'76 280Z Question on dist/manifold vacuum, dist timing, fuel pressure, brake booster

[FastWoman]

Hey Jenny, great news!

What would cause you to run rich? Dunno... Is your coolant temp sensor reading correctly? That's probably the biggest thing affecting the mix. If it's reading too high a resistance for a given temp, you'd be running rich. Same for the air temp sensor, except that would have a lesser effect.

If I remember correctly, I had a rich running condition in my '75 280. It was caused by a bend in the AFM vane assembly from engine backfire. I fixed the problem by tapping out the vane with a hammer. The '75 AFM vanes didn't have backfire relief valves. I think they fixed that in '76.

I doubt your ECU has drifted to the rich side. Most linear circuits tend to break down in a similar manner across units.

Anyway, if you're running correctly on the road and are idling incorrectly, you can tweak the idle mixture by turning the idle mixture screw near the outlet of the AFM towards the bottom. You'd screw it in to richen the mix and screw it out to lean it. (This adjustment affects only the mix at idle.) That said, I didn't find the screw did much on my car. I set it at 5 full turns opened up from fully closed (fully clockwise), but this was arbitrary.

[Jennys280Z]

Hi Sarah thank you! It's because of you guys that I've gotten along as well as I have. xx

Coolant temp sensor? My temp gauge reads just right if that's what matters!

Setting the idle air is a way I could go...but shouldn't I just test/fix or replace my AAR? If my car had a few minutes of 1200+RPM while it warmed up I'd consider that another problem solved! A lot of benefits with that...my car warms up faster, plus the idle would already be high enough to drive well when it kicked off.

My daily driver (Camry) always starts off at 1500RPM and drops down slowly. I love that! I want my Z to do that too

[Jennys280Z]

Here's the Air Regulator for the 1976 280Z:

BOSCH Part # 64402. It's only $83 at Rockauto.

Having a bad AR could cause a rich condition and give me idle issues to boot. Sarah and Eric you guys pointed out very early on for me to fix one known problem at a time, and you've helped me peel off the layers of mystery and solve my car's problems and I am so thankful. Y'all knew that multiple problems could be at play with my car and you were totally right!

I have another issue:

Now I'm worried about my clutch master cylinder that arrived today...cozye can help me for sure on this one. The rod (at the pedal end of the MC) is LOOSE. I'm able to move the rod about 20 degrees (edit: 15-20) in different directions. Is this normal?

*pant pant*

Edited January 30, 2011 by Jennys280Z

[cozye]

moving the rod is normal. Mine actually came loose in the box and I had to insert it in the boot and attach the boot. No worries.

Also on the clutch bleed, read the manual. It's a bit different. Once you get some fluid going in the clutch line, all you have to do is keep pumping the pedal with the bleed screw slightly open, with a tube attached and the hose down in a jar of brake fluid. you don't have to close the bleed screw when letting off the clutch pedal like you do when you do brakes.

coolant temp sensor. There are two. There is one for the gauge, which does nothing except make an output to your gauge. The other is the "water temp sensor" with the bosch two lead plug on it (same as fuel injector connector). Thats the single most important sensor in your EFI system. The a/f mixture is adjusted directly off this input. Very important it is reading accurate.

Air regulator, yes, yours may be bad. Mine was mostly working. It would open up some, and it would close when the car got hot. It wouldn't open up enough to give me a good fast idle when it was cold though. It's not important to fix that right now as long as its closing all the way when the car is warm. You can verify this by pulling the hose out of the throttle body boot when the car is hot, and making sure it's not sucking air though the hose. You will have to put your thumb over the hole in the boot when performing this test or the car will die.

I recently replaced my air regulator, it opens further when cold and I get a good fast idle now. Rock Auto did not have the one for my year in stock so I had to pay $100 and order from MSA.

[FastWoman]

Jenny, your air regulator wouldn't affect your mix. The air it lets through (to raise your idle) is metered, so it will come with extra fuel. FAIW, my air regulator gives me about a 1k idle cold -- lower than the normal high idle. Maybe it's a bit sluggish or defective, or perhaps it needs adjustment. Anyway, I don't consider it an important issue, because my car idles just fine at 1k when it's cold. I'm sure without the air bypass, the engine would barely idle at all when extremely cold, so the air regulator is clearly doing something (and doing it well enough).

As Eric said, the coolant temp sensor with the 2-conductor Bosch style connector is the one for the EFI. The one for your gauge has the single wire. There's another doodad in the thermostat housing with a two-conductor Bosch-style connector, and that's the thermotime switch. You don't want to mix the temp sensor and the thermotime up! I'm almost positive the thermotime has the larger base to it. You can verify either by checking for zero-ish ohm continuity between one of the pins of the temp sensor connector and the #13 pin on the ECU connector -- or -- by verifying zero-ish ohm connectivity between the thermotime connector pins and the cold start valve pins.

Anyway, do your temp sensor resistance measurements at the ECU connector for the most meaningful results. Wait until your engine is stone cold and at a known temperature, so that you can compare to the correct value ranges in the FSM.

[Jennys280Z]

Jenny, your air regulator wouldn't affect your mix. The air it lets through (to raise your idle) is metered, so it will come with extra fuel. FAIW, my air regulator gives me about a 1k idle cold -- lower than the normal high idle. Maybe it's a bit sluggish or defective, or perhaps it needs adjustment. Anyway, I don't consider it an important issue, because my car idles just fine at 1k when it's cold. I'm sure without the air bypass, the engine would barely idle at all when extremely cold, so the air regulator is clearly doing something (and doing it well enough).

As Eric said, the coolant temp sensor with the 2-conductor Bosch style connector is the one for the EFI. The one for your gauge has the single wire. There's another doodad in the thermostat housing with a two-conductor Bosch-style connector, and that's the thermotime switch. You don't want to mix the temp sensor and the thermotime up! I'm almost positive the thermotime has the larger base to it. You can verify either by checking for zero-ish ohm continuity between one of the pins of the temp sensor connector and the #13 pin on the ECU connector -- or -- by verifying zero-ish ohm connectivity between the thermotime connector pins and the cold start valve pins.

Anyway, do your temp sensor resistance measurements at the ECU connector for the most meaningful results. Wait until your engine is stone cold and at a known temperature, so that you can compare to the correct value ranges in the FSM.

Wow okay since I have to do a test from the ECU again I'm going to make a long list of a lot of other stuff I'd like to test while I'm in that thing again.

I only tested the stuff the bible told me to test for conditions of loss of power in the engine the first time. Resistance at the AFM, voltage at the fuel injectors, etc.

Yep I will have to look which is which again...I think that's how I remembered it too, that the thermotime connector box is the larger of the two.

It sounds like your AR is functioning mostly, maybe better/similar to how Eric described his old one.

One thing I've been learning the hard way all along is that it's a lot worse having a toast AR in the wintertime than summer. I'll test it before presuming it's bad though, because it is around $100 after all. I wonder if tightening the hose so tight like I had to do, to kill the whistle from the vacuum leak, is symptomatic of that thing staying closed when I'm cold idling. That is, if there was vacuum flowing through there, it'd be a bit easier to make the hose "tight" enough as the air is kindof "taking the path of least resistance" similar to flow in an electric circuit.

Thanks for the wonderful advice I'll follow it all. :kiss:

Edited January 30, 2011 by Jennys280Z

[Jennys280Z]

moving the rod is normal. Mine actually came loose in the box and I had to insert it in the boot and attach the boot. No worries.

Also on the clutch bleed, read the manual. It's a bit different. Once you get some fluid going in the clutch line, all you have to do is keep pumping the pedal with the bleed screw slightly open, with a tube attached and the hose down in a jar of brake fluid. you don't have to close the bleed screw when letting off the clutch pedal like you do when you do brakes.

coolant temp sensor. There are two. There is one for the gauge, which does nothing except make an output to your gauge. The other is the "water temp sensor" with the bosch two lead plug on it (same as fuel injector connector). Thats the single most important sensor in your EFI system. The a/f mixture is adjusted directly off this input. Very important it is reading accurate.

Air regulator, yes, yours may be bad. Mine was mostly working. It would open up some, and it would close when the car got hot. It wouldn't open up enough to give me a good fast idle when it was cold though. It's not important to fix that right now as long as its closing all the way when the car is warm. You can verify this by pulling the hose out of the throttle body boot when the car is hot, and making sure it's not sucking air though the hose. You will have to put your thumb over the hole in the boot when performing this test or the car will die.

I recently replaced my air regulator, it opens further when cold and I get a good fast idle now. Rock Auto did not have the one for my year in stock so I had to pay $100 and order from MSA.

OMG and they wonder why I love you? Silly boys!

[cozye]

OMG and they wonder why I love you? Silly boys!

Also, make sure you watch your fluid level on the clutch reservoir when bleeding. You will get about 5 or 6 "pumps" before you run it dry and have to start over.

[AnthonyG]

Pins AFM 1 AFM 2 (in Ohms)

6-8 226 226

8-9 126 126

7-8 199 200

6-7 73 75

as promised...

6-8 : 186

8-9 : 103

7-8 : 185

6-7: 83

car door plate says it was made in 2/76.

[Jennys280Z]

Thank you Anthony!!! You have good numbers reading according to spec.

My car was mfg in 11/75 FWIW

Well it would seem that when I started this thread, I needed a new Thermostat, Brake Booster, Air Regulator, Distributor, Air Flow Meter, Clutch hydraulics and possibly a Coolant Temp Sensor.

Considering my remaining issues, my car is running well. I'm going to see if I can bark the tires in 2nd on a dry flat road and if I can I might consider this good enough. My car could always do it before on 14x6" wheels and 215mm retread tires. With these 16x8" and ZR 225s, it might be harder for me to lose traction, everything else but tires held constant.

[Jennys280Z]

If nobody can post a 126/226 I'm going to buy a replacement AFM.

Looking back on an old thread, I already tested the Air Regulator and the coolant temp sensor twice from the ECU. On the Air Regulator, I should have gotten "Continuity" where I got 68.7 Ohms. (EFI Bible, Test 1-8, p. 56, Pin 34 to Ground). I asked on the old thread and never got answered so I'll ask again here. Is 68.7 Ohms "Continuity" or am I looking for something like 0 or 1 or 2 Ohms here?

I tested the water temp sensor at 50degF air temperature, and got 4290 Ohms where I should have expected 3250 - 4150 Ohms (at 50degF coolant temp). Maybe it was a little less than 50F outside, and so this result is inconclusive. (EFI Bible, Test 1-6, p. 54, Pin 13 to ground).

If I'm going to blow $700 with the test results I have already, I might as well slap on a $20 coolant temp sensor and make it $720. Looking at my repair records, my temp sensor has gone out once, and my air regulator is original.

[cozye]

ignore the air bypass as long as its closing when hot for now. It won't help your overall tuning issue.

Test the water temp sensor hot, when the car is 180 degrees or so. That's when you will really be able to tell if it is functioning correctly or not. If it's off what the book says by 200 ohms at that point, it needs replacing IMO.

Sorry, I haven't had a chance to test my AFM again for you. I will try this weekend. Been way too busy. Remind me again what pins you are testing on the AFM for those values?