280 was running rich as hell, and it was driving me nuts. This is the list of things I had already done to get to about 10 minutes ago.


Originally the car had a terrible stumble and front fire, and was near impossible to start. Tank looked like a relic from the Titanic, so that was pulled and boiled. In the meantime I did all this stuff below.


I had just reinstalled my fuel tank after having it boiled out and coated.

All new vapor lines.

All new fuel hose and FI clamps.

All new hose on injectors.

Fram G1 before tank.

New MSD fuel pump.

New fuel filter.

All new silicone Vacuum lines everywhere.

Soldered in all new connections to every sensor on the engine. (Soldering is my bag. They were done to NASA specs)

Voltage and resistance checked on everything that can be read with a multimeter.

Valve lash adjusted cold.

All new NGK plugs gapped.

Timing is fine.

Running a tank with 10 gallons of gas and half a bottle of redline SI-1 through the engine. 


Car starts immediately on the first click. Runs strong. perfectly for about 10 seconds. Then it starts running super rich, blowing huge clouds out the back. Plugs are fouled to failure in about 2 minutes...


Clean plugs.

Verify Water Temp sensor resistance cold.

Try again.

Same results.


Buy new plugs.

Buy new Water temp sensor.

Same results. Shut off car before ruining brand new plugs.

Pull plugs. Wet and turning dark black.


Starting to think my ignition is weak as advancing the timing does little to help.

Think about it all night.

Check cold start valve in vain even though that makes little sense, because your cousin suggests it, and he's a better mechanic than you.


Then it hit's me... Switch the connections for the thermo time switch and the WTS... 




Car runs like a top.


So, Z friends... If you're going crazy trying to fix a problem you know the solution for, and it doesn't solve the problem, you're solving it wrong. Think about the stupid variables that you looked over for whatever the reason may be. 


There's no shame in asking for a new set of eyes. You knew what was wrong, you're just overthinking it.


Hope this helps some people. And if you think I'm onto something with this post to help random googlers with a similar problem, go ahead and leave a comment to get it up there in the search results.


Bottom line: If you're running rich, 99% chance it's the water temp sensor.







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I've done that myself and it's one of the first things I now check for Rich running issues.


I'm going to be rewiring a friends car, and all those Bullet connectors are going bye bye. It's getting Deutsch connectors for everything. CTS and TTS are going on a 4 prong Deutsch connector so they can never be mixed up again.


Edit: Did the solution hit you around 3:00 AM? That's when I usually figure things out.... after tossing and turning all night. Keep a notepad by the bed...

Edited by Chickenman
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