I GIVE UP! Bad Ignition or What, Part 2

OK ... I've officially had it. Just replaced the ignition with a new Permatune and a new coil. No better. I'm also running a Carter fuel pump at 3psi, not the small Facet from before.

What have I missed? I'm going to check the spark plugs and pop open the carbs just to see if they're dirty again, even though I just rebuilt them a few weeks ago and installed a new fuel filter. What about valve lash? I don't hear a bad ticker. Maybe a tight one? I'm almost out of time for making my Friday deadline.

The onlt questions I ca think of are ... is the braided line for the ignition terminal supposed to connect to one of the CDS box mounting bolts or to one of the ignition panel mtg bolts? Shouldn't matter, should it? How many connections are supposed to be on the CDS box ground tab? There are 2 tabs (D on the Permatune diagram).

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Brian Scotti
'73 S Coupe

Forgive me if this was covered much much earlier on on the other thread, but did you ever check the valves.

As I understand it, the valves need to be set correctly before adjusting the timing etc, and also a burnt valve could give some of the problems (I think).

A compression test could rule out a burnt valve.

Cam

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Cameron Baudinet
1975 911S

I'm sorry to hear the frustrating news. It sounds like you have reached that level where a break is in order. I tend to make irrational decisions (read expensive)when I'm all out of ideas, so sit back and take stock for a while maybe?? You'll get there eventually!

Warren- please define "across the points" for checking dwell. I've had enough of trying to interpret various dwell meter manufacturers/haynes/word of mouth descriptions on how to connect a meter to our points CDI systems. They all say different things. I just want to know what I clip the little red lead onto, and what to clip the little black one on. It should be soooo simple!!
Thanks.

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'72 911 TE

Brian,

I still think it's the districutor shaft wobble ... so if you need a break from thinking and worrying about the mystery, why don't you pull the distributor, disassemble, and replace the bushings? I can just about guarantee that the engine WILL run better afterwards, and maybe fix the miss!

As for the ground leads at the CDI-unit, my recollection is that the braided pair is terminated in one 1/4" quick-disconnect female terminal, and that went directly to terminal 'D' at the CDI-unit, and that one of the corner bolts of the CDI-unit had a circular, bare spot on the console sheet metal, and that a short, brown jumper wire ran from a circular terminal lug, called a ring terminal, under the CDI-unit, in direct contact with the bare sheet metal ... the other end of the brown wire (approx. 14 ga wire) was a 1/4" quick disconnect, and was clipped on the second terminal at 'D' ... so no 'vacancies' exist on terminal ;'D.' If you did not find a brown ground jumper on your CDI-unit, I suggest you fabricate and install one ... it may be the answer to the miss!!!

Matt,

If you clip the black lead to ground at the distributor, and the red lead to the same terminal on the distributor that the points lead goes to inside the distributor, your dwell meter should work.

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 09-06-2000).]

I hear your frustration, Brian and it's too bad 'cuz you have tried quite hard to solve this, at some expense. The break idea sounds good and, if you can handle it, a rebuild of the distributor bushings. I have done Porsches but if they're similar, putting the distributor body in the oven at 300 degrees, and the new bushings in the freezer, they should pop right in with little trouble as long as you do it quickly. And I also am still suspicious of the distributor shaft play. Respectfully.

Good luck. Take it easy. You have worked real hard.

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'83 SC

Brian,
I remember you saying the timing appeared to be jumping around when you checked. Can you give us some idea in degrees or in inches how much it wanders, (i.e. 1/16" to either side of the mark 1/8" total). Does it slowly wander from side to side or is it jumping around the mark erratically?
Your timing shouldn't jump around or waver. You may want to tackle that first. Then make sure all your plugs are actually firing without a miss. I feel for ya. It's tough troubleshooting when there may be multiple problems. Go for getting that timing mark solid.

Leon 78SC

Thanks for the support guys. It's not like I'm the only Porsche owner out there who's struggled to fix a mysterious problem. I'm sure you all have had a real killer that you lost sleep over. I'm lucky enough to be able to draw from all your knowledge.

I might have forgot to mention that the timing mark holds steady at the proper places. It was wandering because the distributor was not clamped down enough. The timing mark is rock solid.

Warren, I fab'd up a ground wire like the one you described with no improvement. I also checked inside the carbs and they're squeaky clean.

Pulled 4/6 spark plugs and found some with pretty heavy soot, with a tan electrode. Cleaned them up with no improvement. I can't believe the spark is weak. The plugs are the right ones (heat range) because it ran fine for quite a while with them.

Leon, I hooked up a timing light to each plug wire and watched the light to see if it was funky when the engine started to miss. No such luck.

I'm going to take everyone's advice and call it quits tonight before I really break something! My plans tomorrow night are do a compression check and adjust the valves. It's really the last part in the equation that I can think of. I've adjusted lash on my race car, so the challenge here is to move from the top to bottom of the car for each valve! I'll not start the engine at all so that everything is stone cold tomorrow when I do the adjusting.

Man I need a beer ...


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Brian Scotti
'73 S Coupe

Well, I think I found the problem. As I was setting the car up to adjust the valves, pushing the car in 5TH gear until TDC#1), I noticed that one cylinder held little or no compression (it wasn't difficult to rotate the engine that 120 deg). Now the hoping part ... is it a tight valve or a broken valve? I'm hoping for the tight valve! Please hope with me!

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Brian Scotti
'73 S Coupe

You may have a burned valve buddy.

Brian,

It sounds like a burned valve at this point, especially the backfiring at high rpm ... if it was broken, the engine wouldn't be running well at ANY rpm, and would be making serious BAD NOISES from things bouncing around inside!

I know you are hoping not to have to do a teardown, but I have never heard of a valve clearance 'tightening up' enough to do what yours is/has been doing ... I guess it is best that you got this problem nailed down as serious before you tried to run that track event at Watkins Glen. I am sure if you had tried to run there, only more damage would have been the result, and believe me, I understand the desire and pressure to get a car ready for a big event coming up! But, some things are not meant to happen on schedule ...

Seriously, unless I am badly mistaken, a top-end rebuild is in the cards for you in the near future, and I am sure your engine will have many more miles of pleasure for you left in it with a new set of valve guides in those heads!!! Good luck!

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Warren Hall
1973 911S Targa

Well, I'm going to go through the routine of adjusting the valves and a compression check so I can identify which cylinder(s) is the culprit. I need to learn to do those anyway!

I'm not in the position of doing the top end rebuild myself, although I'd like to, so I'll be looking for a mechanic. Any readers out there in the Ithaca/Rochester/Syracuse/Binghampton area of NY have any suggestions? Since this is a pretty hefty rebuild, what else should I do while it's apart? I'm thinking freshen all heads (new valves, guides, springs, etc) and clutch. What is a good camshaft for this 2.7L with Webers? S spec or?

I'll give one final update tonight to close out this week long chase. Thanks agian to all those who stuck with me!

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Brian Scotti
'73 S Coupe

[This message has been edited by bscotti (edited 09-07-2000).]

Sorry to hear that Brian,
Hate to hear you're gonna have someone else to do it though. You'll have all winter to try it yourself...

Leon
78SC

[This message has been edited by leon (edited 09-07-2000).]

I adjusted the valves as best I could. I didn't have the neat feeler guage, so I cobbed my own and got pretty close. If anything, I'm a little loose on the clearances, which is safe. I didn't get to the compression check .. I deserve a break tonight! The interesting thing is I found no tight valves, a few loose, and the car runs a quite a bit better. Could I have a stuck valve? I did clean some baked on crud from the inside of valve covers. Is there something I can pour in the oil or gas to test that theory? I'm still going to do the compression check.

Leon, as much as I'd like to rebuild my engine myself, I have a race car that needs more attention. I just don't have the time to do both.

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Brian Scotti
'73 S Coupe

Hi...kind of a new comer but a Porsche owner for 25 years and I have been pushing Techron on this site when folks talk of cleaning valve trains. Pour in a bottle in a VERY LOW tank and add 1/2 highest octane. Do it again when your down again. I live by the stuff. They pulled my head off my Porsche 944 (1985.5) the valves and springs were spotless at 325,000 miles!! I know Techron did it as recommended strongly by the PCA. Only problem though, change your oil within 500 miles after use as it thins down the oil (it does not burn).
Wished I knew enough to help you out with the real problem, but I know I will be coming to you folks with help as I get settled in to this 1973 911T I just purchased.

good-luck
BR