Parlor Tricks

[ETI4K]

That's a lot of very good information, and of course, it changes the search path.

You wrote the problems lives in 500-2000rpm range.  Perhaps the AFM windings are damaged in that range since that may well be where the wiper has spent most of its time.

If there is any way you could plumb in a fuel pressure gauge to read dynamic fuel pressure it would be very helpful.  That might help separate fuel system from ignition system diagnosis.

As for ignition,  connect a timing light to any plug wire, put the light in the cabin, and go for a drive. If it acts up, turn on the light and point it at anything.  If the light flashes without interruption, it would suggest the problem is not ignition. 

It's a bit of Dr. Frankenstein's monster I know, but perhaps worth the effort.  I've solved more than a few problems this way.

[ensys]

 

Mr.ET14K:

My kudos for your apparently rare sense of persistent helpfulness. I thank you, Sir.

I too, have considered the fuel pump function, especially in light of, if the FSM is to be believed, the fact that the F.I. relay has just passed the muster of diagnostic exam  (thus debunking my current reckon of root cause).

As I continue to hope the fault lies away from the ECU, I am drawn to the remaining suspects, TPS, or (dread the thought) the AFM.

But still, I remain flummoxed by the symptoms: pumping the throttle sometimes restores function, and how ign. sw. play does the same more reliably..

Add to this the fact that I still cannot decide whether the fault lies with fuel delivery or ignition.The plugs still present sooty, but this still only confirms poorly combusted fuel, but fuel none the less.

It does occur to me to monitor fuel pump function as the reading might be clue-like. The problem here, is that the "clue" might well be second hand to the root issue.

The idea of verifying ignition at the plugs has some merit, but when the engine stops, I have no doubt that the ignition has ceased to function. The issue remains, "why?".

At this point, as suspects go, there is the TPS, or a time to re-visit the AFM. Or perhaps the intolerance to load points to the distributor/timing functions.

With the pass of the F.I. relay, I'm running out of suspects.

I can't escape the sense that I am missing something very obvious.

- Edit -

The problem with the AFM theory is that it does not possess the ability to change from sweet to nasty instantaneously. A bad sweep can't turn good and back again at the drop of a hat.

The fact that there is no more "sweet" leads me to believe that whatever the cause, it has failed permanently.

 

Does this point to a distributor function?

 

 

 

Edited September 5, 2020 by ensys

[dutchzcarguy]

On 8/22/2020 at 10:28 PM, ensys said:

Mr.Uglyface is a cranky, ill mannered motor that refuses to idle, won't tolerate throttle, and which bucks and lurches up to about 2K rpm,

I "cleaned"my 280zx engine last week  (and failed.. it needs a brush and polish..)  but after i cleaned it with water from the hose i had some water in the connector on that little box which sits on the throttle shaft and i had an engine that did what yours is doing.. it idled well but i could not get it over 1500-1700 rpm's..  maybe your little box on the throttle shaft is "kaputt"