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

[Dave WM]

Next most common is leaking FPR. odd readings that are not effected by vacuum would be a clue, but a definitive test is to detach the vacuum lead and look for leaks.

checking the cold start valve is easy just pull it and make sure its not leaking. should not fire at all if temps are over about 70f

[Dave WM]

also check the condition of the boot from the AFM to the TB for cracks, unmetered air is covered in the FSM.

On diagnostic that is often used is try removing the oil cap while idling. If the system is working properly the engine should sputter and die. if it runs better then you have a too much fuel situation.

if it has no effect at all then its just running a tad rich at idle.

[madkaw]

15 minutes ago, mbz said:

Madkaw, thanks for the advice.

At this point, my weekend time to trouble shoot car is done, but I am trying to narrow down what I should look at next weekend.

I agree on the battery, but I want to get stable start and idle sorted first.

Yes I have EFI manual (thank you calssiczcars) and have been reading it.

Doing the routine maintenance stuff seemed like the first logical step and it needed to be done anyway (fuel filter, air filter, spark plugs, and found a fuel hose and air hose the needed to be replaced while I was poking around).

I'm leaning towards checking fuel pressure / fuel pump as the next step in trouble shooting and I guess I'm looking for guidance/agreement from the group before committing to that as next weekend's project.

If that checks out, then air intake/throttle system seems like the next logical step.

Am I on the right track or missing the point completely?

The one thought that is nagging me is that the rough idle makes me think there's a misfire, but.....?

You need to lean towards ignition first. Sounds like a weak spark that you have to rev the engine to keep it running. Have you checked spark color ? Have you inspected the dizzy cap for cracks. Is there moisture in the cap. Are the wires tight around the dizzy. Is the coil getting proper voltage? Is it putting out a blue spark?

Now start on the fuel

[Zed Head]

The leaking FPR, through the vacuum hose, and the coolant sensor are high probability and easy to check.  The leaking FPR is one that would come on quickly too.  The diaphragm cracks and it's broken.  If there's gasoline in the vacuum hose it's toast.

Those plugs look terrible, very rich.  And you should use less never-seize.  There's probably enough in the holes now to last the lifetime of the engine.  It's dangerous too because you can over-torque your plugs.  Not good in an aluminum head.

[mbz]

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.

In addition to re-sealing injectors, notes state all mount holders and fuel hoses replaced. Upon inspection that appears to be the case.

PO's mechanic resealed thermostat upper housing.

So I'm thinking I should do this for next weekend's trouble shooting:

1. Check distributor cap for cracks and moisture, as well as checking spark color for blue spark.
2. Remove oil filler cap when engine is idling to determine if engine is running rich or lean.
3. Check fuel pressure.
4. Check injectors, make sure all are working.
5. Check Water Temperature Sensor.
6. Check Fuel Pressure Regulator.
7. Check Cold Start Valve.
8. Check boot from AFM to Throttle Body for cracks.

Is that about right?

If so, I'll start reading up on the procedures and getting tools / parts in order for next round of testing.

 

Edited March 18, 2019 by mbz

[madkaw]

4 minutes 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.

In addition to re-sealing injectors, notes state all mount holders and fuel hoses replaced. Upon inspection that appears to be the case.

PO's mechanic resealed thermostat upper housing.

So I'm thinking I should do this for next weekend's trouble shooting:

1. Check distributor cap for cracks and moisture, as well as checking spark color for blue spark.
2. Remove oil filler cap when engine is idling to determine if engine is running rich or lean.
3. Check fuel pressure.
4. Check injectors, make sure all are working.
5. Check Water Temperature Sensor.
6. Check Fuel Pressure Regulator.
7. Check Cold Start Valve.
8. Check boot from AFM to Throttle Body for cracks.

Is that about right?

If so, I'll start reading up on the procedures and getting tools / parts in order for next round of testing.

 

Sounds like a good list. At least the car had some maintenance, maybe not recent, but some engines get no love. 

The AFM boots crack where you can’t see it, but maybe feel it, or remove and inspect. 

[Dave WM]

Still don't like the idle adj screw not having any effect. There is something wrong there, You are on the large screw with a spring that sits atop the throttle body right next to the dash pot right? 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, OR something going on with the BCDD again bleeding excess amounts of air. that would account for a to HIGH an idle which does not seem to be the issue unless there are other problems resulting in the low idle. Very confusing.

[jonbill]

Those old spark plugs look quite cold, colder than standard which would contribute to fouling at idle. What plugs are the new ones?

[mbz]

DaveWM, yes the large phillips head screw running through the spring that sits on top of the throttle.

jonbill, the old plugs were Bosch, the new plugs are NGK.

[jonbill]

DaveWM, yes the large phillips head screw running through the spring that sits on top of the throttle.
jonbill, the old plugs were Bosch, the new plugs are NGK.

Which NGK? BPR6ES?

[mbz]

Which NGK? BPR6ES?

 

BR6ES

 

I’ll replace them again soon enough and didn’t want to get spendy with the spark plugs until I have the issue sorted out.

 

 

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[jonbill]

 
BR6ES
 
I’ll replace them again soon enough and didn’t want to get spendy with the spark plugs until I have the issue sorted out.
 
 
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OK, they're cool. Never mind me. :)