andyr

Bit of a long running issue this one :
Last year I started having starting issues, car always starts from cold but warm starts are very unreliable - leave the car for a minute or a couple of hours and it cannot be relied upon to start first time. It will always start - eventually, but this can take maybe 10 minutes of trying. Engine turns etc, just doesn't fire.

When the problem first emerged I cleared the CEL codes and then IIRC the current CEL codes indicated crank sensor, cam sensor and possibly coolant sensor (certainly crank sensor, think the coolant sensor was intermittant.)

I've now installed a brand new coolant temp sensor and a replacement (s/h) crank sensor. CEL codes are showing clear (I'll retest again tonight)

What else might be the cause of cold starting being perfect but warm start not ok ?
MAF ?
Is the cam sensor at all involved in starting as I thought it was the crank sensor not the cam sensor ?

Car is std 95 WRX

wrxboy2004

Hi can you tell me where u got ure coolant sensor from as im having the same problem, also is it just coolant u put in that tank or a mix with water also? Cheers.

andyr

Bought coolant temp sensor from Subaru dealer : only around £30 or so. Crank sensor is around £130 which is why I've sourced a s/h one of them.
I topped up the coolant with a mix of water and anti-freeze/coolant. Not too much leaked out whilst I changed it but it's a bugr of a job to do, access to the sensor with a spanner is not good !

andyr

Ok, checked the CEL at lunchtime : shows no fault codes, just the regular flashes.
After speaking to my father-in-law who designs circuit boards etc so knows electronics pretty well, he suggested a couple of things.
Firstly check the old sensors to see what they show using a multimeter.
CTS : checked the resistance of this and when placed in water it changes when the temp changes : ie this item was probably fine.
Original Crank sensor : connected multimeter across the terminals then waved it past a metal object (that it was magnetically attracted to) -
the voltage seemed to be affected when the sensor was close to the metal object so was it ok also ?

Next suggestion not yet tried is to check the earth lead on the ECU.

Any suggestions as to this being a possible issue or indeed anything else to try ?
Haven't yet checked/cleaned MAF, jobfor the weekend probably.

ben5141

I am having a very similar problem with my 95 STI, it starts fine when cold but if you turn it off after its only been running for a short time up to about 10 mins it won't re-start, turns over but won't fire. If you then leave it for 5 mins, it always starts. Does this point to any single sensor or is it just best to take it somewhere they can plug it in, I take it that's what CEL means ? will this deffinatley show up the fault, or could I just be chucking money away. I know this doesn't help you much andyr but I didn't want to post a new thread very similar to yours and you sound like you know more about it than me. Cheers, Ben.

andyr

The CEL codes are read just by connecting the 2 black connectors under the dash. Fault codes are then produced and interpreted by the flashes of the engine check light.
Best however to go through the clear process first which involves connecting green-green and black-black connectors etc (do a search for the details else I can dig it out), then after having driven the car you know that any fault codes are current and not old ones that haven't been cleared down.
Problem can be, I understand, that some faults with sensors don't appear to trigger the code, such as coolant temp sensor sometime does, sometimes doesn't show as faulty, MAF can start to go faulty with no error code.
I want to try and find out all sensors that have a bearing on starting but so far cannot be 100% : Crank and coolant sensor are, cam sensor ? MAF ?

andyr

Just going to add : on a very few occasions this sort of thing has happened, and it occurred last night.
Driven the car adn it's well up to operating temp, park the car (last night I parked at home on the drive to open the garage door) and the car stalled. Wouldn't restart as per normal with hot engine.
Points to prob with dodgy MAF ?

J0NTHELEGEND

I HAVE THE SAME PROBLEM BELIVE ME IT TAKES THE **** ITS THE CRANK SHAFT SENSOR THE OTHER I WAS IN THE GARAGE I DID NOT WANT TO TURN IT OFF BECAUSE IT CANT BE RELIED ON THEN IT JUST CUT OUT BY ITS SELF AND WANT START FOR 20 MIN I HAVE FOUND OUT IF U WIGGLE THE CONNECTOR ON THE CARNK SENSOR IT STARTS TRY THAT

andyr

I'm suspicious of the crank sensor myself however it is very unclear as :
a) I have changed my one - for a s/h one admittedly but the problem remains
b) The ECU fault code is not present
c) I tested the crank sensor (this is the original one remember) in a pretty basic way by connecting a multimeter across the terminals then waving it past an object that it was magnetically attracted to and the voltage seemed to be affected when the sensor was close to the metal object - this, I reckon is how the sensor works so maybe it is/was ok anyway ?

I reckon that the problem is :
a) Another sensor (such as MAF as I very occasionally have the engine stall on me)
b) The connections at the ECU from one or more sensors
c) The wiring between a sensor, such as crank or coolant temp sensor, back to the ECU
d) Earthing on the ECU
or
e) Something else as yet undetermined !

ben5141

Andy, thanks for all that info, I am sure I am going to need it at some point. I took my car down to a mates garage, who specialises in electrics (promised to only charge 1/2 hours labour). He said it was showing an old fault on the crank shaft sensor. He played about with it off and on all day and managed to get it not to start for a few seconds, said he only managed to have it plugged in to his gear for a couple of seconds but that he thinks it came up with the same fault. Trouble was it started so quickly he didn't have a chance to have a good look at it, he also said that when it did start up the signal from the cam shaft signal was a bit wafty (technical term). He is pretty certain its the crank shaft sensor so I am on the look out for another (not sure whether to try a S/H one or bite the bullet and buy new) so I can know for sure !!!
Reading about your problem which does sound a bit different, cause mine doesn't stall, if the problem with yours is intermitant there seems little point testing the sensor out of the car cause it might not be breaking down while you are testing it ?
P.S. How did you find a S/H sensor ? Ben.

andyr

Sensors come up for sale on ebay, also get offered for sale on here too.

andyr

After cleaning various sensors and/or their connectors (crank, cam, tps, maf) on Saturday I cleared CEL, drove car and then when I checked yesterday the cam (code 13) was flashing. Cleaned sensor and it's connector blocks and I removed the air filter housing and cleaned the MAF (looked pretty clean anyway)
Drove car and CEL is clear but I'm just puzzled as to what the source of the starting issue might be.
Does anyone know which sensors ARE involved in the car starting ?

andyxros

am sure cam sensor if faulty would stop the car running as may cut fuel off as it thinks the engin has stopped or cam belt snapage so cuts fuel. if this sensor is not there it would not start or if sensor is intrmiten it would just stop engin when it wants to .sure this used to happen on 3 cylinder corsa engins after 5 mins of driving it would just shut down and not start for at least 10 mins if you were lucky sure that was down to cam sensor