XJ6 & XJ12 Series I, II & III 1968-1992

Adjusting injection for high altitude

 
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Old 08-13-2011, 10:41 PM
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Default Adjusting injection for high altitude

My 83 xj6 owner's manual says to have dealer adjust f/i for operating over 3000 ft. We are at 4200 ft. Here.does anyone know what that operation is and how to do it? Thanks
 
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Old 08-14-2011, 01:03 AM
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No manual adjustments for altitude that I'm aware of, but don't take mine as the final word.
There's a screw adjustment on the AFM but it's for idle mixture only.

Many Ser IIIs ....can't remember the exact details....have a high altitude compensator device installed....it's on the forward wall of the trunk. If yours has one it'll be near the ECM, round-ish, with two wires.

Cheers
DD
 
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Old 08-14-2011, 11:35 AM
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Thanks for your input doug, no sign of compensator. Car spent it's life at low altitude until i got it. I was hoping to find some reason for sluggishness. If you saw my other post about that topic after installing new fuel filter, cap and rotor it literally runs worse. I'm going backwards here! Already did plugs, replacing plug wires next to eliminate some problem sources. Thanks again.
 
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Old 08-14-2011, 04:27 PM
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In theory, no air/fuel adjustment is needed because the EFI system measures mass air flow, so automatically compensates for height unlike carburettors. So the mixture will be the correct ratio, but as the air is less dense at height, engine power will be reduced due to less mass air flow through the engine, the higher you go the less the power.

However, nothing is ever simple, but I would have thought your sluggishness is due to other causes, as 3000 feet is a lot less than the altitude of Denver where there must be thousands of cars being driven around without any sluggishness.

Aircraft piston engines usually use a supercharger to compensate for lower air mass, but of course, planes tend to fly a lot higher than 3000 feet
 
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Old 08-14-2011, 06:47 PM
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Fraser, you are absolutely right. I reread manual, says for continued operation over 4000 ft, take to dealer "for minor tuning adjustment". I am really stumped by this. I put in a new fuel filter, cap and rotor, and it really ran worse! Idles and free revs fine, but has no power under load. Still feels like timing to me but may be fuel. I think i'll repost with different description of problems. Thanks again,terry
 
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Old 08-14-2011, 06:52 PM
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I'm not sure what the "minor adjustment" would be but, whatever it is, it won't make Denver air as dense as sea level air.

Have you driven yours at sea level? How does it behave?

Cheers
DD
 
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Old 08-14-2011, 09:48 PM
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Doug, now i,m thinking it was probably just a idle mix tweak. I've never driven it at sea level, bought from friend of a friend. Had it shipped to our place in alpine,tx (5000 ft and 5000 people) ran smooth but just no snap at all. Two days after we got it a/c hose failed and we hardly drove it . We also lived 5 miles down dirt and gravel road and i just could not stand abusing it. Different deal here in las cruces. We want to drive it, but not running as poorly as it does. Buying new plug wires and timing light tomorrow. I looked at the clamp bolt on dist. Gonna be fun getting something on that! Thanks again, terry
 
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Old 08-29-2011, 04:53 PM
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terry,
ive been chasing the same issue for about a year or so off and on. By no means am i a mechanic but can stumble my way around decent enough. Ive gone through plugs, wires, cap and rotor, fuel pressure regulator, fuel pump, filter, vacuum lines, and just today replaced coil and resistor. i just got off the phone with Dr. Jag here in Albuquerque and he recommended checking the fuel temp sensor on fuel rail. Said it should read 250 ohm when motor reaches 90 degrees c. or in the middle of gauge. Now the issue you are having is the same issue ive been chasing except mine has progressed to the engine dying out and will not start till cools down. figured id share the info maybe save you alot of un needed stress lol. oh also changed in-tank gauze filters. The other issue that may be causing the sluggishness is the cheap gas we have here in N.M. 10% or more of ethanol per gallon. ITS CRAP!!!! i may be on the wrong track all together so if anyone else reads this let us know if you have any other input.

Matthew Rinaldi
Rio Rancho NM
85 xj6
 
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Old 09-07-2015, 09:29 PM
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Originally Posted by Jagvirgin View Post
...I reread manual, says for continued operation over 4000 ft, take to dealer "for minor tuning adjustment"....

Did any one ever find what the manual meant by this and how to perform the "minor tuning adjustment"?
 
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Old 09-07-2015, 11:40 PM
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Originally Posted by rinaldi63 View Post
Dr. Jag here in Albuquerque and he recommended checking the fuel temp sensor on fuel rail. Said it should read 250 ohm when motor reaches 90 degrees c. or in the middle of gauge.


On a Series III with a 4.2 the fuel temp sensor is a vacuum switch only. No electrics; no ohms to check.



Now the issue you are having is the same issue ive been chasing except mine has progressed to the engine dying out and will not start till cools down.


Both the ignition coil and ignition module are known to give trouble when hot and return to normal after a cool down



The other issue that may be causing the sluggishness is the cheap gas we have here in N.M. 10% or more of ethanol per gallon. ITS CRAP!!!! i may be on the wrong track all together so if anyone else reads this let us know if you have any other input.


That's not it. A Series III Xj6 will run fine on E10. We've had nothing but E10 up here for 20 years. All my Jags run fine on it. Now, stale or contaminated fuel might be worth discussing!

Cheers
DD
 
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Old 09-08-2015, 03:14 PM
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Originally Posted by Doug View Post
I'm not sure what the "minor adjustment" would be but, whatever it is, it won't make Denver air as dense as sea level air.

Have you driven yours at sea level? How does it behave?

Cheers
DD
Could they be adjusting long term fuel trim at the ECU? If the car arrives at altitude as in a dealer delivery it would be one way to make it run well quickly vs learning.
 
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Old 09-08-2015, 04:28 PM
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On these old 1970s-1980s Bosch systems there is no "learning", no LTFT or STFT, etc.


Cheers
DD
 
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Old 09-08-2015, 09:26 PM
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Having a reverse time warp, normally I fail to know about advances, now I am trying to give older cars modern features.
 
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Old 09-09-2015, 02:00 AM
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Terry:


Welcome. I was born and raised in a town just a hop, skip and a jump from there.
went there or through there I cars of many specie. Never noticed any loss of power. As a kid, exploring the Organ Mountains was great adventure. And, never realized the altitude.


In uncompensated cars, the mixture goes rich. Same fuel amount, less air. Although the mixture in our T Fords was manually adjustable, we never bothered.


E10 is all there is around here. I've never attributed any engine ills to it.
But, my present LT1 powered S3 and the 4.0 Jeep run great on it I sense no loss of power on going into the mountains. Oops, fairly sophisticated PCM's in each.
Old fuel seems OK as well.


Now, my little one cylinder engines insist on fresh fuel. The two cycles do besat on the price ethanol free mix I buy at the Hdwe store.


Do you suppose the old filter in your car caused a lean mixture and it blended well with less dense air. and, now, with a clean filter, it gets a full dose and has gone rich.


And, timing vs altitude has a relation. But, I think it is in octane required. Forgot just how at this time.


Dirty air filter???? M ixture rich as a result? Blanced by a dirty fuel filter?


Carl
 
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Old 09-09-2015, 07:28 PM
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the altitude adjustment is a gold-anonized "valve" located on the passenger side of the trunk, mounted inside sort-of below the passenger side fuel filler, with two red wires coming out of it.

As I recall the so-called "minor adjustment" entails connecting OR disconnecting both wires from the harness, but I remember early on after I purchased my XJ-6 and started to ask stupid questions, my mechanic telling me to "leave that thing alone unless you move to Mount Everest" ???

there is no documentation for it that I am aware of, just like there is no documentation for the electronic purge valve after the charcoal canister in the early Service Manuals, but then in the revised Service Manuals it is shown.
 
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Old 09-10-2015, 11:59 AM
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Idea for thought. Ethanol will eat the rubber hoses from the inside out, so in turn it is POSSIBLE that a piece of the rubber hose is blocking the flow at a reduction point. I have not seen it on a car from the 80's but most of the 70's and older, i would go thru and replace all the fuel hoses.
Im not saying this is the case here but I have seen these issues in other cars, (mainly carburated) and replacing the hoses stopped the issues.
 
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Old 09-24-2015, 05:58 AM
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Was an answer ever found for this? It was an interesting problem and lots of suggestions were offered. Would be good to know what the issue was if it was corrected.
 
 
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