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

 

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

 

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.

 

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

 

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

 

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

 

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

 

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

 

Did any one ever find what the manual meant by this and how to perform the "minor tuning adjustment"?

 

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





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





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

 

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.

 

On these old 1970s-1980s Bosch systems there is no "learning", no LTFT or STFT, etc.


Cheers
DD

 

Having a reverse time warp, normally I fail to know about advances, now I am trying to give older cars modern features.

 

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

 

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.

 

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.

 

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.

 

Okay. This is now making sense. My '83 XJ6 came to me with a couple of random pink wires coming out of the harness in the trunk that were stripped and just twisted together. I inadvertently and unknowingly snagged them when I was refitting the RH side panel in the trunk. The car would barely run and after a couple of days of troubling shooting I found the wires again, reconnected them and all was well. But I needed to know what the wires were. I found an electrical troubling shooting set of drawings. Jaguar publication, but each system separated, and on this set an "altitude switch" is identified as located in the trunk. I'll attach the diagram. Note the connections are 2 pink wires that run between the air flow meter and terminal 9 on the ECU and a pink-blue wire going to terminal 12 on the ECU that is identified as "high altitude signal". I found that the KU wire is also there as a female bullet connector with nothing plugged in.

So apparently the ECU has functionality to modify the air-fuel mix based on a barometric switch the is normally open and closes at some altitude, perhaps the 3000ft elevation noted in the thread. Since it is designated a "switch" I have to assume it is a open or closed device rather that a linear resistance input tracking altitude. The dealer modification could be simply jumping the KU and K wires together on cars destined for Denver or other higher climes. The Denverite who started this thread years ago could try that if he still has the car. Perhaps even fit a manual switch in case a trip from the mountain ever takes place. The switch itself was apparently not fitted often. It is not depicted on the big factory wiring schematic, nor is it shown in the factory parts manual or mentioned in the factory service manual.

So my mystery is resolved. Incidentally, my unattached pink wires opened the signal from the air flow meter to the ECU, and the ECU interpreted this as infinite air coming into the engine and went to full rich mixture, staggering and belching black exhaust. How they came to be separated is lost to the ages but now reunited and fully understood.

 

Jaguar relied heavily on supplemental publications to convey info on many changes and market-specific specifications. Technical Service Bulletins, dealer training guides, and the like. The diagram you posted, for example, is from the "S57" series of electrical guides for the USA market cars

Cheers
DD

 

Yup. S57 is the document. I don't recall where I found it, but it is very helpful, much more so than the full schematic. However it is the US configuration. I converted the lighting on mine to european configuration, including larger main beam lights with the internal running lights and fog "rear guard" lights. It all works and was basically plug into the existing harness, but I don't have the appropriate schematics.

I did a bit of research and found that the pressure difference between sea level and 3000ft is about 1.5 psi. As it happens this is also the range of pressure that is used to check for air flow in swimming pool heaters. I found an adjustable air flow switch with a standard micro-switch attached with both NO and NC contacts. I'm going to get one and see if I can adjust it such that the contacts are open at sea level and close as the diaphragm relaxes by 1.5 psi at 3000 ft altitude. If it does we have a replacement for the elusive altitude switch in these cars.

Can any one confirm that the original intent and programming in the ECU is looking for a 3000ft signal? Or is it another altitude?