A few Questions about AFM

[FastWoman]

FAIW, I've turned those stupid idle mix screws back and forth, with apparently no effect. I'd be very interested to see what sort of effect that adjustment has on the exhaust readings! I'll stay tuned.

[argniest]

FAIW, I've turned those stupid idle mix screws back and forth, with apparently no effect. I'd be very interested to see what sort of effect that adjustment has on the exhaust readings! I'll stay tuned.

In the little bit of moving the air flow meter bypass screw (the one on the firewall side only) another mechanic did while the car was running last week while at his shop, it made a noticable difference in the engine sound. He 'said' it richened it up. Ill bet it did, I am getting 7 to 8 mpg....but that is a whole other story over here.....http://www.classiczcars.com/forums/showthread.php?41966-noob-valve-adjusting-on-1978-280z

Im seriously looking at getting that CO meter. I have saved up some $ and its more affordable then I ever thought a CO meter could be.

[sblake01]

So, when you are using this meter, how (or what) are you adjusting on the car, to adjust your CO readings?

I basically only used it to make sure my Z and 810 were in spec prior to emissions testing. I'd run them at 2400-2500 rpm, which is the range the California test is taken in and turn the bypass screws until in gave the lowest CO reading. At that RPM, you only get a minor range of adjustment. The only time I had a real problem with CO on either of them is when the 810 needed a catalytic converter likely caused by a rich condition because of a bad temp sensor a few months earlier coupled with the age of the cat itself. As soon as I solved the temp sensor problem and replaced the cat, the car was back in spec, CO wise.

[240260280z]

Lots of info here: http://atlanticz.ca/zclub/techtips/EFI&fuel.htm

I always tuned by my senses. For AFM spring tension I would hold the motor ~ 4000 rpm then manually move the wiper a few mm CW and a few mm CCW to hear the motor sound and rpm change. When the tension is correct, the airflow will keep it in the sweet spot.

I don't have a CO2 meter and there are no emission tests here so I just set the AFM bypass screw to 5 full turns in (on my 77 it has 10 full turns to fully closed). I assumed Nissan/Bosch engineered it for a midpoint default setting like most good engineers would.

I now have an LM-1 O2 Sensor and will take some measurements in a few weeks and report back to the forum

Edited April 15, 2011 by Blue
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[argniest]

Also, I thought it might be good to show a recent pictures of my plugs based on how the engine is currently running.

The plug on the left side is #6, and going to the right side of picture is #1. I have driven it a little more 100 miles? since these pictures. Plugs 3,2,1 seem a little more like tan than gray. Plugs 5 and 4 are always kinds of black. But since this picture, they are starting to look like they have a little brown patch on the tip and not quite as black. Remember my timing was recently changed.

And most interesting to me is how #6 barely looks like its being used. I mean shouldnt it have something on it?

[cozye]

Based on those pics, you've got something else significant going on. All of those plugs should read approximately the same. The black ones are running way to rich. The #6 is a huge miss.

[conedodger]

Based on those pics, you've got something else significant going on. All of those plugs should read approximately the same. The black ones are running way to rich. The #6 is a huge miss.

I agree with cozye. Adjust your valves and do a compression and leak down test.

[argniest]

Well I figured I better post the picture, because I was somewhat baffled how 3,2,1 all seemed to be very similar, and I think are looking OK. But 5,4 are not good, and #6? its like not even burning in my eyes. The thing is, the local mechanics hooked up a oscilloscope with a two tablet computer screens (one big one and a smaller one) and said nothing was missing. I watched them run the test and looked at their computer screens. Of course I have never seen that procedure done before....so the be honest I didnt really know what I was looking at. But they claimed burn time was good, firing pattern looked OK, and other parameters were OK too with the secondary ignition. I didnt really understand all that stuff yet.

If the timing was off, would that cause #6 to be like that?

Those guys did play with the timing, but they thought the valves needed to be adjusted, which was the main cause of the lower vacuum of the engine. And then they said they could set the timing, or dial it in better.

And yup, I am working on removing rocker cover today, and checking valves. I got another thread going about that :-)

Edited April 16, 2011 by argniest

[240260280z]

Here is a few tests to try that are fast and easy and can tell you a lot:

1. Pull wire off each plug while idling one at a time and note drop in engine revs and sound. It should be same for all cylinders. (make sure you have good wires or you can get a shock. Leather gloves may help). Also feel/listen for the spark snap as you put the wire closer to the plug to ensure it is firing.

2. Touch with finger on injector body and feel for its internal solenoid clicking or stick a long screwdriver on each injector body and listen with ear to handle of screw driver... or use mechanic's stethoscope to hear clicking. Note any duds.

3. Pull wire off each injector while idling one at a time and note drop in engine revs and sound. It should be same for all cylinders. You can also swap injector wires between adjacent cylinders to see if plug colour changes. For example if you swap injector wires between #5 and #6 on your motor then #6 plug turns black then you have a problem with the signal on the injector wire #6.

4. If you have a spark problem, inspect rotor and contacts in distributor cap to ensure wear and carbon build up on all contacts.

Edited April 16, 2011 by Blue

[240260280z]

You may also wish to clean the connections at the dropping resistors and at the ECU for good measure:

[FastWoman]

Argneist, I'm wondering whether your #6 injector is injecting. You might have a bad connection.

#'s 1-3 look lean. #'s 4 and 5 look really rich. I'm also wondering whether you have connectivity issues with your injectors or drop resistors.

And of course you might have significant valve adjustment issues. Perhaps Cylinders 1-3 are drawing a lot more air than cylinders 4 and 5. (All cylinders supposedly get the same amount of fuel, assuming the injectors fire.)

What are your compression numbers, again???

[argniest]

I took compression test and leak down tests when cold, well, because I had the car jacked up and in pieces...so I had to. The leak down tests showed like (from cyl 6 to cyl 1) 15, 18,19,19, 18, 22 and compression was like 150 150 155 145 150 140. But engine was cold and also I didnt know to open up the throttle body/flap. I had slightly pushed off the rubber boot from the back of the AFM, but that was it. I didnt take it off, just disconnected clamp and pushed it off a little bit.

So I have been told that could have effected my compression and made the numbers lower than they could have been. Possibly even 5 to 20 psi lower, because of the way I did the tests. But its the best I could do at the time. If i could borrow my neighbors large compressor, i could do them again with engine warm...and figure out exactly what to do about throttle this time. If it would be helpful, I could do that again.

I listened to all the injectors with a stethescope and I could hear them all clicking away making the same kind of a noise...at least as far as I can tell. It seems they are all working. So that was another reason, it got bumped down the priority list. And all my injectors are brand new too. Im not saying they couldnt be bad, or that I didnt foobar installing them...

One my local mechanic friends also did that too (but he used a screwdriver), and said yeah they sound like they are working. We sprayed carb cleaner all over the place by the injectors and intake manifold, didnt make one ioata of a difference in sound of the running engine.

FUEL INJECTOR CONNECTORS....I have brand new ones sitting on my parts bench. They are the quick disconnect type. I havent got around to putting them on yet. I have been a little worried as usual about doing that job, so its on hold for right now anyway. But I mean if I can hear the injectors clicking (I have checked several times now), then that tells me the existing connectors much be working. However, with that said, the connectors themselves do not stay on the injectors very easily. I mean they are pretty easy to pull right off, I have never liked that.

It seems my engine is going insane and me along with it. One plug clean, two plugs rich?, three plugs maybe lean. But from what I read grey or tan coloring is OK. And its really hard to tell from the pcitures of the plugs, but they seem to be somewhere between gray or tan. So I was thinking 3,2,1 were all looking sort of OK. BUt hey, what do I really know anyway

Edited April 17, 2011 by argniest