Mechanics

SUBARU IMPREZA SENSOR PROBLEM

2005 Subaru Impreza • 103,000 miles

You might have to get creative and think outside the box on this one. I’ve been to probably 2 dozen mechanics and they’ve been very little help. My Impreza is slowly dying. Back in 2009, at about 70,000 miles on the odometer, I got a tank of ethanol-free gas (This after running it on 10% ethanol since 2007 or whenever that junk came out). What happened when I did this was the phenomenon known as “phase separation”. Pop Mechanics did an article on it. At first, I noticed the car shifting early, probably the result of running on pure ethanol for a bit. Later throughout the tank, the car began to get really slow and almost stall, due to water. I later found out that the car was not shifting into last gear, so I was driving 60-75 mph on the highway in second to last gear, with the pedal almost to the floor - which probably trashed whatever part is still making the car slow (and possibly draining the alternator/battery).

The first thing I did right when this problem happened was take it to the dealer, where they gave it a tune up to no avail. A friend from church told me that week that water got in my fuel system, and to replace the fuel filter. I did so (along with the pump, as it’s the same assembly), with great improvement. The car is able to shift into last gear. But, the whole time since the fuel filter/pump replacement, there is still this hesitation, and it’s not as quick as it was before this problem. Normally Subarus are very responsive off the gas. Now it’s like driving a Ford Fiesta or something. It also upshifts way too early, further making acceleration a drag.

I’ve had many tests done: engine compression, fuel pressure, oil pressure, vacuum, ignition timing, long term fuel trim, voltage regulator, throttle system, I had the fuel system drained months later, which I’m sure was completely pointless.

I’ve had multiple fuel system cleanings, including Sea Foam and Amsoil system cleaners. No noticeable performance improvements.

I have replaced the following, with some improvement in performance:

As mentioned, new fuel filter/pump (same assembly)
new battery right away (it was just about dead after all this)
new front oxygen sensor
new fuel lines
new fuel injectors
engine (~60k miles on it)
new throttle body/TPS sensor
new cam/crank sensors

I have replaced the following with no improvement in performance:

tune up + new spark plugs
air filter
drained fuel tank
fuel pressure regulator
mass air flow sensor
catalytic converter
replaced fuel filter again just in case
replaced transmission (it got burned out, needed to be replaced. Sounded like metal
parts scraping together, gear slippage, etc.)
timing belt replacement (head gaskets were leaking too, so those got replaced at the
same time)
rear oxygen sensor
MAP sensor

throttle sensor/control relay

pulleys/idlers

coolant temp sensor

alternator

accelerator assembly (including sensors)

spark plug wires

EGR system cleaned

ECM

fuel pump relay


The transmission was discovered to be burned out from this whole ordeal upon the next service – Feb. 2011 - and had to be replaced.

The entire time since the catastrophe, there has been some bubbling/gurgling sound coming from the gas tank for a few seconds at start up.

The alternator crashed at about 93,000 miles, giving off the most horrid screeching sound I’ve ever heard in a car.

The problem very well could be electronic or fuel delivery, because I replaced the entire throttle system. I read how the fuel pump relay amplifies the charge coming from the ECM, and how, if the part is damaged, fuel pressure can be ok but delivery can be slow. Since it takes extra pressure on the pedal to get my car going, I thought “well, perhaps this is my problem.” It wasn’t, so now I’m not so sure if it’s a fuel delivery problem.

This whole thing seems to be coming to a head. Last summer I noticed the dashboard/headlights starting to flicker, and just noticed that the light in the trunk does it too. The vent system oscillates a little, depending on throttle pressure. It all seems to be getting progressively worse. I replaced the ECM recently, thinking that was the problem. No difference.

The heat system takes almost 10 minutes to warm up now. The engine has always taken an extra long time to warm up since the catastrophe, and now it seems to be worse. This is why I suspected fuel delivery, which could stem from an electronic problem, I don’t know, I’m not a mechanic.

I wonder if maybe the battery is drained again, and that’s causing funny behaving accessories? I’m going to get it tested soon. But if the battery is dying, why? What would drain the alternator and a battery with less than 30k miles on it? Maybe my battery terminals are shot?

Does anything else I haven’t replaced effect fuel delivery? Are there any other signals between the pedal and fuel pump I haven’t replaced?

Could the timing or ignition switch be trashed?

Could it be the main relay switch?

I will give $40 for the solution.
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December 6, 2012.



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