Long Cranks only after engine off an hour or so

[ajay]

Hi inspired by SBQM I’m trying to troubleshoot this issue. The issue only started after I had the injectors removed and pro-cleaned, any tips greatly appreciated. The symptoms are;

1. The issue only started after I had the injectors removed and pro-cleaned
2. If the engine is fully hot she starts quickly no probs
3. If the engine is fully cold she starts quickly no probs
4. If the engine was turned off 45 to 120 minutes it struggles to start with cranking 5-15 seconds
5. Hasn’t failed to start
6. Once started the engine idles fine, runs ok
7. The starter motor cranks quickly and seems powerful
8. No loss of oil or coolant, no leaks on engine casing
9. Holding accelerator down for clear flood mode during warm start helps a little with the long cranking

I tried;

1. Using new genuine injector seals and o-rings when re-installing injectors
2. Looking for leaks around around injectors when viewed from above, all dry as a bone
3. Replaced engine coolant temperature sensor with genuine part and burping the coolant system
4. Watching LTFT, both banks within 5%
5. Injector leakdown test at a different company, all passed with identical flows and resistance
6. Checked connections around camshaft position and crankshaft position sensors
7. Fuel pressure is exactly within spec of the service manual at idle
8. If the fuel system is de-pressurised after removing the pressure gauge the engine starts quickly no problems
9. Taking the car to a workshop for diagnosis was inconclusive although they suggested it could be a fuel pump problem

Kind of wondering now if it is the fuel pump or if an injector started dripping gas into the manifold only when it gets really hot causing the mix to be too rich. Can an injector leak only when hot ?

The vehicle is 2007 subaru outback 3.0R six cylinder, dealer serviced to date.

[Matt]

You need to test fuel pressure bopth static and running.

[ajay]

Took a look… with the engine off fuel pressure goes straight to 52psi steady when the computer runs the pump for 2 seconds after ignition on. After that it goes to 48psi until the engine is started and idling where it stays at 48psi. The factory service manual describes 48 to 52 psi, return less system with no FPR under the hood.

[pete]

What was the reasoning behind having the injectors cleaned in the first place? And could this be a contributer to the fault you’re having now?

Do you have any computer based diagnostic equipment available to you at home?

So many questions:)

Pete

[ajay]

Hi, this is the first car i took a real interest in and doing my own maintenance. Had the injectors cleaned because the commute takes me past an injector cleaning company and eventually curiosity won over! The long cranking problem definitely started after the injectors were back in.

Yes I have access to the engine computer parameters with the neat open source FreeSSM and RomRaider projects which run on a laptop computer and have scan tool and logging capability when connected to the cars OBD-II port.

[pete]

Nice! curiosity has indeed killed the cat then 😉

When they cleaned the injectors out, could they have disturbed wiring to the temp sensor/sensors? I see you’ve replaced one already, but i cant help but think that the computers over fueling on a warm start up due to incorrect information being sent to it via one of the sensors/wires. Just a thought!

Pete

[ajay]

It sure did ! 🙂

I removed and replaced the injectors myself for the cleaning, was reasonably gentle on the car although not having done that before could have knocked something. Also you got me thinking again about the ECT sensor.

Today waited 90 minutes after turning the engine off hot as this guarantees long cranking and saw the scan tool report coolant temperature at 60 degrees Celsius. Started the engine which struggled as expected and then waited until the temp got to 70C. Turned the engine off and waited until the coolant temp was back down at 60C to see what would happen cranking again. She started up fine so to be sure repeated that test several times with the same result.

I’ll also try to use some fuel hose and a schrader t-connector to get the fuel pressure gauge inline with the feed for each bank of three injectors and clamp upstream to see if the pressure drops. And if the results are even for both banks. I guess there’d be no other place for gas to go than via the injectors.

[ajay]

An update further to Matt’s suggestion about checking static fuel pressure. I went ahead and checked leak down with a hot and cold engine on both fuel rails separately. The gauge went onto the short hose that feeds the rail with the hose upstream clamped so the only place fuel could escape would be through the injectors, hose or perhaps a leak in the gauge.

When cold both banks dropped 5-10 psi after 90 minutes. With the engine hot bank 2 pressure dropped to zero and bank 1 by 20+ psi. Also noticed that with the clamps removed the engine started much better. So perhaps fuel was getting through the hot injectors somehow.

I purchased and installed three new fuel injectors for bank 2, the long cranking situation is still present but consistently improved. I’ll grab another three injectors in the future when conditions permit and report back. Thanks again.

[tallpilot]

Nice work. Did you repeat the leak down test with the new injectors to get some quantitative verification of the repair?

[ajay]

Resolved! Replacing the fuel injectors on both banks fixed this warm start long cranking problem. Thanks again for the advice here. Unfortunately I didn’t get a chance to test hot leak down with the new injectors installed but changing out the fuel injectors was the only modification made to the vehicle to fix. New o-rings and lower seals were used each time the injectors were moved with FSM fuel rail torquing so I figure that even if the injectors pass a cold leak down test there was a hot leak happening.

[Author]

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