Hello F-chatters: Any experience here on how to help this? The lambda system works 'perfectly' meaning the rich-lean-rich etc crossover occurs as best to optimize catalytic efficiency; however, it creates this surge when driving which ironically screws up the CA SMOG test when it's designed to reduce emissions. The surging causes "ACCELERATION" failure and will abort the test. Funny (or not funny) that unplugging the O2 sensors will eliminate the problem, but lose the precision and constant mixture control. Another thing weird is it's inconsistent. Sometimes worse than others. If the car is driven on a long trip, it might have periods where it's great, than get bad, on-and-on. The SMOG shop was able to run the cycle, and it smogged clean, but not without the frustrations. Thank you for any help!
My experience with what would suggest a fuel delivery issue turned to be an iginition concern. I exprienced a similar condition with my QV and first leaped in the CIS. After new new injectors the condition remained. Then new wires, extenders, plugs and cleaning of distributor caps solved the issue.
Unplugging 5he sensors puts it in open loop at a fixed mixture. My 930 has the same system and was acting up at weird times running stupid rich... Do you have an AFR meter? Pretty much a necessity to diagnose some of this stuff...
If unplugging the O2 sensor fixes the problem, I would try replacing that first. If that doesn't fix it, I would look for another injection control unit. There are places that rebuild them, but with an intermittent problem like that, I would rather try another unit.
Thank you. Pretty sure it's not ignition. Unplug O2 sensor, and all is happy, meaning no surging. I have scoped with exhaust gas analyzer. Mixture can be set to whatever is desired manually, but O2 in closed loop maintains pretty much spot-on 14.7 AFR. Again, ironic that surging coincides with lambda rich-lean-rich swing, and this surge makes it abort the @#$%#@% SMOG test The workshop manual ( i.i.r.c.) states 1.5 - 2.0% CO at idle as a starting point. With O2's unplugged, wonder if set as mentioned, the fuel mapping is still good through RPM range?
This is "normal" for these cars now, 35 +/- years since new. You can spend thousands digging under the hood to force the O2 sensor to stop this - maybe. Or you can just unplug it which will harm nothing. This "fixes" it 100%, 100% of the time.
The O2 sensor is screwed into the cat. One simple thing you could try would be to run a fuel system cleaner like Techron. Over time fuel leaves behind deposits that can block small passages in the FD. These small passages come into play when altering system pressure as part of the Lambda operation.
Will it pass the actual smog test on the dynamometer in Southern California with the O2 sensor disconnected ? I'm not talking about the visual.
Don't know. We dont test here in Alabama. I will say this, though. Mine was a Georgia car its entire life when I bought it in 97. The O2 sensor was disconnected when I got it and had clearly been disconnected for a very long time. Georgia tests.
First make sure that the oxygen sensor is nearly new, as their response time slows with age (causing surging). At operating temperature, disconnect the oxygen sensor and measure the voltage at the oxygen sensor wire from the lambda computer (green with with male pin connector) to ground. It should be approximately .5V. It this is ok you may proceed. If it is not around .5v, then you have other problems with the lambda system that need further diagnosis. Now with the oxygen sensor still disconnected, check the voltage between the oxygen sensor wire (black wire, female connector) and ground. It is is above .5v, then the fuel mixture is too rich, below .5v then it is too lean. If it is not close to .5v, you will have to adjust the fuel mixture at the airflow meter. There is an anti-tamper plug which is probably long gone and a special slotted head screw that covers the port. Drill and remove the anti-tamper plug with a sheet metal screw if it is still there. Remove the port screw and get a 3mm long allen CIS adjustment tool. Adjust the fuel mixture until the disconnected oxygen sensor voltage is approximately .5v.(clockwise is richer, counter clockwise leaner). A litle adjustment goes a long way. I turn it 1/8 turn at a time. After each adjustment you have to plug the adjustment port, as it is an unmetered air leak that affects the fuel mixture ( I use and old VW port plug that is has a rubber plug with a wire/loop molded to it), but any rubber plug that seals the hole is fine. Once you have adjusted the mixture to the .5v reading, when you reconnect the oxygen sensor, there should be little change in the idle speed. I rev the engine up to 3000rpm and look at the oxygen sensor voltage with it connected. If the lambda system is functioning correctly, the voltage should be cycling back a forth above and below .5v very quickly (which is when the mixture is stoichiometric). You should be able to hear the engine note change as it cycles, but not feel it when you are driving the car. A good/hot oxygen sensor should cycle very quickly. Put the screw/plug back in the airflow meter adjustment port, make sure that the oxygen sensor is connected and drive the car. You may have to readjust the engine idle speed as you go ( use the large bypass screw on the throttle body, do not adjust the position of the throttle plate.
There are other inputs to the lambda ECU that control its function: throttle switch (wide open throttle enrichment). Oil temperature switch on the front of the engine at the base of the oil banjo on the sump (cold enrichment). I have seen intermittent operation of the oil temperature switch cause problems with the lambda system.
