O2/Lambda/CO troubleshooting

[Rich_NYS]

I'm testing with a fluke meter set to 4 cyl:

When I have the meter connected at the bulkhead frequency valve connector and the pins jumpered at the RPM relay plug, I get >80 with the black probe on the bottom pin. With the leads reversed (red probe on bottom, black on top) I get 45.

Leaving the meter connected where I get a reading of 45, if I press the full throttle microswitch the reading goes to 32-ish.

When I start the car it hovers around 40-50 until it's warm, then the idle starts to mildly hunt and the reading moves 40's-80's.

If I unplug the O2 sensor it idles smooth.

Any thoughts?

[Jonathan]

What does the car do in terms of idle RPMs? Idle hunting, low idle, high idle? Everything plugged in as it was intended (that you know of) versus sensors or the like unplugged?

Is this your auto car or the new one?

Any other relevant info like what it was doing the last time you drove it, or condition of gas in tank, charge on battery, etc.?

[Rich_NYS]

What does the car do in terms of idle RPMs? Idle hunting, low idle, high idle? Everything plugged in as it was intended (that you know of) versus sensors or the like unplugged?

Is this your auto car or the new one?

Any other relevant info like what it was doing the last time you drove it, or condition of gas in tank, charge on battery, etc.?


This is the auto, and the mild hunt condition it had since I've had the car. We talked about it when you explained the microswitch to me when you were here.

Here's the RPM gauge that shows the mild hunt (I know, it's really not bad but I'd like to get it 100%.)

https://www.dropbox.com/s/63ox69l64h5rwek/3-16-15_RPM.AVI?dl=0

[hmcelraft]

The D engines all "hunt" some (I'm assuming OEM). The lambda is monitoring for the "ideal" mixture. Based on your warm reading swings you appear to have a vacuum leak(s) somewhere. The high swing is a call for more fuel that swings too high - probably because of oxygen from vacuum leak or leaks. This is where the smoke machines can really help.

[Rich_NYS]

The D engines all "hunt" some (I'm assuming OEM). The lambda is monitoring for the "ideal" mixture. Based on your warm reading swings you appear to have a vacuum leak(s) somewhere. The high swing is a call for more fuel that swings too high - probably because of oxygen from vacuum leak or leaks. This is where the smoke machines can really help.

Thanks, I found a small leak recently using cigar smoke and things are a bit improved. I didn't check in the console or brake booster, so I guess a vacuum leak is still a possibility.

I'm still wondering: why does it idle smoothly with the (new) O2 sensor unplugged?

[Ron]

Leaving the meter connected where I get a reading of 45
Need to know if this is cold or warmed up...

======

The 40-80, warm, indicates too rich.
$.02: Eliminate vacuum leaks, warm up and set CO to hoover at 40.

Pressing the microswitch should force it to 87 or greater.
Check out your connections/grounds, ...maybe borrow a lambda unit??

[Rich_NYS]

Need to know if this is cold or warmed up...

Cold, and car not running..

======



The 40-80, warm, indicates too rich.
$.02: Eliminate vacuum leaks, warm up and set CO to hoover at 40.

Pressing the microswitch should force it to 87 or greater.
Check out your connections/grounds, ...maybe borrow a lambda unit??


I'll do the above tomorrow...Thanks! :thumbup:

[DMCMW Dave]

Need to know if this is cold or warmed up...

======

The 40-80, warm, indicates too rich.
$.02: Eliminate vacuum leaks, warm up and set CO to hoover at 40.

Pressing the microswitch should force it to 87 or greater.
Check out your connections/grounds, ...maybe borrow a lambda unit??

Cold or jumped RPM relay brown to yellow should be at 45. Warm should bounce 35-45. Microswitch should lock it to 55.

40-80 is kind of a wide swing, would indicate a small vacuum OR unmetered air leak.

Connect the dwell meter to the orange test wire NOT to the FV connection. The impedance of the FV connection is not compatible with some meters and will give erratic readings, whereas using the real test port will give consistent readings.

[Rich_NYS]

Cold or jumped RPM relay brown to yellow should be at 45. Warm should bounce 35-45. Microswitch should lock it to 55.

40-80 is kind of a wide swing, would indicate a small vacuum OR unmetered air leak.

Connect the dwell meter to the orange test wire NOT to the FV connection. The impedance of the FV connection is not compatible with some meters and will give erratic readings, whereas using the real test port will give consistent readings.

Thanks!

I'll retest tomorrow using the orange test wire and look for vacuum leaks again.

I'm pretty sure there's no vacuum leaks in the engine bay...where's the usual suspect aside from the engine area?

[Bitsyncmaster]

Cold or jumped RPM relay brown to yellow should be at 45. Warm should bounce 35-45. Microswitch should lock it to 55.

40-80 is kind of a wide swing, would indicate a small vacuum OR unmetered air leak.

Connect the dwell meter to the orange test wire NOT to the FV connection. The impedance of the FV connection is not compatible with some meters and will give erratic readings, whereas using the real test port will give consistent readings.

+1
Your meter should read the 45 degrees on either FV pin (cold) but you should have the black meter wire grounded. When using both pins your getting twice the noise. Using the orange test wire is a little cleaner signal.

What causes the hunt on most cars is the O2 sensor changing it's reading at idle speed and the lambda ECU following that change so the mixture swings rich and lean. I think the major problem is because our O2 sensors are not heated and run right on the edge of working at idle speed. It's not a problem at cruse speeds.

[Ron]

Microswitch should lock it to 55.
OOPS, bad edit job. :banghead: Thanks Dave!
... Actually it should be 50-60 and STEADY (as in previous PM, Rich).

Note he was getting 37! Suggested connections/ground(s)...or borrow a control unit.

======

">86 and STEADY" is correct for grounded O2 sensor wire. Sorry for confusion!

[Jonathan]

I'm pretty sure there's no vacuum leaks in the engine bay...where's the usual suspect aside from the engine area?

Have you replaced these gaskets recently on your car?

http://store.delorean.com/p-6436-intake-manifold-gaskets-pair.aspx

The pair of gaskets aren't expensive and replacing them isn't difficult. It could be one possible location of an unmetered air leak.

Another place to check is on the ends of your vacuum hoses where they slip over the barb or fitting on the component they connect to. Give a close inspection especially the underside of the hose that isn't easily visible from above. If there is a small split in the end of the hose, it can extend beyond the sealing surface of the fitting and you'll lose some air/vacuum there.







Otherwise you should go looking for this lawyer named Kobayashi...

[hmcelraft]

Thanks!

I'll retest tomorrow using the orange test wire and look for vacuum leaks again.

I'm pretty sure there's no vacuum leaks in the engine bay...where's the usual suspect aside from the engine area?

Usual suspects for vacuum leaks are fuel injector boots, the paper gaskets at the manifold to throttle assembly, and the idle motor tubing at the manifold. The vacuum hoses feeding the brake booster and the vacuum reservoir can leak at the connection points when the hoses get aged and hardened.

[hmcelraft]

Thanks, I found a small leak recently using cigar smoke and things are a bit improved. I didn't check in the console or brake booster, so I guess a vacuum leak is still a possibility.

I'm still wondering: why does it idle smoothly with the (new) O2 sensor unplugged?

The reason the engine idle stops hunting when you disconnect the oxygen sensor is because the lambda goes into a "locked" signal - 50 degrees on the dwell meter - the same as the full-throttle enrichment switch action. No variable dwell = no change in the fuel manifold pressure and no hunt.

[David T]

The reason the engine idle stops hunting when you disconnect the oxygen sensor is because the lambda goes into a "locked" signal - 50 degrees on the dwell meter - the same as the full-throttle enrichment switch action. No variable dwell = no change in the fuel manifold pressure and no hunt.

The motor hunts for a lot of reasons. Any imbalance between cylinders, the Lambda system lags, the idle system can't react quickly, the K-jet system does not respond fast because it is mechanical, etc. It is hard to get it to run smooth but not impossible. The first thing to do is a compression test and see if all cylinders are within 5% of each other and all of the spark plugs are gapped as close as possible to each other. Vacuum leaks are important to fix too. On one car the reluctor gaps on the impulse coil were not all set the same so it made the idle hunt. Adjusting the mixture screw is the LAST thing you do to get the Lambda set accurately. EVERYTHING ELSE must be just right to be able to get the mixture set correctly.

[Rich_NYS]

I was able to get a really good smoke test this evening. The only spot where the was a leak: where the auxiliary pipe (from the idle speed motor) connects underneath the mixture control unit.

It pulled out easily and I see there's an O-ring on it. I removed & replaced it a few times, but that didn't seem to stop smoke from seeping out from that area.

From what I'm seeing, I'd say that qualifies as a small air/vacuum leak....does that sound like a condition that would cause the mild hunt?

Spraying the area with starter fluid doesn't have an effect.

I'm going to do some flow tests now....

[Ron]

From what I'm seeing, I'd say that qualifies as a small air/vacuum leak....does that sound like a condition that would cause the mild hunt?
Yes -- Fix that and why pressing the microswitch does not force it to ~55 and STEADY, then retest everything.

[Rich_NYS]

Yes -- Fix that and why pressing the microswitch does not force it to ~55 and STEADY, then retest everything.

What is the common fix...new o-ring? That does not look like an easily accessible location...:ehh:

I connected the meter to the orange wire & ground: jumpered RPM and cold running both measure 45 solid, pressing the microswitch read 53 solid.

Warming the car up now for more readings...

BTW, when I spray starter fluid in the direction of that leaky auxiliary pipe, the engine idle doesn't change...any thoughts on that?

[Rich_NYS]

I connected the meter to the orange wire & ground: jumpered RPM and cold running both measure 45 solid, pressing the microswitch read 53 solid.



Warm readings:

27-45 when the car was ~120 degrees

30-54 when the fans came on

[Bitsyncmaster]

Warm readings:

27-45 when the car was ~120 degrees

30-54 when the fans came on

Those readings look pretty normal. It's hard to get a perfect average without a meter that can filter the readings. I just make sure the average it below the solid cold value reading.

On the pipe o-ring seal, I coat that pipe and o-ring with grease which helps sealing and installing the pipe. Your lucky your o-ring "hold down ring" has not popped out on you. I locked that hold down ring in the unit with loctite.

[Rich_NYS]

Your lucky your o-ring "hold down ring" has not popped out on you. I locked that hold down ring in the unit with loctite.

Actually, the O-ring & hold-down ring came out with the pipe.

Today I'm going to put everything back in place and will use loctite. Does the O-ring seat in the bottom of the mixture unit & the ring holds it in place, or does the O-ring fit into the ring and the two get installed together?

Looks like a pain in the balls..........

[Bitsyncmaster]

Actually, the O-ring & hold-down ring came out with the pipe.

Today I'm going to put everything back in place and will use loctite. Does the O-ring seat in the bottom of the mixture unit & the ring holds it in place, or does the O-ring fit into the ring and the two get installed together?

Looks like a pain in the balls..........

The ring is just a "cup". From what I remember, the outside of the o-ring seals onto the edges of that cup. So try not to get to much loctite on the inside of that ring. I used a very thick loctite used for hydraulic line sealing.

[Rich_NYS]

Got the pipe, O-ring, & brass ring nicely re-installed, seems to have no effect.

So, the dwell readings are good and no vacuum leaks when smoking the engine....:dunno:

[Ron]

When warm, it should be pulsating at 40 (+/- 5). You started with "40-80" or 60 (+/- 20), and now have 30-54 or 42 (+/-12)... Sounds like one small leak fixed and ~one to to go... Try plugging all of the vacuum taps on the engine. A gauge on one of them and a reading at idle wouldn't hurt!

Wondering why the micrioswitch is working now.

You might do the rest of the tests:

http://dmctalk.org/attachment.php?attachmentid=33525&stc=1