91 threatening to stall

[foshka]

I'm hoping those of you with more experience than me, like jtgh, might be able to help me figure out which repairs I need.

I have a 91 sidekick jx, 4wd, with the 8v tbi engine.

Last half year I've been smelling gas, shortly after starting up, and gas milage has been poor, but it was otherwise running fairly well.

In the middle of a cold night last week, I tried to turn the engine on and the CEL lit up and it 'guttered' out. Turning it on got it going, CEL stayed on, but I smelled gas when the wind blew my way, and the tachyometer was going crazy. It would shoot up for a moment then come back down, then do it over and over. As the car warmed up, it continued to jump but was not going as high. It would eventually jump only .1 on the tachy or so, almost a flutter up, but you could hear the engine run at the slightly higher level then go back down.

If I depressed the accel slowly I was able to get the engine going at higher rpm's, and the 'tic' of the tachyometer became almost unnoticable at those rpms. But if I depressed the accel quickly, the engine made a yawwing sound, the rpm sagged, and it almost stalled out, but then pulled out and accelerated up to higher rpms.

When I tried to take it in, turning it over the car stalled out. It took 3 tries to get it to stay on.

I was able to drive it to shop, and noticed that when I came to stop at a stoplight for a while after driving for a half mile or so, the rpm sagged again, and it helped avoid that by putting it in neutral as I came to a stop. Also, when going slowly in reverse (in gear at low rpm's), rpm's sagged and it threatened to stall.

After an overdue tuneup that did not help, the shop said the ecu needed replacing (wanting to charge me $800 for the privilege) and also said fuel pump was bad, that it was producing low psi at idle. They could not explain why a constant-pressure pump would somehow be working fine when the rpm's are high then suddenly work less well when the rpm's dropped. I didn't understand that. Could the ECU be the cause of all of this, or is it likely both are wrong? Any suggestions? I've been taken advantage of recently with this car at another shop, and don't care to repeat the experience, and a little insight from those of you others who are familiar with symptoms might make a big difference for me.

Thanks in advance!

[jtgh]

welcome , i can help !
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?

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)
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?

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.

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.

[jtgh]

if it were mine and troubleshooters were sparce.
get a $70ecu from ebay,

see my link on my dead ecu page.

cheers.
1/10 price.
many happy ppl here from him,

im not affiliated...

[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!

[foshka]

Originally Posted by jtgh

if it were mine and troubleshooters were sparce.
get a $70ecu from ebay,
see my link on my dead ecu page.
many happy ppl here from him,

Motoguys is also on ebay and for $149 they also have a 5 day free try to see if solves my problem. That looked good.

[jtgh]

sorry misinterpreted guttered,
could'nt figure did lamp gutter or did engine, now i know it was the engine.

we get huge power loss fails on these cars. posted here, huge. after all your mech cant fix it so ppl post here.
or mech wants 2 times cost of car to fix it. welcome, we can help.

Ok fuel pressure
that
ground wire behind left rear tail Light. runs pump.
common fail here.

next,
lets not guess? can be expensive.
can you keep engine running with fast right foot.

when you say smelling gas,
like raw from tank like when cap is off or filling car
or burned gas , black rich stinking poorly burnt gas from end of tail pipe.
?


you said CEL stayed on (after starting) wiell pull the codes.?
any time the cel is on , running the ecu is trying to talk to you.
just pull the codes.

this ecu never sets the cel (running) unless something is GROSSLY wrong.
find out what it is FIRST.

couild be eGR stuck open.
who knows,

this is true btw for all cars with obd1 or obd2, no matter what the car ,
do read the DTC failure codes.

then repair these gross errors first.

on newer cars you can get a fist of errors. post them.

thanks for sharing.

cheers.

[jtgh]

Check Engine Lamp stuck ON?

listen for the fuel pump at the gas cap hole.
it only runs for 3 seconds each key on.
helper time.

if no sound , check power to pump
if it buzzes ,then check pressure.

very simple logic. here.

see if car starts easier with 5% extra throttle.
add ing air , if that helps , then the IAC is not opening , allowing correct AFR.

the unflood mode WOT can hellp start car.

if car is flooding for get fuel pump.

the 8v will flood if
1: IAC base thermo is clogged.
2: IAC electric is clogged.
3: fast cold start idle dash pot is INOP
4: Fuel pump regulator is stuck closed (rap the dickens out of it) with screw driver.

when the car does not start.
determine
1: loss of spark
2: loss of fuel
3: too much fuel

if you can answer the 3 primaries (there are otherss)
then you may quickly , head in the correct direciton.

#4 cam belt slip

I never advocate throwning parts. ever.
its your $


cheers.


tell how car starts and runs and makes power.
1: cold
2: hot.
and hot starts
and does it have full power hot can cold.
can it climb a hill hot and cold.
a full spectum symptoms, tells volumes about what is wrong.

what is working correct can really help the tech.

cheers.

[jtgh]

2 rules.
dont throw parts.

say what works good and what dont work.

my car is hard to start hot and cold
and when i can get it to start, it has no power hot or cold.

what do I do next.

by using unflood mode the car starts in a black plume at tail pipe.
also i can keep it going with added throttle .

this is an example.

[jtgh]

My Car Is Strange

my getting started page.

[foshka]

okay you did a few posts here.

I tried to pull the CEL code, and am pretty sure I found the SES switch (though on my 91 JX it faces up and moves from side to side).

However, the CEL remains constantly lit. No code blinking even when short is in place according (91, so I found hte white plug hanging next to fuse box and battery, put in jumper paperclip). Not even 12, just constant CEL.

The dealership told me that there was an internal error and it needed a new ECU (gah the price they quoted me though was $800), and they said the fuel pressure was low at idle.

It is hard to start cold, have to turn it over a few times before it stays on, otherwise the rpm sags roughly and it dies, and I smell scorched gas. No smoke, or if so it clears so fast I can't see it.

Before its warmed up, depressing the accel makes the rpm sag and it almost dies.

When warm, if I press accel all the way, for a few seconds it struggles then revs. But if I push accel slowly down, the engine goes up okay.

Most worrying symptom to me is the tachyometer tic. The rpm needle jumps up and comes back down. Then after a bit jumps again. When cold, it happens BIG. The jump is over 1k. When warm, the jump is small. When high rpm the jump is small. My suspicion is that it is the ECU bad doing this, so I am going to try a new ecu next day or two and see. I could be wrong. If wrong, I don't know what I'll do.