'87 XJ6: Help identifying vacuum port on throttle body / throttle cable housing with unattached hose? Just failed smog

Agree with Carl on possible dirty air filter condition which can cause rich running.

Carl / Terry,

Thanks for these tips. Carl, in particular, I was unaware of ports underneath the intake manifold. I’ll examine those for sure. Yes, a flooded canister would also cause this behavior. It happened to another vehicle of mine, a '79 International Scout that was nearly impossible to diagnose the run-rich issue – it turned out to be a flooded canister. Excellent suggestion to check. (Realistically, I’ll go in and simply plug the ports for the next test.)

The air filter is brand new. As are the plugs, wires, rotor and cap.

Previously in the thread, I DID come to the conclusion that the vacuum port for the cruise control bellows was disconnected and was causing a vacuum leak. I capped it directly at the throttle body as the cruise control is inoperative. I re-ran the emissions test, thinking that it was sufficient, but not at all – still ultra rich, even when the car was plenty hot.

My plan:

1.) Check the manifold vacuum ports / spigot from underneath the manifold.
2.) Check / disconnect the carbon canister (discreetly, so it passes visual)
3.) Pinch the cold start injector hose completely closed.
4.) Replace the CTS (which is out of range upon test)
5.) Replace the fuel rail pressure control unit. (Both of these already on order from Rock Auto.)

With all of that done, I’m going to bring it back for a pre-test at the smog center. I really hope that does it, there isn’t much left. I’ve checked for a misfire by pulling each injector connector in turn – each is operating properly as is ignition.

Again, thank you for the immensely valuable suggestions!

One last question: I gave a cursory look for where that carbon canister is located and it appears to be in the side firewall. Can anyone definitely confirm how to access it? All I see is the “tee” hoses branching off straight into the wheelwell.

Thanks much!

On early cars the canister was readily accessible with the bonnet open, Brian - on later cars it was in the left front wheel well…

The operating principles are the same for all, but more sophistication was added as time went on.

  • One canister hose is connected, via a ‘T’ and
    the C-pillars fuel separators, to the tanks -
    above max fuel levels.
  • One hose is connected to a vacuum source,
    nominally the crankcase ventilation - and a
    restrictor to reduce vacuum to a minimum
  • Charcoal is fitted to divide the canister in two;
    one part, with the vacuum hoses - the other
    open to ambient air.
  • With engine stopped, vapor from the tanks are
    vented through the charcoal to open air. The
    charcoal adsorbs the fuel vapor from the tanks
    so no fuel is vented out.
  • With engine running air is sucked from the
    tanks and also through the charcoal from open
    air. Adsorbed fuel in the charcoal is drawn into
    the engine and is burnt. Hence there is no
    actual vacuum in the canister just air flow…

If the charcoal solidifies, preventing air passing through; there will be vacuum in the canister - which may be passed on to the tanks. However, with normal fuel levels, only air is sucked from the tanks building up tank vacuum - which may prevent tank venting, and the tanks may ‘implode’. Remedial action is to replace canister/charcoal - which is a scheduled maintenance operation anyway…

If a tank overflows for some reason, usually failed return or changeover functions, liquid fuel may indeed be sucked into the engine - causing fat running.

In principle; the closed ventilation system/canister is an unlikely source of failed smog - but not impossible. The CSI is a more likely prospect, but other factors, like CTS, fuel pressure regulator and the AFM, cannot be excluded, of course…

xj6 85 Sov Europe (UK/NZ)


Thanks for this. I’ve done some additional reading on the topic and believe my “vacuum valve to pressure canister” has failed, part number CAC3101 which is no longer available. In addition, one fuel tank has already been replaced on the vehicle. When I open the tanks immediately after a drive, there is a larger than normal “whoosh” sound, and when I don’t, I hear a tick, tick, tick, from the rear of the car which may very well be the tanks returning to shape, having been deformed from excess vacuum.

As the California Smog test also tests pressure of fuel tanks, luckily there isn’t an adapter for the Jaguar fuel fillers so that test is excluded. I’m not opposed to allowing the tanks to vent to the atmosphere for now. Since the carbon canister tank is hidden, it can’t easily be inspected.

Thinking out loud, if I occlude the vacuum port for the charcoal canister system at the throttle body (and then re-hook up the hose for visual), and then disconnect the lines from the fuel tank that go to the charcoal canister, would this effectively ensure that fuel isn’t being drawn in via a filled charcoal canister?

The more I think about how the vehicle behaves with the massive vacuum in the fuel tanks, and the fact that this exact scenario happened to me once before on my International Scout, I’m keen to (safely) disconnect the system for the purposes of the smog check. I’m really leaning toward this as a problem, if not a contributor to the problem.



  1. fond memories of my 9 IHc Scout II> Sure liked that old Binder. Only the fact tht it laced AC caused me to part with it. Looked great . ran great. took lot to get it past SMPG. even had to go to a referee at one time.

Get it good and hot Screw down the idle jets til it barel kept runnign. Oh. I swppped in a Ford Ctalyctic coverter. Mush better than the GM pan cake tpe. then, shop made a cat a back dual syste Ran and sounded much better\\Visoit almst amny “junk yard” that has some old Gzm cars. rob one of the cnnister. Same as the jaguar un it!!!

Cut ylurs open. recharge the charcoal fish stores have it\The cannisters do not haave a bad effect on engine performance.

CA SMOG is a PITA!!!

hate each session. altough st f the folks are nice.


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To elaborate, Brian - the valve is not really vital for tank venting…

The ‘normal’ source of tank vacuum is the consumption of fuel - as levels drop, the vacuum increases. As vacuum increases, the valve opens towards(!) the tanks (at some 1,5? psi) to let air into the tanks.

(This is the vital point; without air let into the tanks the very powerful fuel pump will eventually remove all fuel - and vacuum may theoretically reach near 14+ psi. At which the atmospheric pressure on the tanks’ outside metal will be 14+ psi - and the tanks will collapse long time before that)

Likewise, if tank pressure increases, fuel expanding, like while standing in the sun; the valve opens from the tanks - venting vapor into the canister. Pressure in the tanks is of course not a problem - it will be very low and the tanks can easily take high inside pressure…

When engine stops the vacuum in the tanks (1.5 psi) will be retained by the closed valve. The Californian regime of testing basically checks that the tanks are not leaking fuel into the atmosphere - that indeed the fuel fuel is sealed in. Whether they test this by applying vacuum or pressure, or whatever, I don’t know…

However; working as it should the system is supposed to maintain tank vacuum build-up after driving/using fuel - and you get the ‘whoosh’ when opening a tank lid. It does not in itself imply any malfunction…

Assessing the ‘whoosh’ is somewhat tricky; the amount of ‘whoosh’ depends both on the vacuum level, the amount of fuel used and the amount of air space/tank levels. The less fuel in the tanks or the more fuel used, the more ‘whoosh’…:slight_smile:

Also, the tanks’ ventilation commute - tanks are connected to each other via the fuel separators, and have the same vacuum. So if you open one lid you get the ‘whoosh’ when you then open the other lid - there is no ‘whoosh’…

Of course, if engine vacuum is applied to the tanks the vacuum build-up is more rapid. This usually caused by solidified charcoal in the canister blocking the canister’s air inlet - the charcoals special characteristics deteriorate over time, ‘poisoned’ by fuel. Otherwise the engine will rather draw air from the canister’s air inlet remedies by replacing the charcoal/renewing the canister. There is normally no actual vacuum in the canister; its more a matter of a slow air flow throughout…

There are other fault permutations, but these are the main ones…

As an aside; on later cars a ‘purge valve’ was added - a vacuum operated valve closed the connection between the canister and the vacuum source. To preventing the vapor escaping to open air via the engine…:slight_smile:

A second aside; it’s very unusual for raw fuel to be drawn into the engine via the canister- it can, as said, only happen when the tank level reaches the vent hose at a tank. Which requires that the tank overflows - which is a fault in itself. To be remedied by appropriate actions…

A a third aside; check where the canister vacuum hose is connected to the engine. On later versions it was connected to the crankcase ventilation pipe - which has relatively low vacuum. And check also that a restrictor is fitted to the hose…

xj6 85 Sov Europe (UK/NZ)

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The quest continues: I retested yesterday and missed it by that much – on the 25 mph test.

1.) The CTS was DEFINITELY bad. Upon removing it, I noticed the internals were essentially powder and the two prongs could touch each other.
2.) I replaced the fuel pressure regulator on the rail as the original was still in place.
3.) I thoroughly examined the evap canister, valves, and lines. To cure the “fuel tanks whoosh” I took a 1/8" drill bit and cleanly drilled through the valve going to the fuel tanks. Worked like a charm. No more “whoosh.” (Records show the previous owner had to recently change one of the fuel tanks due to a leak, and I hear the telltale clacking as the tank resumed it’s shape after a long drive.)
4.) I took an air hose nozzle and checked for flow through the canister (and back and forth to the fuel tanks) with the improved (drilled) valve. Plenty of airflow in both directions and the canister is not prohibiting airflow. I also tested the canister in reverse and blew into the outlet to atmosphere. Plenty of flow.

Thus, the smog guy says when variations like this happen mid-test, it’s usually the O2 sensor. The only thing I did NOT change as it looked like it’s been changed already. His rationale was that as the car had been running richly for so long it’s likely fouled the sensor regardless of how long it’s been there. A new one from Rock Auto is only $27, so it’s on the way.

I’ll pop that in and go for a long drive and then the retest. That said, the improvement made by replacing the bad CTS made an enormous difference in the test numbers thus far.

I thought I’d post the update for those following the thread and also as an opportunity to say THANK YOU again for all who have contributed.

– Brian in San Diego.

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That is much appreciated, Brian - too few do that, leaving us in the dark as to the solutions, thank you!

The importance of the CTS is of course as expected. The numbers indicates that the engine is running too rich, and the inspectors remark is likely well considered. However, the O2 sensor shouldn’t really have to work very hard if the mixture control on the AFM is correctly set - probably set too fat. To be considered if a replaced sensor is unsatisfactory…?

Drilling through the relief valve is one way to eliminate all ‘whoosh’, of course, and certainly eliminate tank collapse. But it will also fail the Californian fuel tank pressure if applied. There should indeed be a bit of ‘whoosh’ with the system working correctly…:slight_smile:

Was the CSI clamped for testing, or is it working properly - or at lest not leaking?

Thanks for reporting back - and a final report?

xj6 85 Sov Europe (UK/NZ)

Thanks Frank.

Good note on the CSI. I was so convinced in the CTS fault, given it’s patent obviousness after testing, that I neglected to tie off the CSI. Mostly because the smog shop won’t pass the “visual” inspection with a hose clamp on my fuel system, but also my own hubris in my diagnostics. I’m going to properly disconnect it before the next test after I replace the O2 sensor.

Great point on the fuel tank pressure test at Smog. The Jaguar is exempt from that test due to the fact that they do not have an adapter to fit the fuel fillers. I knew this prior to drilling out the valve.

I realized that I can’t remove the O2 sensor without the special socket wrench so that’s on the way. I’ll circle back in a week or so once I’ve got the next iteration of fixes.

If it fails again for any reason, the shop agreed to play with the AFM adjustments while on the exhaust gas meter for me. That’s our last resort.

As always, thank you, and I’ll be back!

That really is an essential adjustment with a marginal ‘fail’, Brian…:slight_smile:

If you got those test readings with CSI connected; it’s working as it should - no need to clamp or disconnect it. You could of course clamp it while the shop checks exhaust gas - just to verify that it plays no part…

As an aside: the blow-through at the canister will work either with the charcoal intact or if the charcoal has shrunk/is missing to allow air to bypass it. In the latter case; the system is inoperative - but you don’t need to tell the inspector that…:slight_smile:

xj6 85 Sov Europe (UK/NZ)