Where to start? 911SC - it went bad fast

[schoward]

All - Long time SC owner here. My SC has been pretty darn good for nearly 20 years and I've had tons of interesting problems along the way but always got back to a stock SC with CIS well sorted (after the first few years anyway).

Looking for advice on where to start - fuel, electric or ??

Situation:

1. I recently had the distributor rebuilt (Jan.) and re-installed myself and running fine since Feb. Green wire replaced at same time. The distributor went back in aligned as removed and miraculously it started right up and ran great but could tell timing probably a little advanced - and due to winter never got a chance to drive extensively nor fine tune the timing. Sure enough with the nice weather now, I checked it after a decent drive and found it at about 9 deg BTDC and set it back to spec 5 degrees at idle per procedure on decklid label with vacuum hose removed. Easy and all normal. Checked mixture (still fine) and set idle speed all good. Essentially minor touch up to timing and set idle speed.

2. As I was wrapping up, I noticed the tach bounce between 1000-1500K a bit (fluttering/jumping not in line with engine speed) and engine kind of bobbled and then seemed to go back to 'normal'. When I drove it, tach would oddly flutter and engine stumble sometimes slightly between 5-6K rpm. All else normal. Thinking alternator or voltage regulator - Checked voltage at battery and observed ~13.5v at idle and 13v in engine bay.

3. Immediately after this I now have a hot start problem! Cold start after left along for long enough is ok as always, but after some running it was like the classic SC hot start problem which I worked through probably 15 years ago (FP check valve/fuel accumulator changed). It started once with extensive cranking and a strong fuel smell. In the last round - moving the sensor plate up to overcome what I figured was the classic pressure related hot start issue did nothing (no help). Would not start even with cranking it to death.

4. In the process above, swapped out the CDI and Coil with good spares and no change. Would run when it would run as before and same hot start issue.

5. Cold start this morning perfect! Barely warmed in garage then hot start issue again. Cranked and cranked , moved sensor plate up (Freq valve buzzed) but no help. Strong fuel smell.

6. Come home later today and now - No Starter!. Battery reads 12.5v. When I hit key to start position I hear the FV and fuel pump turn on.

Ok- I know I have to get starter going somehow to do anything - but any stance once that is going?? Start with Fuel pressures or does something seem amiss electrically or possibly in distributor that I need to probe further?

Nothing is ever easy and I accept probably multiple issues I have to work through procedurally, but it was like something suddenly happened with me watching it (#2 above) and am stumped.

I'll take any advice - Thanks in advance - sorry if hard to follow, but this is how it went.....

[timmy2]

Disconnect and clean the 14 pin engine harness connector. Both male and female terminals.
Could be the classic yellow wire not making contact.
Ground strap from case to body too.

[schoward]

Originally Posted by timmy2

Disconnect and clean the 14 pin engine harness connector. Both male and female terminals.
Could be the classic yellow wire not making contact.
Ground strap from case to body too.

Thanks for the tip. I check my mixture with a dwell meter on the test port right in that area - maybe i jostled the big plug. And yeah it’s so boring but I need to go through ground straps….

I used your kit for my green wire and worked great - but as I sit here stewing and reading posts I wonder if I have an issue in the ‘old’ section of my green wire. I recently bent it a bit to loop it in a large sweeping curve to take up the little bit of extra length now present with the new extension green wire (genuine Porsche part). I wonder if reshaping the old section a bit chafed it or nearly broke it internally a bit giving me what is possibly an intermittent no spark situation given CDI and coil are fine.

[moparrob]

One possible clue - you said that when you turned the key to the start position you heard the fuel pump come on, even though the engine was not cranking. The fuel control relay should not allow the fuel pump to come on if the engine is not actually cranking, so it may be bad.

However, if your engine was just cranking slowly, that may provide enough of an RPM signal to allow the fuel pump to run. Thus, if your engine WAS actually cranking it probably is not the control relay.

Good luck.

[schoward]

Originally Posted by moparrob

One possible clue - you said that when you turned the key to the start position you heard the fuel pump come on, even though the engine was not cranking. The fuel control relay should not allow the fuel pump to come on if the engine is not actually cranking, so it may be bad.

However, if your engine was just cranking slowly, that may provide enough of an RPM signal to allow the fuel pump to run. Thus, if your engine WAS actually cranking it probably is not the control relay.

Good luck.

No - absolutely no crank - dead starter (not even a click) but swear I hear the fuel pump come on when I turn to key the spring loaded 'start' position. I have a spare red relay somewhere so will have to check that once I get some action from the starter. Thank you.

[pampadori]

Just a guess...Loose nut at starter where alternator charge wire connects to the thick positive cable.

[JSV798]

I think that it is normal for the fuel pump to run with the key in the start position. If the starter doesn't turn you will hear it run, but when the starter turns you won't hear it run. If the engine starts then the fuel pump will continue to run with the key in the ON position. If the engine doesn't start the fuel pump will stop running at least on my SC.

[7783911]

I believe on the 81 sc the FP wont run unless the throttle plate is lifted

[theiceman]

couple things here ....
1. many people misidentify the whining of the CDI box with what they think is the sound of the fuel pump running.
2. In stock configuration the fuel pump on an SC does not run in the ignition "run " position. It only runs in the " start position" ( cranking ) and then the fuel relay latches when it starts.
3. Some people bypass the safety switch on the air plate so the pump will in fact run in the run position. Usually its to fix some starting issue that they were unable to resolve but this is seen as a "fix" sometimes , so you have to be aware of this.

[JSV798]

Your first problem is to get the starter to turn. I suggest you check the battery earth strap and battery terminals for corrosion. If that doesn't solve the problem then you need to get under the car and check for 12V at the solenoid, where the thick black cable is attached. This is permanently live, so care is needed not to accidently earth that terminal. If you are getting 12V here then you could try shorting the two main solenoid terminals with an insulated screwdriver. This will produce some spectacular sparks so you may not want to do this.
If the starter motor turns then you have to suspect the solenoid as this shorting process is doing (partly) the job of the solenoid. If the starter motors turns it will not start the car as the pinion will not have been levered into mesh by the solenoid. The solenoid does two jobs: first it levers the pinion into mesh on to the flywheel teeth and then it closes the contact between the two main solenoid terminals.
If none of this works you need to check the earth strap on the transmission; might be best to check this strap before attempting shorting out the solenoid terminals.

[SkunkWorks]

On mine my intermittent no start ended up being a slightly loose 14-pin connector in the engine bay.

[targa80]

Originally Posted by schoward

All - Long time SC owner here. My SC has been pretty darn good for nearly 20 years and I've had tons of interesting problems along the way but always got back to a stock SC with CIS well sorted (after the first few years anyway).

Looking for advice on where to start - fuel, electric or ??

Situation:

……

6. Come home later today and now - No Starter!. Battery reads 12.5v. When I hit key to start position I hear the FV and fuel pump turn on.

...

Fully Charge your battery and then try starting.

[schoward]

Thanks all

Fully charged battery and removed and cleaned and secured ground straps and no change. Cleaned the engine bay harness plug by the fuse panel and no luck either. Hit the starter with a hammer while wife hit the key and starter worked first try. Would go a few times and then would have to whack it some more to get more action out of it.

So starter is shot. But now have no start when cold as well when I could get starter to work. Not even a kick - just cranks. Next step is check for spark even with the bum starter and a hammer. Will Swap fuel pump relay as well as a trial.

Question on starters - have never touched mine in nearly 20 years of ownership and nothing in records going back to 1996 - may be the original. What is current stance on replacement for a stock SC? Most important to me is reliability and longevity. Bosch rebuild or some other aftermarket recommended? Are there aftermarkets that fit the bill better than original nowadays ? While I would gladly save weight but it’s not the top priority and motor is stock.

Wayne’s book says Bosch rebuild for stock SCs but that was a long time ago….Bosch has had ups and downs - what’s the current consensus?

Thanks all - while car is still dead, the above is actually some decent progress….

[targa80]

Originally Posted by schoward

Thanks all

Fully charged battery and removed and cleaned and secured ground straps and no change. Cleaned the engine bay harness plug by the fuse panel and no luck either. Hit the starter with a hammer while wife hit the key and starter worked first try. Would go a few times and then would have to whack it some more to get more action out of it.

So starter is shot. But now have no start when cold as well when I could get starter to work. Not even a kick - just cranks. Next step is check for spark even with the bum starter and a hammer. Will Swap fuel pump relay as well as a trial.

Question on starters - have never touched mine in nearly 20 years of ownership and nothing in records going back to 1996 - may be the original. What is current stance on replacement for a stock SC? Most important to me is reliability and longevity. Bosch rebuild or some other aftermarket recommended? Are there aftermarkets that fit the bill better than original nowadays ? While I would gladly save weight but it’s not the top priority and motor is stock.

Wayne’s book says Bosch rebuild for stock SCs but that was a long time ago….Bosch has had ups and downs - what’s the current consensus?

Thanks all - while car is still dead, the above is actually some decent progress….

Since you were able to get the starter to kick over with a tap of the hammer tells me your starter problem is probably with the main battery contacts to the starter from the solenoid. They can get charred from arcing causing high resistance contact that eventually prevents battery voltage to the starter motor. You could remove the starter and remove the solenoid to clean the contacts or order a replacement solenoid. Also, while it is removed check the brushes and replace if they are excessively worn.
If this doesn’t sound like a DIYer fun project then just order a new or refurbed starter. The starter is a pretty reliable part and in my opinion a refurb starter is just as good as a brand new one and probably a lot cheaper.

[Superman]

My preference with starters and alternators is to have a reputable local shop rebuild them. The guy I use locally will retire soon. This means two things:

1) He has entire career of experience rebuilding these things
2) I need to take my alternator to him pronto. He already did my starter

However.....not everybody has a local reputable shop.

[JSV798]

Originally Posted by targa80

Since you were able to get the starter to kick over with a tap of the hammer tells me your starter problem is probably with the main battery contacts to the starter from the solenoid. They can get charred from arcing causing high resistance contact that eventually prevents battery voltage to the starter motor. You could remove the starter and remove the solenoid to clean the contacts or order a replacement solenoid. Also, while it is removed check the brushes and replace if they are excessively worn.

This what I did a couple of years ago. I fitted a new solenoid which cured the problem. Also checked out the brushes on the starter motor and they were fine, The contacts inside the solenoid take a beating as I found out when I took the old one apart. I cleaned up the contacts, put it back together and now keep the old one as a spare.

Or you just go out and buy a new starter, which will come with a new solenoid.

[Walt Fricke]

So - two or three issues, some likely unrelated, some perhaps related: can't start because starter not working right.

And hot start issue, combined with a fuel pump which will run with the key in the run position, but with the engine not running.

And an occasional? 5-6,000 rpm stumble. And an off idle tach bounce.

The work which preceeded these changes was rebuilding the distributor and replacing the green wire to the CD box.

Work to fix: retime distributor a bit, no real help. Grounds and 14 pin plug connections cleaned. No joy.

Obvious work suggested by readers: fix the starter/solenoid. In the old days you'd have a nearby auto electric shop with guys who are whizzes with alternators and starters, but you've advice on this subject. It seems highly unlikely that the hot start issue is related to the starter won't turn issue.

As to the "fuel pump runs when it shouldn't": The most common reason for this is the Bosch plug on the backside (from a mechanic's perspective - hard to reach) for the safety switch in the neighborhood of where the fuel metering air plate is to be unplugged. No reason R&Ring the distributor should dislodge this, but it should be checked. When an engine has been out of the car, it is easy to plug the cold start injector plug into the safety socket, and vice versa. Not sure that would affect hot starting, though.

In theory, with the engine not running, having the fuel pump run ought not to cause fuel to squirt into the ports. The fuel distributor ought not to allow enough pressure to get to the lines to the fuel injectors to exceed their cracking pressure when the engine is not running, and the air meter flap system isn't opening the passages from the inlet side of the FD to the outlet side. However, injectors can go bad, and allow fuel to dribble out at low pressures. There are ways to check how the injectors are doing.

Again, not entirely sure how this nominally excess fuel would cause a hot start issue.

I think that fuel pump relay issues don't usually present as a defective safety system issue. Easy to check, as you can just swap in one of the other relays (the horn, if that is the only other one) and see if the behavior changes. And before some point the CIS didn't have this safety system - the fuel pump system was wired so the pump came on in the run position. This wasn't the cause of hot start issues in those CIS models. You should fix this fuel pump running issue just because you should, but unclear it will fix other issues.

The fact that the pulse width modulation of the frequency valve is in spec is a good thing, and doubtless a reasonable indication that you don't have deeper CIS issues, it can help diagnosis if you can check the hot and cold control pressures, along with the residual pressure. That can, at a minimum, reduce the number of possibilities. The fact that the raise the air flow measuring plate trick didn't resolve the hot start issue does suggest you aren't facing a vapor lock or similar issue, but confirming the CIS numbers are in spec is still useful in the differential diagnosis process.

As long as the starter will turn over the engine, and it won't start, especially not even show signs of trying to start, the obvious questions are fuel and spark. Since it ran, I don't suppose there is a spark issue, though that is easy to check for starting speeds. What you report doesn't sound like getting two spark plug wires mixed up, though that is always worth checking. I've taken to using starter fluid as a diagnostic - if a cranking engine won't start, but a shot of ether will start it briefly, you know you probably don't have a spark issue. So you can concentrate on the fuel side, and air leaks (don't sound all that likely here) and such.

A bad O2 sensor ought not to affect starting. The FV system is not controlled by the sensor at idle/during starting (where your foot ought to be off the gas pedal), but by the switch which senses a closed throttle.

What about the cold start system? You should be able to troubleshoot to see if the cold start valve control sensor in the left chain housing is behaving as it should to prevent extra fuel being injected by the CSV when the engine is hot. Or, if you are having cold start issues too, if it is giving that extra fuel.

At least none of what you report sounds like a failing alternator or general low voltage.

[schoward]

Thanks Walt and all

Starter needs to be addressed somehow. I will probably just replace.

Pulled a plug and checked for spark while my wife cranked (after tapping starter with hammer). NO SPARK.

Had her try again while I manipulated the OLD section of the Green wire to distributor... Signs of life (SPARK). Had her do it again and got to section where I could bend it and have spark - then no spark etc. So at least this part is solved. Will replace green wire or at least splice in a Timer Jr kit on the good / non brittle section of green wire. I disassembled the wire harness to get to fresh green wire which is nice and soft compared to the brittle section which has been hovering over the hot motor for 40 yrs. Cut out the bad section of green wire and sliced off sheath and found outer strands of coax baked and partially broken. When I rerouted the old section of green wire (mentioned above), the bending of the old brittle wire must have done it in....

Next is to get it running again and see what's what. I have a feeling this is likely a big item or possibly the root cause (stumbling, bouncing tach, no start)...

[Superman]

Originally Posted by schoward

I have a feeling this is likely a big item or possibly the root cause (stumbling, bouncing tach, no start)...

Yes, it was.

[Walt Fricke]

So the problem was the section of the green shielded wire which connects the CD box's 6 pin plug to the 2 pin plug which connects the other green wire to the distributor? I'll keep that in mind. I've replaced the distributor wire because it got brittle and discolored, but never thought the next stretch of the wire was close enough to engine heat to have this issue.