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Paul M ASE Master
Paul M ASE Master, ASE Master Tech
Category: Subaru
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Experience:  ASE Master Tech 20+ Years
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1991 Subaru Legacy: dies at idle and while accelerating..fuel pump

Customer Question

Hi - my 1991 Subaru Legacy dies at idle and while accelerating from time to time. No one can figure it out. I rep[laced the fuel pump and filter and it still does it. Then replaced the wires and plugs - was a bit better - ran longer, but still dies after a while. Put fuel stabilizer in to remove possible water, and still no better. I was told that the engine analyzer can't help with this problem. Any thoughts?? We are desperate, and may have to buy a newer car.
Submitted: 6 years ago.
Category: Subaru
Expert:  Paul M ASE Master replied 6 years ago.

Hello and thank you for using Just Answer

 

does it ever stall while driving? or only at stops? idle speed?

 

when it stalls does it start right back up?

 

Paul

Customer: replied 6 years ago.
Thanks so much for your reply. YES, it does stall while driving - often when turning or going up hill - and sometimes on the straightaway and sometimes downhill as well.

And YES, it always starts right back up when I turn the ignition, but sometimes it stumbles a few times after that, but if I keep it moving just above idle for a bit, and then slowly increase the speed it seems to run OK for a good while - then much later on - sometimes the next day, it does the same thing. Almost like it's starved for gas. But like I said, a new in tank pump and a new fuel filter didn't help at all.

Usually it doesn't stall until it's been running for a while, but when first starting up, if you let it idle for a minute or two without giving it gas, then it dies - RPM holds at @ 750, then it sinks a bit, and then suddenly stops. I tried it without a load (i.e., in neutral) & it doesn't seem to die.

I doubt it has anything to do with it, but I forgot that the the power steering has been out for quite some time - the rack & pinon leaks fluid like a sieve. We're used to driving it that way though. And the stalling and dying has been a fairly recent thing, while the power steering has been out for a long time. Still, I wonder if the dry pump was causing undue friction on the common belt. I am totally confused about what might be happening here. Thank you so much for attempting to deal with this baffling problem!

Ira
Expert:  Paul M ASE Master replied 6 years ago.

So it stall when in gear but not nuetral

 

I am attaching a list of things to check... check the throttle plate is clean first. and check for cracks in the air intake tube.

 

---------------------

 

Stalls in drive or reverse

 

Likely Causes
Throttle Body -
Carbon build up on the throttle plate or any other cause of low base idle speed can cause the engine to stall when the transmission is shifted into drive or reverse.
Idle Air Control (IAC) Valve -
A dirty or defective IAC valve can cause the engine to stall when the transmission is shifted into drive or reverse. NOTE: May also be referred to as a bypass air control (BAC) valve.
Overlooked Causes
Wiring Harness -
Engine movement can cause the wiring to rub through into a component and short out or cause broken wiring or poor connections to open causing the engine to stall when the transmission is shifted into drive or reverse.
Grounds -
Due to engine movement, loose engine control module (ECM) grounds located on the engine can cause the engine to stall when the transmission is shifted into drive or reverse.
Intake Air Boot -
A crack or split in the intake air boot can open up with engine movement causing the engine to stall when the transmission is shifted into drive or reverse.

 

------------

 

there is also some cases of the ECU connector causing a bad connection and a stalling

 

you want to check out all these items

 

let me know what you find and if you need more help

 

Paul

Expert:  Paul M ASE Master replied 6 years ago.

Please ignore the last message I had some technical problems with the page

 

So it stall when in gear but not nuetral

 

I am attaching a list of things to check... check the throttle plate is clean first. and check for cracks in the air intake tube.

 

---------------------

 

Stalls in drive or reverse

 


Throttle Body -
Carbon build up on the throttle plate or any other cause of low base idle speed can cause the engine to stall when the transmission is shifted into drive or reverse.




Idle Air Control (IAC) Valve -
A dirty or defective IAC valve can cause the engine to stall when the transmission is shifted into drive or reverse. NOTE: May also be referred to as a bypass air control (BAC) valve.





Overlooked Causes



Wiring Harness -
Engine movement can cause the wiring to rub through into a component and short out or cause broken wiring or poor connections to open causing the engine to stall when the transmission is shifted into drive or reverse.




Grounds -
Due to engine movement, loose engine control module (ECM) grounds located on the engine can cause the engine to stall when the transmission is shifted into drive or reverse.




Intake Air Boot -
A crack or split in the intake air boot can open up with engine movement causing the engine to stall when the transmission is shifted into drive or reverse.

-------------------------

 

there is also some cases of the ECU connector causing a bad connection and a stalling

 

you want to check out all these items

 

let me know what you find and if you need more help

 

Paul



Edited by Paul M ASE Master Tech Subaru Tec on 5/19/2010 at 3:19 PM EST
Customer: replied 6 years ago.
Thanks so much Paul - but your understanding of the problem is a little off, so I'd like you to re consider the situation before I start doing anything.

It DOESN'T happen when I place it into gear (BTW it's an automatic); rather, it shifts without and any problem, and runs for a while, or sometimes only few minutes before there's any trouble, and then when I take my foot off gas and run it just above idle, it can get through the episode, and then run fine for some time - but especially when accelerating up hill, it always stalls every two or three minutes if I put too much gas on (i.e. don't keep it just above idle.

While running the car today, it suddenly occurred to me that I should have checked the air filter. It was loaded with fine silt, though clean on the engine side, and I could see through a few of the creases. That couldn't have helped - so I just changed the filter, and will run later today up some hills to see if that helped. Also, while I think I know where the throttle body is (but not sure) I definitely don't know where the ECU & IAC are. Is there a web site that will have Subaru engine diagrams or photos that old('91)? Like I said, it has brand new ignition wires, so I doubt that there's a short there. Any possibility of the computerized module (if there is one) that controls running and ignition being the culprit? I live far from a garage, and the fact is that they haven't been of any help at all anyway. Please help me a bit more if you can, and I'll gladly deal with the whole acceptance process.
Expert:  Paul M ASE Master replied 6 years ago.

There have been cases of the ECU harness connector not making a good connection causing this type of stalling

 

Click here to view the report

 

run the engine while moving the connector and see if you can get it to stall

 

Paul

Customer: replied 6 years ago.
Hey Paul - sorry, but that had NO effect at all - and I believe that I was moving the ECU connector (wire clusters and connectors above and on the side of the right passenger foot well behind a carpet flap? I can't find a picture anywhere, only a brief desciotion of where it is located). And, even with the badly needed air filter change, it still seems to stall once and a while - though it seems like it is a lot less, but then I haven't really had time to do any serious hill climbing yet. I'm very perplexed about this, and am starting to feel that solving this is going to be just impossible! Car has 256,000 miles, and maybe it's something related to that? Yet, it seems to have lots of energy and umph, except when it stalls, or better said, stumbles, because it usually keeps running if I feather the pedel. Sorry to be so difficult about this, but nothing I've tried or that you've suggested seems to work.
Expert:  Paul M ASE Master replied 6 years ago.

On the right side kick panel is listed as a cruise control module

 

the ECU says it is under the left side of dash

 

unfortunately I do not have a graphic of it's location

 

the ECU has 4 seperate connectors that go into it

 

let me know if you locate it

 

Paul

Customer: replied 6 years ago.
Thanks Paul! That's where the unit was. But moving it made no difference at all. Still perplexed.

BTW, I read somewhere that loose baffels in the muffler could cause something like this. There is an occasional rattle somewhere in or around the exhaust system, though I think that it my simply be the protective cover.

Ira