Engine stall on steep grade

[Guest Grounded1]

Hope someone can give me a new direction here or its Suby goodbye.

Whenever I go up a steep grade at about 35-50mph the engine will lose rpm up the grade and I'll ofcourse give it more gas. It makes no difference and the engine rpm willgradually drop until it stalls out. If I continued to give it more gas as it loses power the engine will sputter and kick. If I let off the gas before it stalls I can rev the engine up and clear it out and it will be ok (if I dont continue up the hill). It doesn't happen above 55mph. I have a vacuum gage in my car and the loss of power wont happen until I get the engine vacuum under 5 inches which means almost WOT. If I let it stall the engine won't start unless I shut off the ignition and turn it back on.

I started having this problem last August and have been progressively checking everything under the hood and replacing the marginal ****.

I've replaced the knock sensor, water temp sensor, the O2 sensor and the Mass airflow sensor. The stuff I've checked per the Subaru shop manual is....everything. The throttle position sensor is good, the idle air valve is good, the coil is good. I have new plugs, wires, filters (fuel & air). My fuel pump pressure is perfect, the fuel regulator checks out fine with a vacuum pump and fuel pressures are good at the vacuum settings in the manual. The pinch off pressure for the fuel pump is fine(75 psi).

Even if I anticipate the hill and throw it into 3rd the rpm will go to about 32-3400rpm and still do its power loss thingwhen I get cole to WOT(less than 5 inches vacuum). Reset the computer, no help. THis is getting really annoying. Any leads would be appreciated. I wouldn't wish this on a ford.

Oh yeah, NO CODES ever. No freakin codes!!! The only thing I haven't done yet is do the D-check mode. I'll do that tomorrow and hope that something pops up but I'm not hopeful. I think I might invent Subycide.

 

Pat

91 2.2L 4EAT

[Guest Legacy777]

hmmmm......that sounds very weird......sounds like you're doin your homework checking the different stuff......even the MAF.....

 

Is yours turbo or N/A?

 

What is your vacuum? Does it only do it goin up a hill? Or does it do it when you're flooring it and engine is under load?

 

Have you tried replacing the fuel filter?

 

what about plugged cat converter?

 

How many miles you got on her?

[Guest rcoaster]

That sounds like a problem I had with my old Mazda. Whenever I would climb a grade or go faster than 50 mph, the engine would shudder and loose power. It turned out that the fuel filter was so clogged that it had a restricted fuel flow that it couldn't keep up with the fuel demand.

 

The funniest thing is that after taking it to the garage several times, they kept looking in the wrong spot! They blamed it on the choke and carb but couldn't find anything wrong.

 

Also, you might want to check if there's any forgeign object in the gas tank as well, something that a low rate of flow or the angle of the tank wouldn't cause a restriction of flow.

[Guest orphan]

Yeah, try the bucket test for fuel quantity. Sounds like your mixture is leaning out at WOT under load. Most likely the fuel filter. Get an OEM filter from the dealer; the aftermarket ones suck major league.

 

orphan

[Guest meep424]

agreed--- too lean under load.

 

Fuel filter = great idea, in concert w/ a couple of cleaner treatments (techron, stp, etc).

 

Also-- fuel tank pickup... it's on the front of the tank, right? check for rust holes that might suck in bubbles of air when goin uphill. Does it do this when tank is totally full?

 

Meep

[Guest Grounded1]

Yeah thats pretty much were I am now. I did the D mode check. No codes at all. I drove it around trying to reproduce the problem while in D mode but there are no steep grades long enough to do it. It only happens on those really steep grades that are 150 miles from were I live while on vacation. I changed the fuel filter when the problem started last August. Before I change it again I going to pull the fuel pump like you suggest. Some else told me to check that pick up screen in the tank. Maybe the uphill agle has something to do with it and the pick up screen is getting covered. Its naturally aspirated not turbo and the problem isn't there all the time. Only for those long grades up that never seem to end. Its got to be a mechanical problem if there are no codes. I hope I find before I go insane.

 

Pat

[Guest Grounded1]

Checked the fuel pump, pick up screen and checked the inside of the tank for debri and something that might restrict fuel flow. Nothing. All clean as a whistle. I got a direct reading oil pressure gage and (againts all common sense) T'd it into the output fuel line of the fuel filter. The gage is inside the car. The next time the stall happens at least I'll see if I'm losing fuel pressure and causing a lean die out. So far the fuel regulator is working fine and the pump output is normal. I need to stall it to see where I stand. Thanks for the input.

 

Pat

[Guest St Nickolas]

Look at the list of codes and note what is NOT tested. Not a great number of things that are. Fuel pressure and flow are not.

 

It could be an intermittent electrical problem or a mechanical problem.

 

If the fuel pressure test yields nothing.........

 

I'd put a (digital; high impedence) meter on the O2 sensor wire and the knock sensor wire and see what is occuring there. If you have access to one of those meters with an oscilloscope you could probe the fuel injection pulse width, too.

 

The cheapest manual for the pinout diagrams on the ECU is the Popular Mechanics CD-ROM.

 

 

Hope you solve it soon.

 

Nick

[Guest Grounded1]

You almost rang the bell Nick. Since I've been watching my fuel pressure I finally caught something. I went to start the the engine and turned the key to the ignition detent without the engine running yet. The fuel pressure slowly rose to 20 psi and stayed there. I started the engine and it idled yet stumbled. Pressure still 20 psi. I reved the engine up to get the vacuum changing. No pressure change. 5 minutes later it slowly it came up to normal (reving the engine) to 28 psi @ idle and 38 psi @ WOT. If I was at WOT on a steep grade with 20 psi no doubt it would stall and lose power. The fuel regulator normally passed all the tests and the fuel pump pinch off pressure was well over 70 psi. Because the regulator didn't bump the pressure up @WOT when I had 20 psi makes me think its the regulator not the pump. The next time it happens I'm either going to check the pinch off pressure to rule out the pump or just drive it to see how long it take the regulator to go "normal". A lot of things fell into place here. All the stalls I ever had happened within the first 15 minutes of driving after start. The stumble at idle I got with 20 psi I had before every once in a while but never connected it to low fuel pressure. I didn't know what the fuel pressure was. After this is all over I'm keeping the fuel gage connected. Very valuable to see whats going on. I just need to be absolutelty sure its the regulator or fuel pump. Also @ WOT with 20 psi I'm sure the knock sensor heard quite a bit. Thats pretty lean, 20 when it should be 38.I'll keep you posted. Almost out of the woods...

 

Pat

[Guest rcoaster]

Let's try this.

 

Disconnect the vacuum line going to the fuel pressure regulator, and check the fuel pressure. Does it go up to the 70 PSI immediately which was the highest reading you got? If it takes a while, then your fuel pump might be on it's way out.

 

If it does hit the 70 PSI right away, then attach a vacuum pump (also used to bleed brakes) and apply vacuum to the regulator and check the fuel pressure to make sure the pressure drops. Remove the vacuum to the regulator and see if the pressure rises immediately. If it doesn't, then you should replace the regulator. If it does, then you might have some kind of blockage in the vacuum line that it almost acts as a check valve. What happens here is that the vacuum might come up quickly, but doesn't release fast enough for the fuel pressure to rise.

 

Hope this sheds some light on what might be happening here.

[Guest Grounded1]

I did that check first. With vacuum at the regulator diaphram I get 28 psi, Suby calls for 26 - 32 psi. Vacuum line off I get 38 psi that also is what Suby calls for. Pinch off pressure is 75 psi , Suby calls for "over 70" so thats ok. I think the regulator is hanging up open allowing the fuel pressure to just return to the tank rather than build up fuel manifold pressure. The big thing is it does not happen all the time. As soon as I get it to repeat I'll be able to find out if it is the pump or regulator.My fuel pressure tap off for my gage is right after the fuel filter in the fuel line to the manifold. As soon as it repeats with a low pressure I'll pinch off the line. If I get over 70 psi the pump is good and wants to build pressure. It would be the regulator allowing the pressure to return to the tank and not build up. Until then I have to wait. Its working fine now.

 

Pat

[Guest PaganQWA]

One thing I didnt see you mention yet is Fuel Injector(s). I had issues with one of mine and the ECU was not detecting any problems so no codes. Quick OHMs resistance test on all the injectors could reveal a culprit.

 

Hope this helps Thx

[Guest Grounded1]

Did that too. I checked all the injectors with a multimeter. The ohm readings were good and input voltage was good. From what I read the only way a fuel injector can cause low fuel pressure is if one or more are stuck open. I think the engine would run like crap if one was open. So far when I had the low pressure, the engine ran fine and smooth so I kinda ruled it out. And I never got any codes. I have a couple days off this week so I hope to have a repeat performance so I can be sure if its the pump or the regulator. If it is the regulator I thinking of getting a peformance one that you can adjust. I think Teagues sells them. From what I've seen the OEM one and the performance one are not that far apart in price. If I need one I might as well get one that I have control over.

 

 

Pat

[Guest St Nickolas]

Good to hear you're getting closer.

 

Neither fuel injectors, pump or regulator are monitored by the ECU on the Gen 1 Legacy. Somewhat surprising that no codes have been generated. Seems that the ECU would come up with some excuse (erroneous code) for the stalling. When the fuel pressure is low, the injectors must be firing for a longer period of time. Tis possible to overheat them at some point leading to their demise.

 

Have you thought about used parts?

 

www.car-part.com/

 

Thanks for the insight into how you are going about this. My 91 rolled over 170,000 miles last week and I plan to keep it for a while.

 

Nick

[Guest Grounded1]

I thought there would be some sort of code. You'd think running that lean that the ever famous over sensitive knock sensor would have flagged something. No matter I'm just glad I found something. The last couple of ays I've noticed the fuel pressure is never the same at WOT when I need the highest fuel pressure. With all conditions the same sometimes I get 38 - 40 psi at WOT. Other times it stays between 26 - 32 at WOT (which is the idle or lower power setting.) I think the fuel regulator is hanging up. I going to take it out today and clean it. When here is no vacuum at the regulator diaphram there is a spring that pushes the valveinsideof it to closed, so pressure builds up. Either the spring is shot or the valve is sticking from crud or something. I'll clean it today and see what happens. Thats for the link I will use it.

 

Pat

[Guest PaganQWA]

Injectors ARE monitored by the ECU on a first gen Legacy. There are error codes for them and I have recieved them in my ECM.

 

Although when one of mine went bad it didnt throw a code Odd huh? Cant always rely on that electronic crap

[Guest Legacy777]

the injectors are monitored.....however if you have a mechanical failure of the injector or it's plugged up.......it's more difficult to throw a code......especially with OBD-1.....less diagnostic type stuff.

[Guest St Nickolas]

I had forgotten the injectors are monitored.

 

However, I suspect they are monitored similar to the O2 sensor and could be effecting performance before they set a code.

[Guest Grounded1]

Ok, I removed the regulator and cleaned it out. So far its working as before. I just have to keep an eye on it for when it hiccups and stalls me out. I'm sure this is the problem. I did another pinch of pressure check of my fuel pump and it went to 80 psi.

For anyone who has this problem and wants to clean theirs out here it goes. To remove it is two 8mm bolts, one hose clamp and one vacuum line. Once you get the bolts and clamp loose, work the regulator off the fuel rail first. As gentle as possible if your re-using the O-ring on it. Then pull it out of the hose that you loosened the clamp on.

To clean it you need to open the valve. I found out that you need pressure on both sides of the diaphram to open the regulator valve.Pressure on one side or vacuum on one side just won't do it. Its a combination of both. What I did was apply a regulated shop air supply set at 30psi. I used one of those hand air blowers with the rubber tip to the O-ring side of the regulator. I had a vacuum pump connected to the vacuum port. As you pump up the vacuum port (while having the 30 psi at the O-ring side) the regulator will start to open. It cracked open at 12 inches of vacuum and continued to opened in proportion to how much more vacuum you give. Basically I squirted some penetrating oil and contact cleaners inside the valve end and then blew it out with the procedure above. I blew it out into a clean rag and noticed nothing that could hang it open. I worked it open and closed a lot. Nothing unusual happened. If I stall again and see it is due to a low fuel pressure I'll just buy a new regulator.

Just as a note I used 30 psi air pressure because the fuel side of the regulator sees 26 - 38 psi. 30 seemed like a safe number. I didn't want to blow the diaphram. If you use a higher air pressure (but under 3:cool: the valve would probably take less vacuum to open. Well thats it until I stall again. I just want to be sure. I've already shotgunned enough parts at this point. I've learned a valuble lesson in the OBD-1 world. If there are no codes most likely it is a mechanical problem not monitored by the ECU. There are exceptions I'm sure but it is a pretty good rule of thumb. I'll keep you guys informed on the next hiccup.

 

Has anyone out there ever thought of binding the "Best Of" problems here and selling it as a trouble shooting guide??

 

 

Pat

[legacy93]

Hello-

 

I hope you are still available to respond.

 

My 93 Legacy is doing the exact same thing your car was doing.

 

Did you finally isolate the problem. I am desperate to know because the Subaru dealer is suggesting several repairs at a huge expense to me.

 

Thank You

 

Chris

Hope someone can give me a new direction here or its Suby goodbye.

Whenever I go up a steep grade at about 35-50mph the engine will lose rpm up the grade and I'll ofcourse give it more gas. It makes no difference and the engine rpm willgradually drop until it stalls out. If I continued to give it more gas as it loses power the engine will sputter and kick. If I let off the gas before it stalls I can rev the engine up and clear it out and it will be ok (if I dont continue up the hill). It doesn't happen above 55mph. I have a vacuum gage in my car and the loss of power wont happen until I get the engine vacuum under 5 inches which means almost WOT. If I let it stall the engine won't start unless I shut off the ignition and turn it back on.

I started having this problem last August and have been progressively checking everything under the hood and replacing the marginal ****.

I've replaced the knock sensor, water temp sensor, the O2 sensor and the Mass airflow sensor. The stuff I've checked per the Subaru shop manual is....everything. The throttle position sensor is good, the idle air valve is good, the coil is good. I have new plugs, wires, filters (fuel & air). My fuel pump pressure is perfect, the fuel regulator checks out fine with a vacuum pump and fuel pressures are good at the vacuum settings in the manual. The pinch off pressure for the fuel pump is fine(75 psi).

Even if I anticipate the hill and throw it into 3rd the rpm will go to about 32-3400rpm and still do its power loss thingwhen I get cole to WOT(less than 5 inches vacuum). Reset the computer, no help. THis is getting really annoying. Any leads would be appreciated. I wouldn't wish this on a ford.

Oh yeah, NO CODES ever. No freakin codes!!! The only thing I haven't done yet is do the D-check mode. I'll do that tomorrow and hope that something pops up but I'm not hopeful. I think I might invent Subycide.

 

Pat

91 2.2L 4EAT

[Setright]

Someone from Oz was on the board about a year ago, with a similar problem. I suggested the fuel pressure regulator, and what do ya' know, it was!

 

The regulator is easy is to replace, so it's a good place to start. Fuel pump is a little more time consuming, and expensive. Buy a genuine Subaru regulator and replace it yourself, before you start paying big money to the dealer.