how do i read a dwell meter for lambda AF mix

[tirwin]

OK, new Actron meter. Green lead clipped to green/white post in test port. Black lead clipped to ground. Now I get no reading. (Engine is already warm.) Needle stays at 0. What am I doing wrong???

There are 3 pins on the test port. The first time I did it I thought I was clipped to the green/white but I wasn't. Upon further inspection I realized the wires twisted right at the end of the harness and I was plugged into the wrong one. :-/

[Baby]

Sorry, engine running already with the new meter. Needle stays at zero.

[Baby]

Bump

[Jim Williams]

My apologies if I missed this in the previous discussions - Have you verified the ECU is talking to the Frequency Valve? The FV should be buzzing if there is power to the ECU. It needs 1) the fuse, which is the same fuse for the interior lights. Then 2) the fuel pump should be powered, as that is how the O2 relay is energized. If the FV is buzzing and you get no dwell indication on your meter, then something is amiss in the ECU, or your dwell meter is inoperable.

A wiring diagram for the ECU is on my website. Check here.

I just posted these pages today. If you find any broken links on the site, please email me.

[Baby]

Thanks, Jim. I'm familiar with your CIS primer, which I have found very helpful in my (sort of) understanding of the systems. It's invaluable for those of us learning, and I thank you for making the effort to share your knowledge.

I do hear the FV buzzing, and the fuse is good. I assume the fuel pump is powered because the car runs.

I don't know if you saw how this thread began, but when I connected my dwell meter (pos/neg/clip to test port) the needle spiked all the way to the right. Even before the ignition was turned on.

When I tried a second meter, this one a two-connector job (neg/clip to test port), the needle won't move from zero even with the car running and warm.

I found this thread and will test for ground at the ECU: still no reading from dwell test

When it comes to circuitry, I'm a #10 idiot, so I'm crossing my fingers I don't fry anything.

[Bob Kontak]

Originally Posted by Baby

When I tried a second meter, this one a two-connector job (neg/clip to test port), the needle won't move from zero even with the car running and warm.

Try the other end at the test post. Are you saying the black one is on the test port or that you grounded black and then the other to the test port?

Never mind - I see where you connected it correctly in an earlier post

[Bob Kontak]

Originally Posted by Jim Williams

Have you verified the ECU is talking to the Frequency Valve?

While the car is idling would you please pull off the O2 relay under the passenger seat to make sure the car runs more poorly?

If it does, we just need to track down where the circuit is messed up to the test port. That should be pretty easy. Edit - let me say "do-able" not necessarily easy as the test port originates in the Lambda box. You could at least test continuity between the test lead and the G/W wire leaving the box under the seat.

[Baby]

Thanks, Bob. I had assumed that relay was working because I can hear the FV. I will pull the relay when I get home, which will be in about 5.5 hours.

[Bob Kontak]

It is surely not the issue but just want to eliminate a variable.

If it does spit and cough after pulling the relay, look in the Tech Info Center in the PP site. There is an 82 diagram that is ok to use for 81-83 - look at the last page of the diagrams and you will see the test port wire leaving the Lambda box at connection #17. I have never done this but put a multimeter between that connection and the test pin . Car off - just want to check there is continuity.

[Baby]

Will do. Does that accomplish the same goal as described here (from the thread I linked to a few posts up)?


Get a test wire with aligator clips on both sides. Clip on side to the test port green wire pin and the other side to the nut on top of the fan that holds the coil.

Then go to the ECU and unplug the connector from it and test for ground at the pin mentioned above by Paul (17). If you have ground it is fine. If not there is a break in the wire.

[Bob Kontak]

Originally Posted by Baby

Will do. Does that accomplish the same goal as described here (from the thread I linked to a few posts up)?

Never thought of doing that. Yep, that would work plus you don't have to string up a piece of wire eight feet long.

The other lead of the multi meter needs to be on a ground as well.

[Baby]

Well, I'm stumped. Warmed up the car, pulled the O2 relay. No change in how the motor runs. Bought a new relay and plugged that in, pulled it, plugged it in, etc... still no change.

2 bad relays?

[Baby]

Which is pin 17? I want to test continuity to the test port.

[Baby]

It's this one, isn't it? This is the only one that has continuity to the test port, so I assume....

[tirwin]

Tony and I were talking recently and he mentioned that the O2 sensor relays can be bad when they are new, so it is possible. Not sure why that is the case...

[Baby]

Tim, thanks for responding. I believe it. Turns out, when I had no continuity anywhere (!), I traced the wiring harness back and found the multi-pin connector at the front of the engine bay was slightly loose. Plugged it in and got connectivity in the green/white wire. The relay test showed a slight difference with the relay unplugged. And the dwell meter works at the test port.

So, weeks later, I can begin to set the a/f mixture....

Now, with the car fully warm after a 1/2 drive, the needle is dithering between 5 and 10 on the 8 cyl scale, which is 10 and 20 on the 4 cyl if I'm not mistaken. I assumed I was rich, so I leaned it out quite a bit, but there isn't much difference in the reading.

Question: am I correct to think I'm still way rich?

[tirwin]

Hey, that's great progress!

The way to read the duty cycle is 45 on a scale that goes to 90 is 50% duty cycle. (45 is half of 90) The duty cycle is the amount of time the frequency valve is open. 0% would be always closed and 100% would be always open.

Edit: when I say more time open that means the ECU is making the mixture richer to compensate for a lean condition and more time closed means it's making the mixture leaner to compensate for a rich condition.

You want the needle to dither around 45.

[Baby]

Right, and the less frequent the cycle the more often the system isn't bleeding off fuel pressure, so the richer the mix is, right? I get that it's supposed to be at around 45, but when I lean out the mix screw the needle isn't moving toward the higher numbers on the scale, even when I lean it out so much the car won't start. I can get it to where it runs well, but the meter is still reading between 5 and 10. Time for more searching and reading!

[tirwin]

I can't remember -- have you done the fuel pressures test yet? It sounds like you're base condition is too rich. If you haven't done those tests, that should be up next.

[tirwin]

By the way, remember that the mixture screw only affects idle mixture. It is not like carbs. The way to adjust the mixture is via the fuel pressure so the WUR is the primary component to look at. I'll bet your cold control pressure is too low.