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

[Zed Head]

1 minute ago, mbz said:

Flogging a dead horse on that point.

It's your horse.

I think I'm out.  This isn't about making an old Z run right anymore.  Good luck.

[mbz]

1 minute ago, Zed Head said:

It's your horse.

I think I'm out.  This isn't about making an old Z run right anymore.  Good luck. 

Thanks for your help Zed, have a good one.

DaveWM, I'll check back in tomorrow when I have a different fuel pressure gauge.

I'm going to go clean up.

Edited April 14, 2019 by mbz

[mbz]

16 minutes ago, Zed Head said:

The AFM has probably been adjusted, by somebody, in the past.

Maybe it's time to take it to an expert for correct calibration?

Or perhaps the AFM is better off being replaced?

Edited April 14, 2019 by mbz

[Patcon]

1 hour ago, mbz said:

Maybe it's time to take it to an expert for correct calibration?

Or perhaps the AFM is better off being replaced?

Very few experts still alive for these AFM's. Stick with it and these guys will help you get it sorted. Even some of the refurb'd AFM's run rich. Your problem is solvable. Just need to have confidence in the test results. Confirming your gauge is good is probably a good move.

[Dave WM]

I am going out to the garage and see if I have one of those gauges like you have just for fun. The hardest part about remote diagnostics is the remote part. It can be frustrating when you cant actually be there and feel/smell/touch parts that may give a clue. No reflection on your effort, its just hard to do. Some times you go down rabbit holes, but eventually most of the time it gets sorted out, often with something simple. as far as AFM, there are test that can be run, but again no reason to start down another path until this is resolved one way or another (fixed or ok all along and just a gauge issue). The new FPR seems to be reacting to vacuum since it doe change pressure downward so that's good.

Edited April 14, 2019 by Dave WM

[Dave WM]

 

Edited April 14, 2019 by Dave WM

[Dave WM]

Note I used two different gauge types not the same exact gauge x 2. The theory being its un likely that two completely different gauges would both be wrong and have the exact same wrong reading. If you bought two of the exact same brand/type/function, I suppose there is a possibility that a manufacturing defect could effect a single lot of product. Just something to consider. ANY kind of gauge that you could rig up would be fine. in this example I used a oil pressure gauge. I had to get creative hooking it up since the treads for the oil gauge were not compatible with my T adapter I used for the fuel pressure gauge. Any generic gauge with a decent sized readout would be fine.

[240260280]

Made in China.... no quality control.... just ship them all and let the people down stream deal with the flaws.

[mbz]

I have results from the loaner fuel pressure gauge..... they're good.

My fuel pressure gauge was way off. (chicken dinner for Zed) ?

Here's the results:

Fuel Pressure with Fuel Pump ONLY: 36-38 psi (hard to tell from angle of camera, but well within spec)

Fuel Pressure with Engine Idle: 34 psi (RPM = fluctuates between 400-500 at idle)

Fuel Pressure with Engine Idle and OIL CAP OFF: 32 psi (RPM = fluctuates between 600-1,000 at idle)

When idling, if I open the throttle.... initially the engine hesitates then starts to rev to higher RPMs.

With the oil cap OFF the engine will return to idle.

With the oil cap ON the engine will drop to idle, then stall and will not start.

Edited April 14, 2019 by mbz

[Reptoid Overlords]

Is the engine producing any type of smoke out of the exhaust when it's running with the oil cap on? 

[mbz]

Just now, Reptoid Overlords said:

Is the engine producing any type of smoke out of the exhaust when it's running with the oil cap on? 

When at idle, NO / negligible.

When RPMs are increased, YES.... LOTS of BLACK smoke.

[Dave WM]

So now on to more test, this time you want to move on to the water temp sensor, check a the 36 pin connector, compare to the FSM. this is important since you don't wan to have the thermotime and water temp sensor leads mixed up. Reading at the 36 pin connector make sure wiring is correct and connection are good.

After that you want to check the AFM air temp sensor and the Static reference resistance readings I think its 6&9 one of them should read 100  ohms.

Also if not already done clamp off the fuel supply to the cold start valve. You don't want to be leaking. If its clamped it can't let any fuel in, even if it is defective.

 

Edited April 14, 2019 by Dave WM
added stuff