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Discussion Starter #1
Well, I bought this cherry 79 with all of 48k miles on it a few months ago. I wasn't impressed with the 16.5 mpg city, and 19.8 mpg highway I was getting, so I tinkered with the air flow meter potentiometer. I'm getting 17.5 in the city now, and a whopping 25 mpg on the highway! Now that's what I'm talking about. And it's still running just a hair rich!
 

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Re: HOLY MPG! (280zx)

Nice work! Did you use the manual for specs or did you simply "fly by the seat of your pants"? If by the seat of your pants, what criteria did you use to determine how much and what direction to twist the thing?

thx,
_c
 

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Re: HOLY MPG! (280zx)

I wanna know what the **** you did! My mileage sucks!!!! like 15 hwy or something. I need some of that action you have now!
 

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Re: HOLY MPG! (280zx)

Me too my MPG sucks I would like to know what you did too... I'm running fairly rich though... lots of black smoke out the pipe but only when driving hard/high RPM shifts...


Dan
 

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Re: HOLY MPG! (280zx)

Share the wealth of knowledge. :) I too could use a fix like that. Have the whole black smoke at high rpm. Where exactly is the thing you messed with.

Thank,
Ant
 

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Mess with AFM at own peril

Rant mode on -

Before everybody jumps on the "tweak the AFM" bandwagon, think about what you are really doing.

You are really taking the perfectly tuned factory setting (which was capable of getting that kind of mileage and better), and messing with it in an unscientific method in order to compensate for a failure somewhere else in the system.

Really. Find the problem that is causing it to run too rich. Did you mod the fuel flow? More likely you have a failed sensor, or faulty wiring, or cracked air hoses, or flaky cam timing. All of these things are many times more likely to be your real problem than a maladjusted AFM would be.

Now that you have read all this, go for it. Crank up the spring tension and lean that puppy out. When the new problems pop up, it will be that much more difficult to find the answers. A smooth running FI system is fuel efficient by it's very nature. Your tinkering with the parameters of this "fixed" system will bring nothing good.

Do everyone else a favor, though. Put a label on the AFM detailing your mods. When your car ends up in the junkyard with a blown engine, we will know which AFM NOT to use.

Thanks for the chance to rant.
 

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Discussion Starter #7
Ok Mr. Pissy (j/k), some more info...

and this is for everyone else too. Before I messed with the air flow sensor, I checked EVERY other component and sensor in the EFI system, and checked the mechanical condition of the engine. Messing with the air flow meter is a last resort, and Zuber is right in that you should check everything else first.
Now here's the caveat with my situation: the air flow sensor on my Z is the only non-maintenance related part on the car that isn't original. It's a reconditioned unit the original owner had installed in '99, and it wasn't calibrated properly; I fixed it (See, that's why your rant doesn't really apply, but you had no way of knowing that).
My Z is running better than ever (at least since I've owned it), and I'm not pissing raw fuel out of my tailpipe. If you know what you're doing, this mod is no big deal, and you're nuts if you don't think the potentiometer's spring tension doesn't sag after more than 100k miles (as most folks have on their Zs) and couldn't use a LITTLE tightening in some of those older cars anyway; again, only AFTER ensuring everything else is ok.
Anyway, Zuber is also right in that this isn't something you should do if you don't know what you're doing. Since most of you don't seem to know what I did, I'm betting you don't understand what you'd be doing, how to do it, and the ramifications. If you still wanna try it, though, e-mail me and I'll give you the rundown.
 

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Re: Mess with AFM at own peril

2 years ago my gas mileage dropped on my 83 280 ZX Non turbo. It also started blowing smoke, like it was running rich. The exhaust would burn your eyes.

I have another 280 so I started swapping parts, from the Air Flow to the computer. Nothing helped. Finally, I changed the Oxygen Sensor and immediately gas mileage jumped back to normal range, around 27mpg highway

No more smoke or black film on rear bumper.
 

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Re: HOLY MPG! (280zx)

I get around 23 mpg and that is a combo of highway and city. It's an 82 ZXT with 165,000+ miles...go Z!
 

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Re: Ok Mr. Pissy (j/k), some more info...

Mr. Pissy?

Whatever. Tell all the gullible that tweaking their AFM will bring them miracle mileage. I don't get my parts from junkyards anymore, anyway.

There are very specific reasons for ever messing with the inside of the AFM. Improving gas mileage isn't one of them. 99% of the people who complain about gas mileage have some other problem, and haven't corrected everything thats wrong. Dirty connections #1, vacuum leak #2, etc...

Give the masses their magic bullet. Tell them what they are screwing up, though. (You know, the little fact about leaning the mixture too much during low throttle aplications. Don't forget to mention what chronic lean situations do to an engine).

Hows that for pissy?
 

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Let's remember our common bonds here!

Whoa guys! Obviously you're both well versed in the intricacies of our beloved z's- thank you both very much for your perspectives... it's nice to hear about the victories that can be achieved with educated tinkering (beyond my own meager abilities) and the warnings about messing with closed systems is good for the naiive to hear- thank you all for the benefit of your experience... this thread has inspired me to be more careful in looking before I leap! (but it won't keep me from the leap after the good look has been taken!)

You guys all rock!

_c
 

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Discussion Starter #12
Dude, I was teasing w/the insult...

'cause you know, you "turned the rant mode on." We're both on the same page here. I know the condition of my Z, and I know what I'm doing. I'm young, so I've only had the opprotunity to learn and work on L-Jetronic for about 10 years, but as I said previously, I'm fully aware of, and have checked, every other component on MY car; including the AFM.

I was only posting to share my satisfaction with MY particular experience; it wasn't meant to inspire others with a magic cure. And gas mileage is directly related to air/fuel ratio, so when you mess with the AFM, you ARE messing with it for mileage. As I also said before, MY reconditioned AFM was out of specs, causing MY rich condition. The AFM was the LAST thing I checked afer making sure everything else was good (sensors, vaccum lines, connectors/connections, ignition, compression, harnesses, full tune up, filters, get the picture?). And my car is not running lean under low throttle conditions because I made a conscious effort to leave the AFM spring a BIT loose to ensure I still have slightly rich conditions for better performance.

Like I said, we're on the same page. No one should tamper with their fuel injection system unless they know what they're doing. I didn't post to encourage others to follow my example; I was only sharing my experience. I recommend everyone get a copy of "How to Tune and Modify Bosch Fuel Injection Systems" as a primer.
 

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Discussion Starter #13
P.S.

In case there's any confusion here, I only mentioned my bad mileage because it alerted me to my rich-running condition, which is why I started trouble-shooting to begin with (that, and my blood-shot eyes and gasoline cologne on long trips).
Remember, my AFM is not OEM (it's a rebuilt AutoZone unit from Mexico); hardly Nissan-level workmanship.
 
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