I don’t think it would run. I still don’t think it would run with a broken AFM. Not that I know the solution… with the AFM disconnected mine doesn’t start. Since slight changes in the AFM flap position kill the engine and since it moves a bit during idle, I‘m not too sure it is at fault.
I would be desperate by now and worry about valve timing (but the compression is fine) and the distributor (but it would not idle then) because I really can’t imagine anything that would hold idle besides a broken throttle.
It must be something that changed but had no impact on idle air or idle mixture and -adjustment. What happens when the AFM flap is slowly pushed in during idle?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
43
Is a vacuum gauge available? I would like to know what the intake manifold vacuum is at idle, and what happens when the throttle is opened.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
44
Might as well check for a blocked exhaust system.
The quickie check for a plugged exhaust is to remove the oxygen sensor and fire that mutha up. If it runs much better with a gaping hole in the exhaust system, that indicates the system has a blockage aft of the oxygen sensor. Of course, if there is a blockage forward of the oxygen sensor, this test won’t help.
That is a valid idea, Kirbert; an engine not only need to get air - it also has to get rid of it…
Vacuum should drop gradually - but the drop may depend on how clogged the exhaust is. It may be stable at idle - but with increased idle; vacuum will then drop as air gets in without more air going out.
I won’t state that you have cracked it, but it is a good crack at it - and besides; vacuum is a valuable diagnostic tool anyway…
I got the gasket to the Throttle body and all is mounted again I do not found any thing wrong with any of the parts. I can start the engine and it runs perfect idle but when I pull on the gas pedal do there happen nothing I have spark and gas pressure so back to square one.
Next: I have a vacuum gauge where do I connect I can not see any studs on the intake manifold.
Remove the oxygen sensor and fire that mutha up
Hello Niels - since you state you have a 10.81 K ohm reading between pin # 6 and the engine ground, I would suggest cleaning your ground connections to achieve a lower ohm reading thereby ensuring a better ground available on pin # 6, which may in turn help provide a stronger signal to the ECU _ Tex Terry, II - 1991 XSJ V12 Classic Coupe, 1986 XSJ V12 Coupe - sent 9/12/2020 2020hrs. EDT USA.
Heed Kirbert’s input, Niels - blocked exhaust is a distinct possibility; to be pursued - your symptoms fit…
Connect a vacuum gauge to the fuel pressure regulator’s vacuum hose - it reads manifold vacuum. At idle the normal reading would be 18" Hg, steady - a clogged exhaust may cause a ‘0’ reading - at which the engine will not respond to the gas pedal, just idle…
And if you haven’t got a vacuum gauge; get one - it is genuinely necessary whatever your problem.
A more positive test for clogged exhaust is to disconnect the exhaust system at the manifold.
Monday.
Hi Frank and Kirbert The vacuum gauge showing 0 Hg I also mounted a notlight on fuel nozzle there show constant impulses from the ECU
I am agree with Frank to disconnect the exhaust system at the manifold also because I suspect that the catalyst converter is melted down. I can not make that noise where I liver so the tow truck have just pick up the Jaguar. I will keep you up to date.
Niels
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
56
Wow. Man, I’d be double-checking that I connected it correctly! But yeah, it sounds like your exhaust is totally plugged. I’d still unscrew the oxygen sensor and fire it up – just for a few seconds – as a test, but at this point I’d probably go ahead and yank the cat out rather than go to the expense of having the car towed. Unless you need to have it towed to get it worked on anyway.
**
If you do have the catalytic converter, it’s almost certainly the cause of the problem, Niels - exhaust clogging for other causes is almost unknown…
For once I would have suggested replacing the converter on mere suspicion, without sending it away…? Indeed, the noise from plain manifold exhaust is indeed spectacular…
As an aside; ‘0’ vacuum means that both sides of the throttle is at the same (atmospheric) pressure - and throttle movement therefore does not increase airflow.
frank
xj6 85 Sov Europe (UK/NZ)
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Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
58
We had a guy on here, many moons ago, who had an inner section of pipe collapse, plugging up his exhaust. I agree, though, it’s almost always the cat. And I guess that would have a cause, typically a misfire sending raw fuel and air into the exhaust tract. Hopefully the misfire has been rectified in the course of trying to find the cause of the lack of throttle.
Kirbert and Frank
The shop just call me and told me that the exhaust is NOT clogged.
The auto shop (there do not know any thing about Jaguar) think that it is the timing chain there have moved a tooth ???
Niels
Removing the cam covers and rotating the engine until the cams have the locating notches lined up is an easy way of checking if the timing has slipped.
Yeah but this is really unlikely, like not at all. Having a look is quick and relatively easy. If the notch has moved a lot then either the idle will be bad or the thing won’t have power at the top end. I don’t know if there’s a spot that produces a good idle with no breathing capability above.
Too bad it is not the exhaust as this was the only good and easy idea so far.
Let them check the vacuum reading again and have them move the AFM flap once more. Something MUST happen if the engine idles well and the throttle is opened. Really really strange now.
