I'm About Done With The %**&ing Efi

[Captain Obvious]

So here's a question. When was the last time you had the car at a more typical altitude? Did you still have the same problem when you were down off the peak?

 

And I'm not sure that really even has anything to do with it... I could see running at altitude would make you run richer than necessary because the air is so thin, but how could it drop the gas mileage to an unreasonably low value.

 

Think about it this way. Your car runs great at 1000 feet. Gas mileage is 20 mpg. Then you drive up to 10000 feet and the car runs rich. But the gas mileage should still be the same since the injector pulses are still the same width. In other words, the altitude increase won't make the pulses wider, they'll be the same width but are now wider than necessary. (Haha! Did I say that right?  )

Just tossing out ideas...

[rcb280z]

The reason I asked about an altitude switch (back earlier in this thread) is because it affected my 77 280z when it went bad. But then realized the 75 didn't come stock with one. I lived in Vegas for 17 years and would cruise to Mount Charleston which is over 9000'. One day My Z was running like crap (started midway up) and ran that way all the way to the top. Long story short, it was the "altitude switch". Even though the switch only compensates by 6% (leaner) it was enough to foul my plugs when it didn't work.

 

Wonder why Nissan didn't later fit the 75 and 76 with them after realizing it was needed. Especially if the switch connector is wired in the harness as Mike has already verified. That tells me it was considered correct?

Mike it is a 2 wire connector if that is what you found. And the other interesting thing is I do not see it in the 75 wire diagram. Explain that one, someone please.

 

Another time I burned up what seemed to be a 1/4 tank of fuel going up the mountain because my advance wasn't working. 20 minutes of up steep mountain climbing. 

[mjr45]

Captain, at this point all idea's are considered to be valid and worth some thought. To be honest this car has never been at anything lower than about 6000' so I couldn't tell you if run s better or not.

 

rcb, there are 2 wires hanging by the ECU with no connections, I think they were for the altitude switch since they both disappear into the wiring harness and I haven't bothered to peel the harness ro see where they end up.

Mike

[240260280z]

Hi Mike,

Maybe we should all step back and look at some other areas.

A picture of all 6 plugs side-by-side would help determine if it is a broad over-fuel issue or localized to a few cylinders.

Have you conducted a pressure test recently? if so the results would be interesting.

Have you checked the valve lash recently? How is it?

[mjr45]

Captain, see the pic of the plugs in post #78. The last pressure test I did was 6 mos ago and I got #1-6 120, 125, 130, 118, 122, 121, I know that sounds low but when you use the 0.7860 as the compensation for 8000' (chart didn't go any higher) with 160PSI as good pressure at sea level, you get 125PSI (corrrection factor X 160) as good, so at 9000' I figured they were OK #'s except # 4. The valve lash was checked and adjusted cold then hot last summer and I really don't think they could have changed much if any with less than 1000mi on it since then, but I can always re-check(when it gets above 20° in my garage).

Edited March 25, 2015 by mjr45

[240260280z]

Thanks. That sounds fine.

So pictures of the plugs side-by-side would be the last item to review.

[Zed Head]

 

Captain, there is no altituce switch but there are 2 wires hanging by the ECU that I suspect is for this.

 

Those are diagnostic wires, apparently.  The wiring diagram says "Control Unit Checking Terminal".

 

I can feel the frustration in this thread but I still don't see any measurement of actual mileage, and can't see any problem based on the information supplied.  If gas mileage was not raised as an issue, a person could look at all of the measurements, pictures and part descriptions and would say "congratulations, your engine is running as well as it ever will".  I just can't see anything to fix.  The plugs in Post #78 look fine, except for two that look rich.  But the others will probably go too lean if you make changes to overall engine tune.

 

If you could get to flat land, fill your tank, drive a 100 or mile miles, refill and calculate mileage, that would be a good "calibration" check against the rest of the world.  You're up in the mountains, climbing some hills, and might have unrealistic expectations.

[mjr45]

Zed, I'll get you some real milage figures soon, I'll fiil'er up again and get actual milage, can't for the next couple of days, it's SNOWING AGAIN and I don't drive her in the snow. I agree that by looking at all the #'s the plugs, etc. it looks like its running well and it does except for bad MPG. Where is Washington County? Our oldest son is moving to Astoria, leaving sunny Maui for the Oregon coast. You may right in that I have unreal expectations of MPG.

 

Blue, check the pic in post #78.

 

Thanks

Mike

Edited March 25, 2015 by mjr45

[mjr45]

Zed, I filled up today and got 12.3/mpg, but the car is running well so I think I'm just gonna live with that alesat for awhile.

Mike

[240260280z]

A winter thought: Is the thermostat working and keeping the engine hot? A cold engine burns a lot of fuel and runs rich.

[superlen]

It sounds like you've covered a lot of bases. I think I'd drop back to dead simple basics for your MPG issue.

 

1. Check compression

2. Adjust/check the valves

3. Timing, ignition (new plugs)

4. Gearbox/rearend oil (mine was installed my Moses )

5. bearings/wheel drag

 

After that, then go back to fuel delivery issues.

 

The high RPM problem you mentioned i don't think is related, but sounds ECUish or maybe AFM. I don't remember if it was mostly rpm related or load related. Load related points to AFM.  RPM regardless of load is an ECU issue, Also, really triple check your ignition. The ECU gets it's primary fire signal from the flyback on the positive side of the coil. It's possible that this signal is breaking up at the higher RPM & confusing the ECU (it could miss a pulse and go lean, or see multiple pulses and go rich). Note: the coil could still fire the plugs normally, but the flyback through the primary and what ultimately shows up at the ECU input could be funky. A quick check would be to try a new coil and/or ignition module. Even new plugs might fix this if thats the problem. Note: I wouldn't normally think this as a possible solution, but when you try the normal culprits and it's still broke, we get creative.

 

Len

[mjr45]

Blue, it runs a little cool with outside temps in the mid 60's, but not overly cool at least I don't think it is.

 

Len, when its gets a little warmer I'll go back and recheck all the things you listed. On the ignition stuff, I really need to replace some of the wiring at the coil which I think may be a little funky. Thanks

 

Mike