My 1998 Subaru Legacy has hesitation on acceleration between 1500 and 2500 rpms. This starts to occur after oil changes, and usually lasts for 3-4 weeks. Searches of websites have indicated that an air pocket in a new oil filter creates an initial vibration in the engine when it is first started up after an oil change. The knock sensor incorrectly reads this as an engine knock, transfers the info to the ECM, and subsequently retards the ignition timing to -10. This has happened three times in the past year, always after an oil change. The first time it went away on its own after 3-4 weeks, the second time I followed a procedure for resetting the ECM and the knock went away. The procedure for resetting the ECM is to disconnect the negative battery cable for 3 hours, then let the car idle for 15 mins without touching the gas, then turn the car off, and restarting and driving around for a while under normal commuting conditions. This time that procedure didn't seem to work. Anyone have this problem???

Originally posted by crazyjam

My 1998 Subaru Legacy has hesitation on acceleration between 1500 and 2500 rpms. This starts to occur after oil changes, and usually lasts for 3-4 weeks. Searches of websites have indicated that an air pocket in a new oil filter creates an initial vibration in the engine when it is first started up after an oil change. The knock sensor incorrectly reads this as an engine knock, transfers the info to the ECM, and subsequently retards the ignition timing to -10. This has happened three times in the past year, always after an oil change. The first time it went away on its own after 3-4 weeks, the second time I followed a procedure for resetting the ECM and the knock went away. The procedure for resetting the ECM is to disconnect the negative battery cable for 3 hours, then let the car idle for 15 mins without touching the gas, then turn the car off, and restarting and driving around for a while under normal commuting conditions. This time that procedure didn't seem to work. Anyone have this problem???

 

Why not fill the filter with oil before installing it?

Last time I filled the oil filter as much as I could. I think the air pocket still existed though. It is very strange how it correlates with oil changes, to a T.

My '02 OBS had a knock sensor that was being triggered more or less constantly by mechanical engine noise, but I fixed it.

Originally posted by blitz

My '02 OBS had a knock sensor that was being triggered more or less constantly by mechanical engine noise, but I fixed it.

 

 

Well........................Explain please.

Reset the ECU. Should be enough to disconnect the battery for an hour. Connect, idle up to operating temp, and shut off again.

 

You might want to replace the knock sensor. Sometimes they break down interally and create a "lose connection" which amplifies engine noise, and gives you timing retarded to the back-stop.

Somebody has covered this in detail. It involves a small electronic box which smooths or removes the noise from the knock sensor, can't remember where I saw it though....damn

see this website for Gary's cure:

 

http://www.geocities.com/hobiegary/hesitation.htm

Originally posted by DaveWV

Well........................Explain please.

 

Well... since it wasn't smart enough to be able to distinguish spark knock from normal operating noise, I removed it from the circuit and substituted a resistor in its place to keep the ECU happy.

 

Now I'm the arbiter of timing adjustment via a 6-position switch on the console. If you'd like details, speak up and I'll ramble-on.

Yes, please ramble-on.

I'd like to hear some more rambling too. And please...some wiring diagrams...

 

Pat

Originally posted by 99obw

Yes, please ramble-on.

 

Sorry, didn't want to hijack the thread with my technobabble unless someone was actually interested.

 

Anyway I installed a 6-position rotary switch that allows me to add resistance in series with the IAT sensor in 5 steps 2.2k, 4.7k, 10k, 22k, & 56k. Each step gives about 1 degree of advance on the butt dyno (and on the spark-knock-o-meter), so I load up the tank with premium and just crank the knob all the way to the right. It also adds fuel to the WOT (open-loop) map, but doesn't affect the part-throttle fuel since closed-loop mixture is based on the O2 sensor target.

 

Most modern emissions engines seem to have timing retarded a fair amount in an effort to reduce peak combustion pressure/temperature, so adding advance really wakes up the throttle response and the low & mid-range torque. It doesn't seem to add anything to the top-end (above 5k). The timing advance work really well together with cold-air induction, like peanut butter & chocolate.

 

As mentioned, I have the knock sensor removed from the equation. If I hear any trace of knock, I just back the switch down a notch. If my exhaust system were louder, I'd probably use the knock sensor to trigger a dash-mounted LED that would indicate knock.

Thats pretty interesting. Can you see the timing change if you checked it with a timing light and dialed around? I have a friend with a 91 Jeep Cherokee that has the same resistor dial up in place of his coolant temp sensor. He tows his boat around and during tow he dials up a cold temp to the engine goes max rich and keeps cool. At idle you can actually hear the rpm change while dialing in different resistance settings. THanks for the info.

 

Pat

I never measured the timing change, but it's noticable both in throttle crispness and in octane requirement. I'm not too keen on the fooling the coolant temp sensor. It would seem like cruising with a rich mixture would kill your fuel mileage and overheat the cat converter. Fooling the air-temp sensor actually improves the cruising mileage because of the bumped-up timing.

I am trying to locate IAT sensor and knock sensor. Is this correct?

 

 

 

Of course, it would make much more sense if blitz can upload the pic of the knock sensor & IAT fixes.

 

Thanks in advance!

IMG didn't seem to work. Trying "attach file" option.

I think the thing you have labeled IAT is a ground, and the thing you have labeled knock sensor is the oil pressure sensor.

Picture of the KS, I believe the IAT is on the intake near the air filter....

 

http://www.main.experiencetherave.com:8080/subaru/images/injectors/DCP_2481.JPG

Sorry, I haven't been following closely. I'm not a Sube expert, so my knowledge is limited to my vehicle, but I'll explain what I can. This trick is universal to most modern EFI vehicles.

 

Some Sube models have a stand-alone IAT sensor mounted on the front of the air filter housing. On my '02 2.5, the intake air temperature sensor is combined together with the MAP sensor (it's a two- in- one combo), and it's located on the top surface of the intake manifold plenum just to the right of the coil pack (looking into the engine bay). It says Bosch on it.

 

A four-lead connector (labeled #1 - 4) mates to it of which leads #1 and #2 are associated with the IAT sensor circuit and the added resistance can be inserted into either lead.

 

In order to get a feel for the range of resistance that the sensor normally shows the ECU, I heated it with a heat gun and put it in the freezer. Here's what I got:

 

100*F - 800 ohms

28*F - 9k ohms

 

A general rule seems to be that a value higher than 100k is out of range and will throw an error (CEL). By messing with various values, I found no noticable change in the map beyond 47k. I reasoned that a log curve is probably used at the input to make a linear change at the output so I settled on five fixed values:

 

Position 1. OFF

Position 2. 2.2k

Position 3. 4.7k

Position 4. 10k

Position 5. 22k

Position 6. 56k

 

The switch is available at Radio Shark.

Based on your data my guess is that the IAT sensor is an NTC thermistor.

 

The resistance measurement can be converted to temperature in the ECU using one of several techniques.

Thanks everyone.

 

Now I even know where the oil pressure sensor is!!!

 

By the way, I am wondering what you guys do for a living. Perhaps automotive design engineers?

I am an engineer (civil) - not anything automitive but also full time sooby nut.

Originally posted by 99obw

Based on your data my guess is that the IAT sensor is an NTC thermistor.

 

Yeah, I think that most all light dependant resistors and temperature dependant resistors that are based on the natural characteristics of organic materials have a curved transfer characteristic that starts out fairly straight at one end, and compresses at the limit.

 

The resistance measurement can be converted to temperature in the ECU using one of several techniques.

 

Thanks, good info ...that.

Originally posted by hb_kim

By the way, I am wondering what you guys do for a living.

I went to an auto repair vocational school after I graduated high-school, and became ASE certified in all areas but didn't relish the thought of breathing hydrocarbon fumes 40 hours a week. I own a little shop where I service guitar amps & vintage studio gear, etc. My famous client list:

 

Sheryl Crow

Oasis

Weezer

Bush

Fuel

Kid Rock

Sponge

Dokken

Joe Strummer

Lenny Kravitz

Cold

Ron Asheton

Thin Lizzy

Eric Johnson

Romantics

Juice Newton

White Stripes

 

I love dropping names, it's such a cheap way to latch onto stardom. Also if there's any guitar players reading this and you're hip to the Naylor amp, I designed that in '93.

 

I'm a hopeless tweeker, so there's no way I'd be able to tolerate a daily driver suffering from a poor fuel or timing map for more than half a year with out devising a solution. The amazing thing (to me anyway) is that electronic controls almost seem to make tinkering easier.

Cool. I'm jealous. That's what I wish I did for a living. I have been playing guitar and bass for 16 years but have yet to do anything substantial. Lately most of my focus (no focus really) has been on classical guitar. My brother is seriously into vintage amps and gear and might know who you are.

 

I am an electrical engineer, but I work on telecom stuff. I did work on the automotive stuff for a couple of years in college for Motorola. I did mostly comms stuff like CAN, UART, and J1850 VPW. I would really like to tinker with the electronics aspect of the cars more, but my responsibilities keep me pretty busy most of the year.

 

Blitz, it might be fun to colaborate on a music or automotive electronics project. My forte is mostly digital so if you wanted to put a microprocessor or DSP on something I'm your man. My brother and I have been kicking some ideas around for a while. Fun stuff.