Mixture stuck at 50%

[sdg3205]

I'm having a tough time with my mixture. It seems to be stuck running open loop, with two different dwell meters (one analogue and one digital) reading 50% constantly, even at normal operating temperature.

I went back to the glass bottles and reset the baseline (cracked the injectors) and went up in micro increments, replacing the CO plug after every micro turn (like a tenth of a turn!) until it started running too rich. All the while i never found that sweet spot that sent the Lambda system into closed loop swing.

Yes, the FV buzzes, the ground off the intake is good (verified by unplugging it) and the O2 sensor is hooked up. It was previously running within range before I replaced both the ISM and the ECU.

ECU and ISM are both in good working order.

Thoughts?

[Bitsyncmaster]

First thing to check is the WOT switch. If it is on you should be reading 60% but I think if it's on from engine start the lambda ECU may stay at 50% (it's something I saw one time). So unplug that switch and test.

Did the problem just start happening?

Just saw you stated it just started to act up. Did you connect all the grounds when you replaced the idle ECU?

[sdg3205]

My car is wired backwards, so the WOT reads 40. Reversing the polarity of the meter wires yields 100, so i just deal with reversing my numbers!

[Ron]

What do you mean "wired backwards"??
If I understand what you are saying, if it reads 40 it should read 60 when reversing??

FYI- 50° steady dwell can be the O2 sensor is bad or its circuit is open, or, the temp sensor thinks the engine is below 15C (59F), or, both...

[Bitsyncmaster]

What do you mean "wired backwards"??
If I understand what you are saying, if it reads 40 it should read 60 when reversing??

FYI- 50° steady dwell can be the O2 sensor is bad or its circuit is open, or, the temp sensor thinks the engine is below 15C (59F), or, both...

If you read from the orange "test" wire to ground and it reads backwards then it's just your meter. Yes the meter should read with the leads swapped.

I think the temp sensor just tells the lambda ECU if it should use 60% (very cold start) or 50% (normal cold start). The ECU goes closed loop when the O2 starts outputing voltage. When a narrow band O2 is cold there is no voltage output.

[Elvis]

Temp sensor or full throttle switch broken or a short to ground somewhere.

Or - ECU dead - but I've never seen a bad Lambda ECU so I don't believe in that one.

[Ron]

Hehe...I wasn't confused about that, but what he was saying ???

And I meant the Lambda Thermal Switch (AKA Thermal Throttle Enrichment Switch in the manual, or commonly ECT, engine coolant temperature sensor), not to be confused with the Thermo-Time Switch, or the Thermistor.
I understand they rarely go bad on a D, but ya never know and it's easy to check...

=====

Shorted O2 should give "87° minimum (steady reading)".

[Bitsyncmaster]

Hehe...I wasn't confused about that, but what he was saying ???

And I meant the Lambda Thermal Switch (AKA Thermal Throttle Enrichment Switch in the manual, or commonly ECT, engine coolant sensor), not to be confused with the Thermo-Time Switch, or the Thermistor.
I understand they rarely go bad on a D, but ya never know and it's easy to check...

=====

Shorted O2 should give "87° minimum (steady reading)".

I had to unplug that ECT sensor when I went to wideband. What it would do is drive a wild idle hunt (only when really cold) since the wideband goes closed loop in 15 seconds from start.

[Ron]

Didn't know that.

I remember you were playing with the wideban with good results (...Are you still playing with them, or satisfied?)

[sdg3205]

I have a new O2 sensor, ill try swapping out the old one and see what happens.

[Bitsyncmaster]

Didn't know that.

I remember you were playing with the wideban with good results (...Are you still playing with them, or satisfied?)

I have not had any problems with my wideband. Only thing I want to do is get a better switch for the ECON/POWER selection.

Funny a lot of new cars have that ECON switch.

[David T]

It could be a bad O2 sensor. One way to check it is to use the procedure in the manual and ground the O2 wire, check the readings and then apply 1.5 volts to the wire and again check the readings. That will prove out the wiring to the ECU and the ECU. If you don't get the proper responses you have to test the other inputs to the ECU, the temp sensor, voltage and ground, and the WOT switch. Other things that can mess with the O2 senor include a blocked cat, a very rich mixture, and exhaust leaks. If you replace the O2 sensor you should also reset the Lambda counter and check the valve adjustments.

[sdg3205]

It could be a bad O2 sensor. One way to check it is to use the procedure in the manual and ground the O2 wire, check the readings and then apply 1.5 volts to the wire and again check the readings. That will prove out the wiring to the ECU and the ECU. If you don't get the proper responses you have to test the other inputs to the ECU, the temp sensor, voltage and ground, and the WOT switch. Other things that can mess with the O2 senor include a blocked cat, a very rich mixture, and exhaust leaks. If you replace the O2 sensor you should also reset the Lambda counter and check the valve adjustments.

Thanks Dave, I'll check the manual. As for the valve adjustment... one thing at a time!