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Misfire, but no DTC's?
oops no xls.?
the maf is ok.
the short pendings list is only what the ECU thinks is important for P300.s.
that maf unplugged test seems to me the injectors are clogged,or fuel pressure low , only on full demand(flogged up hills or wot)
or main filter is dirty. does the filter look 20 years old. if yes probably is, just glance at it, and can tell.

yes the balance test needs and injector pulser tool, to it pulses it and not burn up the 10 ohm coil inside.
my guess is this balance test is a waste of time if all 4 are equally clogged, as yours seem.
the injectors have 10micro sized screens inside (4 times smaller than main filter) an only back flushing them can clean those out.
the CAT is not melted or vacuum will seem backwards as you gun the throttle. (act so odd you will not miss that once seen)

if fuel pressure is at spec, at the bog, the injectors are clogged i bet.
if the propane test shows power returns the injectors may be clogged. (2 man test , one on propane hose , inserted in to IAT sensor port, pulle.
vacuum leak would have to be massive.
good luck to you, any have great NEW YEAR.
or remove 1 injector
turn it upside down an tap it gently on white paper towel. see if a bunch of rust falls out, or green slime?
the balance test works of the leakdown test passes. holds pressure for 1minute or lots more, and steady so you can pulse it an see the time it takes to drop to near zero PSI. (this test is crude flow rate test)
many times the leak down test fails,due to bad FPR/ or injector leaks or that silly check ball valve in the pump is bad.
making this test not easy unless lucky.
Darn it - It looks like I forgot to hit the "Add Attachment" button after selecting the Excel/.xls file... Here it is...

Attached Files
.xls   P0300 Code_X90 OBD2 Data 19 DEC 18.xls (Size: 32 KB / Downloads: 1)
the real confusing thing is pram 10, long term fuel trim.
short is +9 (super lean) (adding lots of fuel here. so is lean at this high power demand) (this means adding 9% more after maf is computed)
long is -0.8 (seems late to catch up to above.) could be late and no valid.

i guess its bogging, starving for fuel.
i'd try propane tests (add this new fuel to see if bog abates some)
make sure fuel pressure is at spec, at any bog. (can be very hard to do this) I know.
there is no data there to tell why it leaning out, besides.

my trim looks like this. bottom red lines.


the maf never goes normal, at wot ever. never goes near 50, (sure if no fuel flow how can it)
the 300 DTC happened at 1/2 engine load, 50 % approx. (cant go higher due to bog)
my guess is it is going lean, and if felt as a smooth non violent bogging, like driving in deep mud or a swap bog. lack of power, engine I guess is putting out 40HP max, not 95HP/
the maf can not reach 50 because the fuel injectors are not flowing.fully.
this old ECU does no have injector PULSE width, readings , but im sure its going to max, if the MAF works so be PWM to the injectors at max, flogging it wot.
the fuel pressure are very important, for sure a working FPR, to get that
the FPR runs pressures to max at wot. full 36psi on mine, (30 at idle) but must rise by 6psi, or the fpr is dead. usually if keyon, no start is 36psi its ok.
if all that is ok then the injectors are packed. (gummed up from bad fuel)
January was cold, and February was snowy AND cold, so last week I ended up taking the X90 to my auto repair guy who has better diagnostic equipment than my Autel AL619.

He showed that the voltage output of the coil was very low when the throttle was applied quickly.

I ordered a WPS DST25404 distributor, got a new set of spark plugs and the o-ring for the distributor housing.

A couple of hours working in sunny and 53 degree weather, and the X90 now runs great! Now to part it out so I can put the G16B in my Samurai!

thanks for the update
seems the spark induction coil in side the distributor is bad, and is common this old.
he must have scope like ,me. to see it fail at high RPM.
good deal

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