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1977 280z EFI Nightmare


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ey guys!

I have a 1977 280z which used to have the California specific emissions tech. I recently "refreshed" the engine after I got it. I completely redid the fuel tank and fuel system from the tank back going as far as to replace all the hoses for the vapor tank as well. 

I am just going to list off new things.

  • rebuilt fuel injectos
  • new fuel pressure regulator
  • new fuel damper
  • fuel lines
  • fuel pump
  • rebuilt fuel rail
  • rebuilt head and new headgasket
  • all new seals around the engine
  • spark plugs
  • rotor
  • distributor cap
  • plug wires
  • oil pressure sender
  • water temp sendor
  • water pump/ radiator / fan clutch / thermostat etc
  • cold air intake
  • intake hoses at AFM
  • vacuum lines
  • new fuseable links
  • new fuses inside the car under the passenger dash area
  • several cleaned up grounds throughout the car

 

I also modified the EGR system by removing it, along with the BPT system. I just did this to simplify things. I also have a 6 to 1 header from MSA going back to a 2.5 in exhaust. This deleted the catalytic converter it had.  Other major change is I removed the AC. Might still be some things left over like the vacuum canister, but they aren't hooked up.

Anyways, I am positive the mechanical timing on the engine is solid. I also set the ignition timing as the sticker on the hood. I think it recommended 10degrees BTDC, could have been after tho. The car starts beautifully like a top. However, cold or warm it cannot rev the car. If I hold the gas pedal down it will slowly rise, but then it sounds terrible and won't go further. My assumption could be it is misfiring. In addition as the car heats up it will begin to stumble, buck, and eventually die.  Quite sad to watch. I would also like to mention it idles right around 850rpm. Even when cold.

So I went to troubleshooting. If I unplug the water temp sensor the car will die pretty much immediately, so I know that it is at least getting connection. I tried adjusting the idle speed and it pretty much has zero affect until i close it, and then it will choke out and die. I also tried to test vacuum. People recommended removing the oil cap and see if the engine runs worse. I did, and it made zero affect to how the engine ran. Which made me think a vacuum leak, although I can't find one for the life of me. Except that maybe I did not plug the EGR right.

Next came the AFM. I noticed that as the car warmed up I could watch the counter balance thing on the AFM begin to bobble (representing the vane itself inside bobbling). As the car got to operating temp the AFM bobbles more and more until I can see it making extreme movements to stay alive. Then the car dies. So I thought, lets help the little bugger out. So I had a friend slightly hold the AFM open so it would run a little richer. The engine immediately ran SOOO much smoother. I tested further and had him open it slightly more as I followed with my foot on the gas pedal. And the engine would rev up with it. I actually could get it to rev all the way to 6k rpm. Sometimes it took a while to get there, other times it would rev there super quick. Never would reach redline though, most likely because the mixture was still way off.  So to me this rules out that spark as an issue. But I just have no idea what it could be. I really don't know where to start. I never got to see the car start before I redid it, because it was so crusty and likely had a blown head gasket.

I actually drove the car about a quarter mile, by running the AFM about 3 cog teeth richer. Although I had what felt like 50hp. Can't say it was a great idea, but I needed a pick me up.

I will provide some photos and let me know if you see anything immediately wrong with how I hooked things up. This is my first z car and I am on that initial steep learning curve. 

I also am based in Phoenix, Arizona. If you or anyone you know would want to help I'd be happy to host. 

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Edited by ckurtz2
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I believe the hose from your valve cover needs to be behind the throttle body vane..

Also, i cant see the ground connections from the EFI wiring harness.  They should have just enough length coming out of the harness to be connected to the intake manifold.

Edited by Reptoid Overlords
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Here's your other thread, in case anyone thinks they've seen this one before.  Reptoid is right, there's something off about your PCV system.  Looks like the valve cover is open to the atmosphere.  That's not good.

 

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Just now, Zed Head said:

Here's your other thread, in case anyone thinks they've seen this one before.  Reptoid is right, there's something off about your PCV system.  Looks like the valve cover is open to the atmosphere.  That's not good.

 

Ok, I am totally up for suggestions, I tried to just "copy" what the engine looked like before I played with it. Here's a photo before I went and started toying and refinishing things.

D6806BA0-99B7-4DE8-8A53-6199108330D1_1_100_o.jpeg

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31 minutes ago, Reptoid Overlords said:

I believe the hose from your valve cover needs to be behind the throttle body vane..

Also, i cant see the ground connections from the EFI wiring harness.  They should have just enough length coming out of the harness to be connected to the intake manifold.

 I believe different 280zs had different PCV setups. Not sure if mine is right, but I do have it like it was when I got the unmolested car. Like everyone says though, who knows if what the original owner had was right. Regarding the EFI ground. If you mean the two connectors that ground on the intake, I believe it is grounded. You can see it on the first image below the air regulator. 

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1 hour ago, ckurtz2 said:

 

  •  
  • rebuilt head and new headgasket
  •  

 

Who rebuilt and installed the head?  Is it the one the car came with?

Your PCV hoses look right, I couldn't see that the one in front of the AFM was an elbow.

I'm afraid you have the typical internet dilemma of assuring everyone out here that things like cam and ignition timing are "right" and don't need to be verified, yet you can't get the engine to run right.  It's hard to get too involved when you don't have verification of those important things.  No offense, but the thought that runs through your mind is "why should we believe this guy"?

Anyway, two things that come to mind are:

1. a rotten EGR passage, where the blockoff plate doesn't work because the passages themselves are rotten.  Somebody had that problem a few years ago and he had all kinds of odd problems with the way the engine ran.  I think that he might have found it by measuring intake vacuum.  It was much lower than it should have been.  You might take an intake vacuum measurement since it is a measure of how the engine is pulling iar through the manifold.  It's a clue.

2.  

 

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In short - your symptoms seem to fit an engine that is not pulling through the throttle body.  Could be pulling through the PCV system, or the EGR system, or the valves and/or pistons are not generating enough suction.  I think that explains the AFM vane not moving.  There's no air flowing through it.

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36 minutes ago, Zed Head said:

Who rebuilt and installed the head?  Is it the one the car came with?

Your PCV hoses look right, I couldn't see that the one in front of the AFM was an elbow.

I'm afraid you have the typical internet dilemma of assuring everyone out here that things like cam and ignition timing are "right" and don't need to be verified, yet you can't get the engine to run right.  It's hard to get too involved when you don't have verification of those important things.  No offense, but the thought that runs through your mind is "why should we believe this guy"?

Anyway, two things that come to mind are:

1. a rotten EGR passage, where the blockoff plate doesn't work because the passages themselves are rotten.  Somebody had that problem a few years ago and he had all kinds of odd problems with the way the engine ran.  I think that he might have found it by measuring intake vacuum.  It was much lower than it should have been.  You might take an intake vacuum measurement since it is a measure of how the engine is pulling iar through the manifold.  It's a clue.

2.  

 

I had a machine shop resurface the head, and do a valve job, and install springs. I installed the cam and rockers and such. I was super carful when installing. Made sure the engine and head were both at TDC before installing. Of course there is always room for error. I think the next step is to do a compression test for me to check that. I am at college, and go home during the weekends to work on the car, so I can get you official TDC verifications this weekend. Trans is out to fix a leaky freeze plug, so I will give the compression check at a later date. Thanks for the help so far!

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9 minutes ago, Zed Head said:

In short - your symptoms seem to fit an engine that is not pulling through the throttle body.  Could be pulling through the PCV system, or the EGR system, or the valves and/or pistons are not generating enough suction.  I think that explains the AFM vane not moving.  There's no air flowing through it.

I agree, and I will do some more detective work in the upcoming weeks to give everyone some real numbers. Here is something I noticed. Does it matter the way the PCV system is set up? I noticed through a lot of photos people doing it different ways. For example, I have mine hooked up before the throttle vane, while some images show people capping it there and setting it up like this. Essentially, the reverse of how mine is capped.

I would give everyone numbers now, but the trans is out. The freeze plug behind the block had rusted through and was leaking. Took the liberty to change to a 5speed while the trans was out.

 

280z Real PCV setup.jpeg

280z alternate PCV setup.jpg

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Nissan changed the hose routing in 1977.  

Here's something I've found useful.  The cars on BAT all have numerous pictures and usually run like tops.

Here's a 78. (Funny though, I see that the guy left the brake fluid reservoir open.  Still got a good price.)

https://bringatrailer.com/listing/1978-datsun-280z-84/

image.png

 

 

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The PCV hoses, while kludgy, are connected fine. The valve cover is correctly connected upstream of the throttle butterfly.

Two things catch my eye quickly... First, your fusible links are in the wrong locations. You've got the large BLK link in the back position, and it should be in the front position. It won't explain the performance issues you're having, but fix them now before something goes wrong.

They should look like this. The largest link should be the front outboard position:
77-78links.jpg

Second, I'm not liking the tube connected to the vacuum port on the bottom of the throttle body... There are two vacuum connections on the throttle body, one that points toward the front of the car, and one that points towards the rear. The one pointing forward is for the distributor vacuum (and carbon can). The one pointing to the rear is for the EGR system.

What I'm not liking is there is a hose connected to the vacuum nipple that is pointing rearwards, but you've removed the EGR system. That nipple should be capped off with no tube attached. The hoes you have connected to it seems to wrap around underneath the throttle body, and my suspicion is that you're using it for distributor advance. Is that the case?

And lastly... The temperature sensor is often the culprit in lots of EFI issues. Have you taken meter measurements to make sure it's working properly?

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@Captain Obvious

Great catch! Could of just save me my car in the future:)

Now the connection pointing towards the rear is the one for the BCDD correct? In my sixth photo. Actually looking at it I don't think it is. Anyways, I can't remember why I did it, I think I saw a diagram somewhere online. But I believe I have that running to the smallest line on the carbon canister. No idea if that is right. I had tons of photos on my phone when I disassembled the motor, but broke the phone before I got it back together, and didn't have the photos on the cloud. Was a catastrophe for me pulling up diagrams and what not. I remember connections like this confused me.

 

Regarding the forward pointing vacuum port, which one are you talking about? 

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Here's some pics of the throttle body. You can see there are two small vacuum tube connection nipples on the bottom.

The nipple on the left in the pic (points toward the radiator) should run to a "T" and from that T, it runs to both the carbon can and the distributor vacuum. The nipple on the right points downward towards the rear of the car is used for the EGR system (and only the EGR). So if you've removed the EGR stuff, you can cap that one off completely.
P1080095.JPG

Here's a closer-upper of the nipples. You want to use the one on the left and cap off the one on the right.:
P1080098.JPG

Edited by Captain Obvious
fat fingers
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IMHO, I think the two first steps would be to a) make sure the electrical connections to the EFI system are clean, tight, and making really good connection. Paying special attention to the temp sensor and the AFM, and b) simplify as much of the tubing as you can in order to minimize vacuum leaks. After you have simplified and gotten the basic system leak free and running well, you can start adding stuff back in.

For example... For now, you can just cap off all the stuff running to the carbon can. You can also take off everything having to do with the AAR. The car will idle low until it warms up, but once it's warmed up, the AAR should be doing nothing anyway. I don't remember what they use the TVV stuff for... If it's EGR and EGR only, then you can cap all that stuff off too.

Just trying to minimize all the tubing because each end of any tube is a potential vacuum leak. Make it leak free, get the basic system working, and then start putting stuff back on.

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@Captain Obvious

I know 100% then that I have the throttle body vacuum messed up, not sure how I have it setup until I get home this weekend. I will let you know then. Plans are to get the new rear main seal, freeze plug, lightweight flywheel, clutch, and  trans into the car this weekend. Switched to the 81zx 5speed for that nice overdrive. Still probably a month out till the motor is safe to run and begin diagnosing again. I need to figure out which driveshaft I need, whether the 81zx, or the one that came with the car (seem to be about 1/2  to 3/4 inch different in length) rebuild it and toss it into the car. As well as decide which clutch collar I need to use, whether from the 4speed that came with my car, or the one from the 5speed. Seems to be some debate with that, because it says to use the proper collar with the clutch it is meant for. But my clutch is an ACT aftermarket clutch for the coupe models with the smaller coupe flywheel. I got it from here... https://www.autohance.com/act-nx1-hdss-clutch-kit-heavy-duty-hd.html?gclid=EAIaIQobChMIhISB4qnW7wIVTx6tBh0pFQwAEAQYBCABEgJDpvD_BwE . Which is compatible from 1975 all the way through the 90s. I don't know if it actually matters what collar I use.  If you have any advice that would be wonderful.

You are right. Going to start with a compression check. Then I think I will test the water temp sensor and then AFM. If those check out I believe it is going to be my vacuum issue you recommended. Like you said, peel away the layers on that onion haha. Thank you everyone so far for helping me out, I have been on my own for a while now and it is really nice to get some advice.

Found this, which will come useful when testing the AFM and such.

280z EFI Bible

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I started "ripping and tearing" the emission stuff off mine. That little hose on the right of the throttle body had me stuck dead in the water. I do believe Mr Obvious saved my arse on that as he has many times. Thank you @Captain Obvious if I haven't told you lately. LOL

 

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Your original driveshaft should be the one to use with the 5 speed.

Carefully compare the height of the original clutch pressure plate with the new act one.   If they measure the same height, use the original collar.  If not, you will need one of the correct height to go with the act plate.    Search for the many threads on how to measure this.

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2 hours ago, siteunseen said:

 I do believe Mr Obvious saved my arse

LOL. Glad to help my friend!!  I'm just a guy with a Z who types a lot, but I try to add value where I think I can.   :beer:

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5 hours ago, ckurtz2 said:

Found this, which will come useful when testing the AFM and such.

280z EFI Bible

Yes, read through the EFI bible. And then read through it again.

Compression test. Intake manifold vacuum test. Fuel pressure test. Ohmmeter tests. Ignition timing test.

And if you have a few extra minutes, clean some connectors. If you're looking for a place to start, start in the passenger footwell where the heater core leaked and corroded the connectors on the passenger side of the trans tunnel. Also do the temp sensor, the AFM, the fusible links and the fuse block.

There are other people who can add much more value about the transmission and driveshaft stuff than I can. I could survive in the wild there if I had to, but there are other people who are experts in that area that will cover you there.

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4 hours ago, S30Driver said:

Your original driveshaft should be the one to use with the 5 speed.

Carefully compare the height of the original clutch pressure plate with the new act one.   If they measure the same height, use the original collar.  If not, you will need one of the correct height to go with the act plate.    Search for the many threads on how to measure this.

Best thread I found was this.

What you recommend makes absolute sense to me. Thanks! Do I just measure the PP heights, or do I set the PPs on top of their corresponding flywheels and then measure? Reason I ask is because I am using a Fidanza flywheel and it may be different from the chunky original.

@Captain Obvious   Roger. I will get back to you in the future with the demons that I come across. I am sure I will need assistance doing away with them🙃

 

 

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  • 4 weeks later...

Time to reboot this thread again @Captain Obvious

I got the freeze plug at the back of the block where it was leaking replaced, a new 5speed, clutch and all those fun things with it installed as well. Now back to the engine demons. All I have left is to try and fix all those vacuum issues I had, and fix up some new alternator wiring for an 80amp one I got before I try to fire it up again.

The more and more I started looking closely at how my vacuum lines are set up the more disappointed at myself I have become. I had ran the vacuum from the front facing point on the throttle body straight to the distributor. I also had run a vacuum line from the one that faced back on the throttle body straight to the carbon canister. Not to mention the line was to big and pretty much floated on the ports. So ummm yah, disappointed in myself regarding that. Plugging the rear one, and then fixing the forward facing one to a T running to the canister and vac advance should fix that like you mentioned. Just waiting on 4mm vacuum line because my local auto stores did not have them. 🙂

I also noticed that the large vacuum hose for the air regulator did not have any clamps and was actually pretty loose which also I am sure added to my vacuum problem. Just fixed that today.

And the icing on the cake was thermal vacuum valve. I have the coolant lines properly set up on it. However, I capped one of the vacuum ports and sent the other straight to where an AC vacuum line is supposed to be (and it was also loosely fitted). I also have no AC. So my question is, Should I completely remove the thermal vacuum valve, or should I just plug the vacuum ports for it? What exactly is its function? I deleted EGR and BPT. 

 

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