I purchased a 85’ V12 motor for my 89’ XJS but it wouldn’t start once I put it in the car. The Lucas distributor’s High Tension Rotor was pointing the correct direction when at 1A ”0” as seen under the motor. On a whim, I rotated the cables on the distributor from the spark plugs 180 degrees and fired right up. However, it now surges high and low when it idle’s, but drives great. Very annoying and doubtful it will pass inspection. Any thoughts?? Jeffrey

 

When surging what's the RPM swing? If several hundred RPM the most likely cause is a stuck Aux Air Valve. Too much air comes in so the idle speed increases...up to the point where the ECU turns off the fueling and the idle drops. The the fueling is turned on and the RPM increases again. Repeat, repeat.

Remove the LH air filter cover and the air filter. You'll see a 1" hole in the rear housing. This is the inlet to the AAV. Start the engine and momentarily plug the hole with your thumb. Does the surge go away?

There are other possibilities but I'd begin with this.

Cheers
DD

 

Welcome to the Forums.

When the beast settles, please do an Intro in teh New Members Aream it keeps the boss happy.

Doug has naiked the #1 reason for surging.

Your fitment of yje dizzy is missing something, OR its a typo.

The engine is set at TDC 1A Compression Stroke.
The dizzy is juggled in and when correct, the Rotor Arm Point is pointing in the "general direction" of 1B. Dont overthink it, its a Jag.
The cap, usually, has a #1 cast into the top adjacent to the 1A lead post, and the firing order is Counter Clockwise from there.

Your timing is possible out a tad, and since you appear to be in the USA, that could be causing surging also. Your market emissions "junk" reeked havoc with the V12, and some settings that our market would forgive, yours dont, sadly.

Out of balance throttle rods/discs is another surge creator.

TPS not set in range, is another.

 

Checking the timing on the V12’s is nearly impossible. It’s at the bottom of the engine so a really long set of leads is required. Then crawling out from underneath and trying to change the position of the distributor is a complete exercise in frustration.

 

Agreed, thats why I dont do it that way.

I gave up the Brave Pills, many years ago, and static time it, then drive time it, better results all round.

Couple of attachments, just because.

Simple engine the V12, so simple.

 

There are several ECU’s that make life so much simpler. If you want plug and play there is the MAXXECU. If you want much lower cost you can get a MEGASQUIRT MS3 Pro
or the new mini MS 3. Then you can toss away the whirly gizmo thing-a- mobob. In the center and just use trigger wires on the coil on plug. So much neater. Plus changing timing is a few key strokes on a lap top. You can also adjust fuel mixture to compensate for modifications. ( such as Turbo chargers, camshafts, cylinder port work, etc. )
It is also one inexpensive sensor away from flex fuel capability. Where the ignition and fuel is automatically adjusted for whatever gasoline/ alcohol you use.

 

Doug,
Thanks so much. I did what you suggested and blocked the 1" hole inside the left air filter. It immediately stopped surging for around 30 seconds. Funny thing is that I replaced the AAV unit three times already with units that should be good.
I also noticed that when I adjust the distributor ,the surging increases or decreases, depending on the direction of the adjustment. As I indicated, I got lucky that it actually started, as I had to rotate all the distributor wires 180 degrees to make it fire, 6A now occupies 1A's spot. Wondering if it will stop surging if I would rotate the distributor gear shaft 180 degrees to its home position?

 

Grant, my apologies. My account was XJS Fanatic years ago, but I was not able to login and created a new one titled: ThreeBlackJags. Not sure if we can consolidate these, or if I should go back to the original XJS Fanatic that my PC is defaulting to. Either way, nice to finally use the available resources from this Jaguar Forum.

 

Maybe a naive question, but you weren't mistakenly aligning the opposite end of the rotor arm, were you, this installing the distributor 180 degrees out? And then when you swapped all the leads, you effectively corrected your error? If so, you might want to swap all the leads back and reposition the distributor to the correct position as you've currently got the lead to 6A in the position on the distributor that is marked with "1", which will perpetually cause confusion to you and any future owner.

Just a thought...

Paul

 

GGG is the only one that MAY be able to unite the 2, but I seem to think NO.Surging, oh boy, that list is long and grows daily.

My findings, and ONLY my findings:

AAV, hence the deletion of it and the balance pipe.
TPS, PITA, so I stole an XJ40 3.6 unit, and adapted to my 85, chalk and cheese difference.
90deg elbow on top of the AAV splits on the underside, DUH, and I ALWAYS tell people to get a new elbow BEFORE touching what you have.
Inlet manifold nuts need a tighten, NOT stupid tight, COMMON SENSE tight.
Throttle discs are out if adjustment, AND coated with Goo as only the V12 can do if the Emission Junk is still used.
Throttle cross rods are NOT set equal, more of an issue at :just off" idle, when the 2 engines get unbalanced.
Blue/White Full Fuel capsule is AWOL, or it needs adjusting.
Timing, BUT that can only be sorted when the rest is playing the game as designed.
Vac leaks, HAHAHA, check the spigots at the rear of the A Bank Inlet. One will be a cap, they fall off, oops. Vac hose that travels behind the heat shield, A Bank to Trans Modulator, they leak. Brake Booster plastic Inlet elbow, nothing plastic lasts long in here.
Over run valves, another item I removed and binned.
ECU Pot needs a tickle. ONLY when its at Operating Temp, AND ONLY at idle,
This is ONLY if you have the PCV connected:
Oil Cap seal is intact.
Rubber plug at the front of teh A Bank head (timing chain ratchet access hole), is intact.
Any other similar things, as they will allow a Vac leak if not in good nick.
O2 sensors and Cats, NO IDEA, we NO got that stuff.

 

If someone has had the distributor apart (to free the seized centrifugal advance) it is possible to reverse the upper shaft in relation to the lower. Also, as someone has stated, it is possible to have the rotor pointed 180 degrees out when installing the distributor. No harm running it as you have it, just confuses the next owner.
As far as the idle surging, check for vacuum leaks; also do the throttle adjustment procedure by the book, and measure the blade clearance (.002”). Check that the TPS works and is adjusted correctly.

 

So I rotated the drive shaft below to “0”, took out the distributor (with the spark plug wires off by 180 degrees) then rotated the drive shaft below 360 degrees and put the distributor back on in the same position then put the spark plug wires on the correct position - rotated 180 degrees. The distributor was then in the proper position and started fine, exactly what was predicted in this thread. It then was idling much higher than before at around 2000 rpms and started to surge once again going from 500 to 2000 rpms like before. I referred to my XJS manual and noticed that the tension rotor appeared to be off by around 15 degrees. Pulled out the gear and rotated it 15 degrees clockwise then put it all back together. Fired right up and idled right at 900 rpms with no engine surge!! Probably mostly luck, but appreciate all the suggestions.

Jeffrey S. - Northern California
3 x 80’s V12 XJS’s
94’ straight 6 XJS (daily)
15 F-type R

The XJS is great to take on long road trips up the California coast into the wine country. Nice that it now has the distributor dialed in correctly with no surging idle!