I have two issues with my 1984 XJ6. Both only occur when the car has run for a few minutes. When the car is cold or up to temperature the car runs fine.
About when the temperature gauge moves, the car acts like it is fuel starved. Poor acceleration.
At idle, the idle will fluctuate between 0 to 800 rpm.
I have checked the CTS and the wiring for the CTS sensor - I replaced the ground as it looked suspect.
I bench tested the CTS (ohms vs temp) and it checked out fine.
Any ideas?
Thanks!
David,
I have never encountered exactly what you describe with my 2 XJ6s, but something to investigate is the Auxiliary Air Valve (AAV). It should be open at cold start to allow additional air, and indirectly fuel, to get the engine running properly at a slightly higher RPM. Then as the engine warms up the AAV starts to close off reducing air and fuel until normal warm idle RPM is achieved. In addition to coolant rail heat the AAV has and electrical heating element inside to assist in valve closure.
If I had the problem you are describing I would remove, inspect and test the AAV as well as inspect the two AAV hoses for cracks, and security. The one beneath the intake manifold can be a challenge to remove and replace.
You didn’t mention it, but did your engine typically accelerate to about 1,100 RPMS on a normal feet-on-the-floor cold start and then gradually decelerate to idle (750-800) RPMs as the engine warmed up? If it did, then that was the AAV doing it’s job. Since it is not doing that now, I’d say the AAV is a likely suspect.
Paul
David,
I should have mentioned that Jaguar sometimes calls the Auxiliary Air Valve (AAV) the Extra Air Valve (EAV) depending on the model and document. The part number is the same, EAC3883, even though Jaguar calls it by different names.
Paul
Thanks Paul.
I will look at the AAV this evening.
What is confusing to me is when I connect the CTS wires together, the car performs properly. Good idle and good perfomance. This is when the engine is still warming up. Not cold, but not fully to temperature.
I will report back on my findings.
Thanks
David in Atlanta
David,
The Coolant Temperature Sensor (EAC3927 superseded by DBC3728) has been known to fail and the wiring to the sensor has also been a problem to many. I usually recommend against throwing parts at a problem but the CTS is a relatively inexpensive part ($30-40 US). If the AAV/EAV works properly and the two hoses look good you might try a new CTS to see if that fixes your problem. If it doesn’t, we’ll you have a spare CTS for the future.
Paul
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The CTS’s resistance vary with coolant temp to vary fuelling, David - the fuel mixture varies with engine temps, information provided by the CTS.
When you short the wires, fuelling goes to minimum - engine runs lean. When you pull the plug, resistance go infinite - max fuelling; engine running very fat.
The xk engine will start run OK with a wide range of mixture, and it may start cold and run reasonably even on a lean mixture unless the engine is very cold. Since you have already tested that the CTS gives correct readings there might be something wrong with the wire connection to the ECU - causing fat running. Engine will then increasingly misbehave as it heats up…
Depending on how you shorted the wires; the ‘short’ may bypass a break in the plug. Check for a break in the CTS wiring; disconnect plug and measure resistance between the wires, not inserting the probes too deep. Resistance should read around 2 Kohm - but more importantly; the reading should not vary when you bend and twist the connector and wires. A plain break will of course read ‘1’ on a digital meter - and a break is usually in the connector or the end of it.
A quick-test; with the engine idling, just pull the plug off the CTS - if the engine do not change, you have a break. To be located…
The AAV has a different function; it allows more air into the engine when it is cold - increasing idle to counter cold engine ‘drag’. The AAV is only relevant with the throttle closed - at higher throttle settings ample air is provided by the throttle. The AAV has no influence on fuelling - and its malfunction is only noticeable when starting and idling…
Frank
xj6 85 Sov Europe (UK/NZ)
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Im following this discussion as my 91 XJ6 does the exact same thing. Ive replaced the sensor, and it didn’t change anything. I also noticed while it is going through this rough idling, there will be some black smoke coming from the exhaust. This is in conjunction with a FF44 code that i haven’t been able to resolve…
Thanks all…
Did you measure your oxygen sensor, which is what ff44 indicates, did you clean your idle air valve (which might be electrical, and stuck), and your MAF; what about air leaks?
One car used to do this and it turned out to be the idle air valve. The car tried to compensate for the lack of air by overfueling thus the smoke; and naturally the mixture sensing device was blamed even though it indicated the correct value… as the IAV bypassed the MAF as far as I remember.
Brake cleaner or whatever did the job.
Try unplugging components one after another and see what changes; disconnect the battery in between is the usual answer for troubleshooting.
I could be wrong; however the methods are of course universal!
Marco,
Your 1991 XJ6 is a completely different car, with a different engine than the Series I, II, and III XJ6s and XJ12s that are discussed here. None of our cars were equipped with OBD or provide fault codes. Although your car is badged as an XJ6 it has its own list on Jag-Lovers, the XJ40 list. XJ40 was the internal Jaguar project code for the entirely new model introduced in the US in the 1988 model year. If you are looking for help with your issue I suggest trying the XJ40 list because that is where your model is discussed. Good luck.
Paul
will do,thanks anyway
I am happy to report that changing the CTS and the CTS connector largely rectified the problem. Idle is steady, and acceleration is smooth.
There is still a bit of a miss when the temperature gauge is just off the peg, but only when I floor it. Not quite sure what the issue is there.
Thank you Paul and Frank for your help!
David
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As you say, it’s not quite right, David - the engine should ‘take’ perfectly at any time…
There is a very specific issue if the engine misses, and exhaust smokes on acceleration while warming up - but it would do so at even medium pedal changes. So that’s probably not it?
Might be an ignition/timing issue…?
Frank
xj6 85 Sov Europe (UK/NZ)
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Well, I spoke too early.
The problem persists, except now it occurs when car is cold.
When cold, I have a good steady idle, put poor acceleration . Once the temperature gets warm, but not fully warm, the car performs properly. At temperature, it continues to perform well.
Over the course of several years, the following components have been replaced. All are in good shape.
Fuel pump
CTS and CTS connector
Spark plugs
Spark plug wires
I cannot think of any reasons why the car is misbehaving. Spark plugs are a nice tan. Ignition timing is correct, or close to it. I even swapped out ECUs (I have spares) to see if that was the issue. No improvement.
Where else can I look?
Thank you !
David
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Look at the exhaust when accelerating cold, David - if it is smoking; look up ‘capmod’ in the archives…
A ‘sometimes’ problem is arcing in the AFM as the wiper arm moves over the resistors. This disturbs the ECU and causes overfuelling during warm-up. The remedy is connecting a capacitor across two wires - described in the Archives…
The symptoms are almost unique; only when warming up and only while the pedal is being moved - when hot the engine is working perfectly…
As a first step…
Frank
xj6 85 Sov Europe (UK/NZ)
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I did the capacitor modification and the car now behaves properly under all conditions.
I am glad my soldering skills are hidden by the rubber boot!
Thank you Frank for your help on this. On to the next problem!
David
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I’m happy to say the so are mine, David…
Frank
xj6 85 Sov Europe (UK/NZ)
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