Hello.i need YOUR HELP. I have an issue with my xjs. she is slow to start.Seems cylinders are catching up one after the other. Then all is correct for a few minutes, then it start to run unevenly. revving between 500 and 1500 rpm.for some minutes,Not always the same.Sometimes it resume to normal idling other times not. BUT if i put it in gear all is correct and i can drive as much a i want to. Did that 3 - 4 years ago then stopped doing it by itself but just resume doing it now. i am a Mechanic and owned 3 jags before.But now i'am puzzled.. Thanks for tour help. Yvon

 

Yvon,

As you have already posted a separate Intro thread, I've moved your question from New Member Area - Intro a MUST to XJS forum. Members here with the same model will be able to help.

Graham

 

If the revs are bouncing between 500 and 1500 rpm, then it is likely the AAV is stuck and it is allowing too much air in at idle. when it reaches 1500 the ECU will cut the fuel until the revs fall, then it bring back the fuel and since the AAV is allowing too much air it revs back to 1500 and the cycle repeats. The AAV is on the left side water rail, near the back. Find the hose that comes out the rear of the left air filter housing and follow it back.

Try screwing in the adjuster bolt on the side to cut back the amount of air, and if that doesn't work then generally replacement is the only answer.

 

Yvon,

As I mentioned in that other request attached to my Sticky on July 8, we really need to know if its a Marelli, or Lucas system.
The diagnostics and sorting are quite different.

Please count the HT leads:
13 = Lucas
14 = Marelli.

Then, the CORRECT info can flow, and the guess work is removed.

Good luck.

 

Hello. Good morning Thanks for the answer. I had a spare valve and tried it. Still hard to start, Starting is painful just one cyl after one.then it resume unevenly.righ after the last cyl comes on.After a while 3- 4 minutes idle sets at 900rpm.Then all seems ok but the adjustment nut have no effect on the idle if only 50 to 100 rpm.As said before even when running unevenly IF i put it in gear all is ok 8-900 rpm and i can driveway with no problem..I noticed the temperature seems higher than normal as before.. I dismantled the air valve cleaned it and reinstalled it. Car start differently but with the same results. Not sure a new valve will cure the problem.What do you think.Any idea??? Thanks Have a good day Yvon I have checked all the vacuum hoses to be sure.

 

If that's a US spec '89 then it will have the Marelli distributor. They can fail in weird ways. It should be fully on within two revolutions, since it takes three revolutions for the first cylinder to fire twice. If the car is only running on one bank you may get the running you're experiencing. That is the most common way for that distributor to fail.

So check that, just to be sure. Even if that's not the problem its worth checking anyway.

You may also have a leak allowing more air into the engine. There are lots of vacuum hoses that can crack and cause these problems. Unfortunately it requires systematic examination to find the problem, and there may be more than one at fault.

 

Mine is a 89 US car and it is Lucas....... it seems there is a mix around this time.
Must say I am pleased it is a Lucas, even if it is the prince of darkness!

 

Maybe the last few posts in this thread ......

https://www.jaguarforums.com/forum/x...2/#post2415773

.....can be moved over to here?

Cheers
DD

 

Right. The Marelli ignition was introduced at about 156xxx. This was about half-way thru the (USA) 1989 model year

Cheers
DD

 

Yvon,
I have copied this reply from the one I wrote as reply to your Lucas answer in my Sticky. I will leave it to Graham to delete that duplicated answer if he sees fit.

THANK YOU for that.
Lucas is easier by a long stretch.
Reading all this again, the engine starts, and slowly takes up all 12 cylinders, not good, as you know.

Over many years with these I suggest the following as a starting point. I know you are a mechanic and I mean NO negative attitude at all, just I work systematically with these engines, it saves time. So, if anything I suggest is "done" ignore that suggestion.

1) Spark plugs, age, and correctly gapped at 0.025".
2) HT leads, average in that engine bay is 5 -8 years.
3) Dist cap and rotor. NOT a common issue, but age again is against the original.
4) Coils. You have 2, one in the V, Main, one out the front as a "booster", for want of a better word. Check the Ohms, +ve to -ve, NO other wires attached. Looking for about 1.2 each coil. Connect the "booster" to the Main with the loom provided, read the Ohms again, looking for 0.6ish, and no higher than 0.9.
5) Inside the Ignition Amp is a Condensor. Remove it, it is redundant, and reeks havoc.
6) The TPS (Throttle Position Sensor) may be out of range. It will NOT cause the odd start up, just mentioning it as part of the checking.
7) Check the volts at the White wire at the +ve terminal of the Main coil. Ign ON, should be battery volts, or close. Read again as it cranks, should NOT drop more than 1volt, give or take.

Concentrating on the odd start up, as in one cyl and more cutting in as it warms up, then settling down to all 12 cyls.
Injector pulse is erratic. Can be caused by:
A) Grubby plug and socket of the EFI Resistor Pack. Located in the engine bay, RH front corner, near the radiator RH tank. I use lemon Juice to clean those items, and rinse with WD40.
B) EFI loom, the one in the bottom of the V. Age is way past use by date for this, and erratic Injector operation is almost always this loom. Make a new one, simple enough, although time consuming. New looms are out there, I have NO knowledge of their quality, always make my own.
C) Engine earth strap fiasco, Run a dedicated earth lead, engine to chassis. The factory twin braided nonsense, is just that, and age again has it reeking havoc.
D) Main EFI ECU, in the boot. Unplug the multi pin, clean it as with the Resistor Pack, and replug. Check the small Vac hose on the side, they crack/split, and cause all sorts of issues. Some markets have a Black Plastic "filter looking thing" in that Vac line (usually just under the battery). These also crack, remove it, run anew small Vac hose frron the floor spigot to the ECU.
E) Spark plugs, as mentioned.
F) HT leads, also mentioned.

The AAV, you have addressed, will NOT cause erratic start up as you describe. It is simply an Air Bleed device for Extra Air at Cold, and then Air Bleed, via the 13mm hex bolt, for HOT idle adjustment. If it jams OPEN, then the bouncing HOT idle is always going to happen.

A few attachments that may help.

 

There is a REAL possibility that what you think is idling "ok" when in gear is actually a car running at high idle but slowed by the fact that the car is in gear, which brings the idle down. Are you having to press the brake extra hard to stop?

It sounds like you have a massive air leak(s) somewhere. The bouncing idle is the engine trying to protect itself. I would guess that if the idle wasn't being controlled by shutting down the fuel (protection mode) the "idle" (reving) would go much higher than the 1500, 1600 or 1700rpms...

The small bolt in the side of the AAV (is this what you are calling a "valve" above) will only shave very small amounts of engine speed (RPM) when fully warmed and running properly. It will not fix this issue or get it right. It's a fine tune.

900 roms is not normal. Its idling high.

Check ALL linkage and the openings of the throttle bodies. The butterflies. See if one is stuck open.

Check ALL potential vac hoses and potential leak points into both intake manifolds. Check or recheck the AAV and it associated hoses - especially the elbow. Check both hoses to the crossover pipe. Check the auxiliary air valve hose under the RH side intake. All vac points.

I think you are getting lots of extra air.
Car is running rich rich rich. And at this point ya may have some fouled out plugs - and stuff.

When was the last time it ran normally?

 

I have to agree with JayJagJay. you have a vacuum leak. A BIG one! Normally what you describe is a bad AAV - quickest way to tell is at a cold start - remove your left side air filter cover and start her up. either you or a helper cover the grommet that supplies the AAV on the back plate of the air housing with your palm. Does your idle become more controlled?
Other things that are hard to detect are particular vacuum lines. If you have a vacuum pump with a test gage, there are two things to check -
1. one is from the rear of the right bank that goes to the Trans Modulator (I, for one, had this issue a with two separate vehicles). where this line attaches to the modulator is a rubber elbow. due to being right above the exhaust and CAT, this is notorious for disintegrating. (Does not do the modulator any good, either) It is best to test with the vacuum pump/gage from where it attaches to the intake because then you can verify not only the line being good, but also the modulator. If you are going to get access to fix one, do both!.
2. the other comes from your cross pipe in the back of your motor and goes to your ECU in the trunk. if this has a leak or an issue in the past, it is such a POS to get at that it is usually blown off - (screws with your curves, though). all other lines you can do with a quick visual.
Good luck and let us know what you find!

 

good afternoon This is my 3rd Jaguar and never experienced this kind of situation.all you are telling me make sense.will get at is seriously next week. Don't like to see the hood opened and not able to ride. Have a nice weekend Yvon