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I found the operational ceiling of a stock 1975 EFI. the car had no problems at all on the nearly 4000 mile round trip from FL to CO, but did not quite make it to the top.

https://youtu.be/QodLZs49sSc?t=395
Pretty incredible Dave, thanks for posting this. Do you have any other car videos from your trip?
 

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Discussion Starter #4
I have several will be posting later in the week. The next best one was going thru a tunnel in the Ozark mountains. The trip started in central florida, thru GA/AL/MS/AR/MO/KS/CO going out, back was CO/KS/MO/IL/KY/TN/AL/GA/FL. I was averaging 800-900 miles per day, drive or sleep at a rest stop until I got to Pikes Peak. It was full on vanishing point...


I would like to make the Denver to SF in to honor Kowalski.
 

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I have several will be posting later in the week. The next best one was going thru a tunnel in the Ozark mountains. The trip started in central florida, thru GA/AL/MS/AR/MO/KS/CO going out, back was CO/KS/MO/IL/KY/TN/AL/GA/FL. I was averaging 800-900 miles per day, drive or sleep at a rest stop until I got to Pikes Peak. It was full on vanishing point...


I would like to make the Denver to SF in to honor Kowalski.
That's awesome, can't wait to see the other videos
 

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Nice video. I can see why turning around on that road had to be done VERY carefully!!

I'm surprised, I would have thought that the FI would have operated regardless of altitude. But there you are...!
 

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Discussion Starter #7 (Edited)
Nice video. I can see why turning around on that road had to be done VERY carefully!!

I'm surprised, I would have thought that the FI would have operated regardless of altitude. But there you are...!
I assume my system is working as it should, have not found anything about the L jettronic having issues at extreme altitudes. I can only think the AFM flap was too much of a restriction, but that is just a SWAG. I was hoping someone could chime in with some experience with like altitudes to confirm or deny the problem.


Note I changed the plugs at the end of the trip, they looked fine, very light tan color on the insulators, some blackish color on the metal rim. This is with about 9k miles on them, I just wanted to see if I had a chronic mixture problem. The current setup is pretty lean (will die very quickly if the oil filler cap is removed). I am running about 10 degrees of advance at idle. (California car) the EGR and PCV are all in place, the EGR appears to be working (at idle I can lift it up at the diaphragm and the car will stumble). Vacuum as sea level is a little lower than I would like (just barely 17 inHg). I can improve it with a richer fuel mix and more advance, but that is the way it is. I have not checked the cam timing, maybe its a bit retarded. I will check the valve lash since its been a while. I "think" I can hear a slight vacuum leak, around the intake manifold, will check with smoke. Cleary a vacuum leak could mess things up....
 

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I assume my system is working as it should, have not found anything about the L jettronic having issues at extreme altitudes. I can only think the AFM flap was too much of a restriction, but that is just a SWAG. I was hoping someone could chime in with some experience with like altitudes to confirm or deny the problem.


Note I changed the plugs at the end of the trip, they looked fine, very light tan color on the insulators, some blackish color on the metal rim. This is with about 9k miles on them, I just wanted to see if I had a chronic mixture problem. The current setup is pretty lean (will die very quickly if the oil filler cap is removed). I am running about 10 degrees of advance at idle. (California car) the EGR and PCV are all in place, the EGR appears to be working (at idle I can lift it up at the diaphragm and the car will stumble). Vacuum as sea level is a little lower than I would like (just barely 17 inHg). I can improve it with a richer fuel mix and more advance, but that is the way it is. I have not checked the cam timing, maybe its a bit retarded. I will check the valve lash since its been a while. I "think" I can hear a slight vacuum leak, around the intake manifold, will check with smoke. Cleary a vacuum leak could mess things up....
Can you explain a bit about how to check the EGR? Where is the diaphragm that you lift?
 

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Discussion Starter #9
the EGR valve is opened and closed by atmospheric pressure. So when there is a vacuum applied in the servo top, the bottom is pushed up, pulling open the valve. at idle it should be closed, you can put your finger under the servo and simply push it up, the car will stumble but should settle right back down as soon as you release it. the bottom of the servo is open and connects to lever that pulls up on the EGR.
 

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the EGR valve is opened and closed by atmospheric pressure. So when there is a vacuum applied in the servo top, the bottom is pushed up, pulling open the valve. at idle it should be closed, you can put your finger under the servo and simply push it up, the car will stumble but should settle right back down as soon as you release it. the bottom of the servo is open and connects to lever that pulls up on the EGR.
So if my EGR is not working, when I push up on the bottom, nothing will happen, right?
 

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Discussion Starter #11
So if my EGR is not working, when I push up on the bottom, nothing will happen, right?
with it idling that is correct. what can happen is the valve get so carboned up that it can hang up and not close, causing a air leak that will mess up the injection system. The valve needs to be cleaned of carbon periodically and the action of the servo should be tested with a vacuum source.
 

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Reminds me of the guy years ago that posted a write up called "Coast to Coast in a Z." He bought a 240z somewhere near Merced, California and drove it back to the East Coast with his son.

I recall he had vapor lock or other issues trying to cross the Rockies. I believe he rigged up an extra fuel pump he could switch on/off from the cockpit and that's what allowed him to cross the peak.
 

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I found the operational ceiling of a stock 1975 EFI. the car had no problems at all on the nearly 4000 mile round trip from FL to CO, but did not quite make it to the top.

https://youtu.be/QodLZs49sSc?t=395
If your car is not a California car (originally) or Colorado car, it likely doesn’t have an Altitude Switch installed. There is wiring in the F/I harness near the steering column that could be used at high altitude by installing a jumper and/ or a switch to manually engage the altitude fuel reduction of about 6%. Wires should be probably taped to the main F/I harness with a piece of blue tape. Two wire T shaped connector likely with plain white wires. On ‘HIGH ALTITUDE’ vehicles (California and likely Colorado) there was a pressure sensing switch that comes on around 3675 ft above sea level to reduce fuel by 6%. This probably would have got you to the top of the mountain.
 

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Discussion Starter #14
I pulled up a wiring diagram and found the 12 and either 6 or 9 pin of the ECU (it was labeled 6bf but not clear but went to 9 on the ecu) went to a altitude compensator switch. I will check to see if I have a female pin on my ECU connector for 12 (the only thing it connected to was the alt compensator switch). Have some spare ECU's can open them up and see if pin 12 connects to anything. I could scope the injector pulse and see what effect it has on them when I close that connection. I don't recall seeing any extra unused T connectors under the dash. The car is a California car (has all the emissions stuff including the EGR and Cat with floor temp sensors and lights 1975) but is a early one IIRC.
 

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If it is a California car it likely already has the switch. (Or had) I think they mounted them near or on the steering column. If it is there you can check it with a vacuum pump IIRC. I seem to remember its maybe like 3-4 inches long and about 2 inch diameter. I used to live in Colorado Springs and have taken my 72 up the ‘hill’. It made it to the top but stunk like a refinery about the last third!!!
 

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Hi Dave, I saw your video on the Datsun Reddit! I have a 75 and its fine near sea level, but at the tail of the dragon in Tennessee (1200ft) it was struggling. I seriously doubt I have a California car.
 

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Discussion Starter #17
Tail of the dragon is next on my list. 1st is I have to fix a broken timing chain guide (tight side), must have happened on the trip, but did not cause any damage, it must have gave way and then dropped harmlessly away, I found it when checking valve lash. Anyway got the rad out, getting it rodded out or re cored as required, it was not leaking but had about 20% build up in the core that I could see. I am removing the cover with the engine in the car, was going well but now I think I will have to move the AC compressor to get at a couple of the small bolts. will have to see if I can unthread them enough to remove the cover or if I have to loosen the comp mount and tilt it out of the way to get access.
 

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Tail of the dragon is next on my list. 1st is I have to fix a broken timing chain guide (tight side), must have happened on the trip, but did not cause any damage, it must have gave way and then dropped harmlessly away, I found it when checking valve lash. Anyway got the rad out, getting it rodded out or re cored as required, it was not leaking but had about 20% build up in the core that I could see. I am removing the cover with the engine in the car, was going well but now I think I will have to move the AC compressor to get at a couple of the small bolts. will have to see if I can unthread them enough to remove the cover or if I have to loosen the comp mount and tilt it out of the way to get access.
Let me know, I'm 2.5 hours away. Really lucky it gave out at home!!!
 

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that's just the thing it gave out I think in TN north of Nashville, but no symptoms but for some noise the all quiet again. Anyway I have all the bolts loose on the TC cover, dizzy off and marked for 11:30 crank at TDC/ Oil pump tomorrow (looks like the sway bar is in the way) then should be able to get the cover off. Really interested to see exactly what went wrong. I did end up having to unbolt the AC compressor to get access to the mount bolts, removed the top ones, loosened the bottom ones, then pulled the whole assy (comp and mount) back about 1" enough to get clearance for the two 10mm cover bolts that were tight under that mount. Got a parts on the way to do the repair, prob be Monday. I will let you know when I go to the tail of the dragon. Will prob do the bottom most part in Ga since I have family near Columbus Ga. I would like to do it during colors, but not sure if that is a good idea if there are a bunch of leaves on the road. I assume during the week is better than the weekend for traffic on it.
 

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I live just outside of Denver (5280 feet) and when I drove my previous '72 up to the Eisenhower tunnel, the engine would kick and stutter horribly the last few miles. 11,000 feet makes a huge difference, especially without a high altitude switch.
 
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