JPS

So, looking for constructive advice as to the best way to proceed. Pretty clear it won't be cheap.

Street / track 95 993 with stock motor and about 74k miles.

Roughish idle and some hesitation about 2800-3000 revs when running up through the gears. I'd hoped for something easy and cheap ala' dist cap or vacuum line or something.

Mechanic just called and said compression in cylinder 3 is in the 90s, vs other 5 cyl strong and consistent (can't recall number but he said all good).

So. Just happened, or at least I just took it in.

What more do I need to find out now to best determine how to proceed?

What are the paths people in similar circumstances have taken?

I'm buying some advice time from Steve W but curious as to what advice you may have as well.

Thx

pp000830

Check it again after tapping the valves to make sure they close fully. Sometimes a valve sticks open a little when the engine is rotated by hand but shuts tight under running conditions.

May be unrelated to"Roughish idle and some hesitation about 2800-3000 revs when running up through the gears. I'd hoped for something easy and cheap ala' dist cap or vacuum line or something"

I would check for vacuum leaks or failed vacuum actuators or vacuum solenoids. I would also run a couple tanks with Techron through it before drawing any conclusions.

NC TRACKRAT

You're going to need leak-down numbers to do a credible diagnosis. If you're lucky, it could be nothing more than a small chunk of carbon holding a valve open. Bore scope will be cheaper than a tear-down.

JPS

Thx so far. Answers:
Performance:
1) Rough-ish idle mostly on startup, but general not as smooth as it used to be.
2) Slight but consistent and, to my observation, increasing very slight hesitation mostly at about 2800-3000 RPM. Less noticeable at higher revs, but still not as smooth.

I took it in hoping cracked dist cap or lose wire or vacuum leak or clogged ISV. Upcoming travels and track days didn't give me any DIY time for ISV or other simple things.

It had a [edit: compression, not] leak down, numbers in the 90s on that cyl only. They haven't bore scoped yet but I will have them do it. Also will find out more about where exactly the leak is with a leakdown

What next?

JPS

I planned on that until the leakdown came.

I didn't realize they didn't do leakdown, just compression. That's coming tomorrow.

Quadcammer

do leakdown to determine source and go from there.

pp000830

Do the less invasive stuff first then investigate the leak-down issue as it may simply be a phantom from the testing process or carbon temporarily stuck on a valve seat. It may be completely unrelated to your running issues.

No matter what feedback you get, run 2 bottles of Techron through the engine with the gas before any more monies are spent. Some find the Sea Foam for fuel injected cars even more effective than Techron. Testing the actuators is very easy, run the engine for a few min., shut it off, have someone turn the ignition on, w/o starting the engine, for you and watch the actuators cycle through a starting test. Then check the one behind the CCU by pressing the top right button on the CCU and listen for an actuation sound.

Here is a thread on the subject:
https://rennlist.com/forums/993-foru...naware-of.html

Rockit

I have a 95 with 185k that runs absolutely perfect. 95's are easier on the valves with less PCV-crank case junk going back in the intake.

You say you just got it? or recently?

If it where me I would not trust one reading, I would make them do it again the next day.

Again if it where me I would look at drivability things like- fuel injector clogged. Vacuum leak, If ALL spark plugs maybe where not changed. When I got my car one plug had never been changed, when they pulled the engine to seal leaks they found it. Make sure the rubber belt on the distributor is good. I would check the basics first.

Focus on that cylinder that is low and change both plugs, one could be loose or the guy just did not get a good seal on the pressure gauge.

95's really don't suffer from premature value wear at 74k. There still could be a problem but I would double check it and or make them show you in person.

Before I had to take the head off I would double triple check....also I would run at least 4 tank fulls of Sea Foam in the fuel first...that's me. Every shop has one good tech and maybe 4 average ones and most don't know the older P cars. Again, I would not trust the report and investigate.

https://seafoamsales.com/

pp000830

+1

mpruden

Leak down will usually be given as a %, whereas compression will be given in PSI. I'm guessing the 90 was 90 psi, a compression test number.

I agree with those that say to find the source of pressure loss as an immediate next step. Is it rings, is it valves, valve guides, which valve(s)? The mechanic should be able to send compressed air into the cylinder and hear/feel the air rushing out. That should give you a pretty solid signal on the cause of the pressure loss.

How's your oil consumption?

Regardless, selling your 993 is not an option. Don't even go there. How many people are left that use a 993 for family road trip duty and track days? Stay strong and fix the engine

JPS

I reported badly. They did compression. Leakdown is tomorrow.

Quadcammer

You do not know what you're talking about.

JPS

Leakdown results in.

Issue is in cylinder #3 only from compression test.

Leakdown test shows rings and intake ok, leak is exhaust cycle.

Thoughts?

Quadcammer

more details please.

What was the leakdown in cyl 3? And from what I'm interpreting, the cyl is leaking out the exhaust valve? Most likely your valve guides are shot and that valve is just not sealing any more. I guess you could take the valve cover off and have your shop remove the valve spring and do some measurements on the valve play, but with 74k miles and some track work, I'd bet at least one, if not more of your valve guides need to be replaced.

Rest of the motor is likely fine. So you're probably looking at top end rebuild and some odds and ends.

NC TRACKRAT

Exact leak-down percentages are needed. I still think it's worth a borescope look-see to determine if it's carbon prohibiting the valve from fully seating. IMHO, valve guide wear would be showing to some extent in other cylinders, not just one.