FF34 and rough iddle after cleaning up the V12 valley : fixed - one blocked injector

[sbobev (Steve)]

not sure what PCV stands for ?

Ignore those comments. The 6.0L does not have the same crankcase venting as the 5.3L

[sbobev (Steve)]

So remember, your PCV is a ‘vacuum leak’ too.

The 6.0L factory set up uses the following part load and full load breathing. No PCV

[xjsv12coupe]

Thanks Steve for clarifying this
I did change the rubber parts on the part load breather system, and cleaned the full load breather filter

I’ll take the AAV out and check it

[xjsv12coupe]

AAV out (easier than I feared, pumping 4l of coolant allowed to take it off without o mess of coolant in the garage)

and tested ont the “bench” (more like SWBO’s kitchen, as I don’t have hot water in the garage)

at 25°C, the top of the piston is at 67.2mm from the top of the AAV, and the air gap is open :

at 80°C ish, the piston raises to 63.7mm, and the air gap is closed : ( I tried blowing air through and it’s very difficult to gat some go through)

so time to refit the AAV, and look for air leaks elsewhere

I’ve seen some pressurized smoke machines which look like god send for such chase, but I doubt my next door garage has one

I thought about air getting in the engine and being thrown in the admission by the engine breather : I’ll try and block those ports and see if it makes any difference

I searched for the O2 sensor connectors, and found the right one , the left sould be similar opposite side, but less easy to reach

[Andy_Broadbent]

I’d done about 40 miles in my 6.0ltr V12 last Sunday & just at the point I removed my foot from the accelerator at about 75mph to slow for a junction, I got an FF36 code. The car wasn’t running any differently, at idle or at revs as I drove home.

I’m thinking I’ve got an oxygen sensor fault due to when the fault code having appeared With a ‘closed throttle’ - if the fault had appeared @ 70mph & 2,000 revs, i would have suspected an injector fault. It could of course be neither & be an engine wiring harness problem.

[xjsv12coupe]

I re installed the AAV, and no surprise , no change, idle is still to high

I blocked the AAV input port in the LH air box, and idle is still 900rpm, no drop in rpm
which makes sense as the AAV is doing its job, air coming from elsewhere

I could hear the air draw on the distributor filter, but wasn’t able to locate an air entry

next step will be to replace the remaining vacuum hoses,:
both in and out the distributor (even if they shouldn’t make a difference
one from each manifold (rear of the RH side, bottom of the LH side) heading to the front of the engine

[JimD_in_Alabama (JimD in Alabama, 95 V12 XJS Coupe, Marelli, LHD)]

Is your distributor cap gasket present? Paperish gasket under the cap.

[xjsv12coupe]

yes, the gasket is there
I fitted a new one when I got the car 4 years ago (limited miles since, and it still looks ok)

[Robin_O_Connor]

Have you tried spraying carb cleaner around the intake area?

[AttyDallas (Paul L.)]

@xjsv12coupe

I spent some time cleaning up the valley of my 6.0 93.5 coupe, changing gaskets, renewing vacuum hoses and cleaning and getting parts powder coated, and on reassembly , the idle is rough, and I get an FF34 error code.
the car seems a bit low on power, but I didn’t want to push it while something is wrong

work done :

• replace all water rail gaskets and O-rings,
• replace all AAV internal with John_John’s kit
• got the cam cover powder coated, fit allumium half moons and replace banjo bolts + gaskets
• renew the cam cover gasket
• clean all injectors, change their filter and all O-rings
• clean and refit the additional air rails, and change all the air hoses
• change all the small vacuum hoses
• clean manifolds and renew all vacuum plugs and manifold gaskets

I checked the following

• all spark plugs and both coils are connected to the right plug, and cords are fully inserted,
• all injectors are clicking : I thing one seems to be clicking slightly less strongly than the others
• all vacuum hoses are back to their original spot

I cleared the code, tightened the manifold nut, and could move the car a few time without getting the FF34 error code, but it came back when I finally got the car back into the garage

FF34 error code is “injection bank A” problem, but I couldn’t find much about it
suggestions are

• air leak in the manifold : I tried to tighten all nuts, none was loose, I couldn’t find any open vaccum port
• bad ignition : all sparks were changed 3000km ago, so I didn’t took them out
• bad or lazy O2 sensor : they’ve not been touched, may be one got some coolant or other fluid during the cleaning up
• ignition amp : I may try and swap those, as I got 2 or 3 cut outs on the road before (rpm drop to 0, then engine restarts and rpm show again, which could be related to the said amp)

Iddle seems to stay a bit high, even with AAV screw full on, I I guess there could be still an air entry somewhere

all suggestion of testing welcome, to try and locate the problem

Dang, I had thought by the time Jag got to the 6.0 they had “corrected the errors of their ways” in the XJS line, but I guess not, from all the work you had to do on yours.

[AttyDallas (Paul L.)]

@sbobev

Idle speed for the 6.0L should be set as in the manual, which I posted 3 posts earlier.

You don’t want it lower, because when there is load, the speed will drop and there may not be enough coolant flow while you’re stuck in traffic and/or the alternator may not charge.

You don’t want it much higher because you don’t want to tax your torque converter and transmission when switching into gear and…because sooner to later the 36CU will have to perform the “infamous” adaptive fuel trim:

Yours truly has spent a large part of the past decade chasing smooth idle out of my 6.0L.
From my own experience, with a rebuilt AAV and new gaskets/vacuum hoses, once you set the idle speed correctly, you won’t have worry about it for some time.

Hmmmm. So wondering now if this “a.f.t.” is what is responsible for the disturbing sound and feel of CLUNK when engaging the trans in gear (D or R) while idling? She does seem to tend to idle @ 1,000 RPMs, and yet I couldn’t figure out why only being about 33%/250 RPMs off could make such a big difference in the behavior of the trans in that regard. btw, what SHOULD our cold idle be on '92 5.3? If the a.f.t. is in fact responsible for the trans issue, how do you clear it out, either temporarily to see if that is what’s wrong or permanently if it is wrong?

[AttyDallas (Paul L.)]

@gregma

Idle should be 750-850rpm in P.

Mine is, and sits at 700rpm in D.

After driving a while and putting it back into P, it can sit at 900-1000RPM about 20 seconds, but within 2 minutes will calm down to 750-800RPM in P. Totally normal. Don’t get hung up on high idle unless it always sits at 1000.

What should our cold idle speed be, Gregmatic?

[AttyDallas (Paul L.)]

@gregma

BTW, the AAV’s on this car are notorious to not function correctly at this age. They are either stuck, or in most cases (like mine) are ‘tired’ and don’t close all the way. I sent mine to a forum member, Jonas, who rebuilds them.
Works like a charm, and then I could set correct idle adjustments knowing that the AAV is 100% functional.

Do you have a current address for him, Gregmatic? I think someone else mentioned earlier that JohnJohn has some kind of repair kit for the AAV, but I don’t see it on his Ebay website. Has he stopped selling those?

[gregma (Greg (1988 XJ-S V12 Lucas))]

You need to contact Jonas (JohnJohn) in a private message for AAV.

Cold idle is very dependent on temperature. Mine is usually around 900-1000rpm, but can be higher on a very cold day. In a hot climate, it could be lower.

[AttyDallas (Paul L.)]

I just did (btw, didn’t realize Jonas = JohnJohn until now ). Also complimented him on his newest item in his Ebay store (added just 2-3 days ago) - the bad-azz throttle bushings!

[xjsv12coupe]

@AttyDallas

Dang, I had thought by the time Jag got to the 6.0 they had “corrected the errors of their ways” in the XJS line, but I guess not, from all the work you had to do on yours.

no big surprise for me, even being a “newer version”, my car is stil 26 years old

my AAV was rebuilt using Jonas (JohnJohn) 's kit, and I also fitted at the same time a pait of his aluminium half moons and revised banjo bolts

@ Robin_O_Conno
I had a try, but nothing was noticeable : I’ll have another go with the AAV port blocked, as it could help

one thing which surprised was the ability to rotate the injectors with out efforts, even after they were back into their location in the manifolds
The gasket seems to be compressed ok,
I would not increase the torque on the manifolds nuts : I went up to 30Nm

edit :
I 'll have a look at the centre vents piping connections : I replaced all the rubber bends and gaskets, so could have left a loose clip / leaking point on one of those

XJS V12 6.0 What are pipes to Marelli Distributor for ...

[Kirbert (Author of the Book, former owner of an '83 XJ-S H.E.)]

@xjsv12coupe

I blocked the AAV input port in the LH air box, and idle is still 900rpm, no drop in rpm
which makes sense as the AAV is doing its job, air coming from elsewhere

Well, that ain’t right. When you block that opening the idle should drop. Whether or not it drops enough is the question. If it doesn’t drop at all, the only explanation I can think of is that it’s pulling all the air it needs through the distributor vent. Which probably means you’ve got the idle screw all the way in.

One thing is simple: If the idle is too high, the engine is getting too much air. Either there’s a leak somewhere, or the butterflies aren’t closing like they should.

[xjsv12coupe]

indeed
I could have saved the AAV removal and testing if I had followed Steve (sbobev) 's suggestion, as the result is exactly the same : blocking the AAV air entry only leaves the Marelli vent as input

I checked the throttle links and removed any restriction to closing the butterflies
the links were a bit short and I loosen them so the butterflies spindles click on their stops

I’m thinking of closing the partial load breather pipes for a test, as I’ve already checked all the lines coming to the manifolds

eidt : I checked those pipes, and one of them had a loose rubber end on the oil separator
I tried to get a better fit, but I’m not really glad of it, and the result is the same as before.

I’ll look for rubber bungs to get both pipes closed, and have another test

[sbobev (Steve)]

I think this thread has ran its course. From the last a dozen or so posts, it is evident that people are not reading the prior messages, and there are now repeats of ideas already discussed.

My recommendation - start a new topic with your quest for chasing the vacuum leak(s). Once the culprit is done, let’s come back to the FF34 discussion.

PS 900 rpm with the AAV intake port blocked is a sign of HUGE leak. You don’t need a smoke machine for that.

[gregma (Greg (1988 XJ-S V12 Lucas))]

Last year, although I had a good idle at 800rpm, when I blocked the aav and breather to distributor, it would only go down to 600RPM. I spent a lot of time looking for vacuum leaks to no avail.

Finally realized I had incorrectly adjusted throttle body gaps, and they weren’t centered correctly. Once I correctly got them adjusted, I had to back out AAV screw a bit for 800rpm. Now when I block off AAV and distributor line, it drops to 300-400RPM.