99 OBW Hesitation

[justducky]

Bought OBW with 46k. Roadtested fine. First time it rained the car started to hesitated when pressing accelerator pedal. Ive had it to two dealers and a real good tinkerer. The plug, wires and fuel filter were changed. Then I was convinced it had to be coil. I changed that ($104.00). It ran okay until the next car wash with an undercarriage cleaning system. It seems to have three problems that are either related or not.

1.) after the carwash or a real rainy day it hesitates immediately. I step on the pedal it coughs , it goes , it coughs, it goes. That goes on for a mile or two and then intermittent and finally seems to clear after a day or so.

2.) from then on once; the car has been run and shut off, if the car is restarted while the engine is still warm it will hesitate the first time I step on the pedal. Dealer theorized that this was caused by the different temperatures of fuel in lines and the fuel tank which confuse the ECU.

3.) when the car is cold it seems to vibrate pretty heavily when weight is add (going up hill)

The car now has 52k and warranty is running out so help would be much appreciated.

[Legacy777]

At night, take a water mist bottle and spray it around the electrical stuff, coil pack, wires, wiring harness and see if you see any arcs. may want to try dielectric grease on the plug wires.

[alias20035]

Originally posted by Legacy777

At night, take a water mist bottle and spray it around the electrical stuff, coil pack, wires, wiring harness and see if you see any arcs. may want to try dielectric grease on the plug wires.

 

This is a good way to identify either cracked spark plug wires or coil pack. But what you may not find is a crack that is on the spark plug wires boot that is inside the head of the engine.

 

Pull the wires off, inspect them carfully and look for burn marks that would indicate signs of electricity arcing through the rubber boot material. I have seen arcing through the boots a few times, and always on the #1 cylinder for some reason.

 

Use of dielectric grease is highly recommended. Lock-Tite Dielectric or Spark Plug Boot Grease is the major version of this stuff out there and is available at all auto parts stores.

 

One question though, have you made any air intake modifications such as removing the air intake resonator, installation of a K&N filter or installed a cold air intake?

 

Subaru's are really sensitive to air intake modifications and you can get a bogging condition that can be mistaken for misfire or hesitation. If you have a stock intake then you really do have a misfire or related problem, otherwise I recommend that you re-install the stock intake and road test the vehicle to determine if the modified intake was the cause. And yes rain will affect modified intakes causing problems (I've been there/done that). Since wet air is more dense than dry air the modified intake will confuse the air density system (Mass Air Flow/MAF sensor) causing odd fuel air ratios, which leads to bogging.

 

The ECU is usually pretty good at identifying misfire, do you have any stored codes? The fact that you did not mention the "Check Engine Light" would suggest that it did not come on, which is why I am questioning if you might have the air intake modification bogging problem instead. But the dealer would have noted the modification and not serviced the car in its modified form.

 

In any case I would check the wires and reset the ECU (unplug the negative battery terminal for fifteen minutes), sometimes the ECU learns something its not supposed to and does strange things. After a reset it may also detect the misfire problem that it apparently does not detect now.

 

I am off for about two weeks, so best of luck. There are plenty of helpful board members who are familiar with hesitation/misfire/bogging problems that can provide further assistance and a few old related posts that you should search out and read.

[forester2002s]

I have experienced a misfire problem due to a cracked porcelain insulator on a spark plug.

 

This was very hard to diagnose, because the insulator only had a hairline crack, that was barely visible to the eye. However, when I wiggled the top of the plug (still installed in the engine), I could detect a tiny amount of movement. The plug had cracked at the base of the porcelain where it enters the steel base of the spark-plug.

 

This type of damage to the insulator can happen when the spark-plug socket is pulled accidentely to one side (very easy to do), and can go unnoticed (except for the annoying misfire).

 

This may not be what you have, but it is worth checking.