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2008 forester 2.5 NA - crank, no start


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Confirmed! Was 10 degrees out this morning and she started! Moral of the story I guess for a no spark condition would be to check at coil connection for computer signal, and don't assume because you are getting reading on a volt meter that it is working properly. Check to make sure the ecm is getting all required inputs like crank and cam sensors (typically if you were missing one you would get a check engine light and a trouble code though). Check power input and grounds at ecm, and if all that fails, do the wiggle test, have someone crank while you jostle some wires at ecm (the one not working properly was the B137 or the one on top when in ecm). That last test saved me like 300 bucks cause I was convinced the ecm was bad after all other tests were done. Edited by koralr33fer
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The Factory Service manuals for most lots of Subaru models are available here for free https://sl-i.net/FORUM/showthread.php?18087-Subaru-Factory-Service-Manuals-(FSM)-Every-Model-USDM-EU

 

Saved me a lot of time and headache having these available. I attached 2 in particular that I used for troubleshooting the no spark (for 2008 legacy). Do the ignition one first, then check the ecm power and grounds. You can find the one for your model by downloading the one that corresponds to your vehicle and then going to engine diagnostic section, also you can do the find in document feature (control+F) and search for "spark" make sure you are in the correct section for your engine.

Subaru Ignition FSM.pdf

Edited by koralr33fer
Added attachment and fixed punctuation
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  • 9 months later...

7 degrees this am in beautiful NE Pennsylvania. And our crank no start reappeared.

 

This condition screams a corrosion/ground issue. It only occurs when temps are below about 10 degrees and the car has been sitting overnight. Putting jumper cables on it from a running car it fires right up. Note the battery is fine, cranks fine without the jump, just no spark.

 

I replaced the battery cables when I did the timing belt at 105k. Car now has 109k.

 

Only other possibility I can think of that I have not checked is the ECM plugs/wiring, like koral33fer above. I do believe that is under the passenger side carpet correct?

 

It's a 2008 Forester 2.5X

Edited by poconoracing
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7 degrees this am in beautiful NE Pennsylvania. And our crank no start reappeared.

 

This condition screams a corrosion/ground issue. It only occurs when temps are below about 10 degrees and the car has been sitting overnight. Putting jumper cables on it from a running car it fires right up. Note the battery is fine, cranks fine without the jump, just no spark.

 

I replaced the battery cables when I did the timing belt at 105k. Car now has 109k.

 

Only other possibility I can think of that I have not checked is the ECM plugs/wiring, like koral33fer above. I do believe that is under the passenger side carpet correct?

 

Yeah it’s under the passengers feet below carpet. Not to hard to get at. I fixed this last winter and it has not occurred since. There wasn’t any sign of visible corrosion within the plug at the ecm, but having someone crank the car over and moving the plug was able to recreate the issue. The wire in particular that was loose was the one that sent firing signal to the coil. You can check for the signal at the coil with a test light, it should strobe or flash, possibly so fast that it just looks on, but either way should light up. If that pulse signal isn’t present you won’t get spark. There’s 3 wires at coil, one is power, ground and pulse signal. It should flash while cranking if computer is trying to engage coil. My ecm thought it was sending it it just wasn’t reaching the coil. When I tested for continuity from ecm to the coil it was present, but just enough slack within the white connection block that it was losing contact at cold temperatures when metal contracted, damnedst thing and really hard to find. Dealer was useless in finding it.

 

If that’s not your issue I would review the factory service manual for no spark condition, very helpful and not too hard to go through steps with a meter.

 

It's a 2008 Forester 2.5X

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  • 2 weeks later...
  • 3 weeks later...

So my no start reappeared. Current temp 16 deg F

 

Turns over fine, no spark.

 

Pulled up the passenger carpet and pulled the ecm out. Played with the harnesses, no spark. Pulled all the connectors from the ecm. No crusties, nothing melted, all the pins were straight and clean.

 

Reconnected it. Nothing. Pushed on each of the 4 wires for the coil (power, ground and 2 signal wires) at the ecm while my son cranked it. Nothing

 

Backprobed one of the two control wires for the coil and turned it over. Scope picked up nothing. there is no signal going out from the ecm to the coil.

 

I had previously checked the cam/crank signals and they are there.

 

Is there anything else outside a dying ecm driver/problem with the solder joints that would cause the ecm not to output a spark signal?

 

I jumped it and it fired right up. Scope sees a waveform on that pin and it runs fine after that. I don’t want to drop a couple hundred bucks on an ecm unless I’m 100% sure that’s the issue.

 

Really frustrating. When it runs, it runs perfectly. No miss, no drivability issues, no CELs pending or stored.

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I would guess it’s more likely you have a weak connection between the ecm and the coil. That is where my issue occurred. If the car works normally in warmer weather than it’s not likely the ecm is failing intermittently. My weak point in the connection was at the white blocks at the ecm. The wire had just enough play, and contracted just enough on warm weather to lose continuity. I would trace that control signal wire back to the ecm. Check it for continuity. The connection was poor enough for the car to not start although there was no ssignal gun of corrosion or any visible damage. Just because the connection looks ok doesn’t mean it’s tight. Those little metal wire holders n the block are s***.

 

What I ended up having to do was drill a wire through the white block in an empty spot, soldering a wire to the correct pin on the ecm and connected it to the wire. In a way bypassing the white block where it was losing connection.

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I would guess it’s more likely you have a weak connection between the ecm and the coil. That is where my issue occurred. If the car works normally in warmer weather than it’s not likely the ecm is failing intermittently. My weak point in the connection was at the white blocks at the ecm. The wire had just enough play, and contracted just enough on warm weather to lose continuity. I would trace that control signal wire back to the ecm. Check it for continuity. The connection was poor enough for the car to not start although there was no ssignal gun of corrosion or any visible damage. Just because the connection looks ok doesn’t mean it’s tight. Those little metal wire holders n the block are s***.

 

What I ended up having to do was drill a wire through the white block in an empty spot, soldering a wire to the correct pin on the ecm and connected it to the wire. In a way bypassing the white block where it was losing connection.

 

The scope was backprobed at pin 18 of B137 at the ECM - no signal. I was not at the coil. i also pushed/pulled all 4 coil wires (pins 6, 26, 18,19) on the attached wiring diagram as my son cranked it. nada

 

Put the 450 amp engine starter on it an it fired right up. i did not remove the back probe or move it in any way and now have a scope signal. :spin:

 

My question was is there anything else that will command no spark signal? My first thought was immobilizer but I have no theft light blinking indicating a fault. I'm leaning toward a circuit board problem that the cold is shrinking the board and causing it to lose contact. It's about $200 and the car will be down a week to get the ECM rebuilt so i want to exhaust all my possibilities.

 

Anyone have any other thoughts/possibilities? The real PITA is it only happens when it's sub ~20 degrees so my ability to test is limited by the weather.

diagram.thumb.jpg.cf71be39ce35298963bd461c1680baa0.jpg

Edited by poconoracing
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So just to be clear, you had no control signal for the coil at the pin on the ECM? After you put the charger on the car you were able to get signal? I would just double check the wires have continuity from ecm to the coil. Should have close to 0 ohm resistance.

 

When I had the issue putting extra juice to the battery would not get the car to start. If simply upping the bolts and amperage is getting the car to start you likely have a weak connection somewhere. Maybe go to the basics and make sure you got good clean grounds and battery terminals are clean. Usually if you can get an electrical failure to work with extra juice it’s a result of high resistance somewhere in the circuit.

 

I’m pretty sure to get the spark you have to have power and ground at both the coil and ecm. Also you must have input from crank sensor and cam sensor. Also, just a heads up, if you get a crank sensor check engine light it’s often a result when you crank the engine a lot and the car doesn’t start. It kind of sends a ghost code to computer as a result of all the cranking. I had that code when I had the issue and I got too focused on the crank sensor when it had nothing to do with the problem. Do you have any codes?

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  • 1 year later...

So the No start reappeared like clockwork earlier this winter. Still sub 20 degrees or so and no spark. No CEL set or pending

 

I bought an ECM off ebay, and before you ask the car is pre immobilizer. Apparently 2008 was the changeover for the Forester, mine is an early 2008.

 

Swapped the ECM and ...... no spark. Note is firing the injectors. Powers and grounds to the ECM check out fine. Cleaned every underhood ground I could find. replaced the battery cables for good measure with OEM.

 

Got out the 450 amp starter .... and it fired right up on the used ECM

 

Only new thing I noticed - on the live data the timing read -7 deg when it won't spark and +15 degrees when its idling running.

 

Anyone know where that timing value comes from? this is a SOHC 2.5L NA motor. I would assume its a derived value from the cam/crank correlation? And what else would cause a no spark? knock sensor? air gap on the cam or crank sensor maybe? I know both are a magnetic field based sensor

 

What baffles me is why the 450amp starter fires it right up, and it starts perfectly for the rest of the day. Maybe the system voltage increase means a stronger magnetic field? It 100% has an RPM signal at the ECM when its not firing, so I'm looking more to the cam sensor.

 

So couple questions if anyone knows subaru timing logic:

 

Does the cam signal trigger the spark?

If I unplug the cam sensor will the ECM use a default strategy?

Same with the crank sensor?

 

This car is now my 17 year olds primary transportation, he can jump it but my fear is eventually it going to leave him sit and for my own sanity I'd like to track this issue down once and for all.

Edited by poconoracing
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This reminds me a lot of this video. (Edit: After re-reading this thread, this might not be the culprit, but doesn't hurt to check or swap relays)

 

TLDR - Worn starter relay contacts, increase system voltage made it start easier since increased voltage was able to overcome crappy connection at relay contacts better, or something like that. Even if that's not the case here, maybe it'll give you some ideas on what might be going on, other stuff to check.

Edited by apexi
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Love scannerdanner. Great diagnostic videos.

 

Yeah it cranks fine, sounds fine while cranking, it is firing the fuel injectors it simply has no spark. no spark signal at the coil from the ecm no spark signal at the pins on the ecm connector.

 

I thought I might have a driver going bad in the ECM, bad solder joint splitting in the cold, something like that, hence the used one, but it did exactly the same thing.

 

I have an RPM signal while cranking when looking at the live data.

 

For the cam it shows timing, not rpm. It had that weird -7 deg ignition timing when cranking when it didnt start, but with the 450amp starter hooked up it showed +15 deg of timing.

 

Swapping the cam sensor is more money and more PITA so before getting out the parts canon I wanted to see if someone here knew where the ECM derives its spark trigger.

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I’m pretty sure the ECM sends spark signal triggered by crank sensor. The crank sensor tells the ecm what position the motor is in and when to fire the spark plug. In my case the ECM was sending the signal to the coil, it just wasn’t reaching the coil. The plug going into the ECM was the culprit. It must have contracted the metal just enough in the cold that the wire and pin were losing contact to the ECM pin. I ended up drilling a small hole through the plug feeding the wire through and soldering the wire directly to the ECM. The issue has not occurred since. This was a battle we fought every winter before so I know your pain.

 

If you are detecting rpm on your live data then your crank sensor is fine and the ECM should be sending spark signal to coil. The coil pack has 3 pins, check for ground, power and when cranking it should receive a signal from ECM. Without all 3 no spark. See which one you are missing and this will help narrow down where to start.

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Ok, 25 degrees and no spark

 

Broke out the oscilloscope - good waveform from the cam and crank sensors when cranking.

 

back probed on the the coil.

 

Pins 1 & 4 - 0-7.8V square wave

pins 2 & 3 - 12V and ground - less than 1 ohm resistance from ground to block

 

FSM says should be 0-10V min or swap the coil and ignitor assy

 

swapped it - nada

 

Son has to go to work - put the 450amps to it ..... fired right up on the new coil. GRRR

 

Perhaps we have some resistance somewhere between the ECM and pins 1&4 on the coil connector? I'll dig up the wiring diagram and start tracing

 

Back at it tomorrow after it sits overnight. Why cant this happen when its 70 degrees and sunny?

 

BY the way if any of you are looking for an inexpensive scope solution. Here is the one I'm using. Works well for $100

 

https://smile.amazon.com/SainSmart-Portable-Handheld-Digital-Oscilloscope/dp/B074QBQNB7/ref=pd_bxgy_2/135-5337730-2946353?_encoding=UTF8&pd_rd_i=B074QBQNB7&pd_rd_r=c25631bd-29a6-4a2f-9d3d-9b95d5065fb3&pd_rd_w=cRY32&pd_rd_wg=a3ryb&pf_rd_p=f325d01c-4658-4593-be83-3e12ca663f0e&pf_rd_r=Z2BKBKNAYR281DJ3CVZW&psc=1&refRID=Z2BKBKNAYR281DJ3CVZW

Edited by poconoracing
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  • 4 weeks later...
Did you end up figuring this one out? Fighting something similar. Thanks

 

Not completely. I know what it is . Resistance in the signal wires between the ecu and the coil.

 

I haven’t had a chance to get back to it. I used deoxit on the engine plug and the coil plug. No change. There are only 3 plugs, the ecu, the engine connector and the coil connector. I’m going to have to trace the wires.

 

It’s definitely on that harness somewhere.

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  • 2 weeks later...
I got mine fixed. Voltage at the coil was dropping to 10.7 while cranking when it wouldn’t start. Swapped out the starter and now voltage to the coil never drops below 11.3 while cranking and it starts every time, no matter how cold.
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I'm glad you found it. How did you diagnose it?

 

My Car has the original starter. Anything is possible, but a high enough amp draw to pull down the entire system on a functional starter engagement would be a new one to me.

Edited by poconoracing
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I thought the same thing but the good battery and the voltage on the positive input of the coil dropping to 10.7 during cranking is what led me there. The service manual said anything over 10v while cranking was fine. The only thing I can come up with is the aftermarket ignition coil on the car did not like the lower voltage. I could add a jump pack to the car when it was cold and it would start every time. I did voltage drop tests on all four wires from the coil, all the way to the ecm on the signal wires also. Additionally did voltage drop tests on the hot lead to the starter. All tested fine. That’s what led me to the starter having high current draw. I’m just glad it’s fixed.
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  • 8 months later...
I thought the same thing but the good battery and the voltage on the positive input of the coil dropping to 10.7 during cranking is what led me there. The service manual said anything over 10v while cranking was fine. The only thing I can come up with is the aftermarket ignition coil on the car did not like the lower voltage. I could add a jump pack to the car when it was cold and it would start every time. I did voltage drop tests on all four wires from the coil, all the way to the ecm on the signal wires also. Additionally did voltage drop tests on the hot lead to the starter. All tested fine. That’s what led me to the starter having high current draw. I’m just glad it’s fixed.

 

Believe or not ... my forester appears to have had the same issue with the starter. Swapped it out a month ago with a new one from Autozone. Not one no start since.....

 

Thanks for sharing.

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