911SC Hot Start Issues

[Coloradocurt]

Runs perfect , drive in hot day 85+ degrees, stop for 30 min or longer and does not want to easily start (seems to starving for fuel)
Replaced fuel pump, check valve and fuel accumulator.
Didn’t cure the problem.
Any expert suggestions??
Thanks.

[T77911S]

year?

I would still check residual fuel pressure along with control press.
could be:
ignition
leaky injectors
mixture
air leaks
timing

[NYNick]

I have this same problem!

[Coloradocurt]

Originally Posted by T77911S

year?

I would still check residual fuel pressure along with control press.
could be:
ignition
leaky injectors
mixture
air leaks
timing

It's an '82, and can take 10+ seconds of cranking to fire off.

[aoncurly]

I also have this problem. Did you finally resolve it? I have an 81 SC, drives perfectly and starts when cold, but a hotter day, and sit for a few minutes and it's real hard to start. It takes about 6-8 tries and eventually sputters to life - like vapor lock?

This problem has been sort of intermittent for a few years. A shop checked my residual fuel pressures and said they were fine. It drove fine for awhile, but it seems to have returned with the hot weather.

I've read somewhere that the fuel accumulator is a part that should be replaced periodically. Mine is original to the car. Should I replace mine?

[boyt911sc]

Originally Posted by T77911S

year?

I would still check residual fuel pressure along with control press.
could be:
ignition
leaky injectors
mixture
air leaks
timing

Ty,

You forgot this one.........fuel return valve seal or defective o-ring inside the FD. The most common culprits for residual pressure loss are defective FP check valve, leaking fuel accumulator, and rarely a leaking FD (something you could not ignore).

Tony

[aoncurly]

Originally Posted by boyt911sc

Ty,

You forgot this one.........fuel return valve seal or defective o-ring inside the FD. The most common culprits for residual pressure loss are defective FP check valve, leaking fuel accumulator, and rarely a leaking FD (something you could not ignore).

Tony

Thanks.
I would see/smell leaking or defective fuel seals, o-rings, leaking FD, injectors wouldn't I? And the other items would affect the normal operation, like mixture, air leaks, timing, and ignition. And again, a shop checked the residual fuel pressure and said it was fine. Car runs fine - only when hot, it's hard to start. No leaks visible, no gas odors.

I am curious if the OP resolved his problem and what was the cause or fix.

[DavidI]

This is almost always the fuel accumulator. Good luck, David

[boyt911sc]

Originally Posted by aoncurly

Thanks.
I would see/smell leaking or defective fuel seals, o-rings, leaking FD, injectors wouldn't I? And the other items would affect the normal operation, like mixture, air leaks, timing, and ignition. And again, a shop checked the residual fuel pressure and said it was fine. Car runs fine - only when hot, it's hard to start. No leaks visible, no gas odors.

I am curious if the OP resolved his problem and what was the cause or fix.

Aoncurly,

You won't see or smell the gasoline because the leak is internal. And it would not affect the mixture, air leaks, etc. It would affect the residual fuel pressure that would cause problem during a warm start. If your mechanic is familiar with CIS troubleshooting, he could individually test the three (3) most common culprits. And if you want to know if your mechanic knows CIS, ask him 'what was the residual pressure after 20 mins. for the fuel accumulator, FP check valve, and PPV (primary pressure valve) respectively.

Tony

[Bob Kontak]

Originally Posted by boyt911sc

And if you want to know if your mechanic knows CIS, ask him 'what was the residual pressure after 20 mins. for the fuel accumulator, FP check valve, and PPV (primary pressure valve) respectively.

That would mean testing the parts individually.

I know you can do this because you are deeply into CIS. I suspect I could if you gave me a weekend and you were close to your phone.

Why wouldn't the traditional residual pressure test be enough for starters?

If you hold 20-ish + pounds that means those individual components are fine.

Just talking, my friend.

[boyt911sc]

Originally Posted by Bob Kontak

That would mean testing the parts individually.

I know you can do this because you are deeply into CIS. I suspect I could if you gave me a weekend and you were close to your phone.

Why wouldn't the traditional residual pressure test be enough for starters?

If you hold 20-ish + pounds that means those individual components are fine.

Just talking, my friend.

Mr. Bob K.,

You have been behaving quite well the past few weeks and keep it that way. And I will give A+ for conduct. Anyway, if you performed the traditional residual test (pressure gauge installed between WUR & FD), it won't identify which one is the culprit. And like most people believe, the FA would be the culprit of choice and replace a good working FA with a new FA and the problem could still persists. Sometimes they get lucky. But you can not rely on luck all the time.

While some trouble shooters would blame the FP check valve as the culprit. Replaced the old FP check valve with a new one and the problem could still persists. This is good for the mechanics or shops because they are paid for the time they work on the car but not good for the pocket of the car owners.

CIS is an old and antiquated technology but if maintained properly, it will perform flawlessly and reliably for a long long time. Problem is that younger generation mechanics are less familiar with this old system. A service manager for a well established and known Porsche/Audi dealership owns an SC. He has more than twenty mechanics at his disposal, and none of them could fix his CIS.

Tony

[aoncurly]

Originally Posted by boyt911sc

Mr. Bob K.,

You have been behaving quite well the past few weeks and keep it that way. And I will give A+ for conduct. Anyway, if you performed the traditional residual test (pressure gauge installed between WUR & FD), it won't identify which one is the culprit. And like most people believe, the FA would be the culprit of choice and replace a good working FA with a new FA and the problem could still persists. Sometimes they get lucky. But you can not rely on luck all the time.

While some trouble shooters would blame the FP check valve as the culprit. Replaced the old FP check valve with a new one and the problem could still persists. This is good for the mechanics or shops because they are paid for the time they work on the car but not good for the pocket of the car owners.

CIS is an old and antiquated technology but if maintained properly, it will perform flawlessly and reliably for a long long time. Problem is that younger generation mechanics are less familiar with this old system. A service manager for a well established and known Porsche/Audi dealership owns an SC. He has more than twenty mechanics at his disposal, and none of them could fix his CIS.

Tony

Thanks Tony. So if I understand this correctly, since my mechanic did the "traditional" test and was ok, this rules out the WUR and the FD.

So, if I replace the FP check valve first and check the car and if the problem persists, I then replace the FA. The check valve is cheap, but the FA is expensive, so I'd rather start there.

BTW, my mechanic is familiar with older Porsches and is used and recommended by many Pelicans.

[boyt911sc]

Originally Posted by aoncurly

Thanks Tony. So if I understand this correctly, since my mechanic did the "traditional" test and was ok, this rules out the WUR and the FD.

So, if I replace the FP check valve first and check the car and if the problem persists, I then replace the FA. The check valve is cheap, but the FA is expensive, so I'd rather start there.

BTW, my mechanic is familiar with older Porsches and is used and recommended by many Pelicans.

Aoncurly,

No. What the traditional or conventional test tells you is that the residual pressure is good or bad. If the residual pressure is good that's great. But what happens if the residual pressure is bad? There are several most likely culprits aside from a leaking fuel line or fitting and they are fuel accumulator, FP check valve, and fuel distributor.

Each of these most likely culprits could be individually bench tested unless you want to replace parts after parts till you correct the problem. Someone claims it is always the fuel accumulator as the sole culprit for residual pressure problem, that is not TRUE. There are two other culprits to consider. So after replacing the FA and the problem still exists, what would you do next? Replace the FP or check valve? Or the FD?

It easy and convenient just to replace these parts if you don't mind spending your hard earned money. But in most cases, car owners want to spend wisely and just replace defective or bad parts only.

Tony

[stlrj]

Originally Posted by Coloradocurt

Runs perfect , drive in hot day 85+ degrees, stop for 30 min or longer and does not want to easily start (seems to starving for fuel)
Replaced fuel pump, check valve and fuel accumulator.
Didn’t cure the problem.
Any expert suggestions??
Thanks.

Even a warm engine without residual pressure should be able to start immediately if the thermo time switch is working properly to engage the cold start valve which is designed to work in a warm engine that has been without residual pressure for over 3 hours.

But to put your mind at ease about residual pressure, you could easily test it without gauges simply by reaching under and pushing up on the sensor plate while feeling for any resistance after 15 mins. If you feel any resistance, you have residual pressure... it's that simple. After 20 min to a half hour all residual pressure is gone and yet your engine should still be capable of starting instantly with the cold start valve, provided the thermal time switch is working.


Cheers,

Joe

[Joe Bob]

Likely, check valve in fuel pump neck, cheap fix for once....

[boyt911sc]

Originally Posted by stlrj

Even a warm engine without residual pressure should be able to start immediately if the thermo time switch is working properly to engage the cold start valve which is designed to work in a warm engine that has been without residual pressure for over 3 hours.

But to put your mind at ease about residual pressure, you could easily test it without gauges simply by reaching under and pushing up on the sensor plate while feeling for any resistance after 15 mins. If you feel any resistance, you have residual pressure... it's that simple. After 20 min to a half hour all residual pressure is gone and yet your engine should still be capable of starting instantly with the cold start valve, provided the thermal time switch is working.


Cheers,

Joe

Joe,

You have been claiming the above statement for years and I have to disagree because it not the case. It is about time we address this myth. I just ran a test a few hours ago to demonstrate and explain the discrepancies of your claim. And I have performed this test so many times to evaluate residual pressure loss in a CIS.

Time (min.).......Pressure

initial..................35 psi.
after 20'..............25
after 30'..............24
after 40'..............23
after 50...............22
after 60...............21.5
after 70...............21
after 80...............20.5
after 90...............20

End of test. After more than 90 mins. there was still residual pressure and heavy resistance when you lift the FD plunger up. This is what a normal CIS residual pressure should look like and a zero residual after 30 mins. simply indicates fuel leak in the system. The pressure gauge would drop to zero reading after several hours (3 or longer) and should be able to restart after several days or weeks.

The TTS (thermotime switch) operates no longer than 8 sec. (+/-1) and will automatically shut off. TTS is not operable (off) when the engine temperature is warm (113°F and above). So you could crank a warm engine (113°F plus) and the CSV (cold start valve) will not come into action unless there is an electrical anomaly in the system.



This is the reason why it won't restart when the engine is above 113°F and has loss the residual fuel pressure. Wait a little longer until the engine temperature drops below 113°F and CSV could be operational again.

Tony

[tito911s]

Back to the topic, please?

It sounds like a few of us are in a similar position. For me, cold start OK, but warm start crank takes unusually long after sitting 30+ minutes, as discussed above. Tony helped me troubleshoot my WUR problem, but it is time to address the warm start issue.

To ask the question again -- what tests/approach is the most cost effective way to troubleshoot the CIS system for warm start issues?

My control pressures and residual pressures all check OK.
Replaced my fuel pump.
Timing all good.
Recent valve adjustment complete.
Mixture is correct and injectors spray as they should.

Should the fuel return valve seal be checked first? Or something else? Is there a source somewhere that details the appropriate bench test?

[kiwiokie]

Just went through this with my '83 SC. Residual pressure dropped off after a few seconds. New check valve cured that problem but while I was in there noticed strainer clogged and tank vent. Also the filter on the WUR was clogged with gunk. Fixed these and adjusted WUR using gauges which initially improved starting but then hot start issue recurred. Quick check of bottom hose on FA found gushing fuel. New FA and now no problems starting cold, warm or hot.

[tito911s]

Originally Posted by kiwiokie

Quick check of bottom hose on FA found gushing fuel. New FA and now no problems starting cold, warm or hot.

When did you check FA where you noticed fuel weeping?

[kiwiokie]

From what I understand the bottom chamber of the FA on my car should always be dry. After replacing the check valve and cleaning the tank etc I set the control pressure but still had the hot start issue. The FA had been replaced by the previous owner so I thought it would be good. Pulled the bottom hose and fuel gushed out. Once replaced runs perfect.