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PorscheMoparLiterbike
 
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oxy sensor klambda problem

Hi Guys

oxygen sensor (new oem) drives to rich mixture....10to1, 9to1.....barely idles etc

warm up normal...as soon as system transitions to closed loop goes rich,,,,unplug sensor and bounces back to 12to1 - 12.5to1...idle steady....been driving with it unplugged.....Car drives fine, cruising, under boost etc



Condition started "all of a sudden" a month and a half ago...while i was driving before the MD ice/salt/tundra came......thought it was the old sensor so ordered a new one.....same problem

I know not a tragedy....richer mixture is nicer pre-boost......however like the better mpg cruising and idle was a bit more stable when sensor was working......also just concerned may be a problem that will affect something else in the future

any ideas? as always grateful for your knowledge
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Old 02-23-2014, 11:00 AM
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I recently had a problem similar to what you describe above, and it ended up being a bad ground . . . there is a ground connection for the primary engine wiring harness that is bolted to the mounting bracket for the coil, so I would suggest that the first thing you do is to remove the cable, and bracket, and clean the wire ring connector, the spot on the bracket where it is connected, the bottom side of the bracket where it contacts the fan housing and the corresponding spot on the fan housing.

Last edited by Ronnie's.930; 02-23-2014 at 12:41 PM..
Old 02-23-2014, 12:39 PM
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Thanks Ronnie....will check per your recommendation
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Old 02-23-2014, 01:30 PM
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It aint the sensor, as you've already discovered with the new replacement making no difference. My guess would be your control pressures are off; WUR issues, one pump or the other not working right, system pressure too low. You should not be running 12.1 or 12.5 to 1 AFR at idle. You could probably adjust it out with the mixture screw, but that doesn't fix the root of the issue.

The other possibility is that your AFR gauge and/or sensor is faulty and feeding you bad information. I had an issue once when my voltage regulator in the alternator was going tits up, and after warmed up (following a short shutdown to heat sink things) my AFR's would suddenly be in the low 12's just driving around normal-like. I was way over charging the battery and causing some funky issues with the Innovate AFR circuits.
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Old 02-23-2014, 01:33 PM
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Thanks Ronnie....you rock..

i have the grounds both for MSD and the harness on the inner stud. (MSD is and has worked fine for 10k miles)

I cleaned the harness ring connector and tightened everything back up.

Bam...it works. Watched AFR during warm up in the 12's then as soon as it went to closed loop quickly ramped to 14 - 14.5....just like before. I believe this is representative of klambda at idle.

Mark...thanks for the input...but it just seemed like something simple because of the sudden change and no difference in boost AFRs (high 11s low 12s) before or after the problem.

I will check pressures etc and tune next but I wanted to get back to where I was before starting and making other changes
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Old 02-23-2014, 02:28 PM
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Quote:
Originally Posted by b5aar View Post
Thanks Ronnie....you rock..
It sure is nice when stuff like that works out! I more or less found my problem by accident when I had the alternator out, for a second time in about six months, trying to find a charging problem.
Old 02-23-2014, 04:17 PM
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Hey, we all like simple fixes....glad yours was as easy as a bad connection. I need people like Ronnie to keep me from over diagnosing...but wtf, here goes anyway.

So, bad connections at the coil.....what, = poor spark? Trying to understand why this caused and fixed your problem. Bad spark would mean poor combustion, which would leave un-burned O2, which would cause a high AFR reading out the tail pipe (that's how these AFR gauges work, they look at oxygen content and can be misleading when it comes to poor ignition).

Plus, I don't understand the comment "as it went to closed loop". I believe the Lambda system is always in closed loop, and adjustments to the AFR are the result of the computer (for lack of a better word) sensing the O2 in the exhaust via the O2 sensor and adjusting the frequency valve duty cycle accordingly. Open loop would happen only when the O2 sensor is unplugged and the frequency valve defaults to 50% duty cycle. Admittedly, I haven't run with the Lambda system for years and am probably forgetting something about it.

After the first few minutes of warmup, the WUR control pressure changes (increases) and your mixture will lean out (AFR's go up). I don't think there's any active temperature feedback to the Lambda circuits, though.

Just doing a random mind dump here, clouding the obvious and confusing the issue I'm sure!!!
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Old 02-23-2014, 05:46 PM
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Mark, the ground wire that I mentioned (ground wire secured to the coil bracket) is part of the Lambda wiring harness, so when the connection was bad (in my case, too much powdercoating in the wrong spots) the Lambda system worked erratically.

I would ask you to go look at the connection on your car, for further clarity, buuuuuuuutttttttttttt, it is no longer OEM

Last edited by Ronnie's.930; 02-23-2014 at 05:57 PM..
Old 02-23-2014, 05:51 PM
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Hey mark. Here goes I'm like a caveman with a hand grenade with this stuff. I know how to pull the pin but that's about it. Haha.

I believe k Lambda is in open loop until temperature switch (weber book pg 77?)send closed -open? signal to ecu to receive closed-loop control.also comes out of closed-loop with a throttle position sensor.....others commented from various threads.

Probst book also describes where closed-loop goes to open loop
Lambda sensor cool
engine cool
wide open throttle.

I know kinda vague language but paraphrasing

Hey..finallyfound the paragraph.

"because lambda sensor operation depends on high temperature the system operates open loop before the sensor warms up this can cause driveability problems and increased exhaust emissions do too imprecise mixture control. To correct this many cars have a lambda thermal switch located in the coolant or on the cylinder head of air cooled Porsches to give the control unit an additional input and ensure proper fuel metering during engine warm up. When the engine is cold the thermal switch is closed the control unit send a fixed slightly rich duty cycle signal of 60 percent to the lambda control valve. When the thermal switch warm enough to open the control unit sense of fixed middle signal 50 percent duty cycle when the lambda sensor reaches operating temperature so it signals are valid the control unit switches to close the loop operation. Remember in closed loop the duty cycle signals are constantly changing cycling back and forth between about 45 percent and 55 percent so that the air fuel ratio is maintained near the way to metric lambda equals 1.
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Old 02-23-2014, 06:23 PM
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Man.....sorry for the Google speak and my fat fingers
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Old 02-23-2014, 06:26 PM
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Old 02-23-2014, 06:34 PM
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Quote:
Originally Posted by b5aar View Post
Hey mark. Here goes I'm like a caveman with a hand grenade with this stuff. I know how to pull the pin but that's about it. Haha.

I believe k Lambda is in open loop until temperature switch (weber book pg 77?)send closed -open? signal to ecu to receive closed-loop control.also comes out of closed-loop with a throttle position sensor.....others commented from various threads.

Probst book also describes where closed-loop goes to open loop
Lambda sensor cool
engine cool
wide open throttle.

I know kinda vague language but paraphrasing

Hey..finallyfound the paragraph.

"because lambda sensor operation depends on high temperature the system operates open loop before the sensor warms up this can cause driveability problems and increased exhaust emissions do too imprecise mixture control. To correct this many cars have a lambda thermal switch located in the coolant or on the cylinder head of air cooled Porsches to give the control unit an additional input and ensure proper fuel metering during engine warm up. When the engine is cold the thermal switch is closed the control unit send a fixed slightly rich duty cycle signal of 60 percent to the lambda control valve. When the thermal switch warm enough to open the control unit sense of fixed middle signal 50 percent duty cycle when the lambda sensor reaches operating temperature so it signals are valid the control unit switches to close the loop operation. Remember in closed loop the duty cycle signals are constantly changing cycling back and forth between about 45 percent and 55 percent so that the air fuel ratio is maintained near the way to metric lambda equals 1.
Very good, you've got "the book" in front of you!! Yes, the throttle position sensor is something I forgot about, which puts everything in open loop when your foot is on the gas and past idle a certain amount. Makes sense, since the lambda system is really meant primarily for at and slightly past idle conditions, and on deceleration. That's where emissions gurus planned to make our cars puke out cleaner exhaust.

I would have to pull out my Bosch K Jetronic manual (which I don't have at the moment, it's being "ozoned" to clean the smoke smell) but I sure don't recall any temperature sensor that feeds info to the computer. But what we do have is a heating element integral with the O2 sensor to get it up to operating temperature quicker. That, of course, will affect how it responds to the presence of oxygen.

This is all fine and dandy, but still doesn't explain why poor connections at the coil caused your symptoms. Maybe the ground is tied to the heating element in your WUR (power for that comes from the rear fuel pump relay); if it doesn't heat up, it will stay in cold warmup status i.e. rich. Again, just brain bouncing here....blah blah blah.....and blah!
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Last edited by mark houghton; 02-23-2014 at 06:40 PM..
Old 02-23-2014, 06:38 PM
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That was brilliant. I usually start with the diagnostic plug.

There is a 35 C oil temperature switch, a 7 degree throttle angle switch, and a 2167 RPM switch. The oil has to be above 35 C, the throttle has to be less than 7 degrees open, and the RPM has to be below 2167 for closed loop operation. This is for M553 (US) systems, 1986 to 1988.
Old 02-23-2014, 06:45 PM
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Ground point XII provides the ground for the Oxygen sensor control unit (under the drivers seat). Ground point XII is at the coil bracket. Again, this is only for M553 (US) systems, 1986-1988.
Old 02-23-2014, 06:53 PM
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not sure how a bad harness ground at the coil bracket affects various sensors. Nothing to do with the coil itself.I think the control pressure regulator wUr is was behaving normally. Warm up 12 to 1. After warming continued gradually settled around 13 to 1 or so low 13s maybe. This is how I was driving around when I had the oxygen sensor disconnected. Again car ran fine a little rich downlow because of open-loop operation and fixed duty cycle for freq valve.

The warm up and open to closed loop transition was easily observed with the AFR guage and was very specific and repeatable. Also followed the description in the Bosh books.
Car warmed up like it always did. As soon as temperature gauge got to the top of the first white mark afr would quickly move within 3 seconds from around 12 To1 to 9 to 1 and stall.

Normal operation - warm up normal as above, temp gauge near top of first white block, AFR 12 to 1 quickly to 14 to 1, stable steady 950.
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Old 02-23-2014, 07:18 PM
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Ground point XII (coil bracket) only affects the alternator field control, O2 control unit under the seat, the throttle switch, the air injection solenoid, and the timing retard solenoid. Nothing else. This is for M553 (US) systems, 1986-1988.
Old 02-23-2014, 07:24 PM
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Great detail SSquirrel!

Thank you
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Old 02-23-2014, 07:33 PM
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Bookmarked. Great info. I need to go dig out my old Bosch books.
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