2008 Impreza Car Barely Starts & No Lights

subaru
lights
impreza

#1

Hi All,

First time to the forum and am looking for some troubleshooting help on my 2008 Impreza.

Start of problem: The problem started a few days ago when I took out the battery to replace my driver side turn signal. Upon putting the battery back in the problem began.

Problem: The problem has evolved throughout some troubleshooting. After putting the battery back into my car it would not start. It would fire up for about 1s then die almost instantly. After a few tries I found that if I started the car and gave it just a tap of gas, the car would start and would idle normally. When I finally got the car to start back up a whole bunch of lights lit up the dash (cruise control flickering, tire pressure flickering, check engine on, traction control on, etc.) and checking Torque the voltage on the battery was low (so many sensor problems pointed to battery) so I replaced it with an Interstate battery after getting it tested at an autoparts store. I fired it back up and now the car barely starts now but did fully start 5 times in a row (it fires up and nearly dies over the course of about 5s then proceeds to idle normally).

Troubleshooting: I tried unplugging the MAF before swapping the battery which very marginally improved starting capability. MAP sensor I also tested before swapping the battery and made the car start even worse.

Current state of the car: I had to drive the car home after replacing the battery and it drove just fine. The car died 3x over the course of about 2 miles but ONLY died when I was coasting in neutral up to stoplights. Engine braking and idling functioned just fine and the car seemed to drive normal. All lights are off in the car.

My next steps for troubleshooting would be to unplug the MAF / MAP and try driving to see if it still installs. I will likely drive it to a nearby auto shop to check the alternator. At this point I really have no idea as to what the issue could be. Google searches for hours really led to nothing.

Anyone have experience with symptoms like this? What approach should I take and what should I look at first?

Side note: About a week before when driving down the road my ABS, traction control and hill assist lights all came on. I did not get the chance to scan for codes as the lights when back off after a few miles. Not sure if this could be related.


#2

Start by measuring the basic battery voltages. It should measure appx 12.6 volts before the first start of the day, and immediately after starting and idling the engine, in the 13.5-15.5 volt range. Measure at the battery posts, and at the connectors. There should be little to no difference. What does your battery measure? If the voltages are ok, presuming there are no stored diagnostic codes in computer memory, my next guess is the computer has somehow forgot the learned engine operating parameters and must now re-learn them. You may need to go to a dealership for help w/this, but you could try driving the car around the neighborhood at slow speeds and see if it starts to behave better the more you drive it.


#3

Battery is brand new, replaced after the old one was tested at napa auto. Torque shows battery at idle is 13.3-13.5v but heavily favors 13.5. Will have access to voltmeter tomorrow.

No stored codes.

What makes you think it may have forgotten operating conditions and how would this have happened? I am not familiar with this occuring. Is there a way to test if this is the case or is this simply the last resort?


#4

The engine control computer is constantly “learning” how your engine operates, what the sensors say, how much time to leave the injector open to fuel each cylinder and many other things as well. It adjusts for variations in components used to build the engine and so as the engine ages the computer maintains the efficiency and emissions. It doesn’t store all these “adjustment” in non-volatile memory so when the battery is removed, the adjustments are reset to zero.

BTW, Torque is telling you \the alternator voltage when the car is running - the 13.5 volts - and the battery voltage only when the car is turned off - the 12.6 volts. On the custom screen, add a gauge to measure battery voltage - the gauge choice with a minimum value and maximum value. That allows you to monitor if the voltage is dropping too low to run everything - 10V or so - anytime you drive the car. Or even drops back to battery voltage anytime you are driving. That will tell you if the alternator is failing.

That’s what I think may be going on,the alternator is failing!


#5

Sitting battery voltage read 12.54vdc and lead on battery negative and positive on alternator showed 14.61v with a multimeter. Battery was around 13.95v when on and turning on radio, headlights and both lights in cabin dropped it to 13.89v. Any other test I should be doing to confirm function? It really wont drive well as it stalls fairly often so probably not going to get averages easily!


#6

Those voltages look ok. Indicate both the battery and alternator are ok. There could still be a problem with the battery connection to the rest of the car, either a problem at the posts, cables, or with the ground connection at the chassis. When you say “all lights are off”, are you referring to the dashboard warning lights? The headlights and tail-lights work, right? Those dash warning lights are supposed to be off when you are driving. That means the electronics think the car is working correctly. They should turn on with the key in “on” before you crank the engine, then go out soon after starting the car. I’m presuming that’s the case for you.

so what’s wrong ? … hmmmm …two guesses, the first I alrealdy mentioned, disconnecting the battery caused the learned engine parameter to be lost, and they have to be re-learned. The other is that somehow a fuse got blown. The latter seems unlikely if the electrical systems are otherwise behaving ok, and the only problem is stalling when in neutral.

I think what I’d do if I had that problem myself – assuming there’s no obvious problem like a vacuum hose has come loose, battery connector loose or frayed or wobbly – is check the idle rpm. First make sure the air cleaner is good, the ignition timing is in spec, and the ignition system & spark plugs are good. Once the engine is warmed up, the idle rpm should be 650 for a manual transmission, and 700 for an automatic (both cases idling in neutral). Next turn on the AC and let the compressor work a full minute. At that point the idle rpm should be 850. Specs for 2.5 L SOHC engine.

Edit: Another idea, disconnect the battery and leave it disconnected over the course of one night. Once the battery is reconnected, that can sometimes cause the computer to automatically enter the re-learn mode.


#7

Yes, you are correct the dash lights are off is what i meant.

The only problem is stalling when neutral coasting and almost dying on startup. I presume they are related but may not be! I have also read some about the tps sensor or wheel position sensor going bad can cause some similarish symptoms as well.

I am currently in the process of moving so i may not get to more troubleshooting until this weekend. I will try unplugging the battery overnight and see what that does for me then go after idle rpm.

Results to come. Thank you very much!