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

[Ownallday]

9 hours ago, Zed Head said:

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.

I was going to check and readjust the valves sometime this week when I get the chance. Not sure how fuel can be the issue out of nowhere especially after a fresh fuel filter. I am trying to get my hands on a fuel pressure gauge hopefully the end of the week. And I plan on posting all the numbers most likely Friday or Saturday when I get more time to work on the car and I will list the numbers to each pin.

 

9 hours 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.

The car was completely stock prior to my issues (besides unclogging the temp housing line). Deleting the vacuum lines didn't change anything. The part of the car that got removed really was the cold start lines which isn't necessary for me living in LA and the temp housing vacuum line (which once again was clogged before and car ran fine).  If you believe it really makes a difference though I will put everything back on.

 

9 hours ago, Zed Head said:

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?

Lol no shop rags missing but I will check into the AFM more when I get a chance. I really want to avoid touching the AFM though.

 

9 hours ago, Dave WM said:

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.

I have tried looking for vacuum leaks in the general afm area and all over the intake but I used the carb cleaner trick (not sure how effective it is). I will give your option a try and see what I can get.

 

8 hours ago, siteunseen said:

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

Me and my friend never removed these wires only the connectors to the sensors themselves

[Ownallday]

Here are two videos of my issue.

 

[AZDatsun]

To me it sounds like it’s running rich if it was lean it would be backfiring out the intake from my understanding. Did you mess with the distributor timing at all?


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[Zed Head]

Are you sure you got your wires back on the same way they came off?  It sounds rough.  1-5-3-6-2-4 counterclockwise.  These engines will run with bad firing order and missing cylinders but they won't have much power.

In your second video it looks like the AFM vane is moving okay.  That weight is connected to the vane.  If it moves the vane is moving.

[Ownallday]

I owe @S30Driver and @siteunseen an apology! Even though me and my friend didn't touch those two connections, one of them came loose and fell off somehow! When plugging it back in I notice the connection is a little lose so I crimped it a little to help hold it in better! Thank you so much to everyone for the help. After plugging the wire back in I was also able to adjust the idle after plugging the wire back on. Drove the car for 10 minutes with no signs of hesitation or bogging even with the tps connected! And I also no longer have to keep adjusting my idle by the looks of things. As a matter of fact the car feels so much faster than before! I really wanted to get this car running asap because she is going to see some autocross action for the first time in 3 weeks.

Here's a video of it running after plugging in the connector.

 

1 hour ago, AZDatsun said:

To me it sounds like it’s running rich if it was lean it would be backfiring out the intake from my understanding. Did you mess with the distributor timing at all?


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It was running lean before I did all the work then started running very rich after at least what my spark plugs indicated!

 

1 hour ago, Zed Head said:

Are you sure you got your wires back on the same way they came off?  It sounds rough.  1-5-3-6-2-4 counterclockwise.  These engines will run with bad firing order and missing cylinders but they won't have much power.

In your second video it looks like the AFM vane is moving okay.  That weight is connected to the vane.  If it moves the vane is moving.

I always put tape on my spark plug wires and number them before taking them off, just a habit I got into.

Edited July 16, 2020 by Ownallday

[Dave WM]

this is why is so important to use the FSM as a guide. So often it becomes a game of lets try this, or replace that, a simple check of the 35 pin connector gets you on the right track (a check of the pin 13/ground for resistance to test the water temp sensor should have shown this as an issue). Here is a tip for you, check the water pump for free play/leakage at the weep hole, Nothing ruins the day like a bad water pump.

[Ownallday]

2 hours ago, Dave WM said:

this is why is so important to use the FSM as a guide. So often it becomes a game of lets try this, or replace that, a simple check of the 35 pin connector gets you on the right track (a check of the pin 13/ground for resistance to test the water temp sensor should have shown this as an issue). Here is a tip for you, check the water pump for free play/leakage at the weep hole, Nothing ruins the day like a bad water pump.

Yeah, I refered to the FSM (kinda) which is why I bought a new water temp sensor (I'm sure my car needs a new one anyways). Does a faulty temp sensor cause these to run rich only or can it cause the car to run lean too? The last thing I wanted to do was replace parts on this stock efi I would like to upgrade to ITBs by the end of the year. Im pretty sure I might've checked the two wrong pins however, now that I think about it the readings were off. I know my water pump isn't leaking (I check every month for leaks and loose bolts) and just checked right now it's as sturdy as can be, zero play. My harmonic balancer does need replacing though.

 

Quick question, I have one exhaust manifold stud that snapped off towards cylinder 1, (getting this fixed next week) can this cause a vacuum leak and a noticeable decrease in power?

[siteunseen]

22 minutes ago, Ownallday said:

Quick question, I have one exhaust manifold stud that snapped off towards cylinder 1, (getting this fixed next week) can this cause a vacuum leak and a noticeable decrease in power?

No, just an exhaust leak which may cause hotter fuel rail, "heat soak". @S30Driver again to the rescue!

 

[Zed Head]

35 minutes ago, Ownallday said:

however, now that I think about it the readings were off.

Come on now.... you did not actually take a resistance measurement at Pin 13 of the ECU connector like the "Bible" describes.  Just say so, and move on.

[Dave WM]

the water temp sensor typically goes high (rich) but not impossible to go low (lean). As far as vacuum leaks the best practice would be just to smoke them out. So many places for problems. One major place would be the O rings on injectors, easy to screw that up when replacing. Next would be the AFM to TB hose, crack can hide in the accordion folds, then the EGR is so equipped, and any mods to the PCV system. I properly setup system will have idle issues if you remove the oil fill cap while running. even just pulling the oil dip stick should show a change in the idle if its all working correctly.

[Dave WM]

here is me messing with my spare engine, using the color tune plug to confirm proper EFI operation

 

[Zed Head]

49 minutes ago, Ownallday said:

The last thing I wanted to do was replace parts on this stock efi I would like to upgrade to ITBs by the end of the year.

The stock EFI system will not run ITB's.  You'll need a completely different engine management system.