1978 280z Won't Run Properly Anymore! Any help is Appreciated!

[Ownallday]

I'm going to try an provide as much information as possible. I've had my 280z for about two years now and for the most part has driven very good besides having a high idle most of the time and constantly having to adjust the idle screw in the mornings to raise the rpms then lower rpms after driving car for awhile. I live in California LA btw. Recently I did a good amount of work to the z

 

Last week me and my friend replaced the spark plugs, readjusted valves, installed a new fuel filter and fuel line that connected below the fuel filter, new upper coolant line and coolant. Now the other thing we did was my car had a broken temp sensor stuck in the thermostat housing since I got the car. We finally were able to remove it by welding on a bolt to it multiple times. We also noticed which looked like a line for the coolant to go through was completely clogged in the housing. We unclogged it and reinstalled everything. The temp gauge finally works!!! BUT not so much my car. Upon starting the car it started and idled like a dream. It sounded very healthy. However upon revving my car before taking it for a drive, it bogged and the idle just dropped. Car would constantly do this, upon inspecting the spark plugs, the car seemed to be running very rich (btw my previous spark plugs indicated my car was running lean). So after all this work my car randomly starts to go from running lean to rich? what gives? I was able to driving the car a couple times after cleaning the spark plugs and deleting one vacuum line but the problem comes back. There was even a point where smoke was coming out the tail pipe but it only happened once when I had to over rev the car moving very slowly. Today I can't get the car to move but I can get it to turn on. At first it seemed like the issue was only when the car was warm but then I noticed it would just come randomly.

 

Recently I have done a Vacuum delete (including a delete for the thermostat housing line I unclogged where coolant comes through since I thought that was the issue but this didn't correct anything) I checked and I have no vacuum leaks anywhere either. Currently I can turn on the car and the car will idle around 700-800rpm and adjusting the idle screw no longer does anything. If I try an rev the car it struggles to even rev or rpms just drop. So I can't even move the car anymore but earlier today after the vacuum delete I was able to drive it around the block then it started to bog again after 15 seconds. If I disconnect the Thermotime sensor and the TPS sensor the car turns on a lot easier and sounds like it idles a lot nicer and I can rev the car just fine but if I try an drive it like this the car instantly dies. Oh yeah, my temp gauge does not work anymore either after unplugging it like two times to see if the would solve anything.

 

The car drove perfectly before this so what do you guys think the issue could be?

[dutchzcarguy]

You where welding near the sensors on the coolant.. maybe you damaged the other sensors..

It is very difficult to say what the problem is as there are many variables.. get yourself a serv.manual and a electronics guy.. ?  

All i can say go through it systematical.. good luck let us know if you find something.

[S30Driver]

With all the work at the thermostat housing, check and verify that you have not swapped the connections to the coolant temp sensor and the thermotime switch.  They are the same and the ecu will not like it,  adding a ton of fuel resulting in a very rich condition.

[Ownallday]

3 hours ago, dutchzcarguy said:

You where welding near the sensors on the coolant.. maybe you damaged the other sensors..

It is very difficult to say what the problem is as there are many variables.. get yourself a serv.manual and a electronics guy.. ?  

All i can say go through it systematical.. good luck let us know if you find something.

This is one of the possibilities I also assumed. I have a new water temp sensor coming this week. But I don't understand why the sensor would get effected from welding near it. The housing was off the car when I was welding. I have already gone through the fsm which is why I ordered the water sensor.

 

1 hour ago, S30Driver said:

With all the work at the thermostat housing, check and verify that you have not swapped the connections to the coolant temp sensor and the thermotime switch.  They are the same and the ecu will not like it,  adding a ton of fuel resulting in a very rich condition.

I've already thought of this lol. My two connectors however won't let you switch up the water temp sensor and the thermotime sensor so you can't even switch it up on my car.

[Dave WM]

the FSM is your friend. You need to start by checking resistance readings at the 35 pin connector. Don't anything more until you do that, or you could just be adding layers of errors. Main one to focus on is the temp sensor (not the gauge but the sensor that goes to the 35 pin connector and is crucial for the ECU to set the air fuel mixture).

Also when ever I hear the word "deletes" it make me cringe. Deleting means the system no longer is setup to the FSM, "could" impact how the test work and the results.

Reminds me of the word "upgrade" that one gets thrown around a lot, and I would say maybe "changed" would be better.

sounds like it did work at one time (but for the idle, which sounds like the aux air control, covered in the FSM).  So each change you make now gets you further from a once working system. Hence the need for checking before any more changes.

 

Edited July 15, 2020 by Dave WM

[Zed Head]

[Ownallday]

1 hour ago, Dave WM said:

the FSM is your friend. You need to start by checking resistance readings at the 35 pin connector. Don't anything more until you do that, or you could just be adding layers of errors. Main one to focus on is the temp sensor (not the gauge but the sensor that goes to the 35 pin connector and is crucial for the ECU to set the air fuel mixture).

Also when ever I hear the word "deletes" it make me cringe. Deleting means the system no longer is setup to the FSM, "could" impact how the test work and the results.

Reminds me of the word "upgrade" that one gets thrown around a lot, and I would say maybe "changed" would be better.

sounds like it did work at one time (but for the idle, which sounds like the aux air control, covered in the FSM).  So each change you make now gets you further from a once working system. Hence the need for checking before any more changes.

 

Forgot to mention that I already dug into the FSM and EFI Bible (which is what lead me to buying a new water temp sensor) I've have also don't a test on the pins for the ECU that lead to the two sensor (which turned out to be good) but I didn't check the others which I'll do tonight. I do have a two other ECU (that I know work) that I'll be trying on the car tonight incase I'm missing something. And sorry I didn't really know any other way to explain it but I removed vacuum lines and plugged them up based off another popular forum. I mainly did this because of the clogged line that me and my friend unclogged. Based on other forums the car should run perfectly with what I removed. Later tonight I'll take a video of my issues and certain test to show a visual and audio explanation of my issue.

 

13 minutes ago, Zed Head said:

Thank you, I already tested the pins but I will retest tonight and update

[Zed Head]

10 hours ago, Ownallday said:

Last week me and my friend replaced the spark plugs, readjusted valves, installed a new fuel filter and fuel line that connected below the fuel filter, new upper coolant line and coolant. Now the other thing we did was my car had a broken temp sensor stuck in the thermostat housing since I got the car. We finally were able to remove it by welding on a bolt to it multiple times. We also noticed which looked like a line for the coolant to go through was completely clogged in the housing. We unclogged it and reinstalled everything.

It's probably something to do with fuel or valves.  People have had the locknuts come loose on the lash adjustment.  Knowing fuel pressure is always good. 

As far as "testing", you need to show the numbers.  So many people try to start out with a couple of easy "tests", but in the end, days or weeks or months later, they almost all have to get the real numbers.  Even the FSM gives bad advice with their "N.G" continuity tests.  Just go directly to real resistance readings.  Make a list.  Seriously, it will save a lot of time.

[Pilgrim]

My normal assumption is that the closer your car is to factory stock, the easier it is to diagnose problems.  I'd return the vacuum configuration to stock.

[Zed Head]

7 minutes ago, Pilgrim said:

My normal assumption is that the closer your car is to factory stock, the easier it is to diagnose problems.  I'd return the vacuum configuration to stock.

This is always good, in general.  Put everything back to where it "drove perfectly".  

The fact that the idle screw adjustment has no affect is a big clue.  Almost sounds like the AFM vane is stuck or something else is blacking the intake system.  Air flow is what controls engine speed.  Are you missing any shop rags?

[Dave WM]

I missed the idle screw has no effect. That is indeed a clue. Have you tried smoking it for vacuum leaks? Blocking the front of the AFM with a foam cup, then blowing smoke from a cigar into the intake manifold (at the brake booster port is a good place), look for smoke. Besides poor electrical connections to various sensors (and grounds), vacuum leaks can plague EFI, it has no O2 sensor and can not compensate for problems if there is anything that is out of spec.

Edited July 15, 2020 by Dave WM

[siteunseen]

4 hours ago, Ownallday said:

I've already thought of this lol. My two connectors however won't let you switch up the water temp sensor and the thermotime sensor so you can't even switch it up on my car.

These bullet connections are what @S30Driver is speaking of, not the ones on the housing. Hope this helps.