Getting K-Jet Running properly: Bad O2 Sensor?

[jmettee]

I’m working on a car of a local owner & trying to eliminate PO modifications & get the car running correctly in stock condition. The car runs & drives decently, but the idle motor doesn’t run & I can't set fuel mixture; which is what I’m trying to rectify. I want to go in strong next time to knock out these issues once & for all, so this is why I am asking for knowledge in advance.

Idle speed: I think the motor is bad. I probed the connector & believe I am getting the proper pin readings when compared to my car (from what I remember – tested my car the following day). Taking a known good idle speed motor will prove this out, but current engine setup is idling with throttle set screw adjustment. We can figure this one out easily once we try with a good ISM & know if it’s a wiring issue or not. If anyone has a guide to proper pin readings & ranges or how to test the motor itself, I'd love to get a hold of that for troubleshooting.

So on to K-Jet. I believe it’s fully functional. The dwell reading is correct for both the disconnected O2 sensor & with the full throttle switch engaged, so the Lambda system seems to be responding to at least those conditions. It’s been a few weeks since we worked on the car, but I know we heard the FV running & I believe it was when doing these 2 tests. When trying to set the mixture, I can go from where the engine hardly runs at the left to where it hardly runs at the right (lean to rich) without getting any real response or change in dwell. It just stays between 10 & 11. The car is just past 30k miles & apparently has been running rich for a while. My guess is that the O2 sensor is bad & why the dwell is not changing while adjusting the mixture screw. We have a new O2 sensor to install when we work on the car again, but if there are any other suggestions on this I am looking for input. If the O2 sensor doesn’t fix this, I’m unsure what to look for next since everything else with Lambda seems to be working.

[Bitsyncmaster]

I think your correct in assuming the O2 sensor needs to be replaced.

The idle motor should have +12 volts on the center pin and the two outside pins are switching to ground at 100 Hz. rate with variable duty cycle (PWM).

You can test operation of the idle system by pulling the idle motor out and turning the key on (not running engine) and the idle motor should jump open about half way and slowly move to full open in about 20 seconds.

[David T]

I think your correct in assuming the O2 sensor needs to be replaced.

The idle motor should have +12 volts on the center pin and the two outside pins are switching to ground at 100 Hz. rate with variable duty cycle (PWM).

You can test operation of the idle system by pulling the idle motor out and turning the key on (not running engine) and the idle motor should jump open about half way and slowly move to full open in about 20 seconds.

I have had limited success cleaning the O2 sensor. You heat it way up for a couple of minutes with an Oxy-Acetalyne flame. It won't be sensitive anymore but it burns off enough to make it work again if only for testing purposes. Also any bad connection point between it and the ECU (including grounds!) will make it look bad. It operates on VERY low voltages. After 30,000 miles it should be replaced anyway. You also should reset the Lambda counter and adjust the valves. As for the idle motor, although it may check out electrically, it could just be stuck mechanically. Remove it from the motor and rotate it quickly in your hand. You should be able to feel the shutter move. You may have to squirt in some cleaner in to get it to move freely.

[NightFlyer]

I replaced my O2 sensor with one of these over winter hibernation - works perfectly and couldn't be happier with the price/quality (OEM Bosch):

http://www.ebay.com/itm/360897044374?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[jmettee]

Unplugging the O2 sensor did get the expected dwell response so that connectivity appears to be good & I also believe I checked over the grounds pretty well, so I'm hoping it's just the O2 sensor. I did already get a new O2 (Denso) for $18 from RockAuto.com since I ordered some other items recently.

As for the ISM, I do plan to remove it & check it out further. We ran out of time, but think we can pinpoint the problem with it off the car & with another known-good one in hand....should know where to start looking if the motor is not the issue.

Thanks for the input on the ISM voltages...will update after we get to work on the car again.

[Rich]

Idle speed: I think the motor is bad. I probed the connector & believe I am getting the proper pin readings when compared to my car (from what I remember – tested my car the following day). Taking a known good idle speed motor will prove this out, but current engine setup is idling with throttle set screw adjustment. We can figure this one out easily once we try with a good ISM & know if it’s a wiring issue or not. If anyone has a guide to proper pin readings & ranges or how to test the motor itself, I'd love to get a hold of that for troubleshooting.
Additional to Dave's input about voltages at the idle air motor try these tips taken from www.k-jet.org:


"If the idle air motor is clogged up with gunk, it can’t change the idle speed fast enough, and the idle will often hunt up and down, eventually finding the right idle speed after several times up and down, ranging from say 300 to 2000 rpms. Often, putting in the clutch or shifting in to neutral will make the car almost die, because the idle air motor cannot catch up quickly enough to balance out the idle.

An idle air motor that just plain won’t work can be detected by trying to start the car and having another person “feel” the idle air motor. It vibrates (buzzes) when it is running. You can also hook it up to a battery or booster pack to test it.

Another way to test the idle air motor is to measure the resistance with your multimeter. A good motor should read +/-20 ohms resistance between any two pins that are next to eachother and +/-40 ohms resistance between the two outside pins."

I have tried the resistance test on the input pins of my current IAM, which works fine, and also on a good spare. The values line up with these.

[NightFlyer]

+1

I've often used the info found at k-jet.org in trouble-shooting k-jet components. Definitely some good stuff there :thumbup:

[jmettee]

Additional to Dave's input about voltages at the idle air motor try these tips taken from www.k-jet.org:



Another way to test the idle air motor is to measure the resistance with your multimeter. A good motor should read +/-20 ohms resistance between any two pins that are next to eachother and +/-40 ohms resistance between the two outside pins."

I have tried the resistance test on the input pins of my current IAM, which works fine, and also on a good spare. The values line up with these.

Thanks, exactly what I was looking for. The motor doesn't buzz at all. Having the resistance values will help to determine if the motor is good or not....along with some other testing. This is good info!

[Bitsyncmaster]

Thanks, exactly what I was looking for. The motor doesn't buzz at all. Having the resistance values will help to determine if the motor is good or not....along with some other testing. This is good info!

There have been a few idle motors that have been shorted and that blows the idle ECU. So the resistance check is a good thing to do, before you swap an idle ECU.

[jmettee]

To close this thread out...

We worked on the car today. Put a new O2 sensor in it & were immediately able to tune the fuel mixture. So that was a good accomplishment & all it cost was an $18 Denso sensor.

The Idle Speed Motor measured OK for resistance. 10 ohm from middle to outers & 20 ohm on the 2 outer pins....which matched the one on my car. So with that, we put it on my car & it hummed, but didn't move. Cleaned it out & worked it back & forth to loosen up the metal valve. Put it back on the car & had an active idle system. Although upon leaving, the car would start & idle at 1500 rpm, then come back down to 750 after about 30 seconds. I think the motor is still a bit sticky & slow to respond, but he said it drive great on his hour trip home....so it was still progress. Another happy owner with a better-running car. :)

[Jonathan]

To close this thread out...

We worked on the car today. Put a new O2 sensor in it & were immediately able to tune the fuel mixture. So that was a good accomplishment & all it cost was an $18 Denso sensor.

The Idle Speed Motor measured OK for resistance. 10 ohm from middle to outers & 20 ohm on the 2 outer pins....which matched the one on my car. So with that, we put it on my car & it hummed, but didn't move. Cleaned it out & worked it back & forth to loosen up the metal valve. Put it back on the car & had an active idle system. Although upon leaving, the car would start & idle at 1500 rpm, then come back down to 750 after about 30 seconds. I think the motor is still a bit sticky & slow to respond, but he said it drive great on his hour trip home....so it was still progress. Another happy owner with a better-running car. :)

Justin, part of your description resembles what I had on my car recently. It was the part about it idling around 1,500 and then settling down (or eventually not settling down). Mine turned out to be a poor connection to the thermistor, located conveniently in the VoD. I jumpered the wires that would go to it at the ECU and have been driving my car this summer without issue since. When/if I have a good reason to go into the VoD, I'll find out what isn't connected properly and fix it.