fredseebeck

I have a problem with both cold start and warm start on my 1979 911SC with CIS injection that I could use a hand solving. Here is a description of what is happening and the results of system pressure readings I took th eother day:
Upon trying to start the car after sitting overnight....(COLD START) the car will fire momentarily for a half second and then immediately quit. After trying to start it this way for 4-5 times it will finally run at high idle 2000 rpm and gradually settle at 1000 rpm after 30 seconds or so as it warms up.
It will idle this way normally for however long I let it run, however, if I shut it off and IMMMEDIATELY TRY TO RESTART (WARM START) IT IT WILL NOT EVEN KICK.

Now I hooked up CIS pressure gages and got the follwoing readings:
Cold pressure= 2.3bar
Warm pressure= 3.2bar
Control pressure (cold, engine off)= 2.8bar
Rest pressure after shut down= 1.8bar
Rest pressure after shut down (20 minutes later)= 1.4bar

NOW HERE ARE MY QUESTIONS:
1) ARE THESE PRESSURES NORMAL OR OK?
2) With the gages I was able to shut the flow valve in the line between the warm up regulator and the fuel distributor when it was running and I SAW NO CHANGE IN THE PRESSURE OF 3.2BAR WHEN I OPENED AND CLOSED THE VALVE, IS THIS NORMAL?
3) WHAT WOULD CAUSE THIS COLD AND HARD STARTING PROBLEM?

Any input is really appreciated as this hass got me at wits end.

Fred

LaughaC

My guess is that a bad accumulator is is causing the restart problem, and old spark plugs are making cold starts a little tricky. The "7th injector" seems to get you started the first time, but very quickl a little bit of block temperature electronically turns that off.

The pressure readings are over my head until I can access my CIS book that is stored in a PODS unit until around the end of August. I would install a new Accumulator and new spark plugs, then drive about 200 miles to see where everything settles.

Peter Zimmermann

Have you set the CO%?
If yes, to what spec, and did you test pre-cat, smog pump disconnected and plugged?
Have you set your sensor plate height?
Is your fuel system clean (remove fuel guage sender with low fuel level and inspect tank)?
As Chris stated, what plugs are in the engine? How old are they? How about the wires?

fredseebeck

To address any questions raised above:
The wires and all the ignition components thru to the CD box are all replaced new.
Sensor plate height is fine.
CO has not been set for awhile since I do not have equipment to do so. Paying a shop to do it becomes expensive.....but the car was running fine until this problem came up about 2 months ago.
So ruling out these possibilities what else could it be.....I am 90% sure it is a fuel system component issue?

psychoideas

Hi Fred,
From the research I've done in relation to my CIS (76), your cold control pressure is way too high.
The first thing you need to do is chase up the 'test specifications' applicable to your car.
If you want to send me your email address I have some generic CIS information that I have gathered that I am happy to send to you.

If you're hooked up correctly and the engine was hot, according to your statement above, your System Pressure is too low.

Please dont take offence to these questions but was the 'flow valve' you shut positioned between the warm up regulator and the test gauge? Because that's where it's supposed to be.
Did you disconnect the wire connector to the warm up regulator? Otherwise it will be Warm Control Pressure pretty quickly.

Do the test again with the engine cold and not running.
Start with the valve shut so you are only measuring "System Pressure" So basically connected to the control line at the Fuel distributor to the gauge and then the valve turned off. After the valve the line continues to the Warm up regulator.

Recard System pressure.

Open the valve to see Cold Control Pressure

Let us know what these two are.

I am baseing pressure references against what's required for my 76 911. the may not be correct for your car, however in saying that CIS systems are all very close in operating pressures.
Good luck!

P.S. have you read both of my posts on my CIS adjustment?

fredseebeck

Thanks for the info.
The gage was hooked up correctly, the only thing I did not do was disconnect the warm up relay plug before the cold test so that may have had an effect like you said on cold control pressure. Will try again tonight.
As far as warm control pressure versus system pressure, I agree with you that it seems the system pressure is way too low. Now Tell me if I am correct and should see the value jump from warm control pressure of 3.2bar to system pressure of about 4.7 bar when I close the valve?
Also, if I do this test with the engine idling, won't the engine stall or flood severely when I close the valve because suddenly the warm up reglator is out of the loop?

psychoideas

G'day Fred,

Firstly, System pressure should remain the same for warm & cold control pressure.



In answer to this Question: Yes. Those figures you mention are definately in tolerance for my car and I'm sure they'll be very close, if not in spec, for your car.


This I cannot tell you because I've never set it with the engine running.

However it is called "Control Pressure" because it puts "fuel pressure" on top of the fuel distributor's plunger, thus "controling" mixture.

When cold, the WUR allows fuel to pass through it rather easily thus putting a 'low' pressure onto the plunger.
This allow the plunger to move upwards more easily giving a richer mixture for start up. (This is as easy as the FD plunger will every get)

When warm, the WUR restricts the flow of fuel through it putting a 'higher' pressure onto the plunger in the FD.
This restricts the plungers upward movement giving a leaner mixture for when the engine is warm.

So in answer to your question, closing the valve and taking the WUR out of the loop will definately lean it out. You should see an increase in idle speed and there will be an increase in Exhaust Gas Temperature. After that it may be too lean to run but I don't know. Try turning the valve off slowly and see what happens.

If your car has a Vacuum connection on the WUR this will alter the CCP and the WCP (it makes them lower to enrichen the mixture during periods of acceleration)

I think you should do your tests with engine off. Record the results and the abient air temerature at the time of the test.

Good luck.

fredseebeck

I know this is a late response but wanted to give a conclusion to this problem.
Turns out I changed the fuel pump with a new one and everything is back to normal. The pump was making presure and the car would eventually run but as described badly. I always thought the fuel pump would either run or it wouldn't.....this is what had me confused initially.
Turns out buying the aftermarket Pierburg unit was probably a mistake since it only lasted 5 years tops since it was installed. The Bosch units are double the price but probably worth it in the end.

theiceman

Thanks for the update .... closing the loop is very important in making us more knowledgeable . Glad you got it sorted.

ice