Can’t see what the effect would be on the idle Kirbert.
The ECU would just default to open loop…
Can you elaborate?
There is a vacuum hose from the balance pipe that goes all the way back to the ECU.
Check it out.
And could it be that the diaphragm inside the ECU is broken?
Yes also…
20 char.
Open loop is stable.
20 char
Yes indeed.
But I can’t imagine that we’ve spent 440 posts trying to solve the normal oscillating idle of the 0² cycle… Or did we ???
Right, with the AAV plugged the idle should drop to about 300-400 RPM with throttles gapped to .002"
The throttles. But I’m sure that’s already been hashed over in this thread.
Cheers
DD
I’ve wondered about possible failure modes (leaking, lazy, inoperative) of the pressure sensor in the ECU and how they would manifest.
I know that disconnecting the vacuum supply gives an unmistakable result: gross over-fueling with engine chugging and black smoke rolling out of the exhaust
Cheers
DD
I don’t know anything about jaguars engine.
but what I am telling you for sure is what is happening.
I verify my setting about vacuum installation. Everything is where it should be and everything is perfectly connected
How can I revisit the crankcase ventilation system ?
For info, my overrun valves have the springs compressed to the maximum.
so today :
1°) I put a vacuum hose directly from balance pipe to ECU
with AAV unplugged => cycling
with AAV plugged => cycling
2°) I removed my vacuum hose and reconnected the original vacuum hose to ECU.
3°) In the air filter box on the B bank, I plug the 3 holes (1 to AAV, 1 to overrun valve, 1 to PCV valve)
=> cycling
then I unplugged AAV => cycling
with AAV unplugged, I unplugged hole to PCV valve => cycling
with AAV and PCV valve unplugged, I unplugged hole to overrun valve => cycling
4°) So I plug just the hole to overrun valve => no cycling, but idle at 1100/1200 rpm
5°) with configuration nr 4, I disconnect the vacuum hose to distributor (just to see if it’s cycling), nothing happened, no cycling. But I create a really air leak.
I don’t understand.
Maybe that’s a clue.
Did you plug both of them?
If only one plug also the second and report back.
Is your idle screw at the AAV valve screwed all the way in?
An other thing to check is the Extra Air Valve, mounted at the A bank/right hand side filter box. It could also be stuck open.
To continue troubleshooting I would leave everything disconnected and all ports plugged until you find the problem, you may have more than one issue.
I guess you killed the advance with the distributor disconnected but the air leak compensated the idle.
On va y arriver!
**
The overrun valves are designed to stay closed at normal manifold vacuum, Jean - opening at 23" Hg during overrun. There are two of them, one each bank, sucking air from the air filter ; you test them in idle by blocking the air hose to them…
An occasional problem on the xk was that the overrun valve was sometimes installed ‘upside down’, causing increased idle. But in case a properly installed valve causing high idle and, not being adjustable, was to be changed. The test procedure for the V12 is the same; blocking the air to the valve(s) should cause no idle change. Conversely, if the idle does change when air is blocked; a valve have failed.
There is no mention of the V12’s overrun valves being adjustable; that the springs are full compressed might mean that the valve, being now closed, is meant to open by stretching the spring. Ie, the valves should be movable, which may be difficult to assess, as would adjustment.
Nevertheless, your test implies that an overrun valve has failed - did you test both? It certainly warrants further investigation - the overrun valves fits the symptoms to a ‘T’. They were prime suspects at the very beginning of this - abandoned for some reason, mainly because the symptoms were not constant?
Frank
xj6 85 Sov Europe (UK/NZ)
So today :
cold engine, first test series
1°) overrun valves A and B plugged + AAV unplugged=> no cycling idle at 1200
2°) overrun valves A and B plugged + AAV plugged => no cycling, idle at 1000
3°) overrun valves A and B plugged + AAV plugged + PCV valve plugged => no cycling, idle at 950/1000
3°) overrun valve B plugged + AAV plugged => no cycling, idle at 1000
4°) overrun valve B plugged + AAV unplugged => cycling
5°) overrun valve A plugged + AAV plugged or unplugged => cycling
I have oil (leak) coming to air box B from overrun hose. I have nothing for air box A.
6°) AAV plugged, the rest unplugged => cycling
The PCV valve plugged, idle goes down a little bit. Not significant.
I have to make again these tests tomorrow, Because I’m sure tomorrow it will not be the same.
And tomorrow I will make the test proposed by Aristides (plug all ports)
You know that the name of this car is CHRISTINE !
1 Like
So better be good to her:-)
So, is this “cycling” you’re seeing the standard fuel cutoff because the idle is too high?
Kirbert, I guess from the little I know about this engine.
**
You do that, Jean - we need some consistency here; inconsistency has repeatedly thrown us off the scent…
At present the A-bank overrun valve seems ‘the’ culprit. Generally, your idle with ‘everything’ closed is still high - which, with any additional air will drive rpms above the fuel cut-off limit. Which cause cycling rather than just elevated idle.
Closing the AAV air supply should really cause no change if the engine is warm enough to close the AAV - during this testing session (1 and 2); the AAV added 200 rpms, the PCV seems more innocent…
Have you done any inspection of the overrun valve to see what can be done with them - short of changing one or both?
Frank
xj6 85 Sov Europe (UK/NZ)
Clearly overrun valve B is leaking. One culprit found!
Your PCV valve seems to be OK.
Leave everything plugged and plug the Extra Air Valve as well.
No, it would have a difference because the idle setting screw is on the AAV.
IMOHO, 200 rpm increase on a stone cold engine is not excessive.
**
Yes and no, Aristides - the closed air supply to the AAV will also close the idle bypass lowering the idle, and adding air supply to a closed AAV will indeed rightfully add 200 rpms to idle, as you say…
However, 1000 rpms with ‘everything’ closed is still to high, to be pursued later. The open AAV, with the engine cold would add at least 400 rpms - so the AAV dutifully closed in this test series. Lets hope that the next test series will be consistent with the first…
Frank
xj6 85 Sov Europe (UK/NZ)
I made same tests again, with other results. I’m tired of it, I don’t care. Let’s go back to what I told you in the last tests
So
1°) I don’t know how I can fix the overrun valve. It’s a spring. I have to unscrew this spring ?
2°) Perhaps one of the elements on the vacuum line is defective (valve delay, vacuum regulator, valve vacuum).
how I can determine which one is not working well ?
3°) can a very slight change in the ignition timing create an air leak ?
because I changed (at a given time) the vacuum distributor unit, and with all my care maybe I modified the ignition timing ?
Let’s check these points first and then we’ll see.
new, even with a good oil level, the gearbox does not engage the gear when I move the lever and there is now like a noise / rumbling.
I don’t know if it’s coming from the gearbox or the driveshaft (but it’s all happening at idle in the garage, I don’t drive the car more than 3 meters each time !)
the horizontal screws (what a heresy!) of the rear support of the box were screwed up and I put them back. It was holding.
Jean,
I think you are trying to solve many problems at once and this can’t work.
You are just tiring yourself.
Troubleshooting is the most difficult aspect of mechanics and it has to be done very methodically.
Here we are trying the elimination process, so every time you reconnect everything you go back to step one and going on circles and more than 450 posts so far.
Leave all the vacuum lines disconnected, AAV and PCV included, until you find the major problem.
Only then connect back one by one and check in between.
Also check again the throttle plates gap and make sure the bushings are good and that the throttle capstan doesn’t stick or pulls the throttles open. And even just disconnect the rods to be sure.
The overrun valves seem to be a problem indeed, so you must remove and check, maybe with an air compressor blowing air on the opposite direction…? If needed make two blanking plates sealed with silicone for testing purposes.
There is a vacuum line that goes to the transmission’s vacuum modulator. Did you check it?
Vacuum advance seems to be working ok, but connect it directly to the inlet manifold.
No.
Maybe, and it could raise the idle, but very little.
Now that’s an other kettle of fish that probably needs its own thread and after you solve your hunting idle.
First thing is to change the fluid and filter.
Second is to check the transmission mount and replace the bushing.
Third would be the shifter linkage.
Also a striped governor gear teeth comes to mind.
All these are relatively easy.
**
It’s the inconsistency that utterly bewilders me, Jean…
Everything pointed to A overrun failure, until 5); ‘A plugged + AAV plugged or unplugged => cycling’. I trust all tests were done with the engine at the same temp - and the plugging was properly done and consistent? What were the ‘other results’ on the retest…?
Answers to this post;
- The xk versions of the overrun cannot be fixed, they must be changed. On the V12. I don’t know - but
can the sprung part be removed from the housing? To be replaced separately…? - The main problem with the ignition vacuum lines and components is that the hoses seems to narrow
to increase the idle more than marginally. Unless there is a component that may be open to ambient
air? - Ignition timing cannot make air leaks - nor changes idle by much…
You may block the crossover pipe and retest. The crossover pipe may feed leaked air from bank to bank, as will the AAV connections - the very high increase in idle cannot conceivably come on with only one bank getting extra air…
And as Aristides say; the gearbox is ‘another kettle of fish’ - requiring a separate procedure. But the gearbox/drive train is not really happy engaging gear from high idle, or running stalled - though it should stand it…
Frank
xj6 85 Sov Europe (UK/NZ)