1986 series 3 XJ6 smog test failure is there a vaccum hose between distributor and vaccum advance?

I brought the car in to a smog test facility today. All the emission test results were good. In the section marked ‘visual inspection’ results, I believe the inspector inputs these values manually. In the section marked ignition timing, which I know is set to 17 degrees BTDC as it’s supposed to, he failed that section and did not input a value claiming I am missing a vacuum hose between the distributor and the vacuum advance mechanism. I cannot find reference to such an item in neither the factory parts manual nor the factory service manual. Am I missing something here? I even looked at my 1987 series 3 XJ6 and cannot see such a hose there either. He claimed some website reference book they use for smog testing shows a vacuum hose should be there. When I told him I have the factory service manual and parts books, he told me to come back next week and bring them. What to do? Please advise.

That is indeed odd. But then, SMOg inspection is now out dated???

Way back when, SMOG demanded a restriction on te advance. In some strange EPa mind, firing late was cleaner than firing early> / there were temp controlled valves. My 69
toyota had the advance cut and p;ugger. ie no advance. i fixed that!!!

Does the distributr have a vacum can mpunted on the distributor? If so, and it shpu;d, is there a line t the inlet manifold.

Nw, shu;d it be connected to manifold vacun or to ported? A whple other story.

I am surprosed that your factoey literaturee does not shw a can and a line???

Relyoing on pure centrigfugal is odd, but has been done.

Ugh, my cars are SMOg inspection overdure. Can n longer stand the nuttiness…


what model distributor is actually on the motor, can you post a pic of it, has the distributor been upgraded to an after market type?

It’s the factory installed distributor

any chance of a pic of the dissy, 'cause even the later models had a vacuum unit

I removed air filter earlier and did not see a place on the vacuum unit on which to attach a hose

so the dissy has a vacuum unit? usually there’s a distributor vacuum delay unit which has a tube from the delay unit to distributor, so does the distributor have a vacuum unit fitted…i know you might feel we’re not hearing you but a simple photo of your distributor & more info about your model will help

I don’t know I think so but it doesn’t look like a Hose would atach

Here are some pictures that might help explain what issues the CA smog technician had concerns with.
This first picture shows the EAC5985 vacuum routing diagram detailing the vacuum system that the USA market cars had installed when they left the factory. Other country markets had different vacuum set ups (even vacuum retard) to meet their emissions regulations as detailed in the Jaguar Series III Service Manual. These decals were installed on the underside of the hood (bonnet) in each car but some may have been removed or damaged over time. The technician was likely looking to verify that this vacuum routing was present.

This next picture from 2019 as I was completing an engine swap in my 1984 XJ6 Vanden Plas with an engine from a crash damaged 1987 XJ6 and before I put the intake manifold on. You can see the vacuum hose connected to the distributor vacuum advance capsule leading to the EAC4399 vacuum regulator and then further on to the other bits of hoses as depicted in the under hood decal.

Here is closeup picture of the vacuum regulator and hoses from beneath the intake manifold looking upward including where the small vacuum hose that attaches to the bottom of the intake manifold is hanging from a clamp attached to one of the intake manifold stud.

Here is a picture of the front of the EAC4399 vacuum regulator found beneath the intake manifold with the “DIST” nipple identified where a hose from the distributor vacuum advance attaches.

Here is a picture of the rear of the EAC4399 vacuum regulator where the other two hoses connect per the routing diagram.

I suppose that if some or all of this vacuum routing was missing or disconnected from your car, then the technician has to detail that in his report per California emissions laws (which I had to comply with for 32 years but thankfully I do not have to deal with anymore since I made my exodus from California and now live in South Carolina).


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In the USA there is a vacuum advance. Other countries had different regulations including some with vacuum retard systems. The Series III Service Manual depicts what type of distributor and vacuum system when to the different markets, not all vacuum systems were the same.


Thanks for your reply and photos. I’ve owned this car since 1996 and I think you judged it at several SDJC concours over the years. Up until today I’ve never had smog test issues. The technician said I’m missing a hose to be connected to the distributor but I cannot see where.Your photos seem to show a hose coming from the capsule not the distributor. I’m not about to remove other components in search of the missing hose if it is anywhere to be found. The underside of the hood of my car contains the same stickers in your photos. I think the technician while trying to work within legal requirements does not really understand Series 3 XJ6 cars. Now even though my car passed the emissions test he failed it on timing which is a visual inspection. My car is set at 17 degrees BTDC and has been for years. When I got home I called the technician and told him I have the factory parts and service manuals and photos do not show any hoses attached to the distributor. He asked if I’m certain that timing is set at 17 degrees BTDC and I assured him it is. He said he has to be careful nowadays since the state conducts all sorts of sting operations. I assured him this is not the case and I’d be happy to bring him previous registration and smog test papers and factory manuals if he’s interested. He said to come back one day next week and would not charge me again. I’m hoping this will be resolved with a minimum of fuss.
By the way, when I purchased the car in 1996 the previous owner gave me a mountain of paperwork including receipts for replacement of the distributor at the dealership from which it had been purchased new at 36000 miles. The receipt showed an itemized agreement the dealership and owner would share replacement costs 50-50. The dealership was Whittlesy in Torrance . No surprise that they have been out of business for years.
Do you think the missing items would have even affected the 17 BTDC timing?
If possible please tell me what you think.

paul, don’t assume i don’t know this, i’m not an apprentice, i started my time in mechanics in 1969…your pictures show a vacuum unit on the distributor…this is what i’ve been asking Mel to post a pic of - his distributor - it’s a simple request yet no response. nobody is going to give an informed solution/answer till Mel posts a pic

All cars, ex factory, use both centrifugal and vacuum regulation of timing advance, Mel - it’s necessary for ‘best’ engine performance…

In your case, the engine runs on centrifugal advance only; set to 17 deg in idle - the advance increase with rpms. Vacuum is added to modify centrifugal advance according to drivers’ pedal inputs. The various ways of doing this is long and convoluted - the inspector just knows there should be a vacuum regulation to comply with regulations…

A PO just removed the dist’s vacuum hose deliberately - for reasons unknown. The engine will run well enough on centrifugal only, but not to specs. That engine complies with smog tests is likely a coincidence in as far as the limited smog test regime goes - it does not concern itself with engine performances outside the test program…

Paul has described very well what the inspector expects to see. If you install them and (secretly) block the hoses; the inspector will be happy and the engine willstill pass smog tests. But without vacuum your engine is still underperforming…

To emphasise; the 17 degrees advance is not(!) constant, it’s an initial setting, but varies with rpms. Without the vacuum connection there is no vacuum influence on advance - the centrifugal advance is unaffected.

xj6 85 Sov Europe (UK/NZ)

In 2005 during my first visit to a random CA smog station in our “new to us” 1990 XJ-S convertible (5.3L V12 with digital Marelli ignition system) the technician asked me where my Check Engine Light was. For those not familiar with the earlier XJ-S (before the 1992 “facelift” redesign) , 1990 XJ-Ss were not equipped with On Board Diagnostics and do not have a Check Engine Light. I showed the technician the owner’s manuals, XJ-S Repair Operations Manual and even sat him in the driver’s seat and showed him that there was no Check Engine Light anywhere on the dash. He insisted that there had to be a Check Engine Light because his book told him that there must be one. I got in my car and drove away telling him that I didn’t want him to test my car because either he, his book, or both didn’t know what they were doing. I subsequently found a CA Smog station recommended by another pre-facelift XJ-S owner and subsequently passed the emission test without a Check Engine Light and no discussion whatsoever with the second technician about a Check Engine Light.

Another time when I took one of my Series III XJ6s in for a CA smog test I asked the technician exactly how he got the ignition timing number in the report since I didn’t see him use a timing light (I had and it was to spec). He told me that they didn’t have time to use a timing light when they test a car and they only look up the timing for each car “in their book” and then input that information on their report. So according to him, at that time, there was no test of the engine timing, only a look up in a table in a book that they was given to them by the state government. I suspect that the same is true with Mel’s results and that the technician never measured the engine timing but only looked it up in his book, so that 17 degrees BTDC means very little. Perhaps Mel should ask the technician this on his next visit.

My conclusions: CA emissions technicians don’t always know what they are doing, the quality of tests can vary between tests stations, and not all the information on their test reports is from testing. Another thing that I found interesting is there is no standard for emissions gas test results across the state and the tests and acceptable levels can vary from one Zip Code to another based on the address that the car is registered at. I was surprised to learn this when I moved from a San Diego city Zip Code to a rural east San Diego County Zip Code and no longer had to have my car tested for Nitrogen Oxides (NOx).



Please remove your air filter again, take a picture of your distributor, and post it in a reply. Your distributor should have a vacuum advance capsule as circled in yellow, and a nipple on it as circled in red in the attached picture where the vacuum line should normally be connected. If it doesn’t then you have the wrong distributor in your car.

BTW, ask your technician how he got the 17 degrees BTDC number in your emission test report. I suspect that he did not put a timing light on your car and only got that number by looking it up in book. That is what a CA smog technician told me about one of my Series III XJ6s many years ago. I have never seen a smog technician put a timing light on any of my XJ6s, XJ12, or XJ-S. I am not saying that they never do that, but I asked and I watched and I believe that they look that number up in one of their CA government provided books and it is not something that they measure.


I had a feeling the 17 degrees BTDC figure is something he would just input in to the computer manually. What is the width of the vacuum hose to be placed on that nipple?
Thanks for the photos and commentary, both are helpful

With the easy solution being to connect a hose to/from where the diagram shows, and because it runs fine and as you like it as it currently is … cut the hose and put it a hose coupling … except that the hose coupling has been filled with epoxy to fully block it.

Inspector is happy that the hose is there.

You are happy because nothing has changed. :cowboy_hat_face:

You are most happy because you pass inspection. :sunglasses:

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The vacuum advance nipple on the distributor is pretty small, I would say something like 3/16" inner diameter vacuum hose should work fine.


Excellent will do.Thanks!


good luck on gettig past the inspection. I hate SMOG inspections. I gotta gt one on my lump. i have had issues at times, and not at aohthers. As paul said, very inconsistent.

It is your car to do with as you see fit. but, If i were ypou and I am clearly not, i would restore a working vacum advance. It is a good feature.

As said perevously, plugging was once, and still may be required for a SMOg pass.

Teh jaguar engineers are pretty smart and the engine managmwent system was tops in it’s time

Even if quite complex.

Paul, I envy you, NOSMOg insections. paradise!!!