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Old 12-05-2018, 03:12 PM   #1
koralr33fer
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Question '08 Legacy - No Spark only when cold!

Having an issue with a 2008 Legacy. Having an issue since last winter when it refuses to start when it's cold outside, roughly 20 degrees F or colder. Car works and operates fine the other 98% of the time here in NY. Just sometimes on a cold morning will refuse to start.

Car cranks over just fine, not getting spark. Timing belt was changed about a month or 2 ago, had this issue last winter before timing was changed, and starts and operates fine when its not cold. So don't think timing is an issue here. Especially since had issue occur previous to changing timing. However, something else is causing a no spark condition when its cold. I'm thinking its maybe a crank or cam sensor that's being quirky when it's cold but can't tell for sure. Especially a pain to diagnose as it only occurs when its very friggin cold out. Today she couldnt start the car, waited 20 minutes and boom, fired up fine (not always the case, sometimes wont start at all on a cold day and works fine the next when warmer outside) Just would like to nip this in the bud before she gets stranded somewhere on a 0 degree day. So looking for a sort of trouble shooting FSM or any other info to help me trouble shoot this next time it occurs.
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Old 12-05-2018, 03:55 PM   #2
yarrgh
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Check the plugs on cam/crank sensor. Maybe the cold is causing the pins to shrink just enough to not make a clean contact. You could always replace those sensors, they're pretty cheap.
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Old 12-05-2018, 04:01 PM   #3
koralr33fer
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I'm going to replace the crank sensor tonight, its only $33. The cam sensors are $65 each so I may wait on those. Also will check grounds and connections tonight. If it fails again I'll go for the cam sensors as well as checking for signal pulse at the coils.
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Old 12-06-2018, 08:47 AM   #4
koralr33fer
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Got the crank sensor in last night, checked and cleaned all grounds, and even took the ECU connection apart and made sure there was no corrosion or broken pins and applied some dielectric silicone before putting it back together. Everything looked OK, just got to wait for another cold day to see if the issue goes away. Wouldn't start yesterday morning at 15 degree's, started this morning ok at 27 degrees with the new crank sensor, but I'm not positive the issue wont return.
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Old 12-12-2018, 11:08 PM   #5
Pasta_hunter
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I'm having a similar kind of issue, did the crank sensor work?
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Old 12-12-2018, 11:12 PM   #6
koralr33fer
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The issue has not occurred again but we havenít had cold enough weather again since to say for sure. Itís been down to mid 20ís but usually occurs when in teens or colder
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Old 12-13-2018, 10:31 AM   #7
koralr33fer
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Quote:
Originally Posted by Pasta_hunter View Post
I'm having a similar kind of issue, did the crank sensor work?
Another thing you can check Pasta if you are having this issue. If its cranking and not starting. When turning over the motor see if the tachometer moves, the RPM gauge. Usually when you are cranking the motor you should see the tachometer move cause the motor is turning. IF THE MOTOR IS TURNING BUT THE TACHOMETER ISNT MOVING is a good indicator that the crank sensor isn't working. If it is then you have another issue, you should pull a wire from a spark plug and put a spare plug in and put against the motor block and turn the motor to see if you are getting spark or not
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Old 12-13-2018, 01:12 PM   #8
Charlie-III
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I have been watching this thread.
If you said issues when hot, then I go to electronics since they can fail with some heatsoak (a sorta common failure).
If fail when cold, I would lean away from coils (mostly spark plugs or cam/crank sensors, cold usually helps).

If you think it's a sensor/coil connection, maybe pull the connection apart and twist (assuming flat pins) a bit, like 5-10* so it sits firmer in the mating plug.
Also just plug/unplug sensor and coil connections a few times may make things better.

I sorta hate intermittents, I prefer a dead die.......then check.

Yes, usually the crank trigger is what drives the tach in the car......no needle movement when cranking, bad sensor......wiring.....tach.
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Old 01-14-2019, 11:02 AM   #9
koralr33fer
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So update: put in the new crank sensor a while ago and havent had issues until yesterday and again this morning. Still not sparking when cold. Was hoping it was a simple crank sensor but no luck with that. Today, Im trying to check if the ECU is sending the spark signal to the coil. The coils for all 4 cylinders are one unit with 2 coils. The connection has 4 pins. Does anyone know how to test these with multimeter or test light?
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Old 01-14-2019, 12:01 PM   #10
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So i probed the connecter that goes to coil pack. It has 4 pins. looking at the connection on the harness, there is one pin with constant 12v power. The other 3 have no power. Im assuming 1 is ground and the other 2 are for signal from the ECU to activate the coil/spark. I took a test light connected to ground and a wire going to the other pins on the connection, looking for a light or strobe light when cranking. The signal from ECU for spark, it should be very rapid and create almost a constant glow on light when cranking. It does not. I could not get any light out of the other 3 connections at all, even when turning the motor.

So i guess the next step is why? For some reason the ECU is not trying to send signal for spark when starting the car, but only in cold conditions, seems to be about 10 to 15 degrees F or less. Is the crank sensor the only input the ECU needs to send the signal to the coil?
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Old 01-14-2019, 12:14 PM   #11
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Also, another tidbit of info, the tachometer doesnt move while cranking the car still when its a no start. Does this confirm the crank sensor again? I've heard on some models you wont see the tach move until the engine has started. I've tried to see it on the tach when the cars working but it fires so quick that you cant see if it does or not.
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Old 01-14-2019, 01:11 PM   #12
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Anyone know what the voltage is supposed to be at the connector for the crank sensor? Its reading 2.4V on a multimeter. I thought these generated their own voltage from magnet and metal movement. Anyone know?
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Old 01-23-2019, 03:59 PM   #13
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Problem is still persisting at this point and have dropped the car off to Mr. Subaru. Unfortunately the issue only occurs in cold weather and the dealer doesn't seem interested in diagnosing the issue. They either wait till noon when its warmer and try to start it which it always does or just a couple days ago finally had the no start occur and never pulled it into the shop after its been there a week and a half....

I changed the crank sensor and am still not getting spark on any of the cylinders. I tried checking the resistances on the coil to see if that was the issue and it seems to check out. I pulled the connection off to the coil which is a 4 pin connection. I got 12v on 1 of the 4 pins and the other 3 all seem to be grounded. I was expecting to see a pulse signal going to the coil from the PCM on this connection from at least 1 of the 3 pins going to coil. I connected a test light to ground on the battery and probed each of the 3 pins while cranking the engine, I was unable to get the test light to illuminate on all 3 pins. Which I believe means that the PCM isnt sending the control signal to the coil. Which means that the PCM isnt getting the required inputs to send the signal OR the computer is supposed to be sending the signal and it isnt or have a bad connection between the two. Can anyone confirm this?

I'm getting desperate, car has been at dealership for almost 2 weeks.
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Old 01-23-2019, 06:44 PM   #14
yarrgh
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Well, the ECU needs info from the crank AND cam sensor. You've already changed the crank sensor...

I hate just throwing parts at a problem. I suppose you could put the cam sensor in the freezer on a warm day to try and replicate the problem.
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Old 01-29-2019, 09:14 AM   #15
koralr33fer
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Well its still at the dealership, it supposed to be cold tomorrow so hopefully they can find something, I'll let ya know what they found out. I guess I kind of overlooked or dismissed the cam sensors partly due to getting a crank sensor a couple times, but I probably should have checked before going to dealer. The cam sensors are a little more pricey too.

I'll wait and see what the dealership says, they've been a PITA. So far I've asked for a diagnostic for a no spark and they've come back with replacing the coil, plugs and wires for $800 and clean the throttle body for $80. Lol clean the throttle body.....for a no spark...and plugs and wires like they would somehow all fail at the same time.....possibly if the coil was bad but the plugs and wires aren't even that old...
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Old 01-31-2019, 12:40 PM   #16
koralr33fer
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Just got a call from dealership, they had the no start occur today and yesterday and came back with a decent diagnosis (for a change, last time I was told to clean throttle body for a no spark condition lol). They determined the wiring for the crank sensor had corroded and frayed inside the wiring harness, between the sensor and the connection for the computer. Not far back from the sensor itself. They said they were able to reproduce the issue by moving the wire around (don't know if I trust them on that tho). They wanted 375 for the work plus the diagnostic. I told them to go ahead and do it (usually I do my own work, first time at a shop/dealership for anything). One reason I'm not is I'm sick at the moment, and two if the issue occurs again I can go back for another free diagnostic. I'll let you know how I make out. I kind of figured it was either a bad wire/connection or the computer. I hate chasing wires though.... I wont say its solved yet though until I see it start in cold weather a few times.
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Old 02-01-2019, 10:40 AM   #17
koralr33fer
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They repaired the wire last night....still no start this morning....I have the worst luck. I am really thinking its really the PCM at this point......anyone know if a replacement PCM needs to be programmed to the vehicle or if you can just get a replacement and plug it in and you're good to go?
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