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Old 01-01-2013, 03:11 PM   #1
mattthegeek
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Subaru Stars hesitation problems after water pump replacement.

Hello all—this is a long posting, but I want to give all pertinent information.

Well, I am a complete Subaru novice, and joined these forums because googling my issues was ineffective. I have also searched these forums for pertinent information, but I have come up empty. I will start at the beginning with my issues.

I bought a 1994 Impreza LS about 1 month ago as a winter car and to hand off to my son in a few months (my first Subaru) . It is the 1.8 motor (as far as I know the only motor that year), automatic transmission, it has about 120,000 miles on it and appears to be stock. I drove it for a day or two (ran like a top) and suddenly it started over heating, I carefully limped it home where I could work on it. I tried a new thermostat and radiator cap, neither of which did anything, so we figured it must be the water pump.

So, we changed the water pump—removed the radiator, and all the necessary stuff at the top of the motor removed the timing belt covers and changed out the water pump which was completely seized up. (The timing belt looked to be in very good condition so I am pretty sure it had been changed) I was very careful to keep the timing belt in the exact alignment/position as it started out (marked the position on the pulley and belt with a marker as well as (temporarily) taping the belt to the pulleys. Put everything back together, filled up the coolant and took it for a test drive. It was Ok at first, then the temp started rising (much more slowly than before) and it started bucking, and hesitating, and losing power. We got it back in the garage and I fairly quickly realized that I was an idiot and had installed the thermostat backwards. (DOH!) so I corrected that situation. And took it for a drive again and the temperature stayed rock solid—right in the middle of the gauge, and at first it drove ok, but then it started hesitating and bucking, primarily in the 2200 -3000 RPM range.

That is the symptom that I cannot seem to purge –When the car is cold, it runs like a champ, accelerating smoothly and steady, holding highway speeds with no issue. As soon as the car is good and warm, it gives a slight stumble on take off, then accelerates a bit then will falter and between about 2200 and 3200 it will stumble and buck and basically run like crap. If I barely feather the throttle I can sometimes get it to accelerate ok, or, if I give it more gas and make it downshift the revs jump to 3000+ and it runs great at those RPM's When I am trying to cruise at road speed (60ish) it will run ok for a minute then the RPMs fall a bit and it lugs—sometimes it just kind of corrects itself if I hold the throttle steady, or sometimes I have to mash the pedal and kick up the RPMs to get it to hold somewhat steady speed. It has also stalled at a stop about 3 or 4 times but always starts right back up. Since this all started happening when I changed the water pump

The car is not showing a check engine light and I have tried the wire connectors under the dash, but I get no codes at all from them –the green wires (stored codes I think) showed nothing, and the other connector (live codes) just blinked steady which I guess is also not a code.

So, here is what I have done so far: Changed the plugs and wires—didn't make a difference. (I seem to have a very strong spark so I think the coil is OK)

I searched for vacuum leaks /disconnects visually and with the carb cleaner method and found nothing.

I Removed the wires from the Throttle position sensor (3 wire unit) and sprayed the inside of the sensor with electronic cleaner. This seemed to make somewhat of a difference for a minute, but it was probably my imagination. I checked the resistance on the sensor, but I couldn't seem to find a good reference for what exactly it should be on the 3 wire unit. I don't remember what the resistance was but it changed (went up then down) with the throttle position. I can recheck the resistance if that is something that could be the issue. --I have had no luck removing the bottom screw from the sensor so it could be adjusted, but if that is what needs to be done I will get it loose somehow.

Replaced the coolant temperature sensor –from doing research this seemed like a very likely culprit—but it didn't seem to make a difference—I got an aftermarket part (not OEM) which I have seen some people advise against, but the nearest Subaru dealer is about 40 miles away.

Replaced the PCV—I didn't really think this would fix it, but it was cheap and easy, so I thought I would try it.

I have also gone through several tanks of gas and put in a few cans of heet, so I am pretty sure it is not contaminated gas.

I also don't think it is the fuel pump/fuel filter, or clogged cat, or clogged injectors, because of the fact that it runs well cold and it runs great over 3000 RPM (if my logic on this is faulty, tell me please)

I am also pretty certain the head gaskets are OK as the oil seems to be not be contaminated, and the exhaust seems normal and am having no overheat issues currently.

I also have disconnected the O2 sensor, which of course gave me a CEL but did nothing for the problem. Ditto for the IAC, and the TPS

I am also considering taking it to the Subaru dealer for diagnostics—On a 94 (pre OBDII) will they be able to get live data from the motor to see if a certain sensor is out of range, or anything like that? I don't really want to pay the big dealership price, but if a diagnostic will let me stop chasing my tail on this it would be worth it. (and on a related note, anybody have experience with either Yark Subaru in Toledo, or Dunning Subaru in Ann Arbor)

Any suggestions, advice, and experience would be greatly appreciated!
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Old 01-02-2013, 11:38 AM   #2
Charlie-III
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Interesting issue, I will get back to this one.

Did you do anything else during the waterpump service? Things like change airfilter, etc?

Free bump up.
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Old 01-02-2013, 01:28 PM   #3
GrundleJuice
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Try disconnecting the water temp sensor
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Old 01-02-2013, 01:34 PM   #4
mattthegeek
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About an hour after I posted I tried disconnecting the coolant temperature sensor but unfortunately that had zero effect.
But it seemed like a good try.
I also disconnected the MAF sensor, and that had no effect.
(both gave me a CEL obviously)
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Old 01-02-2013, 01:36 PM   #5
mattthegeek
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we didn't do anything else when we changed the water pump (at least not on purpose!)
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Old 01-26-2013, 11:02 AM   #6
nickgriffin1
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I'd go back and check the timing.
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Old 01-26-2013, 12:42 PM   #7
Charlie-III
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1998 Legacy 2.5GT
Silver Sleeper Wagon

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Quote:
Originally Posted by nickgriffin1 View Post
I'd go back and check the timing.
+1..... that's the only thing that makes sense. If the timing is a little off, it will run. Running rich while cold may mask the timing issue.
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