Chasing Camshaft Sensor Problems

[CharlieLS]

Hi everyone,

Longtime reader, first time poster...I have done a lot of reading/searching the last few days, and I'm still struggling with a sensor problem.   I have a 1990 Legacy wagon, and it's really been a helluva trooper.  But recently, it suddenly died in traffic, and when I checked OBD, it gave me the code for the camshaft position sensor.  I have gotten this code before, about a year prior, and replaced the sensor and ended up taking it to a shop for the coolant temp sensor and what turned out to be a fuel pump issue.  They fixed those things, but in the process, ended up hardwiring in my camshaft sensor and my crankshaft sensor, because I guess there was old/fragile wiring at the connectors? 

Anyway, fast forward to a couple weeks ago when it dies and I get the camshaft sensor code.  I have had to cut apart the shop's hard wiring to test the sensor/harness, and after a lot of hair-pulling have tested the sensor (it's good), and now am trying to hunt down the problem in the harness wiring.  I am getting no voltage readings from the harness wires with the key in the ignition and accessories turned on (i.e., I believe, no signal/power from the ECM?)  Before I tear apart the dash and everything trying to chase faulty wires in the harness...is there anything else that I could be missing?  I'm kind of an idiot when it comes to electrical stuff so maybe I wasn't doing the reading right?  Maybe there's some other "x" factor that could be causing all of this?  I haven't even gotten to checking the timing belt yet because of mucking around trying to re-wire this sensor, and kinda feel stopped cold with the no-voltage-in-the-harness thing.

The weird thing is how suddenly it failed - I had been doing a lot of driving recently, longer trips too, and it performed perfectly (well, as perfectly as a 34 year old car that I haven't always had the $ to perfectly maintain can!)  No stumbling, weird noises, power fluctuations, misfires, anything.  The only thing that happened between then and when it died was that someone tried to steal it (!??) and had jammed half a pair of scissors into the ignition, but afaik they didn't mess with anything else except jacking a bunch of my stuff out of it.  I don't think that has anything to do with this, though, honestly. 

Anyway, sorry for being long-winded!  Like I said, I'm a long-time reader and admirer of this forum and I just hope I can keep this car going!  Thanks in advance, hope everyone is having a great day.  (better than mine anyway LOL)

[lmdew]

Hard to say, once someone cut into the wires.  You'd need an O-scope to read out the cam sensor as it outputs a signal. 

They hardwired the cam sensor into the harness?  You can check the Timing Belt by pulling both side covers and the crank sensor and looking down the hole to make sure the crank mark lines up.

[CharlieLS]

11 minutes ago, lmdew said:

Hard to say, once someone cut into the wires.  You'd need an O-scope to read out the cam sensor as it outputs a signal. 

They hardwired the cam sensor into the harness?  You can check the Timing Belt by pulling both side covers and the crank sensor and looking down the hole to make sure the crank mark lines up.

They sure did!  It's causing me such a headache, wish I'd never taken it to them   I don't have an oscilloscope but I did get little voltage bumps from holding the sensor near a metal tool and moving it around?  My biggest question at the moment is if it's actually the *harness* that's causing the problem - since I can replace the sensor pretty easily if need be - because I tried testing the harness wires for voltage with the power turned on and got nothing.  I don't know if I did it wrong, or if the wires in the harness are fried.  From what I've been researching, I think the ECM is supposed to output some kind of signal/voltage through the reference wire and the signal wire...?  (sorry if I've got the terminology wrong, like I said, anything electrical is my downfall, which is why this is turning into a kind of nightmare scenario for me 😆)

Gonna check the timing belt tomorrow though, thanks for the tip!

[CharlieLS]

Also, is there a fuse or something for the ECM/ECU?  I'm still getting no voltage reading on the engine wiring harness for this sensor, and I'm pretty sure I should be getting *something* with the ignition turned on. ....? Just wondering/dreading the thought that I accidentally shorted something out when trying to resolve this connector mess...

[wtdash]

Hi, I'm probably less 'electrically inclined' than you, but my understanding is the crank and cam sensors only monitor the magnetic pulse as the cam and crank's triggers spin by. There's no voltage involved, I believe.

The ONLY codes (CEL) now are for the camshaft, correct? Older Subies have a bad habit of spitting out unrelated codes when something fails. Like the CTS you got above when the fuel pump failed. Probably due to how little the ECU actually monitored back then vs. some of today's cars tell you when you take your eyes off the road. 

As you've likely discovered, the '90-'94 engine harness that connects to all the sensors on the top of the engine and the intake manifold/IM are hard wired end-to-end. So, I'd think you'd need to find the complete wiring harness off another '90-'91. The IM harness connectors at the battery differ based on years '90-'91 were either round or square and '92-'94 were the other style (Thanks! Subaru 😞 ), so not easily swappable. 

For the '95-'98 models the Crank/Cam sensors have plug connectors at the sensors and wiring for the TPS is different, so that makes them unusable, AFAIK. But you might be able to retrofit the sensors and wiring for just the Cam and Crank, if you have a PullNSave-type lot in your area*. 

I think (!) the wiring to the cam/crank sensors has two wires, but one is actually just 'shielding' which isn't needed (as long as you're not running a bare wire end-to-end), so should just be able to replace that section with one wire. FWIW, on a previous project I bought some wiring at Home depot that was composed of approx. 4-6 wires in the loom(?)  - not sure what the term is - that I then used to extend from the ECU to the sensors I was using. Worked fine for years. You could do something similar, but accessing the ECU/computer under the dash is a real PITA. Been there didn't like it.  Here's a link to the ECU pinout - if you get that motivated: https://www.surrealmirage.com/vrg3/ecupins/

 

*Portland area should be 'Subaru Central', right? 🙂

Edited May 30 by wtdash

[CharlieLS]

Thanks for the info!  The OG cam sensor (I guess it must have been modified itself at some point?) in my car did have one of those rounded connectors hooking it up to the wiring harness...so I ordered just the connector to see if I can reattach it in a way that makes sense LOL.  It does have three wires, but one of them definitely is shielded, so idk how careful I have to be in making sure there's shielding the whole run?  If it isn't meant to get voltage at the harness, then lmdew might be right and it's a timing belt issue...in which case, thank gods for non-interference engines!  Cuz I definitely instinctively tried to restart it a bunch of times when it died.  XD 

For now, everything is on hold cuz I have to ship off on a boat for work for a few weeks...will continue looking into things when I get back!

Thanks again!

[CharlieLS]

Well I just wanna finish up the story of this issue, in case it will help anyone else coming across the same questions!

Long story short, it ended up being a problem with both the timing belt AND the camshaft sensor.  I don't know exactly how those two things may have been related to each other in the moment, but here's the longer version of what happened:

I checked the timing belt shortly after it was suggested I do so, and laughably, that definitely seemed to be the problem as when I opened up the covers, the timing belt sorta...flopped out.  It had broken in half.  Which frustrated and confused me, since I had changed it less than a year ago!  This time, I ordered an actual Subaru brand timing belt (I *had* done my research to buy the last one, and decided on getting the whole kit from a brand - I can't remember it now but I'll look it up - that was recommended to me as being just as good as getting Subaru parts!), and a friend and I put that belt in and also discovered that the tensioner roller seemed to have seized.  That bushing that the bolt goes through was just....stuck, somehow.  Crappy part?  We're not exactly sure, but luckily I had a new one waiting, and we put that in along with the belt.  The piston tensioner and everything else was fine. 

So we put everything back together and presto! The car started, sounded fine and normal, and I was ecstatic!  My friend went on her way and I drove to the store later that evening -- where, halfway there, the same thing happened as back when all this started.   Very suddenly, the car died, no rough running, no weird noises, just noped out and the engine shut itself off.  Luckily I was on an only mildly busy street and managed to pull to the side as it was happening.  Tried to start it again and it was an absolute no-go.  Starter motor tried, but no crank.  So this time, I didn't sit there with my heat-addled brain trying to get it to start over and over, and just got a tow back home.  Once there, I notice the check engine light is actually on (a rarity in this particular car), and I get the codes for coolant temp sensor, camshaft position sensor AGAIN, and knock sensor.

So my friend comes back over the next morning with all her toolkit and we look at the sensors.  The wiring looks fine, and suddenly, she's able to start the car and it runs at idle without dying.  We poke and prod the wiring harness, can't kill it.  Then we wonder about the signal getting to the ECU, whether it's just weak, or intermittent, or what have you.  The harness FROM the ECU to the sensor tests good (thankfully - my car for whatever reason does not have that big harness connector at the firewall - the harness goes through and into the dash and there's not a damn thing you can do about it LOL).  We test the sensor itself but we don't have an oscilloscope so the best we can do is see that it IS getting some voltage when we swing it past a large piece of metal.  Then we look into the wiring order itself, since neither the sensor nor the cobbled-together connectors I put in have the original wiring color scheme (according to various manuals.)  We decide to swap colors (in this case, the sensor has red, white, and black.  We know the black is the shielded one so that goes to yellow on the harness, which, incidentally, goes back to a large black wire where it pins into the ECU).  Just for funsies.  Because the other two colors on the harness are white and black, and the other two colors on the sensor are white and red, so what if white goes to white, like...ya know...makes sense?  So we do that and immediately get some new information - car does not like that AT ALL.  It starts, it runs, but it makes angry noises and won't go above 3000 rpm.  So, just to be scientific, we take the sensor all the way out to confirm that yes indeed, the car will not start without the camshaft sensor (I mean, ya gotta try, right? LOL)

So luckily, on a whim, I had ordered another sensor off of EBay (because parts stores want to charge me $300 for it and at this moment I'm not exactly made of money, which is why I'm doing all this myself with the help of cool friends).  We manage to find a wiring diagram that includes the SENSOR wiring (I wish I could tell you where, I think my friend still had access to some super-secret mechanics' manuals from when she worked at an auto shop) and discover that it goes like this, for anyone interested who has this particular setup:  ECU big black wire (shield) --> harness yellow wire --> sensor black wire; ECU white wire --> harness white wire --> sensor RED wire; ECU small black wire --> harness black wire --> sensor WHITE wire.

So with the new (used) sensor wired in like that, we start the car up again, everything runs peachy keen, I drive around town a bit with my friend following me in case anything else happens, and the car runs like a dream, except the check engine light comes on again!

I drive home, check the CEL code, and it tells me it's the knock sensor...........which I had forgotten to tighten down way back at the beginning and it was completely loose 😂

That was that, for now, in this saga!  As of this moment my car is running like a champ with no check engine lights and we're hoping it stays that way!  Hope any of this info ends up being helpful and/or interesting to someone, thanks to everyone here for their help and suggestions!

Edited July 1 by CharlieLS