1999 Forester AT EJ253 - Misfire Pulling Away from Stop

[GeneralDisorder]

Have you carefully inspected the plugs and wires? This sounds exactly like what I've seen when spark plug wells get water in them, or plug wire end connectors get corroded, etc. Ohm the wires - looks for cracks on spark plugs and look for burn marks on the plug wire insulators. I've seen them arc out through the insulation to the plug well. It usually manifests just the way you describe because cylinder pressure is rising and coil dwell time is long leading to a lot of secondary ignition voltage and higher resistance at the plug gap....

I would install new wires and plugs and gap the plugs to 0.025" and see if that doesn't resolve it or significantly improve it. 

GD

[carfreak85]

OK, ohm'd the plug wires, and the Densos (that were a few years old, but by no means ancient) were coming out at 7-9 kohms, while the new NGKs I installed were in the 3.5 kohm range.  The throttle related hesitation has all but disappeared during normal driving.  Spark plugs have not been change yet (NGK iridium 11s), but the spark plugs were dry of oil or water.

There is still a slight sag in power after the 1-2 shift on cold mornings, which was the original symptom, so I guess we're back to square one.

[Steptoe's photos]

I hope my 1999 Forester issue does not go on for this length of time ! 

[heartless]

49 minutes ago, carfreak85 said:

OK, ohm'd the plug wires, and the Densos (that were a few years old, but by no means ancient) were coming out at 7-9 kohms, while the new NGKs I installed were in the 3.5 kohm range.  The throttle related hesitation has all but disappeared during normal driving.  Spark plugs have not been change yet (NGK iridium 11s), but the spark plugs were dry of oil or water.

There is still a slight sag in power after the 1-2 shift on cold mornings, which was the original symptom, so I guess we're back to square one.

it has been said many times over...

NGK copper core plugs - you do NOT need the fancy iridium, platinum, or anything else.. just plain old copper cores set to the correct gap

NGK or OEM wires ONLY - anything else is a waste of time and money. Sure, they might work for a little while, but they WILL fail prematurely

 

[carfreak85]

WOW, it's been a minute since I actually logged in here, even had to reset my password!

Quick update:

Anyway, back in ~2023 I finally pulled the plugs (Denso Iridiums) and they were EXTREMELY worn, like, maybe 3mm gap with the electrode almost completely melted.  I suspect they were Amazon knock-off NGKs, since iridium is used in "100k mi" applications.  I replaced them with RockAuto NGK coppers (IIRC), and that fixed the really bad 1-2 shift stumble. 

However, the stumble is not gone.  It seems like cold weather exacerbates it (it's been in the 20s overnight the last week).  Last year after replacing the counterfeit spark plugs I ran some Seafoam through the fuel system, and that seemed to help, but the stumble returned this cold snap and even running another round of The Foam through the fuel system last week didn't seem to help.

Still seeking resolution to this, but the spark plug change certainly helped with the original compalint.

[lmdew]

Coolant Temperature Sensor been changed?

[carfreak85]

Cross-referencing my parts order emails with the CTS part number, I don't think it has been replaced.  I could have sworn I did replace it when I last did the HGs in '17 or '18, but I guess not.

Added to my list for the next dealership parts order, thanks.