Bad air flow meter??

[sboy79]

Before I start here this is what I've done so far to my 1977 Federal 280z EFI:

All EFI Bible troubleshooting-- Everything tests normal

Smoke test-- no vacuum leaks, engine is a steady 16 or so on the vacuum gauge at idle

Fuel pressure with vacuum line off regulator is 32-34 psi (my gauge isn't super precise)

Timing at 10 BTC

Compression 150 psi across all six cylinders

New fuel injectors and fuel filters (I have an additional inline filter before the fuel pump)

Generally, the car runs great. I have a wide band oxygen sensor and display hooked up and right now the idle is right at 13.5 AFR. At any throttle opening above 20% under heavy acceleration I also see about 13.5-14 AFR. Unfortunately I read about 16-17 AFR when cruising at a constant speed or slight acceleration with the throttle just barely cracked.  So it seems like I run lean in the zone between the two throttle switch positions (area between idle switched closed and partial open throttle switch closed and I'm not sure I'll be able to pass emissions running that lean during the 2000 steady RPM portion of the test.

Like I said in a previous post, this car has been in the family since new and I know previous owner (my uncle) did crack open the AFM and make adjustments. It does pass all the checks however (tested at the ECU connector). I performed the Atlantic Z page beer can spring calibration and it did help a bit-- I ended up increasing the spring tension by maybe four teeth.

So I'm stuck. It seems like my air flow meter is bad or misadjusted. Is there anything else I'm missing? I'm also contemplating upgrading to the Godzilla megasquirt system as some of these old EFI parts are becoming unobtanium but I'm not ready to give up yet.

Any further tests I should do? I feel like I've exhausted everything I've seen on the forums.

Thanks in advance for the help!

[Patcon]

I'm not sure that running lean it going to hurt your emissions test. I would think it would help but maybe I'm wrong.

I am also unsure as to whether you can run megasquirt in OR and still pass smog. Many states won't allow that.

[Zed Head]

56 minutes ago, sboy79 said:

2000 steady RPM portion of the test.

Are you sure that you need that for your vehicle?  I only had to do the idle test.  I lived in unincorporated Washington County though.

plus, they will test your car for free, multiple times, as long as you're making progress on meeting the standard.

Edited October 1, 2023 by Zed Head

[Captain Obvious]

1 hour ago, sboy79 said:

I performed the Atlantic Z page beer can spring calibration and it did help a bit-- I ended up increasing the spring tension by maybe four teeth.

Increasing the spring tension will make it run leaner.

Goes like this... Flap will open less, ECU thinks there is less air going in, and will supply less fuel accordingly.

1 hour ago, sboy79 said:

Smoke test-- no vacuum leaks, engine is a steady 16 or so on the vacuum gauge at idle

And I don't remember for sure, but I think I would hope for more than 16 in-Hg at idle. Are you sure you don't have a vacuum leak? Cap off everything not required to make the engine idle and give it another try maybe? For example... Brake booster, EGR system, etc.

[sboy79]

1 hour ago, Patcon said:

I am also unsure as to whether you can run megasquirt in OR and still pass smog. Many states won't allow that.

Yes I'm unclear on this as well. I believe Oregon just checks for a catalytic converter (which my car wasn't equipped with) and sticks the sniffer in the exhaust. I'm don't think the average DEQ technician could tell aftermarket from stock EFI but I could be wrong

 

54 minutes ago, Captain Obvious said:

And I don't remember for sure, but I think I would hope for more than 16 in-Hg at idle. Are you sure you don't have a vacuum leak? Cap off everything not required to make the engine idle and give it another try maybe? For example... Brake booster, EGR system, etc.

I think this is unusual as well. I have an actual smoke tester and when I run it for five minutes (the max before it switches off to not overheat) I eventually see smoke coming out of the intake opening by the right headlight and a TINY bit from the AFM flapper door pivot shaft. If I advance the ignition to 15 BTDC the idle vac comes up to the 17-18 range. I may start disconnecting and capping vacuum sources slowly and see if I'm missing something.

 

54 minutes ago, Captain Obvious said:

Increasing the spring tension will make it run leaner.

Goes like this... Flap will open less, ECU thinks there is less air going in, and will supply less fuel accordingly.

I both increased and decreased the flap tension and it doesn't seem to do a whole lot. The 1K potentiometer inline with the temp sensor is definitely working though. Could I just be WAY off on the spring tension and need to decrease it significantly? I was right on the tension called out by the beer can test which is the only reference I've found so far.

Edited October 1, 2023 by sboy79

[sboy79]

2 hours ago, Zed Head said:

Are you sure that you need that for your vehicle?  I only had to do the idle test. 

Zed you are right.  Just checked and the requirements for 1977 vehicles 300 ppm hc and less than 2.5% CO AT IDLE

[Patcon]

Also many inspection sites have photos of what a stock engine bay should look like. If you went after market EFI you would probably have to preserve the factory look...

[Mark Maras]

We DEQd an 81 RX7 many times in Portland. They could care less about looking at the engine. The first time took a few carb adjustments and trips through DEQ but the entire crew gave us a cheer when we succeeded. Maybe they were just glad to see us go? 

[sboy79]

Hey all! Quick update-- I passed the emissions test on the second try. Barely failed the first then leaned out the air flow meter and passed with flying colors on the second test.

If you are having problems with your EFI system or emissions testing I HIGHLY encourage installing a wideband O2 sensor. You are just guessing without it. I found it incredibly useful all along this journey. Best $200 I've spent on the car yet.

Thanks for all your help! Now onto the 5 speed swap . . .

[Patcon]

That's great!!

[Captain Obvious]

So I'm glad you got your car through emissions and are off to the next issue, but...

You said your car was running really lean. And you leaned it out even more to get it to pass emissions? Are you sure your readings are all lining up? I don't want you to burn a valve or something because you're running scary lean.

[sboy79]

It still goes lean on partial throttle so I’m parking it until I figure that out. After the test I installed the temp sensor potentiometer and set it back to slightly rich for the drive home. 
 

Honestly leaning towards a modern fuel injection system the deeper I get into this one.