Bad air flow meter??

[Zed Head]

The "proper" way to adjust the fuel-air mixture at idle is with the screw on the side of the AFM, not the spring inside.  It's described in the FSM.

Edit - actually, it's described that the bypass screw is not to be adjusted.  But it is the most direct way to lean out or richen the idle mixture.

 

Edited October 4, 2023 by Zed Head

[sboy79]

1 minute ago, Zed Head said:

The "proper" way to adjust the fuel-air mixture at idle is with the screw on the side of the AFM, not the spring inside.  It's described in the FSM.

 

Except when you want it real lean for emissions testing. That screw wouldn’t get it lean enough. There’s a bunch more troubleshooting needed which is why it will be parked for a while. A passing emissions test makes it infinitely easier to transfer out of state titles in Oregon. Now that I’ve got that paperwork I’m not under a time crunch for getting the rest of the EFI sorted

[Zed Head]

3 minutes ago, sboy79 said:

That screw wouldn’t get it lean enough.

Doesn't look like you tried.  You said you were on the edge and passed on the next run-through.  Therefore....

Keep an open mind.  The 280Z EFI system is an excellent learning tool.  Good luck.

[Captain Obvious]

10 hours ago, sboy79 said:

It still goes lean on partial throttle so I’m parking it until I figure that out.

Do you still have the EGR system installed? It will use a leaner mix during light cruise (on purpose) and inject some exhaust gas back into the mix. I think that at light cruise, they were trying to optimize fuel consumption and reduce emissions. So they lean it out, recirculate some exhaust gas, bump the timing advance, and also purge the carbon can. All at light cruise.

In any event, glad you got over your emissions hurdle and good luck with the project.

[sboy79]

6 hours ago, Captain Obvious said:

Do you still have the EGR system installed?

No. The headers I inherited have the provision but the the bung is so far away from where it should be I can’t connect the tube from the intake manifold so I have it blocked off. 

[HusseinHolland]

Adding on here for AFM related concerns - I'm going to go through the EFI resistance tests of the AFM, and then have a go at adjusting the AFM following the AtlanticZ Guide

With the engine running at idle, the AFR's are too lean, and gently pushing in on the counter weight definitely evened out the lean condition. I couldn't do that and watch the AFR's, so I don't know how much it actually enriched the base value, however it was a definite improvement.

I've ordered a new ECT, so I will swap that out when it gets here.

 

EDIT - also looking at ZedHeads suggestion for adding the temp signal POT (ordered 1K pot)

Edited October 13, 2023 by HusseinHolland

[sboy79]

16 minutes ago, HusseinHolland said:

With the engine running at idle, the AFR's are too lean

Definitely go through all the troubleshooting and EFI bible stuff, but if you are consistently lean, the 1K potentiometer trick will richen it up 1-2 AFR. Not sure if that's just a band aid or permanent solution but it works. I'm beginning to think having a wide-band oxygen sensor just shows you how primitive the EFI system is-- you may not even notice how much the AFR swings without the gauge and drivability could be fine. We might just have too much information! Ignorance is bliss and if the car drives well and the spark plugs look good, maybe the swings you see on the wide band don't matter at all.

However based on my experience here I'm definitely moving to a megasquirt setup. I think you miss most of the benefits of EFI without a closed loop (oxygen sensor) system. The EFI system on the early non-o2 sensor cars is making lots of assumptions. I'm not a carb or EFI purist, but I'm fairly certain a well tuned carb does a better job of metering fuel than the early EFI but the EFI does solve a bunch of livability problems especially with cars that sit around with ethanol gas for long periods of time.

This opinion is obviously subjective and if I had my EFI running in tip top shape maybe I'd feel differently. Carb technology was perfected by the time of the 280z but these early EFI systems are really primitive in the world of modern EFI.

 

Edit: Also take my opinion with a grain of salt. I'm 100% sure my AFM was messed with before I got the car so I was working with a bad baseline. In retrospect, knowing that, I should have bought a rebuild and calibrated AFM so I could assume that's not a problem. Would have saved me alot of headache I think

Edited October 13, 2023 by sboy79

[HusseinHolland]

6 hours ago, sboy79 said:

Definitely go through all the troubleshooting and EFI bible stuff, but if you are consistently lean, the 1K potentiometer trick will richen it up 1-2 AFR. Not sure if that's just a band aid or permanent solution but it works. I'm beginning to think having a wide-band oxygen sensor just shows you how primitive the EFI system is-- you may not even notice how much the AFR swings without the gauge and drivability could be fine. We might just have too much information! Ignorance is bliss and if the car drives well and the spark plugs look good, maybe the swings you see on the wide band don't matter at all.

However based on my experience here I'm definitely moving to a megasquirt setup. I think you miss most of the benefits of EFI without a closed loop (oxygen sensor) system. The EFI system on the early non-o2 sensor cars is making lots of assumptions. I'm not a carb or EFI purist, but I'm fairly certain a well tuned carb does a better job of metering fuel than the early EFI but the EFI does solve a bunch of livability problems especially with cars that sit around with ethanol gas for long periods of time.

This opinion is obviously subjective and if I had my EFI running in tip top shape maybe I'd feel differently. Carb technology was perfected by the time of the 280z but these early EFI systems are really primitive in the world of modern EFI.

 

Edit: Also take my opinion with a grain of salt. I'm 100% sure my AFM was messed with before I got the car so I was working with a bad baseline. In retrospect, knowing that, I should have bought a rebuild and calibrated AFM so I could assume that's not a problem. Would have saved me alot of headache I think

Thanks for the input. It definitely does not feel right at all, you can feel the lean miss, so I don't want to drive it & possibly damage the engine. The POT should be here tomorrow, along with a new ECT. I can run the motor with the Volvo ECT pressed against the t/stat housing & get AFR's in. good range overall, but it doesn't feel 'right', so I'm going to use the correct ECT, check the AFM values & wire in the POT. Hopefully Sunday. Tomorrow is gonna be rain all day. 😞

If I have to, I'll mess with the AFM adjustment. I don't want to spend too much $$$ on components like that, as the whole mess will go away when I do the VQ35DE conversion in a year or so. 

[siteunseen]

The potentiometer I have is almost a toy now that it's corrected my below 2,500 rough running. When I'm on the interstate I can dial it around and run cooler temps at higher speeds and also better MPGs. It's a better than futzing with the radio knobs like the old days. I have a love/hate for my smartphone. 

Cost me $5 at Radio Shack years ago.

Good read here...

 

[HusseinHolland]

23 hours ago, siteunseen said:

The potentiometer I have is almost a toy now that it's corrected my below 2,500 rough running. When I'm on the interstate I can dial it around and run cooler temps at higher speeds and also better MPGs. It's a better than futzing with the radio knobs like the old days. I have a love/hate for my smartphone. 

Cost me $5 at Radio Shack years ago.

Good read here...

 

Reading through the whole thing - she gets to the POT input at post 57, after all kinds of futzing with the AFM. Seems like I should leave the AFM alone, and just do the POT.

Important details, post#66

Edit - forgot to say - I wish RadioShack still existed - I used to get all my electronic projects odds & ends from them. I guess there  just were not enough of us to keep them afloat 😞

EDIT - in post 57, she says:

"Anyway, I ran upstairs and grabbed a 5k variable resistor and plugged it into the temp sensor connector. That let me tweak the mix manually. I found that the best mix was achieved in a warm engine with a resistance of 2,550 ohms, while the temp sensor's resistance had dropped to 240 ohms. Thus the mix could be richened about right by adding 2,310 ohms in series with the sensor. Interestingly, I think I remember the value of the previously added resistor being 2.2k, so apparently someone else had been down this road before me. I'm sure at one time it made the engine run very well, and then it got wonky again with age and deterioration."

I only ordered a 1K pot, I'm wondering if I should get one that goes at least into the 2K range....

 

Edited October 15, 2023 by HusseinHolland

[siteunseen]

Fastwoman, Sarah, was the best. She was unbelievably helpful with me and my '77. We all miss her. She was a Volvo lover too then went head first into the efi 280 like you. Once we got them right the fun went away. I can't remember what she bought but I bought two 240s. I kept the best one now I'm bored again. 

[HusseinHolland]

6 hours ago, siteunseen said:

Fastwoman, Sarah, was the best. She was unbelievably helpful with me and my '77. We all miss her. She was a Volvo lover too then went head first into the efi 280 like you. Once we got them right the fun went away. I can't remember what she bought but I bought two 240s. I kept the best one now I'm bored again. 

I don't have to worry about that - I'm going to do a drivetrain conversion on mine 😄

So, I made a couple of resistor plugins - one 2.2Kohms, the other 1.1K ohms. I'll try them tomorrow & see which runs better. I ordered a couple of POTs, one 1K & the other 2.2K, so depending on which resistor seems to run it better, I'll add the pot so I can tweak the value to make intermediate adjustments. I guess I could just use the 2.2K POT, but I don't know if makes a difference to sensitivity of adjustment.