New plugs & wires plus leakdown on '76S

Jim Sims · 10-31-2001, 06:05 AM

Engine was not firing no. 5; spark plug wire or connections bad: no continuity (infinite resistance). Distributor cap okay. Installed new Bosch copper electode plugs (7591/W5DC/0.241.245.552-076) with .7 mm gap, a bit of anti-sieze on threads and 15 ft-lbs torque. Put on new Beru wires (ZEF 309/0300.890.309); old wires appeared to be original: 25 year old external wire braid shielded type(!). Then did a leakdown while I was in there plus reset points dwell to 37 degrees.

Leakdown numbers:
#1 94%
#2 93%
#3 96%
#4 91%
#5 88% (cylinder w/ bad wire)
#6 96%

#5 started at 75%; I did a couple of revs of the engine and redid the test and it came up to 88%. I suspect there is still some fouling to burn out in that cylinder. I'll check it again in a few weeks when I put the car asleep for the winter and surgery. Engine is now running very well. Cheers, Jim

john walker's workshop · 10-31-2001, 07:17 AM

if you had 98% leakage, you would be in big trouble. i suspect your gauge reads backwards from all the others, as 4%-8% is the usual reading for a decent engine. done hot of course.

Jim Sims · 10-31-2001, 07:30 AM

I posted % of pressure retained; engine was at operating temperature.

Pillow · 10-31-2001, 07:35 AM

When I got my SC the braided wires were horrible! It was a darn light show of arcing in the dark

Ran much better after a new set of wires and plugs.

------------------
Adrian Pillow
1979 911 SC
1966 VW Microbus
PCA - Peachstate Region

Jim Sims · 10-31-2001, 09:34 AM

I recall reading somewhere that the factory leakdown specs were: 3% to 6% with 10% being the maximum acceptable. Jim

ohecht · 02-02-2002, 06:28 PM

Is the consensus on the list that the SS braided sheaths found on earlier wires are not necessary to reduce RF interference?

Olivier

Superman · 02-02-2002, 07:28 PM

That's my consensus.

Sputterbug · Sputterbug's Garage

I had to bump this topic up because it's relevant to my situation. I took my car in for its very first pro inspection under my ownership, that is the past two years. Did a compression test that yielded 180-185 in all cylinders except for 150 in #2. The same cylinder (#2) apparently had a 70% leakdown figure. For what it's worth, this mechanic is reading that as "percent leakage." I know this because he told me that 10% is about the maximum acceptable result.

I didn't have too much time to query him about possible causes, because I was in the middle of a meeting at work. The car had to stay overnight to have the oil return tubes replaced (leak was found) and the brakes bled.

My car burns a qt of oil every 500-600 miles, which is about the limit of acceptability for 3.2 engines apparently. It doesn't seem to lack power, and I don't hear anything odd in the engine when it's running. In short, I didn't have a problem when I brought it in; I just wanted some peace of mind. Now, of course, I have angst!

What's the range of causes for such a bad leakdown figure? Any ideas?

Jim Sims · 01:57 PM

I will assume your mechanic did the test with the engine warmed. Did your mechanic attempt to find where the leak was going: exhaust valve to muffler, intake valve to induction system, ring blow by to breather? Removing the plugs to install the leakdown tester can dislodge a bit of carbon which can get under the valves and cause a leak. Was the plug fouled in the leaky cylinder? If I had these results I'd put the plugs back in and run the engine at 3000 to 4000 rpm for 20 minutes and then redo the test. If I still had a poor result, I'd run a bottle of Techron through the fuel system combined with a good hot run of the engine and redo the test a third time but then I'm doing the testing myself. You could have a bad cylinder/head too and the numbers are real although the compression/leakdown numbers of the bad cylinder don't seem to quite match. I would have expected less compression with 70% leak down. Good luck, Jim

Rot 911 · 05-09-2002, 11:04 AM

Quote:

Originally posted by Sputterbug
Did a compression test that yielded 180-185 in all cylinders except for 150 in #2. The same cylinder (#2) apparently had a 70% leakdown figure. I just wanted some peace of mind. Now, of course, I have angst!

What's the range of causes for such a bad leakdown figure? Any ideas?

You don't just have a bad leakdown you have bad compression on #2. Anything more than a 10% difference in cylinders is bad. I agree with the advice on the techron, then retest.

Sputterbug · Sputterbug's Garage

Thanks for the replies. Again, I wasn't able to pepper the wrench with questions because I was essentially ducking out of a meeting at work. I had to get back in ASAP!

I just spent a bunch of time reading some good leakdown threads in the archive here. I learned about the Techron/carbon possibility, and that's my next step. I also saw Early_S_Man's super cleanout routine with the stuff (How to do that with a 3.2? The reference there was for an SC.)

I adjusted the valves myself a few kMiles ago (my first time). Everything has sounded quiet ever since, but maybe one needs a tweak? I'm not panicking yet. I drive the car locally more than I do on the highway, and it doesn't spend much time over 4K. Maybe a good run will clean it out and restore my confidence.

I need to talk in greater detail with the shop about exactly where they heard air escaping when they did the test. That wasn't mentioned to me, and the only 'fix' I heard about in the brief conversation was a rebuild - not just top end, but the whole enchilada. Hmph. I'm not there yet! FWIW, my car has 90K on it.

Superman · 05-09-2002, 12:29 PM

A great deal more investigation is necessary before you go making a rebuild decision. And I;m not sure that this would be the shop to do it. Listening for air escaping is something that IMHO should not have been overlooked. Put th eplugs back in, drive it and retest. Yes, you can safely use B-12 Chemtool or Techron to clean things up.

BAsically, a good mechanical investigator can know pretty much what he's going to find before he removes the engine for a rebuild. Of course, not everything can be known before teardown, but you can know a great deal more than you do now.

And again, I would suggest you quit thinking about a rebuild at least for a bit.

nhromyak · nhromyak's Garage

The valves could be too tight.

Rot 911 · 05-09-2002, 02:16 PM

Quote:

Originally posted by nhromyak
The valves could be too tight.

Ah yes reminds me of the valve adjustment I did where I ended up with ZERO compression on the #1 cylinder all due to a bad valve adjustment on both the intake and exhaust valves. Must have been sleeping on that one.