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Dave WM

Pikes Peak trip!

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I have a fear of heights.  I couldn't watch while you were turning that thing around.  I felt like I  was going over the edge.  :)

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On 9/23/2019 at 12:00 AM, Dave WM said:

I noticed it idled more smoothly at the base (5000 feet). I have mine set pretty lean at sea level (using the AFM bypass for idle mix). Maybe at 5000 it was running richer (smoother).

I have not been able to find out any info on the effects of operating above 12000. I still don't know if it died rich/lean, it did NOT forward fire (pop thru the AFM, lean) or backfire (thru the muffler, rich). It would just die like it was getting no fuel at all. Like it was running on the start fuel pump run. I thought the AFM was maybe not turning on the pump. If I had a flat pull off I would have messed with the AFM (pulled the filter to AFM boot and get to  the flap with fingers.

Were you ever able to figure out what went wrong/what you could modify to go higher?

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nope, I plan to see if I can add the high alt option and will manually trigger it while watching the color tune plug. I presume it leans it.

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On ‎9‎/‎23‎/‎2019 at 5:28 AM, 87mj said:

I have a fear of heights.  I couldn't watch while you were turning that thing around.  I felt like I  was going over the edge.  :)

it was nerve wracking for sure. I am sure the other cars must have thought I was nutz.

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Just now, Dave WM said:

nope, I plan to see if I can add the high alt option and will manually trigger it while watching the color tune plug. I presume it leans it.

Zcon will be in Colorado Springs in 2021 - i plan on driving up to try it, maybe you can give it a 2nd shot then haha

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2 minutes ago, chaseincats said:

Zcon will be in Colorado Springs in 2021 - i plan on driving up to try it, maybe you can give it a 2nd shot then haha

see if you can get past the Bermuda triangle of pikes peak.

You may want to remove the air filter. I would have tried that but with so many other cars on the road I did not want to try it again. Its not a big deal to turn around (could have just backed down if the engine was completely dead) but I did not want to create another traffic jam.

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Just now, Dave WM said:

see if you can get past the Bermuda triangle of pikes peak.

You may want to remove the air filter. I would have tried that but with so many other cars on the road I did not want to try it again. Its not a big deal to turn around (could have just backed down if the engine was completely dead) but I did not want to create another traffic jam.

Is there a way to trick the ECU into going into high-altitude mode?

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45 minutes ago, chaseincats said:

Is there a way to trick the ECU into going into high-altitude mode?

IIRC there are pins on the ECU, your wire harness may not be have matching pins so you would need to figure out a work around for that. IIRC its a simple on off switch that connect the pins that activates it. You should be able to find it in the wire diagrams for the harness.

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50 minutes ago, Dave WM said:

IIRC there are pins on the ECU, your wire harness may not be have matching pins so you would need to figure out a work around for that. IIRC its a simple on off switch that connect the pins that activates it. You should be able to find it in the wire diagrams for the harness.

I have a california car so I'm guessing its there somewhere haha - I'll check the fsm

 

EDIT: I found it - check and see if you have it, it is this gold pod and the wires going to it are solid blue and solid black.  I'm guessing to engage that we just bridge those 2 wires?

 

IMG_6771.JPG

Edited by chaseincats

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Update for you guys.  I created a bypass switch to enable high-altitude mode using a standard flip switch and two spade connectors (one plugged into each of the plug's 2 sockets).  I gave it a quick test and it seems to be working (after confirming continuity).

If your bypass switch is working, you will notice the following with the car warmed up and any vacuum line unplugged:

  • Switch on: the car should have a fairly noticeable stumble
  • Switch off: the car should have a mild stumble if at all
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On 11/27/2020 at 5:05 PM, chaseincats said:

If your bypass switch is working, you will notice the following with the car warmed up and any vacuum line unplugged:

If I did that, I'm pretty sure the engine would stall.  Would you please explain what "any vacuum line unplugged" means?

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1 hour ago, TomoHawk said:

If I did that, I'm pretty sure the engine would stall.  Would you please explain what "any vacuum line unplugged" means?

It just means unplug a vacuum line that goes directly to the intake manifold

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There are several vacuum hoses;  one to the brake booster, one to the heater controls, and one to the distributor.

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13 minutes ago, TomoHawk said:

There are several vacuum hoses;  one to the brake booster, one to the heater controls, and one to the distributor.

Pick any one, except the brake booster one. You just want to create a vacuum leak.

 

I'm skeptical that any of this will help at 14,000 feet though. The problem with a normally aspirated engine at high altitude is the air density. There isn't enough oxygen in the air, and the relative air pressure is much lower than at sea level. When the intake valve opens at sea level, the atmospheric air pressure is something like 14 pounds per square inch, so the air/fuel mixture is easily crammed into the cylinder. The relative e air pressure at 14,000 feet is only around 2 pounds per square inch. At such low relative atmospheric pressure it isn't very easy to get the air/fuel mixture into the cylinder, even with the suction created by the rapidly descending pistons.

What a normally aspirated engine needs at high altitude is the addition of an oxidiser. A shot of nitrous oxide might do the trick. Or some aviation gasoline, which has oxidisers added to aid combustion at the altitudes airplanes operate at.

Turbocharged engines aren't affected by the low atmospheric air pressure, as they use waste engine heat to turn an impeller to force the air/fuel mixture into the engine.

Edited by Racer X

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1 hour ago, Racer X said:

Pick any one, except the brake booster one. You just want to create a vacuum leak.

 

I'm skeptical that any of this will help at 14,000 feet though. The problem with a normally aspirated engine at high altitude is the air density. There isn't enough oxygen in the air, and the relative air pressure is much lower than at sea level. When the intake valve opens at sea level, the atmospheric air pressure is something like 14 pounds per square inch, so the air/fuel mixture is easily crammed into the cylinder. The relative e air pressure at 14,000 feet is only around 2 pounds per square inch. At such low relative atmospheric pressure it isn't very easy to get the air/fuel mixture into the cylinder, even with the suction created by the rapidly descending pistons.

What a normally aspirated engine needs at high altitude is the addition of an oxidiser. A shot of nitrous oxide might do the trick. Or some aviation gasoline, which has oxidisers added to aid combustion at the altitudes airplanes operate at.

Turbocharged engines aren't affected by the low atmospheric air pressure, as they use waste engine heat to turn an impeller to force the air/fuel mixture into the engine.

So with this switch on, the air filter off, and an extra vacuum leak added for good measure still wouldn't get enough air into the engine to get it up Pike's?

Edited by chaseincats

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5 hours ago, Racer X said:

I'm skeptical that any of this will help at 14,000 feet though. The problem with a normally aspirated engine at high altitude is the air density. There isn't enough oxygen in the air, and the relative air pressure is much lower than at sea level. When the intake valve opens at sea level, the atmospheric air pressure is something like 14 pounds per square inch, so the air/fuel mixture is easily crammed into the cylinder. The relative e air pressure at 14,000 feet is only around 2 pounds per square inch. At such low relative atmospheric pressure it isn't very easy to get the air/fuel mixture into the cylinder, even with the suction created by the rapidly descending pistons.

 

Air pressure at 14,000 Ft. would be closer to 8.26 psi.   Still an L28E ruling at factory spec.'s shouldn't have any problem going up Mt Evans even at 60% power.  I've driven a stock 72 240Z up there.  Just thinking out loud - I know nothing about the F.I. on the 280Z.... but for some reason I'm thinking the ECU on the 280Z is an analog computer. 

I'm wondering if that  Gold Canister that @chasincats pictured, with the Blue&Black wires - is a sort of altimeter - that outputs an analog signal of varying strength. So it is not a matter of sending  ON/OFF signal to the ECU - so much as sending an analog signal of the correct strength to the ECU - to adjust the air/fuel mixture for different altitudes. Like a fuel level sender in the tank, or a temperature gauge. Jumping the wires together - might send the opposite signal needed to the ECU and make things worse at higher altitudes.

Does the Factory Service Manual tell you how to test that Gold Canister, or give a signal strength that it should output at Sea Level ? 

 

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11 hours ago, Carl Beck said:

Air pressure at 14,000 Ft. would be closer to 8.26 psi.   Still an L28E ruling at factory spec.'s shouldn't have any problem going up Mt Evans even at 60% power.  I've driven a stock 72 240Z up there.  Just thinking out loud - I know nothing about the F.I. on the 280Z.... but for some reason I'm thinking the ECU on the 280Z is an analog computer. 

I'm wondering if that  Gold Canister that @chasincats pictured, with the Blue&Black wires - is a sort of altimeter - that outputs an analog signal of varying strength. So it is not a matter of sending  ON/OFF signal to the ECU - so much as sending an analog signal of the correct strength to the ECU - to adjust the air/fuel mixture for different altitudes. Like a fuel level sender in the tank, or a temperature gauge. Jumping the wires together - might send the opposite signal needed to the ECU and make things worse at higher altitudes.

Does the Factory Service Manual tell you how to test that Gold Canister, or give a signal strength that it should output at Sea Level ? 

 

This excerpt from the FSM should explain it a little bit:

Capture.PNG

Edited by chaseincats
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4 hours ago, Carl Beck said:

Air pressure at 14,000 Ft. would be closer to 8.26 psi.   

 

Correct. I made an error in my math, resulting in the 2 psi figure. Sorry, eh?

Still, 8 psi is nearly half that of sea level. Consider an older, high mileage engine that isn't producing the original rated output, then cut that output by nearly half, and you now have a huge deficit.

Time for some NOS.

 

 

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9 hours ago, chaseincats said:

So with this switch on, the air filter off, and an extra vacuum leak added for good measure still wouldn't get enough air into the engine to get it up Pike's?

Unless the air filter is really dirty, removing it probably won't lean the mixture out enough to compensate for the lower air density.

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6 hours ago, chaseincats said:

This except from the FSM should explain it a little bit:

 

Thanks- @chaseincats
 

I guess that confirms what I wrote;  “I know nothing about  the F.I. on the 280Z”.   LOL

 
Have to say - even in 1978, I’m surprised they sent the level at 3675ft. - given California is 282ft below sea level in one place and 14,000ft above in others. Perhaps its more an Emission Control thing for Calif. 
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If you live at 3,500 feet it probably changes with the weather.  That would be annoying.

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