Stumble on hot starts

kubuli · 11-02-2020, 01:02 PM

I own a 2004 JDM forester Sti. (2.5 6speed)

Lately I have been getting a stumble and hesitation on hot starts and if I press the accelerator the car dies. I would have to allow it to catch itself before I can move.

Some time back I installed a walbro 255 and it basically choked the car. I had to reinstall the stock fuel pump. Could it be that my FPR is faulty? I also idle at 14.1 to 14.3. Any help would be good because the FPR is located under the intake manifold and would hate to go there for nothing.

Thanks in advance

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Vancouver98STi · 11-07-2020, 04:31 PM

Might be worthwhile to have a fuel pressure gauge installed, to see not only what the fuel pressure is while running, but to see how quickly the fuel pressure drops when the engine is turned off. A rapid drop in fuel pressure may indicate a leaky injector(s).

This is what I installed in my '98 JDM Impreza STi V4 GF8.

kubuli · 11-09-2020, 03:35 PM

Thanks for your reply. Will have a gauge installed. I took off the IM and relocated the FPR to the area neat to the fuel filter. That did not change anything. I then swapped in a new coolant temp sensor which seems to have reduced the stumbling considerably but I still hear a slight stumble on hot starts. I am going to look at the plugs next, probably should have done that whilst doing the FPR relocation. The plugs are one year old and are Denso IKH27.

11-02-2020, 01:02 PM	#1
kubuli Scooby Newbie Member#: 164188 Join Date: Nov 2007 Location: Dominica, W.I. Vehicle: 2004 Forester Sti Blue	Stumble on hot starts I own a 2004 JDM forester Sti. (2.5 6speed) Lately I have been getting a stumble and hesitation on hot starts and if I press the accelerator the car dies. I would have to allow it to catch itself before I can move. Some time back I installed a walbro 255 and it basically choked the car. I had to reinstall the stock fuel pump. Could it be that my FPR is faulty? I also idle at 14.1 to 14.3. Any help would be good because the FPR is located under the intake manifold and would hate to go there for nothing. Thanks in advance * Registered users of the site do not see these ads.

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11-07-2020, 04:31 PM	#2
Vancouver98STi Scooby Specialist Member#: 459287 Join Date: Dec 2016 Chapter/Region: VIC Location: Vancouver BC Canada Vehicle: 1998 JDM Impreza STi V4 GF8 White	Might be worthwhile to have a fuel pressure gauge installed, to see not only what the fuel pressure is while running, but to see how quickly the fuel pressure drops when the engine is turned off. A rapid drop in fuel pressure may indicate a leaky injector(s). This is what I installed in my '98 JDM Impreza STi V4 GF8.

11-09-2020, 03:35 PM	#3
kubuli Scooby Newbie Member#: 164188 Join Date: Nov 2007 Location: Dominica, W.I. Vehicle: 2004 Forester Sti Blue	Thanks for your reply. Will have a gauge installed. I took off the IM and relocated the FPR to the area neat to the fuel filter. That did not change anything. I then swapped in a new coolant temp sensor which seems to have reduced the stumbling considerably but I still hear a slight stumble on hot starts. I am going to look at the plugs next, probably should have done that whilst doing the FPR relocation. The plugs are one year old and are Denso IKH27.