Running rich
 

1975 280z
I replaced engine with a used engine that runs great and good compression. The issue I'm having is ,
When I put engine in. It ran great. But after the fifth time running it , i t started running a little rich and never stopped running rich to the point it fouls
​​​​it.out the plugs , after checking and replacing sensors and soldering new connectors on injectors and sensors , I was still running rich, well after
a week of letting it sit , I started it and again it was burning rich , I kept the engine revved up high to move it , after I moved it out of the garage , I
let it sit for a few hours. I went to move it back in the garage and it started running normal , after starting it several times and drove around the block.
I let it set for a week and I went to go start it and started fine for about 2 minutes and started running rich again. I'm pulling my hair out !
Trying to figure out what I am missing .

What "sensors" did you replace? How many of the old plastic connectors did you replace with new ones?

I replaced the thermo time , temp for Guage , all connectors from switches , sensors, injectors , cold start , aux air valve and maf unit .

A rich condition will most likely be caused by a bad coolant temp sensor or the air flow meter or the electrical connectors associated with them or your cold start injector is sticking open or a bad thermo-time switch keeping it open. Normally the thermo-time switch fails where the cold start injector does not open but its not impossible for the reverse to happen. Disconnect the cold start injector to see if the problem goes away.
There are 2 coolant sensors in your car. One for the dash gauge and one for the ECU. Here is where they are located. The testing procedure can be found in the FSM. You can get the FSM free here,
Free S30 FSM


https://cimg1.ibsrv.net/gimg/www.zdr...d624d91cf7.jpg

Sorry for the missing information. I did replace all three of those. From the repair manual, I tested old ones and they tested good , but I replaced them anyway, now there is one more sensor that was in my old engine that wasn't in the new one. It went in the empty hole on the right side of your picture, it had a red wire going to it , I think it was for the egr. I did disconnect the cold start and it was doing the samething . I am wondering about the fuel pressure regulator .
I really could have swore I heard a click when it started burning rich , but can't think of what that would be.

Try pinching the fuel line to the cold start injector. It could be stuck open.
What year of engine is the replacement?
Photo of the 4th item in the thermostat housing please

Be careful pinching that line as the barb on the cold start injector is long as is the barb on the fuel rail. The cold start injector is plastic.

The engine came out of a 77 280z , the part is at my work , it has one wire that goes to it. I will pinch the line off tomorrow
to see what happens. I really would like to replace the M.A.F unit just because it has been setting for almost 30 years .

Ok , I was just thinking of taking the line off and plug the feed line to it. I think thats the only fuel line i havent replaced

Well , I took out the cold start valve and blocked off fuel line going to it, it runs better than it ever has . I really want to thank you for the direction you guided
me in, sometimes it's good to get a wakeup call ! Thank you.

Even an old dog like me finds a bone once in a while! Glad I could help. As for your MAP you don't have one, you have an AFM. Please don't replace anything just because its been around for awhile. You will end up just wasting money. IF IT'S NOT BROKE, DON'T FIX IT.
Drive it till you break it and then fix it and drive it until you break it again.