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I have a 2002 WRX that I'm having troubles with. First thing…

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Hey, I have a 2002...
Hey, I have a 2002 WRX that I'm having troubles with.
First thing in the morning when it's cooler out, it will start up instantly. Almost strangely fast how quickly it starts. Once it's warm out or if the car has been left for 30 mins or so it takes 5 or so seconds of cranking before it will start, but it always starts.
I have no CEL or pending codes, my MAF voltage is reading 0.70 when not running and 1.2-1.3 when idling, I also cleaned it just in case. My ECT sensor is reading correctly going from live data. My crank and cam correlation is correct also. I have pulled spark plugs (new) to see if I have a leaking injector, they were all dry. I have no vacuum leaks. My fuel trims are sat at 0 also. It doesn't make a difference whether I prime first or not.
Strangely a couple of weeks ago it fixed itself for a few days. When this happened, my morning cold starts took a 'normal' amount of time to start up and not instantly. After a few days it went back to the same issue that I'm having now.
I hope you can help, it's driving me insane!
Thank you
Submitted: 10 months ago.Category: Subaru
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Answered in 23 minutes by:
9/28/2017
Subaru Mechanic: Matt, Engineer replied 10 months ago
Matt
Matt, Engineer
Category: Subaru
Satisfied Customers: 23,465
Experience: Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
Verified

Hello

I'd say that this sounds like the fuel pressure is a little low? or taking its time to build up

so I'd say its well worth replacing the fuel filter with a new item

instructions are attached

it would also be worthwhile checking that the fuel pump is getting a full 12V if the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

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Customer reply replied 10 months ago
The fuel filter is new, sorry I forgot to mention that. Where would I find the fuel pump relay? Is there a relay as well as the fuel pump controller in the trunk?I will also try putting a fuel pressure guage on tomorrow and see what's happening, do you know what the pressure should be?Thank you
Subaru Mechanic: Matt, Engineer replied 10 months ago

Hello

fuel pressure on a running engine should be 3 bar / 44 psi

yes there's a pump relay as well as the controller and the pump relay should be under the passenger side dash, kick panel area. It's a green relay with a green connector.

wiring to it is

Contact: Blue with Red Stripe
Contact: Black with Yellow Stripe
Coil: Green with Red Stripe
Coil: Black

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Customer reply replied 10 months ago
Hey Matt, just going through the fuel system. I checked the relay, fuse and connections to the controller and all are clean.My fuel pressure is at 43psi when the engine first starts, then drops to around 38psi after 30 seconds. I'm not losing pressure over a period of an hour (usually around the time it takes to play up).Thanks!
Customer reply replied 10 months ago
I also just flow tested the pump, when primed it flows 400ml
Subaru Mechanic: Matt, Engineer replied 10 months ago

hello

OK that all sounds reasonable - so its not the pump then

In that case I'd say its well worth checking that the engine ground wires are tight and clean and do the same for the battery connections and there should also be a couple of smaller ground wires that run out of the engine bay wiring loom and are secured to the engine with ring terminals - these are the ECU specific grounds and again must be clean and tight

if that's OK then this could be a wiring issue as things tend to expand when hot and its possible a poor or partial electrical connection is being pushed apart on one of the major sensors so check the connection plug and wiring to the following;

Airflow meter
Crank position sensor
Cam position sensor
O2 sensor
Throttle position sensor

unplug each in turn and use some switch / contact cleaner spray on the pins to ensure its all grease / dirt free

and lastly I say to replace the crank sensor with a new one

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Customer reply replied 10 months ago
Ok I'll try that. What engine grounds are there? I can see the main bellhousing one, the one to the body and the one on the right side of the intake next to the battery which I'm guessing is for the ecu?Thanks
Customer reply replied 10 months ago
Hey Matt, went through sensors that you described. Found no issues, also put a new crank and cam sensor in just in case.I also traced my engine grounds back to check for broken wires.No luck unfortunately, any other ideas?Thanks!
Subaru Mechanic: Matt, Engineer replied 10 months ago

Ok

how about an compression test then?

I know its a major exercise on these engines

but if there was 1 low pot this can contribute to a slow start

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Customer reply replied 10 months ago
I actually did do that about a month ago when I changed plugs, more out of interest then anything else. All 4 cylinders were 135psi. The problem was happening at the time I tested.Thanks
Subaru Mechanic: Matt, Engineer replied 10 months ago

Hmm Ok

then the only other thing I can think of is there's a lazy coil or injector thats only sparking into life once there's some engine speed

might be worth trying some injector cleaner in the tank ?

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