Car is a 95 WRX, pretty much bog standard.
2 or 3 times over the past few months the engine has refused to start :
once it had been left for, I think, a matter of a few hours so would have cooled completely, next time I had filled up with petrol so would have been warm.

Last night I had driven a couple of miles pretty slowly after being parked for 2 or 3 hours as I though that the tank was near to being dry but I only managed to get 45 litres in (50 litre tank ?) so it wasn't bone dry. Previous time the car was parked on a slope and had maybe 1/4 tank or so which got me thinking that there is an issue with it not pulling in the fuel.

Engine turns over very quickly, no lack of battery life, it just doesn't catch.
Last night I tried to start off and on for 15 minutes, fiddling with the CPS as I thought that this may be the issue but no joy until a guy turned up in an RS Turbo and
a) fiddled with one of the other connectors
b) gave the accelerator a couple of blips whilst turning the engine over then it started : he said that his mate had the same issue with his Impreza.

Car is due a service (new plugs etc) but is there anything in particular that might be causing this ?
Is a diagnostic machine likely to indicate anything of relevance ?
Car otherwise seems to run fine and after I got home I switched it off then tried to restart : it did so instantly.

 

I had something similar last week. Car wouldn't start after sitting for 8-9 hours, and had to get recovered home. Next day it started first turn of the key.

I was advised to replace the camshaft sensor and the temp sensor

 

quite common for a temp sensor, however this usually would only manifest itself in 1 condition and not 2, eg when cold or when warm but not usually both.

 

Would the fact that the engine started with a couple of light presses of the accelerator indicate an issue with either sensor ? Unless that was just co-incidence !

 

Have you checked for codes? I had the same problem and when I checked codes I found the camshaft position sensor code and replaced it. Fiddling with the connector will do no good since the problem with the sensor is the magnet itself and not the sensor.

When I still had the problem, the car would start after being left alone for about 10 min.

 

Will try to check for the codes : never done this but I'll do a search.

 

Scoobypedia | Trusted knowledge for everything Subaru | Scoobypedia browse tells you how to check for codes

 

Thanks : now, slightly strangely, the fault codes indicate code 11 and 13 : CPS and CPS !
Guess I need a Crank Position Sensor (or 2 !) then

 

Cam (13) and crank (11) sensors.

 

You're right, Crank and Cam sensors.
Easy to replace ?
Source from main dealer or much cheaper elsewhere ?

Thanks for the help so far - at least I know now what the problem is likely to be.

 

tbh i don't know how hard they are to replace as i've never had to do it.
I've got to speak my garage today so i'll ask them.
The prices i've seen on my local garage is £121.14 for each sensor (i've no idea if that's right or not)

 

Cheers : my mate used to work at a Subaru garage so I'll phone him today also to see what his take on this is.

 

Although the fault codes indicate both cam and crank, looking around on'tinternet it appears that only the crank position sensor would influence starting : that is used for starting then once running the ecu uses the cam position sensor. I understand the crank sensor is under the alternator (no doubt a pig to get to) and can be removed and cleaned often with positive results so I'll be trying that asap and see if that clears the fault code.

 

That is sometimes the problem that 1 thing possibly going wrong puts another thing going wrong etc but all the faults are recorded even if only 1 thing is going wrong.
If it does remember to reset the ecu of all the codes.

 

The crankshaft position sensor is actually very easy to get to, you don't have to remove anything else. And according to the manual any of these two sensors can prevent the engine from starting.

The cleaning did not help me, I tried it, but I never really expected it to work, when did you ever hear of dirt blocking a magnetic field?

My mechanic recommended that I change both at the same time since they usually die in pairs but since I only had a code for a crankshaft position sensor that's all I replaced. In your case, I would suggest you replace both since you've got both codes.

 

Sounds sensible advice : I'll try cleaning it first of all but will also see if the local dealer has the sensors in stock just in case.

 

Not sure if I am being thick here or not !
Removed and cleaned the crank position sensor using carb cleaner spray.
Refitted.
Car still starting fine (as it did during today's use)
Ran the CEL reset by connecting black/black and green/green, etc
Then it didn't want to start : thinking it might be the crank sensor I retrieved a wooden spoon (yes !) from the kitchen to tap the sensor under the alternator. Whether by co-incidence or not the car started.
Took car for a drive and CEL did it's regular flashing pattern within 30 secs or so indicating all clear.
Drove on to a safe spot to stop at then switched off, disconnected the 2 sets of connectors and drove on again. Got home and tried connecting the test connectors to see if the error codes are present still or not : CEL light doing it's safe regular flashing as it did during the CEL-clear drive : so does this indicate all is clear now ?
Really, if any doubt then I'll get a crank sensor anyway as being stranded by a non-starting car is not something I want but if I've resolved the issue then I won't splash the cash.
Thanks again in advance for advice.

 

Back with this again :
I had decided that the CEL lights were the std 'All OK' flash pattern and it has behaved fine but ...
Yesterday it took a good few seconds for the engine to catch and start, as usual it turned over really fast, sounding fine, but took just that bit longer to actually fire so I connected the black connectors and :
long-flash, long-flash short-flash : code 21 = Coolant temp sensor
Now I'm getting confused :
CPS (Crank Position sensor) I am aware can cause starting issues but that is NOT registering as duff, Coolant temp sensor - possible starting related ?
Buy both anyway ?
Checked main dealer cost and Crank is around £130 and Temp around £35
so if I go by the CEL lights then I buy the cheaper one !
Can these sensors be checked in any way (could ask my father-in-law as he's an electrical engineer and can design, build and test cicruit boards so is a techie wizard unlike me)
Which sensors are possibles for starting issues ? as I have had the CEL indicate crank, cam (CEL codes on these now clear) and now temp sensors but I ain't buying them all just to clear them as possible causes unless I know they are worth the expense.

 

Coolant temp sensor could be an issue as it 'tells' the ecu if the engine is cold or hot ( i had mine go on my 93wrx when it had a dodgy idle and normally the fans start swtching on at weird times)

 

After some starting/cold running issues i recently replaced the crank sensor,o2 sensor,maf and coolant temp sensor the coolant was a b***h to get to,much knuckle scraping

 

Car again failed to start for aroudn 5 minutes when I had stopped at shops after driving for around 30 minutes (engine therefore was warm)
Swore a lot and tweaked a couple of connectors (Crank and maybe coolant sensor)
Eventually restarted and ran perfectly fine.
Can someone help me identify exactly where the coolant temp sensor is located on my 95WRX please as I plan to replace this to hopefully resolve this issue : I've searched S'net etc and found some hints (under coolant pipes near the inlet manifold - connector is likely to be brown) but I can't be certain that I can see it and I need to identify it before confirming the particular type it is with the dealer.

 

Looking at my picture it is basically under the bend of the strutbrace under tne rubber hose and is plugged into the block (iirc it's the only sensor there and it is brown with a few wires coming out)

 

failing to warm start is a sign of a failing crank sensor btw.. lucky if you get an error code..

coolant temp sensor failure you get rad fans on when engine is cold and CEL.

Simon

 

Thanks all : need to check the rad fans but I'm pretty sure that they are NOT coming on when cold.
CEL code 21 only shows when I connect the 2 black connectors under the dash - I'll maybe go through the reset CEL procedure again.
PITA if it's the crank not coolant sensor as it's £100 more ! (but easier to change). Hope it ain't both.

 

my cts never threw a code or a CEL,only time it ever gave me a CEL was when the spanner monkey forgot to put the air temp sensor back in its hole after dismantling half my engine bay to fit spark plugs

 

Went to the car at lunchtime so engine would have been cool but prob not stone cold.
Started fine.
Parked up 5 mins later. 5-10 mins later it started ok. Drove for 2 mins then stopped for a good 30-40 mins. On returning I took the opportunity to connect the 2 sets of connectors and went through the CEL clear process but when it came to starting the car it wouldn't. After numerous attempts I disconnected the 2 connectors and then the car started (co-incidence possibly !?). Then switched off, connected the 2 sets connectors again and redid the CEL clear process and this time it started fine and I drove for maybe 20 secs tops and the CEL clear sequence started.
Stopped, disconnected, drove for 2 more mins and then stopped and connected just the black connectors - all clear sequence.
Disconnected then drove for a couple more miles and when I finally parked up back at work I connected the black connectors again : still the all clear.
I'm puzzled !