rough idle, ticking, sudden change in leakdown #s

[Christien]

I sold my 86 911 about a month ago and the buyer has been having some problems with it over the last week or two. A rough idle getting progressively worse, then ticking coming from cylinder #1. He first thought it was a bent valve. He set the engine to TDC for #1, poured gas into the port and it ran through into the cylinder. Leakdown test today showed 2,3,6 were all below 10%, cylinder 1 was at 70%, 4 was at 30%, and 5 was 20%.

When I sold it it was running fine except for an unsteady idle. I had had that looked at recently by a local shop and he said it wasn't anything to worry about. When I bought it in March of 2011 (I only had it for a bit more than a year and 3-4000 miles) the compression and leakdown #s were fine: compression 175/170/170/175/170/170, leakdown 4%/5%/5%/4%/6%/6%.

Any thoughts on what could have gone wrong? He's not looking to me for restitution, just some help, and this has me baffled.

[56 nomad]

a lot can happen in a month...your numbers when sold showed a healthy motor, now not so good...either your mechanic was way off or something/or some one went wrong....how did he drive it? of course it was driven like a little old lady from Pasadena. if it ran well for 3 weeks i would be skeptical.
jm2c, ben

[aigel]

I have never heard of pouring gas into the intake port for testing a valve seal. That's an accident waiting to happen. If you crank the engine over with a flooded chamber you may hydrolock and eff up the bottom end / connecting rod. Next thing you hear is that it spun a bearing ...

The ticking really tells you that the valve isn't closing for some reason. It could be a bad spring, something stuck on the valve seat or a bent valve. Only one way to find out IMHO.

I am not sure how close you are to the buyer of the car, but getting engaged in troubleshooting your sold car can be a slippery slope, be careful.

G

[Alex86911]

Hi guys, I am the one who bought said car from Chris. Chris posted this for me as I don't usually use this site. As said, I am not looking for retribution for the car, more so advice. The car has idled rough since I got it, however it seemed to be getting progressively worse. Also, there is a light ticking from what sounds like cylinder 1. I have driven the car pretty easily, but i have also driven it as it should be driven, however I have never missed a shift, nor have I ever over revved it. Im just looking for advice as I am pretty bummed out.

Thanks guys

[aigel]

Hi Alex,

Thanks for joining us directly! Sorry to hear about the issues you are having. It isn't great to have a new toy that isn't working right, but it won't be the end of the world either. If you are a DIYer, this board can walk you through the required work. If not, folks here will at least point you in the right direction, so you are armed with the right info talking to your mechanic.

You should check out cylinder #1 valve spring, rocker arm and rocker arm shaft. If it is all good, then leak test yourself again and confirm that the intake valve is the issue.

Usually a good run at higher rpm and some WOT will clean off any carbon build up / deposits that may have wedged their way into the intake valve. Sounds like you already drove the car briskly, so that is probably not it.

If the spring / shaft / arm area does show nothing out of the ordinary, you will have to pull the head for exploratory surgery.

G

[56 nomad]

alex,
checking your history looks like you just joined us..what a nice intro...
ticking can be a lot of things as has been pointed out, driving it briskly is a loose term and could mean a different things to different folks..
when was the last time the valves were adjusted? just seems strange to me that numbers were good when sold and within a month dropped like that...agree with aigle dont pour any more gas down the runners.
i would first check the following , check/ adjust the valves as well as the timing when you pull the covers off you might see the problems pointed out in the previous post etc.
if all is within spec go to the harder stuff. ticking can also be a loose plug wire (spark) to ground good luck and for what its worth ... drive it like "you" own it , its a machine and can break then you have to fix it.
good luck let us know what you find. lets hope its an easy fix.

regards, ben

[timmy2]

I'm guessing it's the '86 in Christiens sig that you guys are talking about.
Was it the same garage doing the leakdown tests? (Methodology)
Valve guides? Rockers and shafts, Valve springs, exhaust leak?
When was the last valve clearance adjustment?

[Alex86911]

Hey guys, you have given me some good advice. I have done quite a bit to it since I got it, including plugs, wires, cap, rotor, intake gaskets, etc.

From what I can tell, the valve adjustment was roughly 15,000miles ago.

[JJ 911SC]

Hi Alex

Where are you located? You might be close to a Pelican and you would not know it. You can put you location below you Avatar.

As confirm by Chris and yourself, we all know the the idling was "hunting".

Who did the leak down that shows # at 70%?

While the problem seem to have been progressive the last 2 weeks, can you pinpoint when it got realy noticeable in relation to what you have done to the car. Can you elaborate on the Intake Gasket and Plugs replacement. What shape were they in? Any chance that something may have drop in (BTDT thanl God for shopvacs)?

[T77911S]

could also be some carbon fell and os keeping a valve from closing.
pull the valve covers and check the gap to see if either intake or exhaust is too wide.
you may be able to wiggle the rocker and tell.

if it was idling rough before all this, that could be air leaks, bad injector, igntiion problems, maybe even valve adjustment problems.

[Alex86911]

Well the problem has been there since I got it. The old plugs were in pretty poor condition, all we're ngk with one cylinder being an old Bosch. The plugs did make it fire up a bit easier.

When I did intake gaskets, I noticed number 4 was in poor shape. It did run a little bit better after, but still rough. I made sure nothing made its way into a cylinder.

I am in southern Ontario. The car is currently at Mantis Racing.

[E Sully]

First question, the most important part of a leak down test is where you hear the air leaking out. The numbers show a problem, but is the air leaking out past the valve or the rings?
You say the spark plugs looked bad. What did they look like? Were they oil fouled? One problem 3.2's are known for won't show up in a leak down test. It is valve guides. My 1986 engine needed valve guides at 75,000. miles. Did it smoke when you let up on the gas? This is a sign of oil being pulled by worn valve guides. I did a top end rebuild on mine. Valves and guides and new rings. It ran like new when it was done.
Ticking sound could be a leak at the exhaust manifold, broken head stud, valve train. Pull the valve covers, check the valve clearance, head studs, cam lobes and rockers. Push down on each valve and see if any push easier than others to see if a spring failed.
Injectors can also be a problem. When I bought my '86 engine it had sat for awhile and 2 of the injectors were sticking. I freed them up with carb cleaner, intermittantly applying power and tapping them.

[Alex86911]

The plugs weren't fouled, but just very worn out. The leakdown showed it coming out of the intake valves on two, and both intake and exhaust on the other. Valve clearance is a little on the large side on the two cylinders, and very large on cylinder 1 (cylinder with 70%)

[JJ 911SC]

Originally Posted by Alex86911

The plugs weren't fouled, but just very worn out. The leak down showed it coming out of the intake valves on two, and both intake and exhaust on the other. Valve clearance is a little on the large side on the two cylinders, and very large on cylinder 1 (cylinder with 70%)

With your latest info, I would do a Valve adjustment and another leak down but it might be a bit expensive in a shop but then again...

[Packet82]

Do the leakdown test again and figure out where the air is escaping. Intake, exhaust, or rings. That will let you narrow down the problem pretty quickly.

[Christien]

If you decide to DIY valve adjust (and there's no reason not to - it's not overly complicated, just takes time) Pelican sells a feeler gauge holder that's indispensable. I have one you can borrow, if you want. Just make sure you have new gaskets if they aren't the silicone reusable ones.

[Flat Six]

Originally Posted by Alex86911

Valve clearance is a little on the large side on the two cylinders, and very large on cylinder 1 (cylinder with 70%)

Difficult to diagnose via text from the other corner of the continent, but this ^^ suggests it's possible your valves aren't closing fully on these two cylinders. With any luck, due to carbon between valve and seat.

Good luck.

[T77911S]

from what you said about the plugs and gaskets, i dont think the rough idle and the leak down are related. back to what i said earlier and flat6 said.
bad igntion, leaks, or injectors for the idle, carbon for the leak down.
while you have the valve covers off, check the head bolts.

i bought a used 3.0 and was going to do a leak down on it on the stand, just to see the condition. before i could do it, carbon blocked one of valves so i went on ahead and pulled it apart.

[ant7]

Hi Alex,
Since the last valve adjust it looks like something has either got between the valves holding them open, or dare i say it, the valve is either bent, or there is something wrong with the valve seat in the head, the only way the valves could be bent is if they have come in contact with the pistons either by over-reved, or timing chain slipped, or something stuck between the valve and seat.
Valves usualy get tighter inbetween valve adjusts so i would say if their slack then there is deffinately something holding them open ie, carbon deposts, bent valves, or seat issues.
Hope you get it sorted soon.

Anthony.