1976 280z engine runs rough then dies, will not idle.

[Zed Head]

17 hours ago, mbz said:

Zed, those in the photos are the old spark plugs I removed. They were installed by PO's mechanic. I did not use never-seize when installing new plugs today.

Also in the service notes from PO's mechanic, he adjusted the mixture a bit leaner to pass smog.

Why did you show the old plugs from before the tune-up by the Po's mechanic to pass smog?  They don't tell you what's happening now.

If the PO's mechanic got the car to pass CA smog then it must have been running pretty well.  Most of the suggestions here are for old sat-for-ten-years engines that barely run.  Your problem looks like something broke recently.  So don't go crazy, and make sure that you record every change you make so that you can undo it.  You're on the verge of creating a terrible EFI nightmare.

[mbz]

Zed, I showed the old spark plugs because the old spark plugs tell what the conditions have been present in the engine in the past. My bad.... I thought it was obvious they were the old ones because of how worn out they are.

I can pull the new ones later tonight, take some pics and upload for review.

Regarding work done so far, I have not gone crazy. I did some basic routine maintenance as a preliminary trouble shoot. I don't think replacing an air filter, a fuel filter, 6 spark plugs, a gashed fuel line and a dried up split and cracked air hose constitutes going crazy, nor creating an EFI nightmare.

I can assure you, I am not looking for any more trouble than I already have. I'm pretty upset that a car I just bought (that is supposed to be in good running condition) is not idling well and dies and won't start. ?

I am turning to this group for help (because of the size and combined knowledge of this group) in an effort to quickly and efficiently trouble shoot the matter.... without creating an EFI nightmare. However the possibility that an EFI nightmare was already there and waiting to happen is very real, although one I would like to avoid if possible. If unavoidable, then I'll just have to deal with it because the car needs to be able to pass smog every 2 years until California changes the law (not gonna happen).

Regarding PO's mechanic getting it to pass smog, I suspect it was just a matter of tweaking it until a fellow mechanic's smog machine said it was good to go, then running it past the DMV. Doing just the bare minimum to make it pass for registration and sale. Dump the problem on someone else and be done with it. It's not a pleasant thought, but it happens.

If you believe that something broke recently, do you have any suggestions on what it may be so I can take a look at it? ?

I posed 3 videos with audio above showing what is happening..... no comments on that so far, has anyone taken a look and listen to the videos?

I posted them to provide a better representation of what the problem is in the hopes that someone who knows better than me (probably most people on this forum) can see it/hear it and say "Oh it sounds like it might be _____________", check the "_________________" first, then check the "________________". I know it's not usually that simple, but then again, sometimes it really is that simple.

DaveWM brought up a really good point above about the idle adjuster not having any affect: "Still don't like the idle adj screw not having any effect. There is something wrong there, ...... If its not working I would suspect a mechanical problem with the throttle not allowing the valve to completely close, thereby rendering the idle air bleed useless...."

So far I've gotten pretty sound advice from this group and I think my plan for the next round of diagnostics is pretty solid.... again, not going crazy and creating an EFI nightmare, so I don't think it's time to go into panic bros. mode just yet. ?

I have downloaded and am reading both the factory service manual and the fuel injection service manual (or the FI bible). I also have a Haynes manual (not very helpful as it pertains mostly to 240's and 260's, but does have some updated FI info in the back supplemental section, however that info is also in the FI bible).

Is there something I'm missing besides showing the condition of the new spark plugs?

I don't want to over-react to this, I just want to diagnose and fix the problem so I can get on with the suspension work that is waiting for me next.

Again here is my diagnostic game plan so far for my next opportunity to work on the car:

• Check distributor cap for cracks and moisture, as well as checking spark color for blue spark.
• Remove oil filler cap when engine is idling to determine if engine is running rich or lean.
• Check fuel pressure.
• Check injectors, make sure all are working.
• Check Water Temperature Sensor.
• Check Fuel Pressure Regulator.
• Check Cold Start Valve.
• Check boot from AFM to Throttle Body for cracks. Will probably also inspect the throttle body while the boot is off.... anything I should be looking for?

This all seems pretty simple and straight forward but you know more than me.......so any thoughts on this?

Your help and input is appreciated.

Thank you.

Edited March 18, 2019 by mbz

[Dave WM]

never mind I did not see the last post. get a quick reading off the plugs, even if just for a few minutes.

 

Edited March 18, 2019 by Dave WM

[Zed Head]

23 hours ago, mbz said:

1976 280z California edition (manf. date Sept.1975).

Bought the car in late Jan. 2019, car passed emissions test and it started and drove fine until 2 weeks ago when problem first occurred.

All I'm saying is don't make things too complicated.  It passed emissions in California, which is difficult to do.  I'd be surprised if the days of the shady smog guy are still in play these days.  The fines for doing that are huge as I understand it.  Beside that, the car has been running fine for 2 1/2 months, when, apparently, a problem "suddenly" occurred.  A shady mechanic can't make a car run well for just 2 1/2 months.

The seller of the car probably sold you a good car.  Something small and simple is probably broken or stuck. 

Have you been beating on it?  Taking it up to redline, banging through the gears?  Have you been maintaining it properly?  Has it run low on oil or coolant?  Have you been adding "wonder chemicals" to the gas tank, like Seafoam?

Once you get the EFI systems back in spec. they're pretty steady.  They don't need constant attention.  Watch the oil and coolant levels, put gas in, and drive it.

[Dave WM]

just watched the videos

you def want to listen for injectors all clicking use a stethoscope.

IF all click, disable one injector at a time and see how it effect idle (load test).

will know a lot more based on the above answers AND a reading of the plugs.

Regarding hard starting, this can be a real bear. I fought with it for a long time, I refer to it as intermittent starting, so after you get it to idle smooth and the idle bleed air working you can determine if its hard starting always OR intermittent starting (sometimes it will start right up).

The good news is these engines are extremely easy to work on and the EFI works really well when everything is in spec. The bad thing is the ECU operates in "open loop system" there is no feedback on what the actual A/F ratio is so sensors must be operating correctly, the ECU can not "Learn" or "Correct" for any problems.

 

Rough running has to be:

Compression (a compression check is always a good idea).

Fuel pressure readings ( both with engine off and running will narrow this down) and all the EFI

Air (really proper air metering)

Spark (plugs/wires/dist/timing)

 

you are on the right track just do one thing at a time. Note we forgot to mention grounds, HUGE issue is wire and connectors and grounds. This is one thing the FSM does not go into, I suppose since no one figured the wire harness had to last 45 year or longer. there are several grounds and connectors. Just checking things can cause breaks and lets also discuss NEVER clean the engine with water, no pressure washing, leave it dirty.

 

 

 

 

 

 

 

 

 

 

 

[Dave WM]

you are going to have to eventually fix that idle screw not working, I keep coming back to that since generally speaking something like that is trying to tell you something. The only way it cant work is if the passage that it bleeds air thru is blocked, which would make setting the idle nearly impossible. You also have the AAR valve that maybe acting up both it and the idle bleed air allow air to move thru the throttle independent of the butterfly valve on the gas pedal.

I don't want to sidetrack you too much, its just something that HAS to work if you ever expect the car to run or at least idle correctly.

 

[mbz]

Zed, I'm trying to keep it simple.

I never said it was a shady smog guy (please don't put words in my mouth, I'm not accusing anyone of illegal activity or intentional wrong doing).

To clarify my statement, I suspect that the mechanic knows another mechanic in the same area that has a smog testing machine, that would smog it for him until he gets the proper readings so that it could be taken to a DMV facility for smog check pass.

The car has not been running much at all for 2.5 months, I drove it a whopping total of 4 times....... mostly neighborhood drives less than 10-15 miles aside from the 75 miles drive home after initially purchasing it.

I have not had a chance to beat on it, I would like to really drive it.... BUT IT'S NOT RUNNING!

The oil levels are fine, coolant levels are fine, brake fluid fine.

The only things I have done to the car was listed above. Here it is AGAIN for convenience:

Replaced air filter, fuel filter, 6 spark plugs, a gashed fuel line and a dried up split and cracked air hose.

Is there something I'm missing besides showing the condition of the new spark plugs?

I don't want to over-react to this, I just want to diagnose and fix the problem so I can get on with the suspension work that is waiting for me next.

Again here is my diagnostic game plan so far for my next opportunity to work on the car:

• Check distributor cap for cracks and moisture, as well as checking spark color for blue spark.
• Remove oil filler cap when engine is idling to determine if engine is running rich or lean.
• Check fuel pressure.
• Check injectors, make sure all are working.
• Check Water Temperature Sensor.
• Check Fuel Pressure Regulator.
• Check Cold Start Valve.
• Check boot from AFM to Throttle Body for cracks. Will probably also inspect the throttle body while the boot is off.... anything I should be looking for?

This all seems pretty simple and straight forward but you know more than me.......so any thoughts on this?

Your help and input is appreciated.

Thank you.

 

[mbz]

DaveWM, I am picking up a stethoscope this week, will check injectors this weekend. The rough idle makes me think of a cylinder misfire, possibly injector related.

I really think you are onto something with the air / fuel mixture being incorrect and a problem with the idle adjust / throttle not functioning properly. Suspect the engine is getting too much fuel and flooding, hence why it will not start after it dies. Will check distributor and quality of spark as well to be sure.

I did gas up once at the local Costco after purchasing it, still have 2/3 of a tank left. I usually get good gas from Costco and never had trouble in any of my cars with their gas.

The electric connectors and wires look very old and brittle as do some of the hoses. I am trying to be very very very careful when working in the engine so as not to cause any new problems. Hoses I will replace as I find cracks and splits.

Quote

you are going to have to eventually fix that idle screw not working, I keep coming back to that since generally speaking something like that is trying to tell you something. The only way it cant work is if the passage that it bleeds air thru is blocked, which would make setting the idle nearly impossible. You also have the AAR valve that maybe acting up both it and the idle bleed air allow air to move thru the throttle independent of the butterfly valve on the gas pedal.

I don't want to sidetrack you too much, its just something that HAS to work if you ever expect the car to run or at least idle correctly.

I Completely agree with this and suspect that the core of the problem lies somewhere in here, but need to do some more diagnosis first.

Thank you for the great advice! Much appreciated.

[jonathanrussell]

Hi and welcome. Sorry you are having problems with your new 280. Keep this in mind though. it ran well recently so chances are you will get this sorted out and it will run well again.

It worries me a bit that the prior mechanic wrote that they leaned the mixture. There really isn't a way to do that without screwing with the AFM which causes all sorts of other problems. Hopefully he did nothing.

FYI, I watched your video. It sounds a lot like my 75 did at one point.

I like your list of things to check this weekend. I would also remove the AFM boot(s) and check the inside of the AFM to see whether the Flap is stuck open. It should close when car is off and move freely up and down. I have seen an intake (not exhaust) backfire in a 280 cause the AFM flap to bend slightly. When this happens it can get stuck open. If it gets stuck open the car meters all the time like you are at WOT. My 75 had this problem and ran very much like yours in the video.

Best of luck. Don't get discouraged. You are going to really enjoy the car once you get it sorted.

 

[Dave WM]

the ground connections are all over the place, and there is not a real good test for them. Treat them after going thru the stuff already if nothing helps. The only way to test is to wiggle to see if they are broken, clean the spade and make sure you have good contact with the chassis ground. The really tough dogs are things like the grounds. Unrelated but still interesting, I used to do a lot of vintage electronic repairs on old TV's, vacuum tube stuff. In one set I had a very slow moving hum bar (horz bar moving upwards thru the picture, distorting the image). Generally speaking they were a result of a DC power supply that had excessive AC ripple to it. I ended up replacing the filament current with DC from a 6v battery pack before I got rid of it. Then I started trying each tube going back to AC for the filaments one at a time. when I get to the vert sweep board, it finally returned. The final analysis was there was a loose screw that secured a printed circuit board ground, not firm enough, and the filaments shared the ground stake. This low resistance allowed just enough hum to get into the ground circuit of the vert sweep tube, result, hum bar. tight the screw and bar goes away (I soldered a buss to it anyway, dumb design IMHO for rely on pressure to maintain a ground but that is EXACTLY what our cars do. Now with the car a slightly imperfect ground does not show up like it would on a CRT, but the point is pressure contacts for grounds are suspect.

[Patcon]

You mentioned fuel and I don't wan to muddy things up but you might consider a bottle of fuel treatment in case you got some water in the last fill up.  With the help you already have, you should be able to get this sorted. Just keep trying what they ask and feed the results back.

[madkaw]

Just watched the vids and my money is still on ignition. That ignition coil looks like the original . I was go to fuel last . The fact that it happened kind of all the sudden, I would think ignition.