1986 Xj6 SIII engine not compensating for AC compressor
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From: Los Angeles
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.
KirbertAuthor of the Book, former owner of an '83 XJ-S H.E. Oct 2019
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."
Rgds
David
KirbertAuthor of the Book, former owner of an '83 XJ-S H.E. Oct 2019
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."
Rgds
David
I will certainly check this! I originally thought the damper was failing when the timing would wander before I had the distributor rebuilt. Since the rebuild, I have checked the timing a few times and it isn’t wandering anymore. So I ruled out the damper; however, perhaps it’s still an issue and probably would be a good idea to replace regardless as in my opinion it’s a bit foolish to expect much out of nearly 40-year-old rubber. I will look into that and I’ll check the depth. Do you have a part number or link to the correct damper? Really great suggestions, thank you. I will keep you posted.
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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.
https://www.amazon.com/Fused-Relay-1.../dp/B07P6SBGWJ
I will defer to Doug for addition long shots at this problem
Rgds
David
- 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.
https://www.amazon.com/Fused-Relay-1.../dp/B07P6SBGWJ
I will defer to Doug for addition long shots at this problem
Rgds
David
This is also a good suggestion. I have a spare CTS. I will try this and the rest of these as well!
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From: San Francisco, CA
Me too
I have an 1986 Xj6 Base and had the same problem. To some extent, it still drops more than I like with AC on, but the idle smoothed out substantially when I did the o2 sensor upgrade described in https://www.jag-lovers.org/xjlovers/xjfaq/3wireo2.htm
It has a ground wire and heating wire. I also worked hard on cleaning up the ground wires throughout the whole car, and that might have been the main issue. Grounds were really corroded.
Though the idle is smoother than its even been, it still drops 150-190 or so with the AC on.
It has a ground wire and heating wire. I also worked hard on cleaning up the ground wires throughout the whole car, and that might have been the main issue. Grounds were really corroded.
Though the idle is smoother than its even been, it still drops 150-190 or so with the AC on.
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I have an 1986 Xj6 Base and had the same problem. To some extent, it still drops more than I like with AC on, but the idle smoothed out substantially when I did the o2 sensor upgrade described in https://www.jag-lovers.org/xjlovers/xjfaq/3wireo2.htm
It has a ground wire and heating wire. I also worked hard on cleaning up the ground wires throughout the whole car, and that might have been the main issue. Grounds were really corroded.
Though the idle is smoother than its even been, it still drops 150-190 or so with the AC on.
It has a ground wire and heating wire. I also worked hard on cleaning up the ground wires throughout the whole car, and that might have been the main issue. Grounds were really corroded.
Though the idle is smoother than its even been, it still drops 150-190 or so with the AC on.
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From: San Francisco, CA
I would defer to the pros here. I'm not sure it was the sensor or if the cleaning of ALL grounds was responsible for the improvement. Properly grounding both the o2 sensor along with the engine and the rails seems to have helped me in many ways.
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From: Pacific Northwest USA
I think the original intent of the heated 3-wire sensor was to get the system into closed-loop operation sooner and to keep it in closed-loop operation during conditions where it it might fall into open-loop. This is most likely to happen at idle where the exhaust temp might be a bit cooler. Some cars are more prone to this than others. It's a fair guess that this was done to meet emissions standards. Any improvement in general running is a bonus.
Adding a redundant ground to a 1-wire sensor is an old trick used on many cars as a cure for lazy O2 sensor performance.
We should probably talk about the capacitor mod as well. It was designed to cure a specific over-fueling fault but many reported better overall running.
Cheers
DD
Adding a redundant ground to a 1-wire sensor is an old trick used on many cars as a cure for lazy O2 sensor performance.
We should probably talk about the capacitor mod as well. It was designed to cure a specific over-fueling fault but many reported better overall running.
Cheers
DD
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From: Pacific Northwest USA
I doff my cap 
Over the decades I've read the trials and tribulations of those before you trying to achieve the same thing. The level of dedication was admirable.
Until buying my 2005 S-type every Jaguar I've owned (there have been several) has suffered some sort of idle quality issue despite considerable efforts and expense on my part. It rankled me to no end for years. I eventually threw in the towel ....and did so a lot sooner than many others.
But that doesn't mean you should !
Cheers
DD
Over the decades I've read the trials and tribulations of those before you trying to achieve the same thing. The level of dedication was admirable.
Until buying my 2005 S-type every Jaguar I've owned (there have been several) has suffered some sort of idle quality issue despite considerable efforts and expense on my part. It rankled me to no end for years. I eventually threw in the towel ....and did so a lot sooner than many others.
But that doesn't mean you should !
Cheers
DD
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From: Edmonton, Alberta, Canada
^
Doug,
I have owned three Series 3 VDP’s. an ‘87 and two ‘92’s, one of which was a daily driver for 15 years and happily did road trips as long as 3,000 km. The current daily driver is an ’01 XJR. All four of them idle(d) as smooth as silk in neutral and in drive.
Doug,
I have owned three Series 3 VDP’s. an ‘87 and two ‘92’s, one of which was a daily driver for 15 years and happily did road trips as long as 3,000 km. The current daily driver is an ’01 XJR. All four of them idle(d) as smooth as silk in neutral and in drive.
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From: Pacific Northwest USA
Braggart
I will say that my V12 Jags have given me the fewest idle quality problems. Generally quite smooth. Occasionally not. I've never been able to discover the fault.
The Series III XJ6 was the worst. It generally idled well but was always subject to momentary "idle tremble" for all the years I drove it. Passengers would never notice but I surely did.
My XJR/6 interestingly idled rough only in "P" or "N". This was due to injectors responding lazily to low pulse width operation.
Cheers
DD
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Apologies… It was also a V12. I should have mentioned that but forgot that while all VDP's in Canada were V12’s but the badge was also used on some US 6’s.
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