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Discussion Starter · #1 · (Edited)
So I am at a loss in trouble shooting this problem and would like some advice. The car is a 1980 280zx NA.

The short version is I bought the car in a no start condition, the only thing the guy I bought it from could say for sure was if you turn the crank manually it was able to turn freely. I was able to get it running fairly easily after I replaced the fuel pump, filter, and the injectors. The car ran smooth and responded well after these repairs so I began driving and was able to pass emissions first try. Just over a week after beginning to drive the car, it would drastically loose idle rpm after driving for about 5min, no power, wanted to die when pressing the gas(unless you floored it, then it would pretend to want to rev, get stuck about 1900-2k rpm but only out of gear).

First time this happened I called a mechanic who brought a timing gun, attached to #1 spark wire, and retimed the engine. I left it parked, but would start and idle the engine, revving it to around 2500-3k rpm to see if it would keep timing or try to die out again. After a couple days like this, the rpm had not decreased so I decided to drive it. The rpms seemed to stay put, but I had to ride the clutch more than I felt necessary to keep the engine from stalling when putting it in gear. Then again after driving it for a few blocks the idle rpm had dropped below 500 and if I released the clutch completely it would stall out.

I had the same mechanic take a look at it again and he felt it could be a vacuum issue as some of the lines showed cracking at one or both ends. I went through and replaced the lines that were cracked, replaced a couple clamps that were clearly not providing enough clamp force on hoses connected to the TPS, and did the spark test on each plug wire as well as the line from the coil. Now when I try to start the car it tries to fire, I can feel/hear the fuel igniting, but it won't keep going. When this happens it smells like the mixture is too fuel rich, but if I try to open/close the air valve(I don't know if that is the right term, I just know it is the screw on the intake that you adjust for AFM purposes) I get worse results.

I believe the next best thing to check is the coil, but honestly I am also kinda convinced that it may be a timing issue. I believe the FSM says the timing chain should be replaced around 100k miles, the car does have 104.5k but when I pulled the valve cover it didn't look to be in bad shape and I didn't see any damage on the guide that I can recall. So my question is this, does it make more sense to start with the ignition system, timing, or am I even looking in the right direction?

Edit: Ok so the last sentence in the next to last paragraph is incorrect, it is the Idle Speed screw, not even remotely AFM. Sorry for any confusion.
 

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You will need to go thru and check all of your electrical connections, especially the AFM (air flow meter) and the CHTS (cylinder head temp sensor) the CHTS is located between spark plugs 5 & 6. The CHTS will make the biggest changes to your fuel system. This sounds like a poor connection condition. You should go thru the entire engine bay and check/clean all of the terminal ends. They corrode because they are not water proof.
DONT OPEN THE AIR FLOW METER COVER AND MESS AROUND INSIDE THE AFM. There is a 5 spade connector under the AFM, pull it off and clean the terminals on both the wire and the AFM.
And a fuel pressure would be useful as Pilgrim states.
 

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Discussion Starter · #4 ·
I am pretty confident I haven't touched the Air Flow Meter, mostly because I don't know what it looks like and I haven't taken anything apart other than a few hoses. I have gone around and checked any electrical plugs I could find and removed any corrosion I saw. I will do a second pass just to be sure because it is very possible I missed something. when you say "between spark plugs 5 & 6" you do mean on the passenger side of the engine correct? I will find a fuel presser tester and see where that gets me.
 

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Discussion Starter · #8 ·
Ok, so I didn't end up needing to go very far through the individual tests before finding what I believe to be the culprit. The CHTS is not good, at least that is the way it looks. I pulled it out after checking the connections and the part that should have a spring, freely slides back and forth. I don't even need to put pressure, gravity will pull it in and out if I just turn it upside down and back. I did test the fuel pressure before removing the sensor. Since the car wasn't starting I pulled the little wire on the starter so the pump would run but the engine wasn't turning, I got a steady 40psi. So I think my starting point is going to be replace the sensor and then make sure I didn't mess up the timing. Thanks for the tip about the sensor!
 

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If that doesn’t do it, I might try putting another new fuel filter on it. Maybe there is a bunch of rust in the tank and it’s mostly clogged the filter back up already. Would be interesting to see what the pressure is when it is running.

It’s cheap and easy, or just pull the hose off the tank side of the filter and catch it in a white cup. You may be surprised what you find.


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Discussion Starter · #10 ·
If that doesn’t do it, I might try putting another new fuel filter on it. Maybe there is a bunch of rust in the tank and it’s mostly clogged the filter back up already. Would be interesting to see what the pressure is when it is running.

It’s cheap and easy, or just pull the hose off the tank side of the filter and catch it in a white cup. You may be surprised what you find.


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Rust from the tank shouldn't be a problem. When I bought the car it didn't have a sending unit or fuel pump. Before I put that stuff in I dropped the tank and cleaned it out. I can still check just to be sure, I can do another pressure test once I get the sensor also. I don't really know how well the engine would run without it installed so I wasn't going to try. I will let you know once I do.
 

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Discussion Starter · #12 ·
Ok here is an update.

@kickstand80 The spring thing is just something I was repeating, I was told the sensors have a spring or something inside that prevents them from sliding around. I don't know how true that is, as I have said before this is all new to me. But he was positive a new sensor would fix the issue. It didn't, the new sensor moves back and forth a bit if you wiggle it just like the old one did. I had to nicely tell my wife I didn't think her "wonderful" mechanic was doing her any favors, she took that about like you would imagine.

Oh well, a new sensor cant hurt and now I probably have a good backup so not a big deal. I put the new sensor in, and the car still doesn't want to start. It will sputter a couple times, to me it sounds like each piston fires or tries at least, then it just stalls. The connecter that plugs onto the sensor doesn't show any rusting or blackening. I found that when the CHTS is not plugged in the engine seems to run, so I started it this way and then plugged the sensor in just to see and once the sensor was connected it would sputter and stall. I made printouts of the following FSM sections: electric, fuel, emissions, maintenance. So now I'm just going through them, let me know if you guys still think this is a fuel issue or something else.

@mailnome since it would run unplugged I did another fuel pressure test. At idle I was reading 36psi, I might have hooked it up wrong but I don't think so. When I pressed the throttle to rev the engine, pressure would jump to 40psi for a second then drop back to 35~36psi. Once I let off the throttle, pressure would drop drastically, somewhere between 5~10psi for a split second, then right back to 36psi. When turned off, pressure would bleed off. I don't know if that is to be expected or not. I did not observe any sudden drops/spikes happening for no reason. I plugged in the sensor to see what would happen, the pressure dropped and disappeared as the engine stalled. Probably to be expected, but the fuel pressure definitely dropped before the engine stalled. It was really fast but best I could tell it dropped to around 28 or so then the engine stalled.
 

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yep that is your CTHS. The nut is supposed to slide so you can make it EZ to put your electrical connector on and take it off. No spring and nothing is broken.
Disconnecting the CHTS makes the ECU go full rich. Do you have an ohm meter? check the resistance of both CHTS. Do this in the house. First put them in water and bring it to a boil, the resistance should be 100-300 give or take. Then put them in the freezer and check them. They should be around 6000-8000 ohms.
When you were checking for vacuum leaks did you check the entire boot on the engine side of the AFM. You might have to pull the boot off to check it. Did you check all of the larger diameter hoses that go from that same boot to the Aux Air Control Valve, the one that goes to the idle bump up device for your A/C and the PCV that is under the intake manifold.


Aux Air Control Valve circled in green
Motor vehicle Electrical wiring Gas Cable Electrical supply

All the green lines need to be checked. There is also a rubber "T" below the idle adjustment screw (lower right red arrow) and the Aux Air Valve is circled in green. In this picture the hoses for the AAV have been removed, they are supposed to be where the green "X" 's are located.
I once worked on my 1981 to replace the rear transmission mount. After I was done the car ran like absolute crap but all I did was change the one mount. WTF! What happened is when I changed the angle of the engine/transmission while changing the mount, the boot cam off the engine side of the AFM. It was not evident that it had come off. It left a gap on the bottom of the boot.
BTW the TPS has no hoses on it only one electrical connector. The hoses are connected to the throttle body, the TPS is attached to the throttle body.


Idle bump up for the A/C when it is on. Check the big hose, it is marked in the photo above.
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Discussion Starter · #17 ·
That is very good information to have, thanks for correcting me on TPS vs Aux valve.

I think I have an ohm meter, if not I can get one and will test.

I did check those hoses but didn't replace because they didn't look bad to me. They didn't feel very brittle either but maybe that doesn't mean anything. I did not check the boot connected to the AFM, it does have some small splits visible on the outside so I will replace that.

Your engine looks to be set up a little different than mine though, maybe just because you have stuff unplugged but it looks like some of your hoses are routed different maybe? Here is a pic of what mine looks like.
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That was not a picture of my engine, just one I got off the interweb. All of my original factory parts are hooked up and functioning as they should so both my cars start instantly when the key is turned. That is what you need to shoot for but ALL of the factory installed parts of the fuel injection system must be there and working they way they were designed. If you don't know how all of the sensors and parts work, watch this multi part video on the Datsun FI system. I know it has a lot of parts to it, but it really gives you a good understanding on how the individual parts work and how they work together.

You have a very typical looking 40+ year old engine. I can see that the electrical connectors have not been replaced, put that on your to do list. The new style Bosch EV1 connectors are super EZ to remove compared to the old style that break and become corroded.
Just an FYI it doesn't matter if you mix and match the injector connectors, all the injectors fire at the exact same time (gang fire). I see you have them labeled, but that is a good habit, labeling the wires.

Then read the FSM to understand how things are tested and what to look for if they are good vs bad.
If you plan on keeping the car and don't want to have to pay thru the arse for someone who doesn't know what they are doing, do some studying.
 

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Discussion Starter · #20 ·
A couple of those new hose clamps look like they're at least one size too big for those hoses.
That is very true, I didn't have smaller ones at the time and they were able to shrink down small enough to seal them so I just left them for now. Not a long term solution by any means, but I'm trying not to piss off my wife too much by always "throwing money away" on stuff I need lol.

Then read the FSM to understand how things are tested and what to look for if they are good vs bad.
If you plan on keeping the car and don't want to have to pay thru the arse for someone who doesn't know what they are doing, do some studying.
I will do my best! The car was purchased as a project so I'm not in a huge rush, other than my wife nagging about it needing to run or it's just junk and she "won't have junk just sitting around making our place look like hoarders" lol. Not that she can do anything about it, but I kinda like not being on her bad side. Thanks for the videos, I can use all the help I can get.
 
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