AFM Adjustment

[UR2H]

My 77 Z gets terrible gas mileage, somewhere in the neighborhood of 12mpg. A mechanic I know who had a CO measuring machine said my CO% were way too high and that I was running really rich. He measured my ignition timing at 9 BTDC. He also checked my vacuum and said it was okay, however I didn't check what his pump read and he isn't a Z guy so I don't know for sure if what he read is where it should be at. I do have all new vacuum hoses under the hood though. Also replaced my auxiliary air regulator not too long ago.

So I was reading up on the AFM adjusting on atlanticz.ca and what exactly is the idle flow adjusting screw on the bottom right corner of the AFM for? It states it works the same way at the idle adjusting screw on the throttle body but which one am I supposed to adjust when I "lean out" the AFM?

I fingered the wiper clockwise for a leaner mix like the site states to do causing the idle to drop a bit. Interestingly when I finger the wiper counter clockwise to "enrich the mixture," i get the same effect. Is it supposed to do that?

Anyways so if I do rotate the black wheel clockwise and set it there, which screw (idle screw on the AFM or idle screw on the throttle body) should I adjust for the idle?

Weird thing is my car was getting around 17 -18mpg before but all of a sudden dropped to the 12mpg range and has been this way ever since. I noticed my fuel hoses to my injectors were leaking so I replaced those along with all the other fuel hoses (on the rail, CSV, return hose, filter hose) under the hood thinking the weathered and damaged hoses were the culprit but even after changing those I still kept getting bad mileage. I then changed out the AAR but that changed nothing either, except for what it is supposed to do with the higher revs on cold starts. I should also note I have new injector connectors, which were put like 2 years back.

I also have a fuel gauge installed right after the fuel filter and it reads ~29psi at idle and like 33ish on throttle.

BTW on a different topic, I just recently did a transmission oil change. The FSM states the 5 speed, which is what I have, holds 4 and a quarter pints. I know I drained all the old oil out but I was only able to put in 2 pints before it started to overflow.

Actually after I drained the oil I wasn't able to get the fill plug loose so I had to get the car towed to a shop where they got the plug loose. It was on there really good as they even had difficulty getting it off and they were using a breaker bar. And apparently the fill plug is tapered so I guess I'm kinda lucky the casing didn't didn't crack from the plug being on so tight, or would the casing not crack because of it's DATSUN strength? Well after they got the plug loose they made certain everything was drained before filling back up.

But 2 pints? What gives? I used Redline MT90 and my shifts have never been smoother. I don't even get the occasional little grind I would sometimes get when racing the motor between 1st and 2nd. But 2 pints? Should I be worried?

If you got this far, thanks for reading.

Edited September 14, 2011 by UR2H

[240260280z]

When I changed my 5 speed transmission oil I put in nearly 2 litres. (Refer to the table below)

For your fuel consumption, check the resistance of your coolant temperature sensor's functioning first at the ECU pins then at the sensor's pig tails using a hand held multimeter set to measure resistance (ohms). Do this with engine cold and with engine hot.

Also check the colour of the plugs.

Transmission Fluid

70-76 Man 1.5 litres 3.13 pints

77-83 Man 1.7 litres 3.63 pints

70-83 Auto 5.5 litres 11.75pints

Engine Oil

70-78 4.7 litres 5 quarts

79-83 4.5 litres 4.75 quarts (turbo is 5.5 quarts)

Differential Oil

70-74 1 litre 2.13 pints

75-83 1.3 litres 2.75 pints

Gasoline

70-74 60 litres 15 7/8gal

75-78 65 litres 17.25gal

79-83 80litres 21.12gal

Coolant

70-73 9.9 litres 10.5 quarts

74-75 9.4 litres 10 quarts

76-78 10.4 litres 11 quarts

79-83 10.5 litres 11.12 quarts

[UR2H]

I wonder why me and the mechanic both thought it was full? This means it's just over half full...

Thanks for the advice. I'll get to measuring the connections at the ECU, the sensor and the pigtails ASAP. I'll post what I recorded as soon as I do. However I won't have any time till probably Tuesday. Was gonna do some work on it over the weekend but things came up and priorities first...I wish my Z could be one my main priorities.

Also sorry for the late reply. I really appreciate all the help I get from this site.

[beermanpete]

As long as the trans oil is filled until oil comes out the filler plug opening it is full.

The factory capacities are always approximate and generaly the amount required after a rebuild, not an oil change, which will be a little less due to the oil clinging to the parts, sides of the case, and such.

2 pints is half of the specified capacity so it does seem odd. Are you sure you didn't mistake the size of the bottles as pints and not quarts or liters?

[UR2H]

As long as the trans oil is filled until oil comes out the filler plug opening it is full.

The factory capacities are always approximate and generaly the amount required after a rebuild, not an oil change, which will be a little less due to the oil clinging to the parts, sides of the case, and such.

2 pints is half of the specified capacity so it does seem odd. Are you sure you didn't mistake the size of the bottles as pints and not quarts or liters?

Actually I just Google'd RedLine MT90 for images and the bottles come in quarts. They look like the same bottles I used. If that's the case, I'm good to go. But I wonder where I got pints from? Do they even come in pints? :stupid::stupid:

[UR2H]

Again I will post what I record, which will probably be tomorrow. Thanks.

[FastWoman]

If idle drops when you finger the AFM either direction, you have the optimal/best mixture already.

Maybe your cylinders aren't all getting the same fuel delivery, or perhaps you have an ignition problem with one or more of the cylinders. I'd recommend pulling and reading the plugs. Do they all look the same? Are they all reading a nice mocha color on the insulators? Also, try pulling injector connectors off of each cylinder, one by one, to see if removing any particular injector connector has no effect on idle speed (which would indicate a dead cylinder).

[Zed Head]

Weird thing is my car was getting around 17 -18mpg before but all of a sudden dropped to the 12mpg range

One possibility is your water temperature sensor. Resistance in the circuit will lead the ECU to adjust for a cold engine and dump more gas.

Another possibility is your FPR. My 1976 car's FPR regulated pressure high when it got hot. Measure fuel pressure when the engine and FPR are hot, but be aware that the oil-filled gauges can be inaccurate when they're hot so make sure the gauge is cool.

[240260280z]

[FastWoman]

I love your reference!

Edited September 20, 2011 by FastWoman

[UR2H]

If idle drops when you finger the AFM either direction, you have the optimal/best mixture already.

Maybe your cylinders aren't all getting the same fuel delivery, or perhaps you have an ignition problem with one or more of the cylinders. I'd recommend pulling and reading the plugs. Do they all look the same? Are they all reading a nice mocha color on the insulators? Also, try pulling injector connectors off of each cylinder, one by one, to see if removing any particular injector connector has no effect on idle speed (which would indicate a dead cylinder).

I pulled off each plug and they all looked relatively the same to one another. The insulator's color at the tip was similar to the picture of the toasted marshmallow. However the prong and the ends of the threads were sooty.

I didn't do the test pulling off each connector one by one to see if there was a drop or change in idle. Since the plugs all look the same, this would indicate each cylinder is getting equal fuel right?

[UR2H]

So I am a bit embarrassed to ask but how do I test the resistance? I found the bullet connections for the water temp sensor but what do I do from there?

I have a multimeter and I read the link "common automotive electrical testing" found at the bottom of the electrical section on the Atlantic Z site but apparently I still don't seem to understand. I apologize but I'm new to testing anything electrical.

However I did try though. So my thoughts was that since I need to check the pins on the ECU, that I would have to unhook the ECU meaning the battery ground should be disconnected before doing so. So in essence testing the resistance at the bullet connectors would involve the same process. So with the battery ground off, I unplugged the bullet connectors and tried getting a reading but I got nothing.

Did I test correctly?

Like I said, I am new to testing anything electrical.

Edited September 25, 2011 by UR2H