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Tuning With An Air/Fuel Gauge


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Well regardless if they flow the same, that's pretty annoying. The color may not matter, but on my engine, I would want everything to at least match.

So I have no idea if the size of the opening on the bottom is the only thing that would affect the flow rate. I kinda doubt it. I suspect there are other internal geometry areas which could affect the flow rate too. In other words... Just because the hole in the bottom is the same, I wouldn't assume they flow the same.

You could test them to compare the rates:
P1100285.JPG

P1100300.JPG

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2 hours ago, Captain Obvious said:

Well regardless if they flow the same, that's pretty annoying. The color may not matter, but on my engine, I would want everything to at least match.

So I have no idea if the size of the opening on the bottom is the only thing that would affect the flow rate. I kinda doubt it. I suspect there are other internal geometry areas which could affect the flow rate too. In other words... Just because the hole in the bottom is the same, I wouldn't assume they flow the same.

You could test them to compare the rates:
P1100285.JPG

P1100300.JPG

Good point about them matching regardless of flow rate.  I just took a look at the bottoms to compare what was on there (left) and the Bosch ones I bought (right) and they look way different.  Are the ones that were on there for the turbo or just some weird reproduction maybe?

IMG_7615.JPG

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Effective fuel hole diameter  in carbs and fuel pressure determine fuel flow. I think it is the same for injectors.

Fuel pressure in injectors is relative to manifold air pressure rather than absolute air pressure otherwise  a negative pressure in the manifold would combine to  "suck extra fuel".

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  • 3 weeks later...

And here is the end of the post-credits scene for this feature-length thread: after 3 separate mismatched injector shipments from rockauto, I finally got 6 matching ones and sent the rest back.

Took the car out today for the first time and interestingly enough, with the new reman injectors, I needed to richen the car a bit to get it to our numbers.  I expected the old injectors to have had a diminished fuel output due to age but who knows.

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11 hours ago, chaseincats said:

after 3 separate mismatched injector shipments from rockauto, I finally got 6 matching ones and sent the rest back.

Woof. I suspect those old injectors had been knocking around in boxes for so long, they probably started consolidating them and mixed them up.

Glad to hear you're back on the money!       :beer:

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  • 2 months later...
Posted (edited)

Here's an interesting observation.  Every so often (a handful of times since finishing this project) I've noticed the car running more lean than usual (in the 16s instead of 14s).  Any idea why that would be?  All the contacts are clean and literally the only thing I do to fix this is shut the car off and just restart it - then the computer behaves properly.

This has literally happened maybe 2-3 times since I was able to read the engine's a/f ratio with the gauge and is a non-issue since a restart fixes it but I am curious.

Reminds me of "The IT Crowd"'s famous line, "have you tried turning it off and on again?"

Edited by chaseincats
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Hmmm. Interesting. And no idea why that would happen.

So have you driven the car with this "lean boot" condition? Does it stay lean the entire time? Or did you shut it off and restart as soon as you saw the issue?

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3 minutes ago, Captain Obvious said:

Hmmm. Interesting. And no idea why that would happen.

So have you driven the car with this "lean boot" condition? Does it stay lean the entire time? Or did you shut it off and restart as soon as you saw the issue?

Lean boot is a fantastic way of describing this.  Yeah it literally will run lean for the duration of that boot.  I ran it like that for my entire trip then when I got in the garage I shut it off and immediately turned it back on and it dropped back down into the 14s.

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Crap. That's the wrong answer.  Haha!!

I was kinda hoping you re-booted it right away and it went back to normal. I think that would be easier to figure out. (Not easy, but easier? Maybe?)

So I got nothing right now... I'll think about it and see what I can come up with? Or maybe someone will chime in with some uber-smart theories? 

Not temp related... Not vibration related... Not system voltage related......... I wonder if my thinking cap will fit under my aluminum foil deflector beanie.

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9 minutes ago, Captain Obvious said:

This is a 78, right? With mostly stock EFI system?

Yep.  The only thing not stock about it is the tuning we all worked through on this thread.

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when it is in this "lean" state, does it feel normal to drive, or hesitant? 

16s is prety lean and I'd expect you'd feel it, so if you don't feel any difference, I'd think it must be an air leak in the exhaust before the sensor. 

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OK. I had a couple goofy ideas.

First thing... The original EFI systems were fully analog and there were no computers used. But then some time along the way (early eighties), they started putting embedded microprocessors in the ECU's and using software to do the control instead of analog voodoo.

Why does that matter to me? Because if it's got a microprocessor doing the control, then this kind of latching behavior would be easier to explain. So I know your Z is a 78, which should be fully analog, but do you know for sure? Have you ever had the cover off the ECU? Got any pics?

Second thing... There's a circuit inside the ECU that is supposed to provide a little extra richness boost immediately after starting the engine, and that extra richness gradually tapers off (30 seconds or so) after the key is released. Maybe that section of the circuit is not functioning correctly, or maybe that circuit is being fooled into thinking that the key is always in the START position.

When you turn the key to START, a couple things are supposed to happen:

The starter engages (duh)
The floor temp lamp light is supposed to light up (lamp test for CA models only)
The cold start injector gets the opportunity to spray (depends on how warm the thermotime switch is)
The ECU get's the signal to begin the START enrichment boost

So here's what I'm thinking... Next time the car lean boots, try this:

1) WHILE THE ENGINE IS RUNNING, pop the hood and disconnect the small Black/Yellow wire going to the starter.
2) Turn the key to START again with the engine still running in lean-boot. Don't worry... With the B/Y wire disconnected, the starter will not engage because you have removed it's signal to engage. But all the other "harmless" functions will be activated. The floor lamp should light up, the cold start injector should give a squirt (if it's cold enough), and the ECU should get a fresh "START" signal.

The idea is that you can flick the key between ON and START a couple times to see what happens to your mixture readings. See if your lean boot symptom goes away without having to shut the car off completely? Maybe it'll go away with just a flick of the START signal.

Like I said, I'm just throwing some stuff out there!  LOL

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31 minutes ago, Captain Obvious said:

OK. I had a couple goofy ideas.

First thing... The original EFI systems were fully analog and there were no computers used. But then some time along the way (early eighties), they started putting embedded microprocessors in the ECU's and using software to do the control instead of analog voodoo.

Why does that matter to me? Because if it's got a microprocessor doing the control, then this kind of latching behavior would be easier to explain. So I know your Z is a 78, which should be fully analog, but do you know for sure? Have you ever had the cover off the ECU? Got any pics?

Second thing... There's a circuit inside the ECU that is supposed to provide a little extra richness boost immediately after starting the engine, and that extra richness gradually tapers off (30 seconds or so) after the key is released. Maybe that section of the circuit is not functioning correctly, or maybe that circuit is being fooled into thinking that the key is always in the START position.

When you turn the key to START, a couple things are supposed to happen:

The starter engages (duh)
The floor temp lamp light is supposed to light up (lamp test for CA models only)
The cold start injector gets the opportunity to spray (depends on how warm the thermotime switch is)
The ECU get's the signal to begin the START enrichment boost

So here's what I'm thinking... Next time the car lean boots, try this:

1) WHILE THE ENGINE IS RUNNING, pop the hood and disconnect the small Black/Yellow wire going to the starter.
2) Turn the key to START again with the engine still running in lean-boot. Don't worry... With the B/Y wire disconnected, the starter will not engage because you have removed it's signal to engage. But all the other "harmless" functions will be activated. The floor lamp should light up, the cold start injector should give a squirt (if it's cold enough), and the ECU should get a fresh "START" signal.

The idea is that you can flick the key between ON and START a couple times to see what happens to your mixture readings. See if your lean boot symptom goes away without having to shut the car off completely? Maybe it'll go away with just a flick of the START signal.

Like I said, I'm just throwing some stuff out there!  LOL

Interesting theories, I'll try and answer them in order!

- I haven't opened the ecu before but there is a number on the side which should denote which it is - I can grab that tonight

- I haven't tried this but am a bit confused.  If the starter doesn't crank and the engine isn't running, how would the a/f ratio be readable?

Sidenote: I forgot to mention earlier that before I shut it off last time when I returned to the garage, I popped the hood and unplugged the TPS to see if it leaned itself out further as it should.  It indeed did go leaner at idle but noticeably less of a change than if it was not in a lean-boot mode.  We're talking going from mid 14s to upper 14s instead of low 14s to 16.  Not sure if that data point is useful or not but I figured it couldn't hurt bringing it up!

 

-chase

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2 minutes ago, chaseincats said:

If the starter doesn't crank and the engine isn't running, how would the a/f ratio be readable?

The engine should already be running. Let me try again to explain.

Next time the car starts and you notice this lean-boot condition. Let it run, but while it's running, pop the hood, get out of the car, and disconnect the small black/yellow wire from the starter solenoid. 

Then get back in the car (all with the engine still running), and turn the key to START. The engine will already be running (because you never shut it off), but the starter will not engage since you have that wire pulled off the starter. Flick the key between ON and START and see if it drops out of lean boot and into regular running mode.

Does that make sense?

You can drive like that with the starter wire disconnected, but just remember that when you shut the car off, you'll need to reconnect the starter wire to get the car to start again.

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45 minutes ago, Captain Obvious said:

The engine should already be running. Let me try again to explain.

Next time the car starts and you notice this lean-boot condition. Let it run, but while it's running, pop the hood, get out of the car, and disconnect the small black/yellow wire from the starter solenoid. 

Then get back in the car (all with the engine still running), and turn the key to START. The engine will already be running (because you never shut it off), but the starter will not engage since you have that wire pulled off the starter. Flick the key between ON and START and see if it drops out of lean boot and into regular running mode.

Does that make sense?

You can drive like that with the starter wire disconnected, but just remember that when you shut the car off, you'll need to reconnect the starter wire to get the car to start again.

Oh gotcha, that makes sense.  I'll give that a shot next time but this literally happens every few months so it may be a while before I'm able to test that theory.

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Understood about the timing. Maybe you'll get lucky and it will never happen again. (Suuuuuuure).

And I'm not proposing any theories yet... I'm just trying to come up with something, anything. to maybe point in the right direction. I'm thinking that if you do the "START with engine already running" a couple times and nothing changes, then maybe it REQUIRES the engine to actually come to a stop to reboot. Injectors need to stop injecting, coil needs to stop coiling... all that.

On the other hand, if you do that test and the lean condition DOES go away, then there might be some info to be gleaned from the fact that the engine does not need to a complete stop in order to make the lean boot go away. Vibrations don't need to stop, starter does not need to suck a big hit of current from the battery. Alternator doesn't need to bootstrap. That kind of stuff.

Just fishing at this point.   LOL

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