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Old 07-13-2016, 11:58 PM   #1
subaruIMPOSIBLE
Scooby Newbie
 
Member#: 401261
Join Date: Sep 2014
Default No Start, Cranks and weak/inconsistent spark...im stumped!

Hi all,

I am almost done replacing the engine in my 2000 legacy outback wagon after an engine failure (metal scraping noises!) I have everything back but the thing won't start I have been troubleshooting all week after work and all day last Saturday but still haven't fixed the problem.

Here is the full story....

After not getting a start I started doing the basic checks. Fuel, check. Injectors firing, check. Good battery, check. Timing(just did it during install) check. Crankshaft sensor test and replaced, check.

While checking the spark I found that it was non-existant and or weak and inconsistant so I tested and swapped in a spare coil pack I had from the donor engine...no change. I tried checking power to the coil, that was good and did NOT dip during crank. I checked coil pack signal, I got some pulses but I do not have a good enough oscilloscope to really see what I was getting(OC is from the 50s...)

After this I started reading through the FSM religiously I found some info about the crankshaft sensor which I know drives the timing for spark, which might explain my spark issues. So I went through the troubleshooting steps for that sensor. The sensor checked out via a resistance check, but I replaced it anyway simply to rule it out.

Next, the manual said to check the wiring by unplugging the sensor and checking resistance to ground. Pin 1 (left most pin) is supposed to read between 10ohm and 100K ohm. I tested it at 90K ohm...so a little bit high.

Pin 2, supposed to be < 10ohm to ground. Tested, 1.5k ohm. So bang out of tolerance. For this the FSM says to

"In this case, repair the following:
I Open circuit in harness between crankshaft
position sensor and ECM connector
I Poor contact in ECM connector
I Poor contact in coupling connector (B21)"

Going off this I figured it was best to isolate parts of the wiring and test them individually. So I tested E10 to E2 AKA the connector to the sensor that then runs to the gray connector that is on the intake manifold wiring said. This circuit checked out A-OK with both wires showing 0-ohm resistance from both ends. Next, I check the other side so B21 to B135 AKA bulkhead side wiring to ECM wiring(middle connector). This also checked out a-ok.

After this, I deduced that it must be the connectors, so I connected everything back together, and unplugged both ends, ECM and sensor side (B135 and E10). Then I tested resistance from end to end and across the wires to make sure there was not a short. Again, everything checked out a-ok.

At this point I was beyond stumped, I seemingly had checked everything and it still wasn't working. As soon as I would plug the wire back into the ECM my test results would be bad. I began trying different ground test points, start, battery, intake manifold, ECU housing, intake manifold. All tested the same or within the margin of error. I even checked the same measurements on a 04 legacy outback I have and the readings I got off that working car for the sensor wire to ground measurements were well within spec.

By now I am pretty convinced that it is a ground issue so I look up all the ground points on the ECU as defined by the FSM. The only one that did not test 0 ohm to ground was ground on pin 6 of B135 ECM connector(middle orange for me). I got a reading of about 320ohm to ground which, is not high, but I think higher than it should be. I chased this wire using the FSM to pin 16 on B22(big brown connector engine bay) I tested from ECM to B22 and got about the same reading again. Which when you think about it is actually interesting. Why between two points that are "supposed" to be directly connected is there the same resistance as there is to ground...that's weird!

I started digging through the FSM again checking the wiring diagrams and finding all the places this wire connect. According to the FSM I have this wire connects to the, fuel gauge sub-module, neutral position switch, vehicle speed sensor, check connector, and data link connector.

That is where I am now, I'm trying to identify all the places it runs and start testing parts of the circuit. But, I figured it was finally time to ask a question on a forum or two and see what you guys think. Am I missing something super obvious? Any tips for tracking this issue down?

The weird thing about this is that the car ran before I pulled the engine and dropped in a new one. I started the process about 3 months ago, and have been slowly working on it till now. During the swap I made sure to keep my intake manifold, and crankshaft pulley. It was an auto to manual swap so there was actually quite a few parts to switch over...so maybe I missed something?


ANY help would be truly appreciated, below is a link to the relevant sections FSM if anyone wants to take a look and double check my findings. I am reallllly stumped at this point.

FSM: Look at engine sections for crankshaft sensor testing and Wiring diagram for plug locations and wiring diagrams.

https://drive.google.com/folderview?...UE&usp=sharing


P.S. Hopefully it didnt take you as long to read this as it did for me to write it
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Last edited by subaruIMPOSIBLE; 07-13-2016 at 11:59 PM. Reason: words
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Old 07-16-2016, 03:53 PM   #2
FierceWRX
Scooby Newbie
 
Member#: 63922
Join Date: Jun 2004
Location: Long Island, NY
Vehicle:
2003 WRX
World Rally Pearl Blue

Default Help diagnosing

Grounds are not tested best with an ohm meter. you could have one strand of wire completing the connection but no current flow. Best to test grounds by checking voltage drop from the component to battery negative while it is powered up. This shows you how good or bad the ground is. You should have very little voltage drop, less than .5 volt for a good ground. It does sound like a ground problem to me and i would measure voltage drop and/or run redundant grounds. To have weak spark shows weak power/ground to the coil or a bad coil, which you have disproven the latter. Hope this helps.
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