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1986 Xj6 SIII engine not compensating for AC compressor
My 1986 XJ6 isn’t compensating for the compressor turning on. The car idles smoothly when the compressor is off, but when it turns on, my engine drops about 200 RPMs and stays there until the compressor kicks off. This causes a rough idle. Any idea why the engine isn’t raising its engine speed when the compressor kicks on to compensate for the drop?
Dakota, My 85 does the same thing. I do not believe that the Jag has a "compensating" system (like modern cars do). I am toying with adding some "extra air intake" solonoid valve thats leans out the mixture when the Compressor kicks on. Got to figure out some port past the butterfly valve to boost the engine speed. Still trying to wrap my head around this. Ian
Jaguar had a kit that added the extra air solenoid as you mention. I think this system was factory fitted on a very few models in the mid 80s for certain Middle East markets....or something like that. I've never seen one. A million years ago the kits would come up on Ebay from time to time.
[QUOTE=iramphal;2832624]Dakota, My 85 does the same thing. I do not believe that the Jag has a "compensating" system (like modern cars do). I am toying with adding some "extra air intake" solonoid valve thats leans out the mixture when the Compressor kicks on. Got to figure out some port past the butterfly valve to boost the engine speed. Still trying to wrap my head around this. Ian[/Ian, let me know how that goes because I would really like to find a way to boost the RPMs when the compressor kicks on. Doug is right; the kit he is talking about isn’t possible to find. Is there any way to boost the “in gear” idle speed but not the “park” idle speed? What controls the in gear idle speed? If I could boost the in gear RPMs just a bit, but not affect the “park” idle, it could better compensate for the compressor. My idle is about 90%, which I’ve been told is really good for these cars. I’ve put so much work into the idle, and I’ve reached the end of the road, scratching my head with nothing left to do to try and smooth it out. It seems to be as good as it can get, and it’s certainly tolerable, but the compressor doesn’t play nice.
Jaguar had a kit that added the extra air solenoid as you mention. I think this system was factory fitted on a very few models in the mid 80s for certain Middle East markets....or something like that. I've never seen one. A million years ago the kits would come up on Ebay from time to time.
Doug thank you for sharing this it is great to have.
s there any way to boost the “in gear” idle speed but not the “park” idle speed? What controls the in gear idle speed?
Idle speed is controlled only by the adjustment at the air distribution block. All that happens with this adjustment is letting more, or less, air into the engine. The system does not "know" if the transmission is in "P" or "D"......just as it doesn't "know" if the A/C compressor is engaged.
If you wanted to fit an extra air solenoid the circuit could be tied-in with the neutral safety switch and an added relay. The neutral safety switch could defeat the extra air solenoid when the transmission is in "P" or "N"
Idle speed is controlled only by the adjustment at the air distribution block. All that happens with this adjustment is letting more, or less, air into the engine. The system does not "know" if the transmission is in "P" or "D"......just as it doesn't "know" if the A/C compressor is engaged.
If you wanted to fit an extra air solenoid the circuit could be tied-in with the neutral safety switch and an added relay. The neutral safety switch could defeat the extra air solenoid when the transmission is in "P" or "N"
Cheers
DD
thank you Doug where could I locate an extra air solenoid for this?
Yes, that's what I was thinking of. Depending on cost I'd experiment with a used one though. And now that I think about it they may use a PWM voltage from the motronic ecm to maintain the opening but may just be 12v of/on when needed. Better look into that first, check any 80's bmw serv manual, or forum.
Yes, that's what I was thinking of. Depending on cost I'd experiment with a used one though. And now that I think about it they may use a PWM voltage from the motronic ecm to maintain the opening but may just be 12v of/on when needed. Better look into that first, check any 80's bmw serv manual, or forum.
does this valve not serve the same purpose as the Extra air valve that on the car from factory EAC3883?
This is an idle-up device used on many V12 Jags. Part number EAC4161. Google that number and see what comes up. You should be able to find a good used one. It can be plumbed as shown in the Jaguar bulletin I post a couple days ago. I'll work out a simple wiring diagram for you and post it
Another thought "Low power at Idle": See attachment. A long stroke straight 6 engine should not bog down when moving transmission from Park to Drive, or 200 RPM drop when A/C comes on.
Idle timing off the sweat spot, or idle mixture off sweat spot will give low power. Many potential issues with timing: Vac advance diaphragm leak, sticky advance mechanism, Vacuum regulator acting up, incorrect Initial timing. Weak idle mixture from vacuum leak (when above 1500 RPM O2 sensor will add fuel to overcome small Vacuum leak). CTS sensor on water rail can give incorrect temperature related mixture advice to ECU. The difficulty on correct idle mixture is the manual tells you on a fully warmed engine, stick a CO sensor up tail pipe and adjust mixture screw on AFM to achieve 1% CO. The dealers had CO sensors, but the average Jaguar owner-maintainer does not.
Many threads on timing and vacuum leaks, and adjusting the idle mixture on AFM; It is process of elimination.
( My 1984 XJ6 S3 idle is set at 825 RPM when fully warm in Park, and will settle in at 700 to 720 when moved to Drive with A/C on.) ( It is a US/Ca. spec. low compression engine that specified 87 octane when new)
Rgds
David
Base timing on a USA '86 should be 17ºBTDC with vac advance disconnected.
Over the years some have success with richening the idle mixture. As built these systems were set pretty lean. This would be more like masking a problem than solving it....but if a little mixture tweak will make the engine happy I'd be willing to shrug my shoulders and smile :-)
If not already mentioned make sure the throttle body is clean.
If the idle speed adjustment and/or mixture adjust have no effect it suggests that something is rotten in Denmark and merits checking.
With age and mileage there can be gradual degradation of.....everything. Injectors might be a little clogged. AFM tracks a little worn. Etc. IOW, a 'stack up" of small faults.
I've often wondered if an elderly a/c compressor might, for some reason, cause more parasitic drag. Same for the transmission....or torque converter.
As long as we're throwing out ideas a compression test wouldn't be a bad idea.
Another thought "Low power at Idle": See attachment. A long stroke straight 6 engine should not bog down when moving transmission from Park to Drive, or 200 RPM drop when A/C comes on.
Idle timing off the sweat spot, or idle mixture off sweat spot will give low power. Many potential issues with timing: Vac advance diaphragm leak, sticky advance mechanism, Vacuum regulator acting up, incorrect Initial timing. Weak idle mixture from vacuum leak (when above 1500 RPM O2 sensor will add fuel to overcome small Vacuum leak). CTS sensor on water rail can give incorrect temperature related mixture advice to ECU. The difficulty on correct idle mixture is the manual tells you on a fully warmed engine, stick a CO sensor up tail pipe and adjust mixture screw on AFM to achieve 1% CO. The dealers had CO sensors, but the average Jaguar owner-maintainer does not.
Many threads on timing and vacuum leaks, and adjusting the idle mixture on AFM; It is process of elimination.
( My 1984 XJ6 S3 idle is set at 825 RPM when fully warm in Park, and will settle in at 700 to 720 when moved to Drive with A/C on.) ( It is a US/Ca. spec. low compression engine that specified 87 octane when new)
Rgds
David
Originally Posted by Doug
Good info, David.
Some random remarks....
Base timing on a USA '86 should be 17ºBTDC with vac advance disconnected.
Over the years some have success with richening the idle mixture. As built these systems were set pretty lean. This would be more like masking a problem than solving it....but if a little mixture tweak will make the engine happy I'd be willing to shrug my shoulders and smile :-)
If not already mentioned make sure the throttle body is clean.
If the idle speed adjustment and/or mixture adjust have no effect it suggests that something is rotten in Denmark and merits checking.
With age and mileage there can be gradual degradation of.....everything. Injectors might be a little clogged. AFM tracks a little worn. Etc. IOW, a 'stack up" of small faults.
I've often wondered if an elderly a/c compressor might, for some reason, cause more parasitic drag. Same for the transmission....or torque converter.
As long as we're throwing out ideas a compression test wouldn't be a bad idea.
Cheers
DD
Thank you guys for your remarks and suggestions. At this point, so much has been done to curb this idle issue, and all have improved it but not solved the issue. Steps taken have been: Valve clearance checked (measures correct: 0.013)
Timing chained tightened
Injectors removed including cold start, rebuilt by “SD FAIRCLOTH Jaguar injector service in FL.” All “top hats and seals replaced along with it
all water rail sensors replaced, including CTS EGR with a brand-new Jaguar (or if Jaguar was unavailable, a brand of equal quality)
all Plugs wires replaced
compression checked and is sufficient
distributor and ignition amplifier rebuilt by “ADVANCED DISTRIBUTORS.”
Timing set to 17 BTDC
all soft fuel lines replaced
fuel pump, fuel tanks, fuel filter replaced
thermostat replaced
transmission rebuilt (Greer Westover)
torque converter rebuilt. ( same idle issue before trans replacement idle was unaffected)
Extra Air Valve replaced
ignition coil replaced (Lucas)
oxygen sensor replaced (Bosch)
motor mounts replaced
vacuum smoke test completed; all vacuum leaks repaired, including cruise control bellows and various vacuum lines engine dipstick seal filler cap seal etc (there are no current vacuum leaks in the system
fuel regulator replaced all
rubber hoses to and from AFM throttle body have been replaced
afm swapped to another AFM I own (car runs worse with the other AFM)
throttle body butterfly confirmed: 0.02
This is all repairs I can think of that could play a role in the idle off the cuff though I’m certain there’s more if I review my spreadsheet of repairs.
Any suggestions would be appreciated.
Car is a daily driver that sees about 500-700 miles a week.(Which I never ever expected to happen, but I can’t put into words my love for the car, even though it has tortured me countless times, which I'm sure you all experience as well.) It runs beautifully and starts at the turn of the key immediately every time. The cooling system is optimal, and the car never experiences anything more than very minor temperature fluctuations in bumper-to-bumper Los Angeles traffic.
It’s come a long way, and after over 100 separate repairs since September 2024 it’s finally gotten where I can actually drive it and not think about it because it just works. I’ve “almost” turned her into a Mercedes.
If I could just solve this idle so I’m not bouncing at a red light, I can finally hibernate into a long rest...maybe..lol
You have done a lot of work, not many squares left on the bingo card.
- take a spare CTS sensor with you on next run in LA traffic, with A/C on and RPM dropping; pop hood and remove wires from CTS, hook wires to room temperate spare CTS, wrap in shop rage and lay on inside of water rail. Test car to see if you get any improvement. A cool CTS will increase fuel richness at idle.
- Try by-passing the Vacuum regulator to the Distributor Vacuum advance, cap existing line at distributor and hook new temporary vacuum line to Manifold vacuum.. you may need a Tee fitting. This should give a few more degrees advance at idle (all UK cars were hooked to manifold vacuum)
- Long shot .. Clean over run valve and turn nut a few turns to increase spring tension.
- If your smog shop in LA is friendly, they may let you hook up CO tail pipe tester, with unit in test mode and you can adjust CO to 2 with screw on AFM.
- Over serviced A/C system??
In the end, you may have to continue with your one-off extra air valve installation that opens any time power is supplied to A/C compressor clutch. Install relay, so clutch power closes relay that sends power to Extra Air Valve. Valve must be normally close, open with power on.
Another long shot: Timing pointer miss-set in past"There are two reasons for TDC pointer misalignment at zero; pointer may be bent out of position (or miss installed after timing case removal) - or the vibration damper, which carries the scale, may be adrift. This may happen when the damper rubber deteriorate.
If you have a suitable depth gauge, the best way to determine that you are precisely at TDC on #1 and #6 is to measure the height of #2, #3, #4, and #5. All four should be exactly the same.
This method is more accurate because those four pistons are in the midst of a stroke so even a hair off would make a big difference. #1 and #6 at at the top of a stroke where the piston is nearly stationary, so a little this way or that barely registers."
When checking the ignition timing at idle does the reading jump up-down? If so, it may be a worn distributor. Just tossing that out as another thing to look at.
Anyhow, here's a diagram that I think will work for your air valve, using two relays
When checking the ignition timing at idle does the reading jump up-down? If so, it may be a worn distributor. Just tossing that out as another thing to look at.
Anyhow, here's a diagram that I think will work for your air valve, using two relays
Cheers
DD
nice! Thank you so much! I acquired an EAC3883 yesterday hopefully I can get this wired in properly
Yes it actually was doing that the reading used to jump that’s where I realized I needed to have it rebuilt after the rebuild it no longer jumps.
1986 Xj6 SIII engine not compensating for AC compressor
