A different kind of hesitation?

[griffenrider]

Time to put a question out there - I've read just about every thread with the words "hesitation" in it, and here's the conundrum:

 

02 OBW ltd, 110k, manual

did the 105k sevice (timing belt, water pump, belts)

new plugs/wires

new air filter and fuel filter

fixed dead front oxy sensor w/ new

P0420 cat eff. error, turned out my doughnut was rusted through and leaking exhaust, and the cat was fried from driving with a bad 02 sensor for so long (expensive whoops), so: new cat, seals, etc.

new clutch kit, as it was starting to slip in 5th on the highway

no errors pending or in memory (so its not a knock sensor issue?)

good gas mileage: 22 mpg city/28highway (better than "sticker")

 

BUT: when accelerating gently there is a significant hesitation between 2k and 2500 rpm - almost identical to the hesitation with a bad 02 sensor, but not quite as bad. Happens mostly in 2nd and 3rd gears, but only because 90% of my city driving is in those gears.

 

Happens more when I have 3/8 of a tank of gas or less.

 

I'm currently thinking water in the tank? I've heard some horrer stories about what "dry gas" (ethanol) does to your gas mileage and the deposits that result. Any other way to get water out short of dropping the tank and pouring it out? Any other theories?

[keltik]

Crack a fuel line and pump some into a clear bottle - should be easy to see the quality of your gas then.

[griffenrider]

Crack a fuel line and pump some into a clear bottle - should be easy to see the quality of your gas then.

 

I don't know much about gasoline quality, what am I looking for?

[nipper]

I don't know much about gasoline quality, what am I looking for?

It will be like water and oil, they will seperate in a bottle, and you will see two layers.

 

Are you sure its not your knock sensor?

 

 

nipper

[griffenrider]

It will be like water and oil, they will seperate in a bottle, and you will see two layers.

 

Are you sure its not your knock sensor?

 

 

nipper

 

sounds fairly obvious, I'll check when the tank gets down below 3/8ths (its full at the moment)

 

As for the knock sensor, no, I'm not certain, but I read somewhere on USMB that if there's not a CEL, its almost certainly not the knock sensor. Is this incorrect?

[nipper]

sounds fairly obvious, I'll check when the tank gets down below 3/8ths (its full at the moment)

 

As for the knock sensor, no, I'm not certain, but I read somewhere on USMB that if there's not a CEL, its almost certainly not the knock sensor. Is this incorrect?

 

Yes and no, it can be functioning fine technically, but be cracked or loose in its bas and give a false reading. If you have a code for a knock sensor, it is almost always a bad knock sensor. It is possible to have a bad one without a code.

 

nipper

 

PS next time you get that low remove the gas cap or loosen it and see if it goes away

[griffenrider]

That makes sense, thanks Nipper.

 

I'll pull it off when I take lunch at work today (yeah, I work Sundays :-\ ) Though I'm still not entirely convinced it's bad - mostly because the hesitation only shows up well below half-a-tank, and only occurs under light acceleration, when even a loose knock sensor shouldn't be getting knocked around much.

 

EDIT: Pulled it, wiped it, ran a piece of cotton around the threads, put it back in. No new CEL (which I take to mean I didn't break it putting it back in, always good news to an amateur like me). No cracks, corrosion, etc. Does this mean its good?

 

I'll let you know in a couple weeks how it all works out.

[triiifashions]

Time to put a question out there - I've read just about every thread with the words "hesitation" in it, and here's the conundrum:

 

02 OBW ltd, 110k, manual

did the 105k sevice (timing belt, water pump, belts)

new plugs/wires

new air filter and fuel filter

fixed dead front oxy sensor w/ new

P0420 cat eff. error, turned out my doughnut was rusted through and leaking exhaust, and the cat was fried from driving with a bad 02 sensor for so long (expensive whoops), so: new cat, seals, etc.

new clutch kit, as it was starting to slip in 5th on the highway

no errors pending or in memory (so its not a knock sensor issue?)

good gas mileage: 22 mpg city/28highway (better than "sticker")

 

BUT: when accelerating gently there is a significant hesitation between 2k and 2500 rpm - almost identical to the hesitation with a bad 02 sensor, but not quite as bad. Happens mostly in 2nd and 3rd gears, but only because 90% of my city driving is in those gears.

 

Happens more when I have 3/8 of a tank of gas or less.

 

I'm currently thinking water in the tank? I've heard some horrer stories about what "dry gas" (ethanol) does to your gas mileage and the deposits that result. Any other way to get water out short of dropping the tank and pouring it out? Any other theories?

 

 

i have installed many drain plugs into gas tanks

 

u just need to drill a hole thread it and put in the correct screw for your threads and a little sealant you can drain it when ever u like

 

however

 

prob not the problem

 

if u had water u would have issues at all speeds and fuel levels

[Gloyale]

I would suggest disconnecting the battery for a while. Then go for a good 20-30 min drive. THis will allow the ECU to *relearn* for the new o2 sensor.

 

if the problem persists, check the operation of you're TPS.

 

You may also want to spray the hotwire of the MAF with MAF cleaner.

[griffenrider]

i have installed many drain plugs into gas tanks

 

thanks to forward-thinking at subaru, my tank came standard with a drain plug. Stuff like this is why subies rule. The problem *does* exist even at full, its just much much less noticable

 

I would suggest disconnecting the battery for a while. Then go for a good 20-30 min drive. THis will allow the ECU to *relearn* for the new o2 sensor.[/Quote]

 

Did that when I changed out my clutch - and I've driven from VT back to NY since then. Problem still exists

 

if the problem persists, check the operation of you're TPS.

 

You may also want to spray the hotwire of the MAF with MAF cleaner.

 

will do on the TPS, it only happens at low throttle, so this could be the answer. I don't believe I have a MAF (or a MAP) on the 02 obw?

[Gloyale]

 

will do on the TPS, it only happens at low throttle, so this could be the answer. I don't believe I have a MAF (or a MAP) on the 02 obw?

 

You have a MAP. My bad.

 

Okay, so check the vac line to the MAP for leaks or obstructions.

[griffenrider]

You have a MAP. My bad.

 

Okay, so check the vac line to the MAP for leaks or obstructions.

 

Vac lines have good suction and no leaks.

 

I reved in neutral at various rates of increase and could not reproduce the hesitation - I take it to mean TPS is ok?

 

Also disconnected the battery again and went for a 30-mile drive on and off the highway, problem still exists.

 

Keep the suggestions coming! This thing's got me stumped.

[griffenrider]

Alright - the update. Took a long time to go through a tank, which is a good thing with today's prices. 4.29 at the cheapest station.

 

Anyway: still happens at all fuel levels, but more frequently at lower levels, but not substantially so.

 

- not (at least if my understanding of Nipper's posts are correct) the knock sensor

- still no codes

- not (if my gradual-throttle test of the TPS is correct) the TPS

- Still happens with a new tank of gas, at full - so not bad gas (at least almost certainly, I use on-brand only)

- cracking gas cap didn't appear to help, though the problem is so intermittent its difficult to tell. I don't want to drive with the cap off to find out!

 

Other thoughts?

 

Thanks,

Luke

[OB99W]

[...]

new plugs/wires

new air filter and fuel filter

fixed dead front oxy sensor w/ new

[...]

Are all these parts OEM?

If not, which aren't?

(In particular, is the front O2 sensor Subaru OEM?)

[judamcadoo]

Hello!

 

We had the "Elvis" hesitation when going up or coming down slight hills - "uh huh, uh huh, uh" as car was trying to shift to different gear or plain hestiatating

 

Subaru check transmission and all the other things to the wheels. Nothing. The sensors seemed OK, but husnband convinced it was a bad sensor someplace.

 

Then he noticed the tube from the air thing feeding the motor that was connected to the "pcv" was not a continuous rubber tube. it was splced, with no clamps on either end, and it was really loose. Probably leaky.

 

He put hose clamps on each end and VOILA! Smooth as the day we bought it.

 

He got the idea from his old truck, which had a bad "pcv" thing.

 

J. sends

[griffenrider]

This may sound silly, but how are the engine grounds?

 

 

nipper

 

Engine grounds are good, I put my multimeter on the most sensitive setting, stuck one lead against the engine block and the other against battery neg, no movement of the needle (with engine running)

 

 

Are all these parts OEM?

If not, which aren't?

(In particular, is the front O2 sensor Subaru OEM?)

 

I got the car used, so I can't be 100% sure, but I believe every part except the oil filter (FRAM) is OEM. All of the replacements I listed are OEM.

 

Also, perhaps another piece of the puzzle: the reason the problem seemed so elusive before is that it seems to occur only before reaching operating temperatures, most commonly half-way between cold and warm. For those who know the '02 OB dash layout, above the many-hashmarks at the bottom, but not fully warmed up.

 

Thanks again,

Luke