2003 H6 hard starting

[Gromit]

My 2003 H6 Outback had a fuel pump failure. By the time I put a pressure gauge in the line it was only managing 15psi and shortly after that was down to 5psi and wouldn't start. It was registering a code for lean mixture on both cylinder banks. Symptoms, while it was still running, were it would start on a few cylinders and then eventually the rest would chime in. With the fuel pump replaced in the sender unit, the pressure gauge read about 32psi. Various online forums reported the typical fuel pressure of anywhere from 35 to 75psi! The car would start, but as before only on three cylinders and then after half a minute of dramatics the rest would eventually kick in. The car seemed to drive fine, though one time it started to hesitate pulling away from a light and I turned right around an headed back home. It did not inspire confidence for a longer trips. It is not registering any error codes in memory. I should also mention I verified the cranking voltage was fine. Thinking perhaps the fuel pressure regulator was dumping pressure at too low a value, I replaced that but it made no change in the pressure. I had read that the vacuum signal to the same modified the pressure , but pinching off the vacuum line to the valve made no difference to the pressure. It is a little too inaccessible in-situ to pull the vacuum line. The only alteration to the fuel pressure that I noted was after a minute or two of warming up, the pressure would suddenly drop from 32 to 28psi and stay there, as if a relay kicked in. Thinking the aftermarket pump was a dud, it was replaced but the pressures were identical. Fuel strainer and the fuel filter in the engine bay were also replaced. One other thing I noticed when changing the fuel pump was that on the fuel sender unit there is a canister that had a crimped on tin bottom cap (see attached). One of the crimps was cracked and the bottom was sitting crooked. I have no idea how long it have been line that. As it had an o-ring, clearly it was intended to hold pressure. I put it back the best I could and got the pressures mentioned previously. Thinking perhaps that was not good enough, today I took the cover off again and welded the crack in the crimp tab and was able to latch the cover on securely and square. Fuel pressure is now only about 15psi. So I am thinking despite being careful with the o-ring under the tin cap, it is not pressure tight. less so when it was practically falling off! I am not sure exactly what the chamber does, but it seems to be in the fuel delivery circuit. Besides that, which I am going to have another go at tomorrow, anything else that would cause low fuel pressure. And typically does low fuel pressure in folk's experience typically cause starting on just a few cylinders before the rest chime in. Though, why would the rest chime in and it not throw a lean code? Is 32psi enough, or is the aftermarket pumps not delivering enough pressure for starting conditions. Further, I would add the problem manifested itself suddenly. I was out for errands, stopped at the bank, and had a hell of a time getting the car started again. I had just come from the gas station and topped up the fuel tank, so initially I though I had taken on a bad tank of fuel and spent a day draining and replacing the fuel (no improvement) before I thought to put a pressure gauge in the delivery line and discovered the fuel pressure was low. Before that it never hesitated to start on all six, cold or hot. 160k miles. -Doug

 

[Gromit]

I just noticed a lot of the technical questions are going unanswered. So as I did find a solution I figured I would post my own reply and close this query out. The issue is a apparently well know one involving an o-ring in the fuel sender unit. These swell over time (not fully ethanol compatible) and push the metal cap off the pressure chamber. Though I had fixed the cap, reinstalled the o-ring, and pressed it back on square it still was not sealing perfectly. On replacing the o-ring the pressure shot up to 48psi and more importantly held pressure when the ignition was turned off. Not perfectly as the fitting on the pressure gauge was weeping, but clearly on the right track. The Subaru is now back to starting on all six cylinders with no kicking and bucking.

 

[Ozark_SyntheticsLLC]

Gromit,
Thanks for the information and the update on the fix. This forum is somewhat fresh on the scene and technical questions are always welcome, but answers are like golden eggs! Congrats on the fix and finding out the problem. Send an update on the first "long" trip it takes.