Actron Dwell meter shows 0 at startup, then swings when warm Cold start sluggish

[dean2526]

I have posted recently and cold start sluggish issues, car runs great once warmed up. I got an Actron dwell meter on ebay. When I plug it on when engine is cold, the dwell shows 0. After it gets up to temp it starts swinging and I have tweaked the fuel mixsture to 17-22 on 8 cyl mode (34-44 on 4cyl mode) and the car runs fine when warm. Two questions:

1) What does 0 dwell at startup mean? I would think if the Actron Meter itself was bad, it would not swing when engine warm.

2) I have seen posts on the throttle microswitch and I don't think it's engaging, I have pushed the flap but I don't think it does anything. Would that have an effect on cold engine running rough?

[Bitsyncmaster]

My guess is the lambda ECU is faulty. Not sure how the stock ECU circuit that puts 45 deg out works. But it sounds like that part of the circuit has failed but the active closed loop part still works. I know the ECU looks for an impedance below 3 meg/ohms to got active.

[David T]

My guess is the lambda ECU is faulty. Not sure how the stock ECU circuit that puts 45 deg out works. But it sounds like that part of the circuit has failed but the active closed loop part still works. I know the ECU looks for an impedance below 3 meg/ohms to got active.

Before you condemn the ECU check voltages and grounds. It is rare that the module itself goes bad.

[Rich]

Before you condemn the ECU check voltages and grounds. It is rare that the module itself goes bad.

Classic DMC (Houston) agrees with David T.

Their Parts listing for the Lambda ECU (https://store.classicdmc.com/101068-lambda-ecu-silver.html) has long carried an advisory about that part:

"Note that this part has a very low failure rate, so be sure that it's what you need before ordering as it is NON-RETURNABLE. If you are unsure if this what you need, contact us (https://www.delorean.com/contacts.htm), and we can help you diagnose your car correctly to ensure you are getting the part you need."

[dean2526]

Classic DMC (Houston) agrees with David T.

Their Parts listing for the Lambda ECU (https://store.classicdmc.com/101068-lambda-ecu-silver.html) has long carried an advisory about that part:

"Note that this part has a very low failure rate, so be sure that it's what you need before ordering as it is NON-RETURNABLE. If you are unsure if this what you need, contact us (https://www.delorean.com/contacts.htm), and we can help you diagnose your car correctly to ensure you are getting the part you need."


So is the 0 dwell at startup an indication of something with the Lamba? I will search the threads for checking the voltages, but if anyone has a video handy or instructions, please post, thanks!

[Bitsyncmaster]

So is the 0 dwell at startup an indication of something with the Lamba? I will search the threads for checking the voltages, but if anyone has a video handy or instructions, please post, thanks!

The lambda ECU has to know when the sensor has warmed up. If it did not know that the O2 sensor cold has zero volts and it climbs as it heats up. If the lambda started adjusting the mixture with a cold sensor it would swing the dwell to the min or max (I forgot which way). The ECU measures the impedance of the sensor to know when it has warmed up. It will force the dwell and hold it at 45 deg until it has warmed. If the WOT switch or ambient temp is really cold, then it will hold 52 deg until it has warmed up.

It switches to normal closed loop when the impedance drops below 3 meg/ohms. I have never heard of the symptoms the user has even when there are missing ground wires.

The OEM lambda ECU has a hybrid circuit board with surface mount components. That board is mounted on the main board inside a plastic cover. It does the magic of providing the normal logic board the O2 signals.

Now it could be something else in the ECU. It does not think the O2 is warmed up because it would not drive the dwell to zero. So it may be the main logic board has a failure.