1/4 5/8 CEL's after starting for first time.

Pull the codes from both ECU's to get a better idea on what to trouble shoot.

Kai

 

Your post does not specify if you followed the procedure to re-initialize the ECU's after reconnecting the battery. It's always best to TRY that first, since it's quick and easy and doesn't cost anything. Next thing would be to pull the codes, as suggested.

Hope you've got her back on the road soon!

 

Could be stale fuel as well.

 

Personally, I would go ahead and re-re-initialize it, just as a starting point (since the battery is disconnected). Make sure you don't touch the throttle pedal, the throttle position sensor might give a confusing reading to the Motronic unit and your baseline would be wrong. It is probably best to run the procedure when the engine is cold. Hopefully once you've got it done and you've erased the codes that are stored, but not active, you'll be ready to boogie.

 

It sounds like it runs fine in open loop (or WOT) but stumbles when it enters closed loop (i.e. receiving information from the O2 sensors). I would start with the O2 sensors - make sure the connectors are cleaned (the 4 connectors under the airbox) and possibly add a ground strap from the sensors to the frame. Next step would be to swap out a known good sensor and test with that (see if the issue only remains on one bank). Kind of strange that both would fault at the same time though - makes me think there may be more to it.

 

Grounding O2 sensors: Use a small metal hose clamp around each O2 sensor and insert a piece of wire with the end stripped against the body of the sensor and then tighten down the clamp. Attach the other end of the wire to a grounding point on the frame. This has worked for a few of the guys, personally that wasn't a problem for me.

I'm still concerned that both are causing trouble at once. Bad gas - maybe. I'm not a big fan of stabilant (anymore - after what several of us have discovered over time), better to thoroughly clean the connector pins with electrical contact cleaner and take a wire brush to them.

Have the O2 sensors been removed at any point? I'm wondering if the element got contaminated and you are seeing both fail at once. A generic Bosch 4 wire O2 sensor is pretty inexpensive and would serve as a test to see if it eliminates the code on one bank. Worst case you wind up with a spare sensor.

To wipe out all the codes, disconnect the negative battery quick disconnect, re-attach and go through the ECU learning process again. When power is disconnected all stored codes will be wiped clean.

 

weak battery, low voltage, or a bad cell in the batt. Load test the battery, not just check for 12v but test it under load. I think some others here can attest to these cars doing funny things when the voltage is a little low.. never mind the fact that it shouldn't matter once the car is running... it does..

 

Take them out and have a look at their tips. If you haven't uset the car in a long time, marginal sensors can fail altogether. When used regularly, the heating cycles ensures there is no moisture in them. Also everytime they are warmed up properly and used they are cleaned by the very hot exhaust gasses. If it is quick start stop without really getting hot, you'll wind up getting excess deposits from the richer exhausts.

Water spewing out of the exhaust is totally normal if the ambient temperature is low (below 10-15 Deg C). What happens is that you have hot and moist air being cooled in a cold exhaust system and water vapor condenses onto the surfaces of the exhaust. As it warms up it warms from the header end with the condensation line moving further and further aft until the exhaust is completely warmed up, when the visible vapor and wetness should stop.

Take the O2's out, have a look at them. The rough idling you suggested really makes me think they are throwing values all over the place. A good way to test if it is them, is to get a AAA battery connected to a variable potentiometer.

Turn the potentiometer until you get about .75V out, then connect this to the sensor wire (positive to the pin where the grey wire from the O2 sensor goes, and negative to where the black wire goes) at the ECU end. If you have a rechargeable AAA battery that is discharged, it should be outputting about 800mV and would suffice without having to use the potentiometer...

The battery is then outputting the average value at stoichiometry (slightly rich actually but OK for the sake of the test), fooling the ECU into thinking it is at the right mixture, thereby simulating the O2 signal. If your CEL lights stay out, then you're all good and you know the O2's are shot. At USD 75 each, the battery test is much cheaper than buying one to test with.

To test the O2 sensors, warm the engine up for at least 7-10 minutes, then plug a voltmeter into the O2 sensor outputs, positive probe on the grey wire, negative on the black one. You should be getting a reading that should vary from 50 or so mV to 8-900 mV. Whatever they are at idle, if you rev up and down you should see the value change. The important thing is that they vary by as much and read the same at idle (let the idle settle for 30 or so seconds before taking a reading. If the ranges or idle readings vary more than 5% between the O2 sensors you have a bad one.

 

A proper heating will clean them as best as possible. If they are old and they are the issue, then get new ones. O2 and MAF sensors are KEY to a healthy engine. Too rich, you'll burn the cats and risk a fire, too lean you'll burn the upper cylinder (valves and seats first)... Not worth it for the cost of 2 O2 Sensor (you should always replace them in pairs). Buy the generic 4 wire ones and wire them up. I can get all the plugs and schematics for you. I can't remember if you are south UK based, if so I can do them for you for nothing...

I used the newer technology planar O2 sensors. They heat up in seconds, thereby going closed loop much earlier in the enrichment cycle avoiding unnecessary fouling. These are bosch O2 Sensors which have planar architecture sensor ends, but behave like standard O2 sensors. They are not 100% planar sensors which are only usable in much newer cars.

Marco

 

That one is easy.

All that code means is that the Motronic is not getting the signal from the cat ecu. You should first look to see if cat ecu on the 5/8 is unplugged. If it is unplugged it may be because the cat ecu has had it? If it isn't hear is the test, swap the cat ecu's from one side to the other, if the 4121 code jumps to the 1/4 bank then you know the cat ecu is shot. But understand that you will not, again, you will NOT get a check engine light for a "missing" cat ecu signal. It's a silent code and only gets stored in the Motronic, so you will have to pull the codes to see if it has jumped sides.

 

An earlier post here states that the stored codes can be erased simply by disconnecting the battery. I'm not 100% sure, but I don't think that's true. Have you actually erased the stored codes using the procedure described in the manual??? To me, it sounds like you just keep bringing up the old codes that are stored in memory, rather than having a NEW incident of the same codes coming up again and again.

 

Procedure is in workshop manual pages C78/C79. If you don't have the manual, one of us can describe it for you, it's just a final step while downloading the codes to "erase error memory".