Hello, my name is Sierk. I recently bough a 1980 Series III xjs formerly owned by forum member Bruce Hugo. The car is beautiful. I have done a tune up (plugs, cap, rotor, oil, and looked unsuccessfully for vacuum leaks) but can’t seem to resolve a couple of issues. It is very difficult to start, and has a very lumpy idle when cold. There seems to be an exhaust manifold leak though I have not removed the metal cover to pinpoint it. The transmission also slips going up hill until it warms up a bit. I think the lumpy idle at cold start impacts the brakes - lack of proper vacuum? There are a few minor issues I need to attend to like the inoperable antenna, the inoperable aftermarket cruise control and the inoperable sun roof but these things can wait. The lumpy idle is a little frustrating and insights would be much appreciated.
Real quickly, Id dump in a can of BG44K, in a half-tank of fuel, and see if the injectors can be cleaned up a bit.
I’ve never used an injector cleaner but I’m willing to give it a try. Thanks.
BG44K is what I used to clean injectors: you can also use Techron, or Techrolene. It works best when used in a half-tank of fuel.
It doesnt always work, but it often can help, plus, there’s no need—yet—to commit to more expensive remedies.
Ill assume the rest of the ignition items are up to snuff.
Sierk,
My 1984 XJ6 Vanden Plas developed a lumpy idle a year or two after I purchased it. I did a compression check and found out that I had very little compression (20 PSI?) on the #1 cylinder, the one closest to the firewall while the others were around 120 PSI if I remember correctly. I removed the cylinder head to learn that the #1 exhaust valve was “burnt” or melted probably because the valve clearances had closed up over the years and they weren’t adjusted. See attached picture of that burnt valve. It is supposed to be round and smooth to close up against the valve seats, but it obviously wasn’t due to the melted area.
In the case of my 1984 XJ6 VdP I removed the cylinder head and took it to a local machine shop for rework. There was a dramatic improvement when I reinstalled it and drove the car. It is possible that these engines ran smoothly when brand new, but a variety issues can crop up over the years to create a lumpy idle. With only 6 cylinders deviation between the cylinders in compression, spark and fuel can create an uneven idle, and vacuum leak issues can only add to the problem.
If I were you I would do a compression check and valve clearance check of the engine before proceeding with anything else. If you are handy, have the tools, and are reasonably knowledgeable Do-It-Yourself mechanic the compression check might take an hour. The valve clearance check is much more complicated, requires special tools and an appropriate shop manual and it might take you a couple of days to do right the first time. I am not certain how many hours a shop might charge to do it, but I suspect it is 6-8 hours along with an assortment of new gaskets and other parts.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
Very good advice! I was coming from the possibility thst had already been done, but that is a fundamental that needs to be determined.
Thanks Paul. I will start with a compression check and go from there. I do still suspect a vacuum leak though I can’t find it.
Easy test for that: use a hand-held propane torch—NOT LIGHTED!!!—and, while idling, pass the slighty-on torch around manifolds/hoses. If there is a leak, the propane will speed up the idle.
After determining if you have compression, given the age of the hoses, you could have a few that are cracked.
Sierk,
Good luck, and please post back with the results of your compression check. Nothing will smooth out a lumpy idle if you have a compression (valve or ring) problem. Once you know the compression numbers it will be obvious if you have a problem there or not.
As far as your cold start problems, two common causes that I have seen on this list are inoperative cold start injector or leaky fuel injectors dripping fuel in the cylinders after engine shuts down. Now an internal combustion engine will start and run if it is compression, fuel, and spark in the right amounts at the right time. The EFI system in these cars inject extra fuel into the intake manifold via the cold start injector during cold starts. If your cold start injector is clogged, inoperative, or if the wires going to it have failed, you will be getting less fuel than is needed to start the engine. Conversely, the fuel injectors should close completely when the engine is shut down and they should not leak fuel into the cylinders. If the fuel injectors leak fuel into the cylinders when the engine is shut down there might be too much fuel in the cylinders to start the engine.
Once you get the compression check done you should look and see if your cold start injector is working properly. It is located on the right side of the engine about in the middle of the intake manifold below the fuel injectors for cylinders #3 and #4. It should be blue and have a blue plastic connector on it unless it has been modified. As far a vacuum leaks, there are lots and lots of possibilities there. Do you have a vacuum gauge?
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
Just to clarify, the hard starting and lumpy idle is only when cold?
The engine starts easily, and idles smoothly, when warmed up?
Cheers
DD
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As Doug says, Sierk - if the problem with starting and idling is confined to a cold engine; the AAV is a prime suspect…
The slipping in gear must be addressed ASAP; if this is caused by a slipping band, the band lining will very quickly wear out - expensive. Try adjusting the front band as a first step…
As Paul says; a compression test is certainly called for, ‘dry’ and ‘wet’ if need be - it’s one of the few unambiguous tests. It will tell if action is required - but how ‘lumpy’ is the idle; it’s unusual for the xk to be silky smooth in idle. What is your idle rpms - the xk smoothes out with increasing rpms even with serious faults…
Frank
xj6 85 Sov Europe (UK/NZ)
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Welcome. I have one of these which I have used to advantage. Mine is about 30 years old and a “Lucas” so it is compatible with vintage Jaguars. Good luck with it. Old school Paul.
http://www.autospeed.com/cms/article.html?&title=Using-a-Vacuum-Gauge-for-Engine-Diagnostics&A=2393
Good point and I was wondering the same thing.
If ‘lumpy’ can be equated to the feeling you’d get, let’s say, by pulling a spark plug wire …then it can certainly be improved upon.
If ‘lumpy’ is a slight tremble that likely goes unnoticed by passengers but irritates the driver to no end, well…it might be as good as it gets. I’m sure you remember the exhaustive efforts of some of our members, many years ago, seeking the silky smooth idle.
Cheers
DD
Paul N.
Wowee, no doubt as to that valves inability to seal the combustion chamber. Why ? Too tight would seem to bun all the way around the seat. .And the pit, even more intriguing. A flaw in the material of the valve ? But, academic, the fix is the same. As you did,
Paul B.
Well, my pair of vacum gusges are not Lucas branded. But, I learned to sue them to balance the two carbs on my Corvairs.
And on other critters since then. Mine have a fuel pressure function. But, only for carb’s. I’ve never sued that feature.
Carl
Frank,
Thanks to you and so many other for jumping in and giving me some advise. What is the AAV? I will try to adjust the bands on the transmission - my understanding is that this is not as daunting as it sounds.
Sierk
Paul,
That is a great link! I have saved it.
Thanks,
Sierk
Doug,
Thanks (and next time I will try to answer everyone in one message). My understanding is that you were quite familiar with my car at one time. The idle is quite lumpy when cold (bouncing under 400rpm) and hard to start when cold. When it warms up its really easy to start, but the idle remains lumpy (though less so) bumping around at just above 500 rpm. I would say it is kind of like missing a cylinder at idle, though it does smooth out quickly at higher rpms. About 17 years ago I had an 86, it was much smoother (granted it was newer at the time). I will start with a compression test this weekend. What is the AAV?
Thanks again,
Sierk
EVERY burnt valve I’ve ever seen—and I’ve seen a lot!— burned in a like fashion, up to and including a VERY large “pie wedge” right out of the valve!
You definitely need to do a compression check and valve lash check, pronto.
The AAV = Auxiliary Air Valve. it admits extra air to increase idle speed when cold.
You cold idle speed of 400 and warm idle speed of 500 are both too low. An inoperative AAV could certainly account for the former.
The hot idle speed can be adjusted upward…which might be all it takes to solve the problem. But, OTOH, other correctable faults could be causing the low idle…in which case increasing the idle speed is just masking the root cause.
I agree that a compression test is worthwhile. If that turns out OK make sure the throttle body is clean and the throttle blade is set at the proper .002" gap…preferably before any attempts at adjusting the idle speed, if you decide to do so
The cold start injector, mentioned previously, aids in cold starting. I’ll provide links to some info and also link for setting the idle speed.
I would also check the coolant temp sensor. This device plays a major role in fuel mixture when the engine is cold. Can be checked with an ohm meter or replaced for about $25 and 10 minutes labor…not hateful as far as guesswork goes.
Yes, I am familiar with the car. The PO was a friend; I helped him with many repairs…but most of them were quite some time ago so I can’t remember all the details. It was lavished with dollars and attention for many years.
http://www.jag-lovers.org/xjlovers/xjfaq/aav.htm
http://www.jag-lovers.org/xjlovers/xjfaq/idleadjust.htm
http://www.jag-lovers.org/xjlovers/xjfaq/roughidle.htm
http://www.jag-lovers.org/xjlovers/xjfaq/testcts.htm
http://www.jag-lovers.org/xjlovers/xjfaq/coldstartchecklist.htm
Cheers
DD