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Cuchulain
21-08-2009, 07:10 PM
If anybody has a solution to this problem I would be most grateful. I own a 1991 Subaru Legacy Turbo Auto, which is experiencing intermitent loss of power under load? Sometimes cuts out at low revs, but easily starts again. The problem is not regular enough for my mechanic to easily diagnose the problem. It seems to have started just after I had a oil and filter replacement, which may have no bearing on the matter or not?

hueybot3000
21-08-2009, 08:33 PM
Welcome to PressF1, you did notice the "Computer" theme going on here right?

Anyway need more info, what kinda power loss? like it just dies? sounds like it could be an electrical thing which youd have to get looked at by an auto sparky. Check leads and plugs and go from there

Phil B
21-08-2009, 10:31 PM
First thing to do is check all your turbo related plumbing for air leaks. If it's doing it under load the turbo is pressurising the inlet system & any leak will give you that symptom. If it's got the standard intercooler on it, check the concertina hoses for splits. You may even have to remove the intercooler & make new gaskets for the aluminium hose connectors to intercooler joints. Do all these as they are the most common turbo faults. After that the diagnostics get too tricky to diagnose remotely

prefect
21-08-2009, 10:35 PM
I would clean out the throttle body and change oxygen sensor.

Phil B
21-08-2009, 10:46 PM
You only spend money on components after doing the basics first. Oxygen sensors very rarely cause a car to cut out. Notable exception for some reason VW

feersumendjinn
21-08-2009, 10:56 PM
First thing to check would be air leaks on intake side especially the (big) hose from the aircleaner housing to the throttle body, the concertina-ed hose can split underneath (out of sight) when it gets hard after a lot of years and cause your airflow not to be measured correctly, check also hoses on intercooler (if its the one that's mounted on the engine), the hoses can get misfitted and/or split if the intercooler's been moved (hose is a neat fit by turbo end) and breather and vacuum hoses.
Also check your cooling system is up to scratch, no leaks/is full/antifreeze fitted, can get an airlock in block if not refilled correctly when drained (best way is to remove top hose at radiator end and refill block from there until coolant runs from rad neck. Check coolant temperature sensor is operating correctly as well as thermostat (this will affect cold/hot starting as well as fuel consumption).
If I remember right, those engines (EJ20?) have a crank angle sensor (by the crank pulley) and a cam angle sensor by the LH cam sprocket, make sure these are ok; another problem that's related to this is the crank pulley can often come loose with consequential damage to the crankshaft/keyway/crank sprocket (and the reluctor mounted on the sprocket) and will cause the valve/ignition/injector timing to move about causing intermittent lack of power and stalling (take a look at the pulley while it's running, if it's wobbling even slightly, it's loose).
Hope this helps.

prefect
21-08-2009, 10:57 PM
Yeah you are right phil probably best to do plug it into a diagnostic machine and do a compression check first.

Sweep
21-08-2009, 11:20 PM
This may or may not fix the problem.

I remember driving a Holden V8 that would stop from time to time.

Fault was traced to a carburettor float which had a hole which allowed the float to sink and thus cutting off the fuel.

prefect
21-08-2009, 11:40 PM
The soobaroo would be injection I think.

hueybot3000
22-08-2009, 12:44 AM
This may or may not fix the problem.

I remember driving a Holden V8 that would stop from time to time.

Fault was traced to a carburettor float which had a hole which allowed the float to sink and thus cutting off the fuel.

i cant even imagine how itd get a hole in it, maybe you fed it too much gravel

R2x1
22-08-2009, 01:01 AM
Too much flawing it maybe?

hueybot3000
22-08-2009, 01:07 AM
accelerators go right to the floor for a reason

SurferJoe46
22-08-2009, 05:15 AM
If anybody has a solution to this problem I would be most grateful. I own a 1991 Subaru Legacy Turbo Auto, which is experiencing intermitent loss of power under load? Sometimes cuts out at low revs, but easily starts again. The problem is not regular enough for my mechanic to easily diagnose the problem. It seems to have started just after I had a oil and filter replacement, which may have no bearing on the matter or not?

Ah! Terminology and semantics can create a lot of grief.

Let me ask some questions first.

1) you said
intermitent (sic) loss of power under load?
...what do you consider "load" - and is this throttle-on or maintaining cruise speed or during passing demands?

2) you said
Sometimes cuts out at low revs, but easily starts again
...is "cuts out" is this to the point that the engine actually dies or do you just feel it might die and you shut it off and restart it? Do you hear any backfiring in the exhaust when this happens or is the condition silent? It makes a big difference.

3) I need to know if other filters were also changed when the lubrication service was done. Fuel filter?

There's a possibility that an oil-pressure qualifier sensor has been damaged and the ECM sees that the oil pressure is incorrectly reported as unsafe and it shuts the engine off.

Is the CEL on? This should at least be an OBD-1 system, possibly even an OBD-2 system but I don't know what models and systems they sell to Upsidedown Land. Typically you are behind the curve by a few years in technology in your automobiles.

I doubt seriously that chasing the turbo or it's intercooler for a problem could manifest as total loss of power to the point that the engine stops.

Cooling systems and other accessories aren't usually culprits for an engine dying either.

Low voltage or an alternator putting out some AC ripple from the DC output can cause a lot of oddball symptoms. The maximum AC ripple that most ECMs can accept are lower than 0.013VAC on the DC line. More just confuses the ECM and the sensors.

Isuzus have a real trouble with almost- or slightly defective/bad alternators - ones that would run well in anything else, but cause fits in themselves. Subarus are in the same boat for needing current purity.

I'll be here intermittently all day today (I'm in Southern California) and will try to answer as soon or nearly as soon as I see your RSVP.

SurferJoe46
22-08-2009, 05:18 AM
i cant even imagine how itd get a hole in it, maybe you fed it too much gravel

Holes in brass floats were the bane of their design. It happened all the time and that's why the carb manufacturers went to poly-foam floats with a thin skin of impervious plastic on them.

Carbs, however, don't exist on most anything with wheels any more and certainly NOT on a 1991 Subaru Legacy, which we also have here in the States.

SurferJoe46
22-08-2009, 05:26 AM
Yeah you are right phil probably best to do plug it into a diagnostic machine and do a compression check first.

The ALDL (OBD1) and/or the OBD2 port will not perform a compression test. It will report a missing spark plug (P0300 codes) or some sensor problems, but as a mechanical quality-of-engine-test it really isn't designed for that.

Compression tests are still done the old fashioned way - with a compression gauge.

There ARE however tests for cylinder-by-cylinder balance or support tests that will quantitatively assure that a single cylinder is pulling it's own weight. If any cylinder is too far out of line, it should pop the CEL anyway.

Besides - compression cannot be an on-off thing and make an engine stall and at the same time allow it to run normally at other times. Hard starting and loss of across the board power from bad compression is possible, but it's not a light switch.

prefect
22-08-2009, 09:21 AM
Never said do a compression test from diagnostic plug in.
I said: and do a compression test.
I always do a compression test (with gauge) and or a leak down test after a cursory glance of spark plugs, leads, throttle body, loose connector wires.
We are not behind the curve in technology here, the exact opposite in fact we are world leaders in innovation.

plod
22-08-2009, 09:28 AM
Have you had the battery disconnected recently? Another simple thing to check is the earth strap.

SurferJoe46
22-08-2009, 10:40 AM
We are not behind the curve in technology here, the exact opposite in fact we are world leaders in innovation.

Hmm - that's where all the world's duct tape goes.

I sent a CARE package of KoolAid, now you wanna have me send some duct tape too?

Phil B
22-08-2009, 11:36 AM
Another thing that's common on turbo cars is the spark plug gap is too wide. Drop it down to 1mm. This will more often than not fix what feels like a boost cut problem, assuming there's no problems with air leaks in the inlet system. It won't be the cause of the engine completely stopping. Check vacuum hoses for security & splits. Good luck with a compression test on those,, they are great fun to do, but that won't make it cut out under load either. Does it run smoothly at idle? Not running on 3 cyls?

Thomas01
22-08-2009, 11:49 AM
If this was a motorcycle I would check the small hole in the petrol cap was not blocked, thus stopping the flow of air to the tank.
If this happens the fault described occurs.
And yes I have met it quite a few times over the last 60 years.
But this is a car.
I don't know if the same fault can happen with cars.
Tom

Phil B
22-08-2009, 11:54 AM
Modern cars have enclosed fuel systems to stop vapour from escaping to the atmosphere, amongst other things. Not sure what bikes have got.

SurferJoe46
22-08-2009, 12:01 PM
Modern bikes do too - and they have catalytic converters - and the whole nine-yards for emission controls.

The last time I can remember getting my crotch wet with gas from a vented cap was on a BSA Victor 441 - nasty powerful thumper.

ubergeek85
22-08-2009, 05:16 PM
accelerators go right to the floor for a reason

And the speedo goes to 200 for a reason too :D

It's a challenge that I accept where safe to do so.

Richard
22-08-2009, 05:37 PM
Not bad for a computer forum eh!

SurferJoe46
22-08-2009, 05:59 PM
Yeah - but look what you can learn!

I'm going to bed now. 22:00 Friday - or close enough!

Cuchulain
25-08-2009, 10:27 AM
Ah! Terminology and semantics can create a lot of grief.

Let me ask some questions first.

1) you said
...what do you consider "load" - and is this throttle-on or maintaining cruise speed or during passing demands?

2) you said
...is "cuts out" is this to the point that the engine actually dies or do you just feel it might die and you shut it off and restart it? Do you hear any backfiring in the exhaust when this happens or is the condition silent? It makes a big difference.

3) I need to know if other filters were also changed when the lubrication service was done. Fuel filter?

There's a possibility that an oil-pressure qualifier sensor has been damaged and the ECM sees that the oil pressure is incorrectly reported as unsafe and it shuts the engine off.

Is the CEL on? This should at least be an OBD-1 system, possibly even an OBD-2 system but I don't know what models and systems they sell to Upsidedown Land. Typically you are behind the curve by a few years in technology in your automobiles.

I doubt seriously that chasing the turbo or it's intercooler for a problem could manifest as total loss of power to the point that the engine stops.

Cooling systems and other accessories aren't usually culprits for an engine dying either.

Low voltage or an alternator putting out some AC ripple from the DC output can cause a lot of oddball symptoms. The maximum AC ripple that most ECMs can accept are lower than 0.013VAC on the DC line. More just confuses the ECM and the sensors.

Isuzus have a real trouble with almost- or slightly defective/bad alternators - ones that would run well in anything else, but cause fits in themselves. Subarus are in the same boat for needing current purity.

I'll be here intermittently all day today (I'm in Southern California) and will try to answer as soon or nearly as soon as I see your RSVP.
Thank you SurferJoe46 for your questions.
I will try to answer them as best as I can.
1/ Load on engine I mentioned refered to general cruising speed.

2/Engine actually cuts out and has to be restarted by key.

3/Only oil filter was changed when last service done.

As an aside, I have followed your advice from a previous reply you posted on another message, suggesting doing a complete oil change and flush, along with using a fuel injector additive (not Sea Foam). To date it seems to be behaving itself, though as the problem was very random previously, it will take some time to be sure.
Once again thank you for sharing your obvious expertise.

SurferJoe46
25-08-2009, 11:25 AM
YW

Phil B
25-08-2009, 10:57 PM
Holding a car at cruising speed is not putting the engine under load unless you're doing about 250.
Lift the back seat & on the drivers side of the car you'll see a couple of electrical connector blocks. Pull them apart & look for burnt connectors. It's another common fault that the fuel pump wiring burns out at the connector block. That could cause your described problem. Low voltage/current will stop the fuel pump from delivering the required fuel flow rate..
Another thing to check is whether the car has an ignition amplifier (igniter) or if they're built into the coils. Check the coils for wires. If there's 3, the igniters are built in.
Does the car instantly start? Or do you have to wait until things have cooled down.
Told you it'll get more involved.
It'll be nothing to do with an oil & filter. Providing you've got oil in it & the engine's not seizing lol

SurferJoe46
26-08-2009, 08:04 AM
Yeah, Phil - I tend to go for the intermittent electrical problem, that's why I asked some of the questions I did.

If it were secondary ignition-related however, most times there should be a loud backfire or exhaust report when the current returns to the plugs and they fire a fuel loaded exhaust system.

If the power loss is at the primary side of the ignition, then we have to remember that the CMP and the CKP are all affected and that would shut off the fuel supply for that moment of time too, and then there's no fuel going out of the engine as unburned to create an exhaust report.

Fuel pressure loss can be among the intermittent problems and that will usually NOT show up as a loud exhaust backfire since the fuel is not getting into the engine to get into the exhaust - and so on. It will be a silent loss of power, but may not be sudden.

One point to consider is a loose or damaged electrical connection on the oil pressure sending unit, since loss of oil pressure will shut off the engine and not just merely make it lose power and sag.

This sensor is usually near the oil filter itself and can be damaged by ham-fisted oafs who change filters by day and flip burgers by night. This usually happens in quickie discount oil/filter service facilities who hire the handicapped (mentally) and allow them to wrench on customers' cars for their socio-economic on-job trades training.

The aforementioned non-savant might have just damaged this connex enough to make it intermittent, making the symptoms vague and inconsistent.

The oil level may indeed also be low (by the same person(s) already mentioned) and as it gets pumped into the circuit at cruising speed, it cannot return fast enough to keep this sensor from shutting off the engine. The timing of the happenstance may not be all that odd to consider - this came about after the oil change.

There are answers to this mystery - but I don't suspect the air induction nor the cooling system as faulty - they would surely raise their heads in a larger and more devastating way.

I love a mystery.

feersumendjinn
26-08-2009, 09:08 PM
Another possibility could be a intermittently blocked exhaust system (either collapsed catalytic converter or loose muffler baffle), can cause complete engine stall then will start immediately (as the blockage drops away with no exhaust pressure; can also happen more if you're accelerating up a hill (gravity :))), put the vehicle on a hoist and check for rattles in the system, alternatively try taking it for a run without the exhaust fitted (illegal and dangerous tho, but will prove the point).

Phil B
26-08-2009, 10:08 PM
I've had a few that have had exhaust blockages. You normally have a lack of power right from the start & they have a very gentle flow of exhaust gas from the tailpipe. No or next to no cylinder pulsing. Sometimes they wheeze like a 20 a day person.
The lack of oil pressure or faulty oil pressure switch won't stop a legacy of that vintage, nor will low oil level.
If the coils have built in ignitors normally only one of them plays up & you can spot it easily. If it's got a external ignitor & it's old, it can & they do pack up when they get hot & restart after a short cooling down. There's no set pattern to how they pack up. Grab another one, even if it's off another car to prove the diagnosis. I think, but not 100% sure that the external ignitor is mounted on one of the suspension turrets or it could be on the top rear engine stabiliser mount, firewall end.
If your mechanic has a scantool he should be able to tell you if you have any sensor faults. Ignition system won't show in a car that old.
Now we've found that the engine's not under "load" then I agree the air leak scenario is unlikely.
Could you imagine going to the doctors with a half baked description of what's wrong, he/she might take a wild guess & poke straight up your jack & look for hemorrhoids.
No offence intended Cuchulain

SurferJoe46
27-08-2009, 07:39 AM
Just a thought:

Let's clean the MAF.

R2x1
27-08-2009, 11:13 AM
The Ministry of Agriculture and Fisheries is corrupt?

That is shocking indeed, forget the boxer engines with their intermittent shorts, we have foul misdeeds afoot in the cow and trout fanciers' retirement home

prefect
27-08-2009, 11:23 AM
Subaroo might have stayed with boxer engine but they sure made it more complex with electronic add ons.
I had 1400DL subaroo ( like swede tourists car killed by ex MPs brother, how do I know? the police came and looked at my car and took some measurements, road test and photos but wouldnt tell me what for) it was quite simple carb and points ignition.

zqwerty
27-08-2009, 04:47 PM
I had the 1600 DL, good car except for the rust. Got an Omega now done 295,000 K's, nothing ever done to the engine. radiator leaking though, clutch cable broke 6 months ago, Subaru's are good cars. My nephew has a WRX sti rocket ship, the cornering G forces give me headaches.

Phil B
27-08-2009, 10:01 PM
Just a thought:

Let's clean the MAF.

You can try that. It doesn't usually work tho. If the car's got a pod type air filter, the MAF could be buggered, it's another thing to check. Get a known good one off another car, make sure it's got the same numbers on the sticker & try it.

The MAF is the mass airflow meter, it's in the hose that's connected to the air filter box if it's a pod filter, otherwise it's mounted to the air filter box with 4 screws.