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[foshka]

Originally Posted by jtgh

you have power loss, forget all else till you solve that first.
see, the fuel pump and ecu are getting a low voltage, lower than normal.

weak pump can be
caused by low voltage. and reving engine changes alternator output and helps the pump. see?

I see, but I don't see how I have power loss.

Originally Posted by jtgh

any time the CEL lamp dims or goes out , at key on , no start, THAT is a power loss.
(could be a corroded FI fuse under dash or any 15amp fuse corroded above knees)

The CEL light does not dim or go out, it stays on brightly. The battery is only a few months old, and the starter works fine.

Originally Posted by jtgh

im hoping it is not the ECU. (91 ecU love to short the main caps out causing this)

i have full schematics for 91 , mine is same in my garage. below is engine schem.

with these any tech can find the voltage loss problem.

guttered out is , when out right?

Guttered means the rpm drop in a rough manner and went out yes. It is only word I could think of, like stalling but struggling as it goes down.

Originally Posted by jtgh

I always follow this flow.
it starts at the beginning of power. the battery.
make sure the power is good (when the problems happen)
at the battery, 12.5 v at the terminals.
then at the cigarette light , (yes) this shows power getting to the ECU is good both the power side and then the ground side.
meter to neg. shell , red lead to center pin, key on , see 12.5v or near.
ok we have power to the ignition switch.

The power then feeds main relay and fuel pump relay.
these too relays must have 12.5 on there outputs at key on.
the pump relay only energizes for 3 seconds at key on.

if you have power here then the ecu must be bad,
you can exchange it on ebay for $70

electrical problems can be hard. sometimes the problem is a short circuit.
these most be found and removed.
http://carfix.stufftoread.com/ECU/91...matic-base.jpg

see ecu/ecm pin b1 and b7 , the power at this node must be at near 12.5v.
if ever below 9v, trouble happens.
it must be 12v min.

the fuel pump could be marginal and the low voltage , shows this weakness.


any tech, with the above schematic in hand, can find the problem.
that is a fact.

if you ever need the full schematic PM me for it.
i can send it to you Monday. Im out of town.

( you could even have a bad battery and or Alternator)
make sure battery voltage hits 14.7v idling. if not turn of head lights.; now .14.7v.
if not battery or alternator are bad.
a bad battery can make an alternator go nutz, so watch that.

The battery is new, and runs the starter well. The headlights are bright and clear. I'll try to test the voltage myself in the morning.

Originally Posted by jtgh

your tech needs to learn to use a voltmeter. swapping parts is folly, usually.

the pump is not constant pressure,
the regulator does that,
if the pump is weak and you raise voltage the pressure can rise to the regulated normal value ,if the pump was below to start.
the regulator starts to work at 25psi and can go above 60 if you shunt the pump.
there are 3 test (8 really) but 1 key on pressure. idling, and shunted pump.
blocking return line shows shunt value.

All this data will allow you to find the real culprit.

cheers.

Okay, thanks for the clues. It looks like fuel pump could indeed be a big deal here. I will try your advice when I get the car back, about swapping the epu.

Thanks for bothering to read the forums and reply, while you're on your trip!