One problem at a time
 

As the title says I'm picking away at small problems on my 83 sc one at a time.

I had the CDI box rebuilt and the vehicle seems to be running real nice now. I'll put a timing light on it once more to confirm but I suspect it is good.

I am somewhat concerned about the low oil pressure at idle with warm engine but after reading a couple of recent posts it appears the problem will be corrected by adding restrictors in the oil lines to the cams. I'll take care of that shortly. With 182K mi. the oil pressure at running speeds is very good.

I am now experiencing, more and more, a very erratic tachometer. It's bouncing all over the place. I dare say it's probably a bad/weak connection somewhere, but where to start.

Do any readers have a suggestion as to where I might start?

Also, Have any of you gone thru the trouble of finding all major ground points on the vehicle and completely re-doing them? It sounds like a smart thing to do with no real downside.

Thanks for the help,
Hughc

for the tach, I would check your multi-pin connections in the engine bay. One at the very back by the driver's side rear corner, and the other by the rear shock mount. The one that is in the back corner came slightly loose on mine and bounced the tach around. And when it completely falls off, the car dies!!! I'd start there. And I'd recommend unplugging it, and then plugging back in. I also put silicon grease on my plugs.

I did go through the more difficult ground straps when I had the engine/tranny out. Engine to alternator, Engine to body, etc. Haven't done the easy ones yet!

Let us know if this helps!
J

^^^ Good advice.

Also be aware that a bouncing tach is also a symptom of a bad VR that is overcharging the battery. Good idea to invest in a $10 Innova voltmeter that plugs into the cigarette lighter so you can keep an eye on battery voltage. If you're seeing voltage spikes at the same time your tach is bouncing, then that is a dead giveaway.

also a bouncing tach is a sign of a .... bad tach ....

if it is swinging wildly after a shift your damping is gone and it likely needs a repair or rebuilding.

Since you had the CDI box out, its connector is as good a place as any to look for a loose tach wire. One of them sends the tach the signal.

This is a good idea.

I am not sure what the level of voltage variance is to cause disruption, but when a v-reg is working it's within hundredths of a volt given a certain load/rpm.

Mine would bounce two tenths to half a volt at idle before changing the v-reg. Probably was worse in driving conditions?

I think a lot of us have had to do this. Once you get your tach problem sorted out this is a good task. It is not a lot of fun though.

My advice is to get acquainted with the wiring diagrams. There are good diagrams in the back of the Bentley if you have it. There are diagrams that show all the ground points. Two big priority points should be the two main chassis grounds (other end of the negative battery terminal and the the transmission ground strap).

After you do that, it is a good idea to go circuit by circuit cleaning the fuse and relay connections. Dennis (timmy2) always advises to take a razor blade and spread the pins on the relays. That's a great tip because they can get loose. I went so far as to replace the fuse panel. One of my problems was a cracked panel that was making some of the fuses momentarily lose contact when they came loose under vibration.

Deoxit D5 cleaning spray and some emory paper are good to use.

I have had to put new terminals on a lot of connections, particularly the ones associated with external lights. Sometimes you need to get to fresh copper.

Thank you for all the replies and suggestions. I won't be doing any checking for at least a week since I'm off on a motorcycle trip but I will keep you informed once I check a few things, such as the VR.

grounds are a VERY smart thing to do and very often over looked.

check charging for tach bounce if grounds don't fix it

Well I finally got a 12v cigarette lighter meter, plugged it in and went for a drive.

The volt meter was indicating 14.2 v around town but once on highway it indicated 17.2 and even a bit more. That doesn't sound right to me.
The tach started bouncing around after about 50 mi. and the voltmeter was indicating 18.3v, so I suspect there may be a problem with my VR.

I did manage to clean the chassis ground on the strap that goes to the transmission but not the transmission end as it was impossible to get at. Will have to try that again once I get the vehicle a bit higher off the floor.
I also cleaned the body ground on the battery neg terminal and the one behind the fuse box in the frunk.
The others will have to wait for a more convenient time.
Anyway, at this point I'll have to find out what the maximum voltage should be from the VR and take it from there.
Cheers
hugh

Vr
 

Yes, it is the VR.

Not a fun task on the 3.2 cars.....

Gerry

I'm not a fan of oil restrictors on the cam feeds. If your oil pressure is fine while driving, leave it alone.

With your concern over low oil pressure, I would change the oil up to a high-quality thicker grade product, especially in summer.

Very, very, very frustrating. Things just seem to be going from bad to worst.

I removed the alternator from the vehicle and had both it and the VR checked by a professional shop and they both checked out OK, although I was told the brushes on the VR were wearing quite badly. The alternator was replaced app 20K mi ago, according to work records but I was also told the slip rings were noticeably worn.
So with the alternator and VR checking out OK that system can probably be eliminated as the cause to the fluctuating tach, but I do have a new VR on the way and will install it as I receive it.

What's even more frustrating now is that the engine is shutting of as I drive it. I went for a drive today and the engine quit at least 8 times. In every case I just had to turn the key off and restart the engine, no problem. Twice I pulled over and came to a stop, did not touch the key, just left everything as is, then with a voltmeter I verified that there was 12v to the FP relay and that was good. What I neglected to notice was whether or not the fuel pump was running (before I removed the relay). As it turned out I replaced the relay and the car started immediately.

So there appears to be an occasional electrical glitch that is causing the engine to quit, but where to look.
As mentioned earlier in my post the CDI unit was recently rebuilt by Bob Ashlock so I don't suspect that unit but I suppose any related wiring might at fault.
Any and all suggestions will be appreciated.
Thx
hugh

Don't drive the car while it's putting out 18v you can ruin a lot of things possibly even burning it to the ground. I would check the water/acid level in the battery because it may be boiling away (the water that is), acid doesn't evaporate.

I can't understand why the digital voltmeter was initially indicating 18.6v.
As previously mentioned, I removed the alternator and both it and the VR checked out OK, so I am at a lost as to why the voltmeter would read as high as 18.6v.
It may be a faulty voltmeter from the manufacturer so I now carry my shop voltmeter with me and if the digital meter again shows an extremely high voltage I can double check with the shop meter.
I'll keep you informed of any developments.
hughc

hugh,

Back a few years ago I had a lot of electrical gremlins. I had all the symptoms of a bad VR. I too had it tested and was told it was good. I replaced the alternator and VR because I simply could not believe I could not have a problem. I posted about it here. Some people suggested that a fail-ING unit could fail intermittently. I decided to replace both for good measure and never had another problem.

Interestingly enough, my CDI also failed around the same time. Something that has been discussed on here before is that some CDIs can be susceptible to over-voltage. I am not a EE and do not pretend to be one. Coincidence or correlation? Hard to say.

As gomezoneill said, if you are getting big voltage spikes and using a conventional lead acid battery, be very careful!

Thank you Tim, I do have a new VR on order and I will be trying it as soon as I can. I really can't spring for a new alternator at the moment and hopefully I won't have to.

Of course the other problem that is annoying is the sudden shutting off of the engine while driving. The engine re-starts immediately, which is good, but the problem has to be addressed. I do have a competent friend that will study the electrical dwgs. and suggest where I should look.
It really is odd that these problems should surface all of a sudden when all along the vehicle was running fine.
I'll update when I can.
hughc

fix the alt problem first and see if it is related to it cutting off.

when it cuts off do any dash lights come on
spin the fuses on the fuse panel. could be bad connection
CD unit. they fail when they get hot, yours may be going bad, but there are still other things that can cause it
coil, same as CD, heat. they fail when hot and can work again when cooled off..
green wire from dist. wiggle it around and see if it cuts off.
bad ign switch.
FP relay
FP

this may be one of those things it ahs to get worse before you can figure it out....usually involves being towed.

Hugh, sorry I can't add anything to the electrical/cutout discussion, but can for the oil pressure. From what I recall, it states right in our owner's manual that oil pressure can drop to almost zero at idle, and to not worry about it. As long as it is good at speed, you should be good to go.
Good luck finding the cutout problems,
Craig

My new VR has arrived and I will install it when I can. I'm not especially looking forward to pulling the alternator out again especially since the voltage readout has been very good (14.2v max) since I had everything out the first time and as I mentioned, it all checked out OK. But I have the new VR so I might as well install it and put that behind me.
I was out for a spin around town today and the vehicle quit again. I noted that the instruments still had power and no lights came on until I pushed the clutch in, at which point the alt light came on and oil pressure dropped to 0. I guess that's to be expected with an engine that isn't running. I'm quite sure the gas gauge kept indicating, so it didn't loose power.
Again, I just turned the key off and on again and the engine started right up. I didn't bother stopping or pulling aside, I just turned the key of and on and just carried on as if nothing happened.
I somehow don't think that heat is the cause as the vehicle starts right up ( less than 30 sec) so nothing has had time to cool off.

It is frustrating but I'm sure it'll get sorted out, and it'll be interesting to know the cause of it.
As far as getting towed, that happened back in June when the CDI box failed. Two hundred miles of towing isn't cheap. The good part is I feel confident the CDI unit is not at fault since it was rebuilt by B. Ashlock, but.......
I will somehow try to check that green wire (distributor) that has been often mentioned. I don't like the way that it is wrapped with tape in the wiring harness which looks to make it less than easy to replace.
I'll keep you updated as I can.
hughc

yea that was my point. if heat was the issue it would not start.

I think someone else had a problem like this and it may have had something to do with one of the electronic devices, maybe RPM limiter switch?

I am not calling into question your rebuilder of your CDI. What I am saying is keep the possibility in the back of your mind that the CDI could have been damaged by over-voltage after it was rebuilt. There are some people who suggest that the older CDIs lack internal protection against over-voltage and that could be the reason for your intermittent cut outs.. I’m not saying that is the problem — just consider it a possibility among others.

If it cuts out after getting hot and then works again after cooling off that will point to the coil or CDI. Keep a can of compressed air handy. The next time it happens turns it upside down and spray the CDI. If it will restart again immediately then you have most likely found the problem. Maybe try replacing the coil. Worst case, you have a spare now.

Check out the transmission ground strap, fuses and all connections for loose connections and corrosion. Deoxit D-5 and emory paper is great for cleaning contacts.

Have you validated your voltmeter?

Yes, I will definitely keep the CDI in mind. In fact the rebuilder has offered to have a look at it if I should so wish.
As I've mentioned previously the engine starts up IMMEDIATELY after it quits. I only have to turn the key OFF and ON and I can carry on. To me that pretty well rules out the possibility of any components being overheated.
I'm in the process of replacing the VR and will of course re-do the alternator ground wire. I'll have to at some point get under the vehicle to double check the transmission ground strap.
The digital voltmeter has been verified in that it has been used in other vehicles and has behaved as it should. It also has been used in the SC and has not shown voltages above 14.2v, so at this point I'm thinking the original VR was working intermintantly causing the voltage to spike to 18.6v. I hope with the new VR that problem has been laid to rest.
My friend is studying the electrical dwgs. to see what else might cause the ignition to fail.
Thx
hughc

18.6, you fried the CDI, search "overvoltage". Every symptom matches the multitude of posts on the subject. Total failure will follow.

ClickClick, thank you for your observation, but obviously I hope ur wrong, but I'm sure the possibility is there that the CDI has fried.
BUT, the thing to take into consideration is that the vehicle is running quite nicely (until it quits) and that would leave me to believe the CDI unit is working as it should.
The idle isn't as smooth as I'd like but I don't know if a lumpy idle can be attributed to a faulty CDI.

I'll soon get the alternator back in and we'll see then if there are any changes.
thx,
hughc

hugh,

I am wondering if the failure mode for a traditional CDI failure and an over-voltage failure are the same. Maybe they are, but I wouldn’t necessarily assume that is the case. If there are different faikure modes, that would be a possible explanation for your symptoms.

+100

Too late GaryR, I've had the restrictors in for at least a month and I don't think I'm worst off for it. Idle pressure is a little better than it was ( app 0.8 bars) and good pressure at hwy speeds (app 3.0 to 3.5 bars).

Before installing the restrictors I did open them up to 2.7 mm (up from 2.0) and that might explain why my idle pressure isn't quite as high as I expected.

If I was to do it again I would remove the original restrictors, weld the holes shut and re-drill somewhat smaller than the originals but larger than what is being sold as replacements.
In my case I opted for 2.7mm.
thx
hughc

There's something about the shape of the hole that sprays the oil where the manufacturers say not to drill them out. I think I read that somewhere. Feel free to disregard, I just don't want you to get any engine trouble.

Thank you Jason. When I was considering ordering smaller holed restrictors I read up on previous posts and there was never any mention of special shaped holes. I corresponded with a person that is involved in 911 engine building and he has used smaller sized restrictors and told me that my 2.7mm would be adequate.
I also just had a look at the restrictors that I removed from my engine and there is nothing to indicate that the holes are anything but just holes, ie, no special shape.
Thank you for voicing your concern.
hughc

I put the new VR in yesterday (pulling that alternator is getting easier all the time) and went for a drive. The car was running quite nicely and I was pleased up until the point where it quit again, and again, and again.
So, problem not solved. It's more than frustrating, as it starts right up again as if there was nothing wrong.
As mentioned before, there is still power to the dash but for some reason the ignition cuts out.


"I am wondering if the failure mode for a traditional CDI failure and an over-voltage failure are the same. Maybe they are, but I wouldn’t necessarily assume that is the case. If there are different faikure modes, that would be a possible explanation for your symptoms" Tim

Tim, You may have something there and I will correspond with the rebuilder of my CDI unit to see if what you are suggesting is a possibility. I may have to return the unit to him for testing, and I hate to have more down time but what can you do?
hughc

Heat, internal and external has a way of precipitating failure modes.

I had a similar problem last summer in the extreme heat. Turn the key off and on reset the CDI box and I was good for another sixty seconds or so. Weather hasn't been as hot since, so I haven't investigated further.

See the discussion here: http://forums.pelicanparts.com/porsche-911-technical-forum/958213-memorial-day-diagnosis.html

Thank you RDM, my problem also seems to be heat related, where the vehicle seems to need to be driven until it is well warmed up and then it starts to shut off.
I'll try to confirm that this week end by taking it for a couple of long drives.
hughc

Have you been following this thread at all? Similar symptoms of engine cutting off once warmed up.

http://forums.pelicanparts.com/porsche-911-technical-forum/928919-3-2-carrera-poltergeist.html

Great suggestion in that thread about running a hot wire to + coil to eliminate the key switch.

Thank you Rob and eastbay. I will read up on that thread. There may be something there for me.
I did go for a run today and the car ran well and didn't shut down. The weather today was much cooler and the engine temperature didn't get as hot as it would on a hotter day, which leads me to suspect my problem is heat related.
At this point I seem to be grasping at straws but I think I will ultimately send the CDI box away for verification because of the possibility tyat it may have been compromised when the charging voltage went as high as 18.6v.

hughc

You might want to jump to the end of that thread I provided above. His issue ended up being 1 or both crank sensors going bad once heat soaked. I believe there was a procedure where you could check the resistance cold and then hot to see it the sensors are failing once hot. Seems easy enough to try before sending your CDI anywhere.

Thank you Rob. I'll have to try to locate those crank sensors. I had a quick look at the Bentley manual with no luck. I'll have another look tomorrow.