Warm start problems
 

Hi all . Car is 2004 subaru impreza wrx sti type uk with 84k on the clock.

The car has developed difficulties in re-starting when up to normal operating temperature. The car drives perfectly for hours until I turn the engine off and try to restart it. It will then only crank and not start. I should note that I would not hear the fuel pump prime until the engine would cool down . Then I could hear the 2-3 second prime sequence and the car would fire into life.it's been into japtech in hull and they suggested I may have spiked the ECU.

Since the problems arose in an effort to fix this I have replaced :
Fuel filter
Spark plugs
Cleaned injectors with new o rings
Crankshaft sensor (oem Subaru )
Second hand FP controller

I've even tried hardwiring the fuel pump to come on 100% at ignition. The problem remains

Ive Noticed the car gets to temperature fairly quickly around than 5 mins or so.( stays just below middle) on dash

Next to check Coolant sensor?

the coolant sensor wouldnt stop it priming.

Do you reckon they're right with the ecu then ? I need it fixed but it's gonna cost a fortune

If you get yourself the ecu with the key that has the small chip and the other thingie under the drivers footwell off a breaker as a set I'm sure Matty on here will have it will take you 30mins to eliminate the problem if ecu won't cost you that much as you're just paying for the parts no coding etc required:thumb:

Cheers I look into it. Hope it works

I had a same thing with my typeR. Cold start no issue and when left running up to temp and go back to start it wouldnt.
Believe it or not mine was sorted by replacing the battery.
I suggest get your car up to temperature and when it fails to start put some jump leads on and see if it fires up then. If it does then battery.

Goodluck

Thanks but battery is only a few months old. I'm led to believe that jumpstarting can be fatal to ecu s in scoobys and it may have caused this problem in the first place. I don't know if anyone on here can confirm or dismiss this

Would be good to take into consideration though mate as ve bought a brand new battery for the golf and it went dead twice again went back to halfords they changed it without hassle problem free now, I've jump started a few scoobs in my time and never had any ecu issues although have known ecu' to be fried through other mishaps but not jump starting from another vehicle to be honest:thumb:

I'll give it a try . Really hope it works . I'm away this week so will update at weekend

Okay so tried new battery and bump start. No joy. Have had the battery disconnected as it is stood on the drive. If I connect it it will start first time and drive healthily until I turn the ignition off. If I go to restart , it will simply crank over and not fire into life. I'm absolutely baffled.

They do point towards the fuel pump / crankshaft position sensor IMO electrical so could be on the wY out bro

If you can't hear the fuel pump prime when the car is warm but you can when cold then this could point to bad wires to the fuel pump or failing fuel pump.

I had a similar issue on my old classic,turned out to be the connecting block on top of the fuel tank,also be worth checking the one that's under the rear bench seat.

It's had new oem crank sensor . No change. I've even hardwired fuel pump to run 100% . No change. Might swap FP out . Clutching at straws now

When you hard wired the pump could you hear it running when the car was warmed up and you are trying to start?
I presume you're not touching the throttle whilst cranking the engine?

In other cars this can be a failing crank or Cam position sensor. What can happen is the sensor impedance changes dependant on temperature, and the signal output can be reduced when hot. This may be fine during normal running when revs are higher, but combined with the reduced signal due to low turnover speed on the starter can prevent the signal being seen by the ECU, so no spark or fuel pump running.

Not saying it is this at all, but it does happen.

EDIT: Seen you have replaced Crank sensor, hopefully someone can tell you if these engines will run with a broken Cam position sensor. If not then perhaps this would be the next this to try (perhaps you could borrow one to test?)

Thanks for the replies.

Yes this problem was present before and after the crank sensor was replaced.

No my foot is off the accelerator at all times when attempting to start the car.

It's been on for diags. With a local specialist. They inferred it was the ecu that had been spiked causing the problems. They suggested the hardwire FP. to get it running and said a new ecu would be needed.
Now I'm all for getting this fixed but I don't wanna lay out hundreds and hundreds for this to remain an issue.

Are there any ecu gurus in here that can advise on what to do .

Many thanks

I have a 04 wrx sti type uk and have the original ecu in the garage after upgrading last year. Make me an offer for it if you want

My 03 WRX suffered similar symptoms - felt like the engine was flooded until you kept the pedal to the metal for a few seconds while cranking - turned out to be the MAF - cheap 2nd hand unit was about £25.

Put new oem denso MAF on. No change.

Imprezagaz the ecu would not be a straight swap though would it . I would need matched keys and barrels to get past the immobiliser? ?