CIS insomnia - hot start problem
 

Hi everyone...
A highly debated issue, but this time, I really need some specialist’s opinion because I could not find anywhere a similar situation.
I have been struggling with this car for 3 months already, doing all the tests and only one issue was detected.

But let’s start from the beginning:

Car: 2.7 1974

- engine was rebuild
- WUR and fuel distributor rebuilt in the UK on a Bosch specialist
- new injectors
- new coil
- new throttle actuated valve
- new fuel accumulator
- new fuel pump with no return valve fitted
- return fuel line checked, all clear up to the fuel tank

Main issue: car doesn’t start when hot

Tests done:

- when cold, if I press the sensor plate, all the six injectors squirt
- working pressure of the system cold and hot : 5.2 Bar
- control pressure: when cold 1.9 bar, after 2 min. 2.6 bar, 3 min. 3 bar. After reaching running temperature, 2.5 bar.
- when hot, switching off the engine, the running pressure drops to 1.2 bar, after 10 seconds it drops to 1 bar and after 20 seconds, to zero. From my short knowledge, this was the main issue but we cannot identify the cause of this sudden drop.

When hot, and I try to start the car, engine runs for half second (sounds like it is going to start), and then dies...

Immediately after this, if I press the sensor plate it shows some resistance meaning there is some pressure on the system... I have to press it a few more times until it gives some signs of wanting to start... when it starts right after this operation it sounds like misfiring some cylinders (lack of fuel?), and if I keep accelerating, it runs normal after a few seconds.

Well, I tried to be as clear as possible, so from this information, if anyone can give me some opinion about the possible cause, it would be of a great help!

(Sorry for my poor English).
Thanks in advance for any help.

I had a similar problem with my ROW 78 SC. Started great cold but was extremely difficult to restart after sitting for more than fifteen minuted or so. Replaced the fuel accumulator. No difference. The problem turned out to be a missing check valve in the fuel pump outlet side. Check valve was internal on original pump and not there on the replacement pump. Pelican sell a 10mm and 12mm check valve.

check valve at fuel pump

Check valve or a bad fuel accumulator!

Thanks for all your comments.

Fuel accumulator was new, so I believe out of the equation... at have tried another (used) with the same results...

Regarding the check valve, I believe it is the one in the outlet of the fuel pump - the pump used is not original - but this is present and tested (only allows the air pass in one direction).

Any other ideas?

Hi Alex. I also have a 74. Are you using the hand throttle correctly on warm startup? In my case I don't use it at all when warm. I don't believe the lack of residual pressure warm should not have too much affect on the 74 as the fuel pump runs as soon as you turn the key. Do you still have the 001 wur on your car as I don't believe they are rebuildable, They are adjustable as there is an allen key screw on the bottom of the wur to change control pressure. The backfiring and rough running actually sounds too rich. Have you checked your CO. There are many mechanical adjustments on the 74 and they all have to work together. Have you checked timing and point gap? Hopefully the brain trust will chime in as I know this is frustrating.

Hi nomore,
Thanks for your writing.
Lately, when warm, the car hardly starts when I pull the hand throttle. If Idon’t pull it, it doesn’t start at all.
Yes, I still have the first version WUR but I didn’t know it was not rebuildable... at least Ipaid for it!
Anyway, control pressure within specs.
CO will be soon checked. I don’t have the right equipment.

In my experience with rebuilt wur's, they are not in spec when you get them, or don't stay in spec long. Put some gages on it and check your rest pressure to.

CIS troubleshooting............
 

Alex,

Your WCP (warm control pressure) at 2.5 bar (36 psi.) is too LOW. You need to correct the WCP. Or install a good working WUR (warm-up regulator).

Tony

Same problem with 911T 2.7
 

Hello,

I also have the same problems. When hot will not start. If I wait for 5 minutes, then starts without any problem.
Question: What WUR means?

Hi again,

Some more facts about this nightmare...

As per boyt911SC suggestion, we raised the control pressure. We set it up un the hexagon head bolt of the WUR. We reached warm control pressure of 3 bar.

New test, run until temperature was 100 degrees centigrade, left stop for 20 minutes and after that, try to start and... nothing...
Leaving the key on, (first position), fuel pump working: we tried to pull the plate up and it was too hard. If we keep on pressing it it finally goes up. After this, the car starts.

It looks like one of the pressures is holding the plate and the start up “suction” is not enough to let the plate to go up.

Now, when cold, the car starts roughly... not enough fuel... we took out the injectors and at idle, the injectors don’t spray. Only a few drops fall from it. The injectors were new.
We also noticed that the left bank injectors let more fuel pass than the right bank, at idle.

The distributor on the car is 0438.100.04

Any thoughts would be a great help.

Thanks

Same issues on my 1973.5T...........

Search HOT START KIT here. Nice thread on the kit and results. Although popular on the 914 models it works for me in hot weather on my 2.4, which by the way has the fuel pump installed in the rear! I went through the same headaches, replacing CIS components, testing, etc until someone recommend the HOT START kit (easy install).

Bob

Hi Alex, Sounds like you had the main parts rebuilt or replaced. Those being WUR, fuel dist, throttle position reg, accumulator and injectors. Your system pressure is a bit high at 5.2 bar. Setting values are 4.9 Bar.

One thing you mentioned is you had a hard time moving the air flow sensor plate which should not be. Have you set the zero position of the sensor plate? It’s a bit fiddly on these early cars with the spring clip, but sounds like you should have a look. If it’s set too low, with high system pressure, this could be your issue. The plate may be too low and consequently the plunger in the FD never moves enough to provide fuel. On cold start you have CSV to help get things moving.

For checking injector flow, buy 6 clear baby bottles and put each injector in one. Turn pump on and lift sensor plate. You will be able to see spray pattern and measure volumes to ensure all are equal. Also you will use the bottles to set zero on sensor plate as well as base line. You do this in the bottles to ensure the plate is not too high, which could cause hydro lock.

It is a system, so it can be an iterative process to dial things in. A CO sniffer would be nice to have.

Also, what warm pressures are you seeing at ½ throttle position and full? These should be checked as well. Lastly, the check valve is irrelevant on the early cars. The pump spools up with ignition, not starter. Just count 3 Mississippi before engaging starter.

Good luck. Wrench / Drive what could be better? Let us know how it turns out.http://forums.pelicanparts.com/uploa...1558588226.jpg
http://forums.pelicanparts.com/uploa...1558588226.jpg
http://forums.pelicanparts.com/uploa...1558588226.jpg

The forgotten Fuel Distributor Pressure Regulator O ring

Here is a thread to research.

http://forums.pelicanparts.com/porsche-911-technical-forum/832578-fuel-distributor-system-pressure-regulator.html

http://forums.pelicanparts.com/uploa...1558632568.jpg

There is how to R and R the Fuel Distributor Pressure Regulator.

http://forums.pelicanparts.com/porsche-911-technical-forum/620037-cis-pressure-regulator-pics.html

Hi Dave, Interesting thread for '75 and later, but we have established residual pressure is irrelevant for the early CIS. The reason being the fuel pump activates with "key on" not starter engagement, the latter residual is important. Alex is rocking a '74 and said he just had FD rebuilt which would include new o-rings on press reg. If the CSV was leaking, this would be an issue, but doesn't sound like it. Wrench / Drive what could be better?

He is losing fuel pressure in 20 seconds- zero. Which means the accumulator, fuel pump check valve or fuel distributor regulator are not holding pressure. Or he has a fuel leak somewhere. And the leak is pretty massive to lose 2 bar in 20 seconds. Didn't the 73-74 have a throttle valve? Maybe that's leaking or defective. All new copper crush washers? Fuel pump banjo fitting not leaking?

I had a couple of of 73.5's and a 75 CIS. The 73.5 had a throttle valve but my 75 didn't. I don't about the 74's. No fuel pump relay in the 75, so when you turn the key, you have fuel to the fuel distributor. Easy to hydrolock if

Is the fuel pump under the drivers swingarm or was it moved near the gas tank? I just don't know when it was moved to the front.

I would think that you need residual pressure of a Bar or it could/will vapor lock upon hot restart.

The workshop manual states -

Leak test- 1.3 bar after 10 minutes
1.1 bar after 20 minutes

Just thinking out loud

Can you explain this pic? I can see where one end of the fuel pressure test equipment is plugged into the FD, but where is the other end going? On the left. I cannot tell where that line ends up. Is it from the fuel accumulator?

Thanks