98' Impreza Outback 2.2 Drivability / Stuttering

[caterpill]

Hey all, i've recently come across an odd problem that would seemingly be common for my particular engine but wanted to at least ask here and clarify what can be done on my part to go about solving this puzzle.

 

First, my problem. Vehicle is a 98' Impreza Outback, A/T EJ22EZ (Single port). Car has about 195k. Vehicle just cuts out like you lost a sensor or fuel, but oddly enough, NO CEL. It usually happens on the freeway, and of course is annoying and can be dangerous due to the lack of throttle response when the problem is occuring. For instance, I would be travelling on the freeway, 55mph @ 2250rpm, 1/8 to 1/4 throttle STEADY and you would feel the car shake funny, lose power, and the rpms start dropping. I've tried a few different things and cannot isolate the problem to bumps / vibrations / humidity, but it does seem to happen multiple times on a longer drive, say 15-30 miles (one way) The engine does not die (well, hasnt yet) during this period which is very odd. I would let off the gas and get back on, and after a few tries it will stop. STOMPING the gas seems to instantly fix the problem, but returning to that "spot" in the throttle (1/8 to 1/4 of throttle) where you were travelling WONDERFULLY at 55mph before the engine started being a b---- takes a while to go away. When the engine starts stumbling on the freeway, i've tried a few things;

 

- Putting the car in neutral while holding the throttle steady where it was before the car started sputtering - the rpms drop, almost to idle but the vehicle never dies (sometimes the sputtering goes away and the engine clears up by itself and REVS)

 

- Putting the car in neutral and revving the engine - NO PROBLEM, revs like a champ

 

- Letting off the gas and then back on - clears up after more than a few tries, I usually end up mashing the gas to clear it up and just ACCELERATE DAMMIT because by then i've slowed down from 55mph to ~42mph

 

I've been in stop-and-go driving scenarios where I would be accelerating smoothly at about 1/8 to 1/4 throttle before it starts sputtering, with the same characteristics described above.

 

It all seems so very like the TSB described in another post both here and the net', but the TSB isolated manual transmission vehicles. I don't know what the difference here is but I wouldn't think the transmission has much to do with it, does it? The gist of the TSB goes along with the fact that the ECM somehow detects abnormal engine knock when it isn't occurring and retards ignition timing by about 10 deg. The ECM "saves" this occurrence of phantom knock in it's memory table which is inaccessible. The recourse is to "replace ecm". (umm ok?)

 

I immediately wanted to condemn the TPS, which is what seems to be the problem, considering I keep saying "1/8 to 1/4 throttle", lol. Well even through i've tested the TPS initially BEFORE changing it, I was like " WTF, maybe it's just acting up when i'm driving, due to the heat or whatever - so i've just replaced the TPS with an OEM one set to proper specs. Just drove the car tonight with the same problem.... UGH. So of course, I threw a part at the car, and it wasn't the problem.

 

SO.. what's next? I did a visual inspection of the knock sensor. I think I see a hairline crack on the sensor, but aren't 110% sure. I haven't checked the sensor for continuity / resistance.. but I would think a CEL would indicate a problematic knock sensor, such as an open, short, etc..

 

I currently use 87 octane, E10 gas. I haven't tried any other gas because I figured it might band-aid the problem.

 

At this point i'm kind of stuck. Any help would be greatly appreciated.

 

I'm more or less stumped because the vehicle has been driving just perfectly before this started happening. I JUST fixed a recurring [ gas nozzle keeps clicking when filling up ] and a [ EGR FLOW ] problem this year.. the car ran beautifully, and then this.. such a shame, I thought I could reach that 300k mark. LOL. Just kidding. But I do try to take care of the car.

 

I have an OBD II cable / PC interface that I plan to try and "datalog" the car when driving to record the parameters when the engine throws a fit - i'm waiting for that to be shipped to my house. Should I be keeping an eye on any particular parameters? I don't know of my MAF is happy, maybe that could be the culprit. I also don't know if I can view the ignition timing PID with the software I ordered - I would assume you can only view that with the Subaru Select Monitor, eh?

[1 Lucky Texan]

just a few thoughts;

 

 

could you test the fuel pressure/flow? Maybe inspect all the relays/fuses/connectors/grounds/wire harness associated with the fuel pump.

 

You could 'force' a cel by leaving the gas cap off - then you might be able to retrieve Fuel Trim and other frezeframe data.

 

any correlation to fuel supply? full tank, near empty, etc.

 

most fuel injected vehicles have a 'flood clear' condition when the pedal is floored. Dunno if that applies while you're moving though.

[caterpill]

Thanks for the reply. Ideally I would have a test port to hook the fuel gauge to, but i'm not exactly sure how these Subarus get it done.

 

I did a few checks to see that the fuel system is in order electrically ; everything seems to be ok. I've never really had any ground problems lately, but I do have large gauge grounds to the battery and various places that are probably overkill.

 

I find it odd that the car seems to act up more often at that particular rpm range when cruising - 2-3k, 1/8 - 1/4 throttle.

 

No obvious connection to fuel tank level. Over the course of the last year though, i've been using all kinds of fuel injector cleaners and "mileage enhancers". LOL. Sea Foam, Gumout, Marvel Mystery Oil, Xtreme Fuel Treatment, this car has probably digested it all.

 

A fuel pump problem is never out of the question, but the vehicle never has any problems starting up, hot or cold. Also, the engine never dies. It just stumbles. I don't really get it myself. I would assume that if the fuel pump had intermittent power connectivity issues, the engine would probably die sometime. It hasn't. I've been having the problem for about 10-15 trips now without it ever stopping completely.

 

Other than timing retard from knock, I just realized that the EGR valve can also just choke the engine very quickly without a CEL and make it fall flat on it's face, so i'm not going to rule out a "sticky" EGR valve.. I may try driving around with the vacuum hose to the diaphragm disconnected.. It's a possibility, I guess.

 

I'm kind of stumped though because the problem is very random, yet occurs often when i'm driving on the freeway in that common crusing speed .. 2-3k rpm. Under what conditions does the EGR valve actuate @ it's highest lift? I've just recently cleaned carbon deposits on the valve itself and the feed tube to the engine block to get rid of a P0400 EGR Flow code, so I don't know if the EGR valve has decided to stick on me.

 

I don't know if it's relevant but I have driven around with the TPS disconnected because I had a hunch it was the TPS sensor - The car NEVER acted up during that drive, but I have my doubts. The ECU was in limp mode, the idle was high @ 1500rpm and somehow it would seem that the ECU would have the car run on the "rich" side / open loop to be safe, while using the MAF and O2 sensor to maintain stoich whenever possible. This one drive made me believe it was a faulty TPS sensor; I should've drove more, but I didn't like that the car idled at 1500rpm (limp mode) - sitting in stop and go driving would definitely overheat the transmission fluid in a hurry.

Edited August 24, 2012 by caterpill

[subaruplatt]

If you can suck some gas line anti freeze through the EGR.

Good cheap fix.

Stange some times I think mine is over idling.

The glide or momentum you feel is in fact computer simulated.

You find this out when you drop it in neutral.