Subaru Impreza GC8 & RS Forum & Community banner
1 - 4 of 4 Posts

·
Registered
Joined
·
20 Posts
Imprezawd,

I have the spicy cams in my car and have not had any hesitation problems driving in the DFW area. A week ago my car had a pretty bad hesitation in it after I filled up with some gas in the Memphis area. I've recently been away from work to take care of some personal matters and have used gas from different locations. The hesitation was in the 4-5k area vs. the 3-4k area that it was at prior to the cam install. I filled up with some gas at a different gas station and the problem went away. This is the only consistency I've been able to find with the hesitation problem. Different gas stations/blends have different effects on our cars. There may be other contributing factors to it, but the gas is by far the largest imho.

I've changed my plugs to a heat range colder since then and cleaned out the spark plug terminals on both the plug and coil end. It seemed to help out somewhat with power and the smoothness of the car.


Regards,


Ethan Fisher
Cobb Tuning
 

·
Registered
Joined
·
20 Posts
Imprezawd,

I believe you'll see timing is pulled out at that rpm. For the most part, it seems part of the character of the car, but Josh was able to get rid of most of his with tuning on the unichip. To be honest, the first time I've had the hesitation in a long time was in Memphis with that one tank of gas. My spark plugs were really bad as well, so that may have contributed. Just some new copper NGKs really woke up the car. I put in a heat range colder, but I don't know how much of a difference that in itself made. Most likely it was just the newer plug and cleaning the terminals. I run amsoil series 2000 20w50 in my car as well. Have you noticed that light throttle doesn't have the hesitation in that range, but heavier loads do?

We're really working on getting our header out asap. We just recently found out the price changed on the header, borla never told us. We had to call them after somebody called us.

nitrohuffer,

I don't think the cams have any effect on the hesitation in that way.
 

·
Registered
Joined
·
20 Posts
imprezawd,

How many miles do you have on your car? My problem seemed to lessen somewhat with additional mileage. The only thing I ever noticed that changed it was the gasoline. Going to a thicker oil might have helped a bit, but I'm not certain. The oil level being a bit low on the dipstick seems to influence it. If it is halfway in between the full and the low mark, then you need just under half a quart. That seemed to be part of my problem. Also, cleaning the spark plug wires/coil terminals of carbon/soot helped out. Changing out the plugs with new copper Ngk's made the car smoother along with cleaning out said ignition components. When you get gas, try driving out to some podunk town to fill it up. My only theory on this is that the places where I've filled up with gas and had a hesitation problem is where the gas was oxygenated with the methanol stuff. Filling up on the outskirts of the city, you're not getting the gas that is required to have methanol in it, and the hesitation problem seems to be lessened.

The under 20% throttle question was just verifying that we were in fact going through the same thing.

Cheers,

Ethan
 

·
Registered
Joined
·
20 Posts
Richie,

It seems that it is something to do with the way either the knock sensor, or possibly another sensor interprets the combustion process. The cams seem to shift the rpm at when the noise is generated. This would appear to be a resonance to me, although I may be completely off the target. I believe it is a combination of a certain amount of air, throttle, gas quality and ignition timing which sets this off. With the larger cams, this resonance will be delayed until further up in the rpm. Furthermore, I believe the methanol enhanced gasoline contributes at the very least, a minor amount to the ecu interpretting this combustion process in a manner which pulls timing. I have not had the Subaru select monitor nor any datalogger on my car when this problem occurs, so I can't see which sensor is getting the reading.

Have you changed your plugs recently and checked the ignition system for cleanliness? Also, what type of oil are you using? Have you driven to a rural area which you know does not have the oxygenated gasoline blends that many metropolitan areas are required to have?

Ultimately, I am still baffled by what exactly causes this problem. I have many suspicions, but non of them have been proved or disproved through an exact experiment/evidence. Hopefully, through other members of the board, we can narrow down the possibilities.


Cheers,


Ethan Fisher
 
1 - 4 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top