porsche wont start after a long drive

[brents42gpw]

today I drove the 75 911 today 45 miles. then stopped for about half hour. tried to start it again. no dice. I learned a trick to take the air cleaner off and push my finder up on the right side. inside that air box itself. and it is magic. but I certainly don't wanna do that every time. I feel like this thing is vapor locking but I dont have a clue what to do to fix. it has done this a couple times here locally. but when I leave from the house and drive. I ususally don't shut it off. I just drive.
any thoughts on what I can do to fix this. summer is coming and I feel that this thing will be really picky with the heat. thanks

brent

[Joe Bob]

Hot start pressure bleed off. On cold start you have a CHT sensor and other systems that assist in cold starting. On warm/hot starts.....there is a check valve that on my 3.0/CIS that screwed into the FP neck.

Was like 20 bucks....there are other things that can be wrong, that is the most common. Usually you need fuel gauges to diagnose correctly. CIS is all about proper fuel pressure.

Lifting the flap gets the fuel pump to bring pressure up and hopefully start.....be a careful not to run it too long as you run a risk of hydrolock on the cylinders.

[ossiblue]

Joe Bob has nailed the most likely cause and most likely remedy. The fact that you can start the car by priming the system--basically restoring fuel pressure by lifting the plunger inside the intake--tells us that you have a loss of residual fuel pressure. The most common cause is the check valve in the fuel pump as Bob mentioned, but it could also be your fuel accumulator ($$$), wur, or pressure relief valve in the fuel distributor. To accurately track down which part it may be, you will need a fuel pressure gauge set to test your system--a basic investment if you plan to do any work on your CIS system. A simple test you can run in less that a minute will tell you if you have a residual pressure loss problem. If you do, a couple more tests will point to the faulty component.

You're lucky, IMO, because you have a 75 and the CIS is much simpler than later models. You should have no trouble solving this problem with a few more questions, some tests, and feedback to the forum.

[80-911SC]

listen to joe and try and fix the issue .. learning the "tricks" to starting or getting things to "work" is not fixing them .... that is called settling .. not fixing ...

Try an Italian tune up ....warm up gently and flog it .......

45 minute drive is barely enough to get the temp up and get fluids running around

[theiceman]

cht sensor on a 75 ?

Anyway most likely culprit is the accumulator if it is on warm start only ..

Here is a simple test . warm the car up and take it for a run , drive home and stop the car .. wait about a minute .. see if it starts .. it probably will .. then turn it off and wait half an hour or so and go back .. if now it doesnt start you have bled down your fuel pressure..


Pull off the vacuum line off the bottom of the accumulator , ( actually you can do this at any time ) if fuel comes out your diaphram is shot and you need a new accumulator. If not doesnt necesarilly mean it is good though.

The reason i mention these points is with your troubleshooting you havent spent any money yet ( well unless the accumulator is bad. ) and you havent had to crawl under the car.

if i actually had to crawl under the car take the skid plate off the get to the fuel pump and check vlave id just replace both. i consider the fuel pump a wear item and if you put one in every 10 -15 years so what . Then you know you have a good fuel pump and check valve and can drop the car without going back under there .

Good Luck ..

[ossiblue]

Originally Posted by theiceman

cht sensor on a 75 ?

Anyway most likely culprit is the accumulator if it is on warm start only ..

Here is a simple test . warm the car up and take it for a run , drive home and stop the car .. wait about a minute .. see if it starts .. it probably will .. then turn it off and wait half an hour or so and go back .. if now it doesnt start you have bled down your fuel pressure..


Pull off the vacuum line off the bottom of the accumulator , ( actually you can do this at any time ) if fuel comes out your diaphram is shot and you need a new accumulator. If not doesnt necesarilly mean it is good though.

The reason i mention these points is with your troubleshooting you havent spent any money yet ( well unless the accumulator is bad. ) and you havent had to crawl under the car.

if i actually had to crawl under the car take the skid plate off the get to the fuel pump and check vlave id just replace both. i consider the fuel pump a wear item and if you put one in every 10 -15 years so what . Then you know you have a good fuel pump and check valve and can drop the car without going back under there .

Good Luck ..

These are all good points. However, if your 75 is stock you don't have a line from the bottom of the accumulator to check. The only way to check the accumulator is to look for leaks (not likely to see) or testing with a fuel pressure gauge.

Unless it has been modified, the fuel pump on your 75 is not in the front under the skid plate, it is above the rear left wheel and is easily accessible with the wheel removed. This is the most likely suspect, at least the check valve is, but you don't want to buy useless parts and waste money. Test your system with a fuel pressure gauge set and report your results.

As you can see, there are many possible reasons for your problem. IMO, the only way to approach situations like this is to have a systematic plan for diagnosis and follow it. Starting with the easiest to test, eliminate each possible fault one by one until the problem is solved. In your case, basic diagnosis requires a fuel gauge set.

[Josh D]

Originally Posted by theiceman

cht sensor on a 75 ?

He likely meant thermotime switch.

[theiceman]

Originally Posted by Josh D

He likely meant thermotime switch.

ah ..

yeah if the pump is in back even easier .. some people have a hard time getting the presure guages for our old cars and the connecions. geat tool to have tho.

[boyt911sc]

Originally Posted by theiceman

ah ..

yeah if the pump is in back even easier .. some people have a hard time getting the presure guages for our old cars and the connecions. geat tool to have tho.

The fuel pressure gauge is hooked up the same manner for all 911 CIS engines. What's this stuff about older cars? Keep us posted.

Tony

[brents42gpw]

the fuel pump is brand new and in the back of the car. I purchased a new one a couple months or so ago. and yes these cars are hard for me to understand. I am taking advice here and doing what I can. in another post I mentioned that I just had the car gone through and a lot of parts changed out. fuel distributor rebuilt etc. so it is hard for me to isolate. but I will print this thread off and go from there.
like I said earlier. it is only when the engine is hot and I feel that the fuel is vapor locking. I do appreciate all the advice. thanks
brent

[brents42gpw]

and there is no fuel leaks anywhere. there were lots of fuel lines replaced. I wonder if one was missed and it is getting air in the line. to loose fuel pressure?

brent

[Joe Bob]

Why toss parts at it when you can isolate the problem with diagnostic tools? Call Pelican and ask for Glen or Darren.

At least the gauges can be resold.....also there ARE some that have them and can loan or rent them to you.

ALSO....the Bentley manual is a good resource...but not the ultimate resource....they copied the a lot of stuff from the 3.2 Carrera manual.......the worst screwup is the direction of the distributor.

THAT is criminal....take the editor out and flog his ass...

[ossiblue]

Originally Posted by Joe Bob

Why toss parts at it when you can isolate the problem with diagnostic tools? Call Pelican and ask for Glen or Darren.

At least the gauges can be resold.....also there ARE some that have them and can loan or ent them to you.

Joe Bob is spot on. Let me put it this way.

You feel "bad", you ache and have a headache. It isn't going away so you go to the doctor. What is the first thing done to you at the doctor's office? Your temperature is taken with a thermometer. That simple test with a simple instrument helps to identify the path down which the doctor will go in his diagnosis.

Your "sick" CIS needs to begin its diagnosis by having its "temperature" taken with a "thermometer". You need to check the fuel pressures using a fuel pressure gauge set. The information you get in return will guide your diagnosis, just like a doctor.

[brents42gpw]

I spoke with richard and I am going to have him help me with this. I appreciate the help
I drove it for an hour tonight came home put it in the garage shut it off. immediately tried to start and it started right up then died. tried to crank again. nothing.. it does the same thing all the time. which is good. I appreciate all the help and am going to get some help and use this a dvice here and get it figured out.

thanks
brent

[brents42gpw]

got a few things figured out on the car. this restart problem only happened when I took the car at least 60 miles. on my own I replaced the fuel accumilator. then the mechanic put his gauge on it and figured out it needed an o ring in the fuel distributor. and a warm up regulator. he had some reubilt ones. that was last week. drove it home stopped. done.. it would not restart then today I took it back and he gauged it again. and it is not loosing any pressure up to 20 minutes realistically it should start every time. today he took the fuel pump off and looked at the check valve in the fuel pump. there was dirt in it. then reassembled and reinstalled. it is not loosing any fuel pressure still. after my 45 mile trip home I stopped. went to restart only difference is I gave it full hand throttle. started. I tried this a few times today in my drive. started every time.
I hope we got it this time..

brent

[RWebb]

Originally Posted by brents42gpw

I learned a trick to... push my finder up on the right side... inside... and it is magic. but I certainly don't wanna do that every time.

I feel that this thing will be really picky

dunno about your car, but...