No, it won’t. Air leaks do exactly the same thing as opening the butterflies a bit. Engine speeds up.
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Yes, but what is then the purpose of the vacuum sensor in the ECU?
TPS is giving throttle data
Air and Coolant Temp sensors give temperature data
Ignition Amplifier gives timing / RPM data
Isn’t vacuum, i.e. engine load, also one of the parameters that the ECU is regulating fuelling with?
And wouldn’t a leak affect the vacuum reading at the ECU?
Is there something lost in translation with my notes?.. also the part number seems to be wrong.
I found an other set of values, apparently from SD Faircloth.
Temperature vs. Resistance
0 C 32F 5.9 kohms
10C 50F 3.7 kohms
20C 68F 2.5 kohms
30C 86F 1.7 kohms
40C 105F 1.18 kohms
50C 122F 840 ohms
60C 140F 600 ohms
70C 158F 435 ohms
80C 176F 325 ohms
90C 194F 250 ohms
And, does the 6 and the V12 have the same sensor?
It’s the main parameter
In the same way as opening the throttle. Consider the opening and closing of the throttles to be a driver controlled vacuum leak. You could pull off a couple vacuum hoses and let more air in, or open the throttles and let more air in. Either way the engine speeds up; the ECU can’t recognize, and doesn’t care, where the air is coming from.
It would be different in a system with an air flow sensor or air flow meter. In that case the amount of incoming air is being measured and reported to the ECU. The ECU fuels according to that measurement. A vacuum leak in that case would be adding extra air that the ECU is not aware of; unreported air. The mixture would then be incorrect.
On our V12s the amount incoming air is not measured or reported
Cheers
DD
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^^^^ this is what I’ve found in both my XJS and Series III manuals for the V12. And the 6-cylinder Series III shows the same values but broken down to 7 step rather than 10
Cheers
DD
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The Manifold Pressure Sensor provides a load signal; the ECU will alter pulse rate based on vacuum and RPM, and temperature. The TPS tells the ECU what is being requested, and whether the engine is at idle. Non feedback systems (no oxygen sensors) should be easier to diagnose.
Find your misfire, verify sensor readings, and make adjustments, no one has mentioned ignition timing; if retarded can raise combustion temps- possibly a failed vacuum advance canister?
Robert,
With the vacuum disconnected from the distributor vac advance the timing is 18 degree BTD. Warm engine with vacuum attached to the advance is, from memory here, about 23 degrees BTD.
Also with vac connected to the advance and engine cold, 18 degree BTD.
Thank you.
Jaye
That sounds about right. I would then focus on the misfire first which may correct the NOx issue.
Robert, et.al.
Right after fixing the known vacuum leaks I will pull the injectors and the spark plugs to see first-hand how they operate and of course expect one cylinder will deviate considerably.
Small bit of trivia about my 1984 Sovereign, the fuel rail was changed at the time the catalytic converters were installed due to a factory issued call to change them. Seems the original used a round metal tubing and the replacement used square tube.
Thank you for the continuing information I receive.
Jaye
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That’s the values given in my manuals, Aristides. And, yes the values are the same for both the xk and the V12…
Frank
xj6 85 Sov Europe (UK/NZ)
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That is spec’ed at 3000 rpms, Jaye…
Frank
xj6 85 Sov Europe (UK/NZ)
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That should be ‘pulse width’, Robert, not ‘pulse rate’ - the injection is triggered once every engine revolution.
But you are right about ignition timing; it should be included in list of suspects…
Frank
xj6 85 Sov Europe (UK/NZ)
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Did the fuel pressure regulator(s) come with the new rail, Jaye…?
With a fueling issue it is important to check fuel pressure. And since you are removing the spark plugs anyway; run a compression test. It tells a lot about the engine state - and a misfire may be a compression issue…
Frank
xj6 85 Sov Europe (UK/NZ)
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You are correct, that was what I meant to say. Owner has indicated timing and it sounds correct.
Frank has a good point; the 18 degrees BTC is at 3000 with vacuum disconnected from distributor. This results in about 4degrees advance at idle with no vacuum- connecting the vacuum should add about 10 degrees (because of a vacuum reducer). Don’t know about cold, as the catalyst cars defeat the vacuum advance for a period on start.
Frank,
The exchange was made before I purchased the car. The new rail has two regulators, which due to gross fuel contamination about 10 years ago I had to replace. [ when I drained the two fuel tanks they yielded dove-gray colour contents. ]
Jaye
Interesting point here:
At idle, I have 18 degree BTD when I disconnect the vacuum. I will check at 3000 RPM.
Thank you
Hmmm. Possible this crud has crudded up the injectors, resulting in lean running? Or possibly crudded up the screens at the injector inlets?
If the same, it could be caused by a seized centrifugal advance mechanism (common). Outline and fix is in Kirby Palm’s excellent book on the XJ-S. Does the ignition advance when vacuum is applied to the distributor? If not, the diaphragm in the advance unit could have failed also (common).
Not sure why, but a couple of my replies have bounced back with a ‘sorry… limited to embedded media…”
Would someone, perhaps the moderator please let me know why this is? Not clear to me.
Thank you.
Jaye