I have a cold start issue and I tested my Cold Control Pressure and registered 3 bar at 32C on my CIS gauge.

My Porsche service manual has a chart covering non-charging pressure and charging pressure specs.

What is the difference of non-charging pressure and charging pressure?

I'm suspecting my pressure is to high and my WUR is lean on cold start.

Thanks!

Rob

 

Rob,

Spec's for the 930/68 motor are:

System Pressure: 6.9-7.1 bar
Warm Control Pressure: 3.75 + or - 0.2 bar
Boost Pressure: 2.90 + or - 0.2 bar

The reference to charging vs. non-charging control pressures has to do with the warm control vs. on-boost fuel control pressures.

I don't recall exactly what the cold control pressure should be, but certainly it will be less than the warm pressure in order to enrich the mixture. 3.0 bar may be OK for cold enrichening, as long at it goes back up to 3.75 once everything is warm.

What kind of starting problems/symptoms are you experiencing?

 

Thanks for the reply!

When the car sits overnight or outside all day the engine will not start unless I put a small ziplog bag of ice on top of the WUR. After 15 mins of icing the engine fires right up. So far I changed the rear fuel pump, accumulator, fuel filter and the check valve on the front pump. The problem has gotten better but, still not fixed. I also took apart the AAR and cleaned it. It's working, I have about a half moon after the car sits and it closes after about 5 min.

Thanks!

Rob

 

I've got to say that that's the most inventive means I've heard of to affect mixture changes. Hard trouble starting??? Just dump your Starbucks ice mocha on the WUR and SHAZZAMMM she fires right up!

I checked my manual this evening and it seems your cold control pressure is right in line with what it should be at 30C (i.e., 3.0 bar). Mine is an '87, don't know what yours is.

So, how about the cold start valve and/or thermotime switch perhaps malfunctioning? Next time you try to start from stone cold, try this: Turn the key to the on position, reach into the engine and depress the fuel metering control arm (using the post that sticks up, where you would stuff an allen wrench to adjust the idle mixture)...push down on that dude until you hear the pumps fire up.....then push down a little more and hold for maybe a scant second. Or if you can reach the blue electrical connector plug at the back side of the fuel head and unplug it, the pumps will start as well.

What I'm trying to describe is this: Get the pumps running, and deflect the metering arm enough to flow some fuel into the injectors and cylinders. Short but sweet, or you'll flood her. If you don't deflect the arm, only the pumps will run but no fuel will flow to the injectors. This should simulate the cold start valve injecting fuel.

If she still won't light up, then I'm guessing some bad injectors leaking fuel into the engine overnight and you're trying to overcome a nasty over-rich condition when starting cold. But, with your iced WUR trick, I guess that reasoning doesn't hold much water. #1Thermotime switch , #2cold start valve, in that order, would be my guess. Unfortunately it (the valve) is a bear to get to, on the back side of the fuel distributor. I've got a picture somewhere of it's location if you need it.

Last resort: Get hold of Jim Fairman....he's in Florida someplace, probably in your backyard! (Jim, you listening?) You will find him lurking on the Pelican forum. An excellent diagnostician when it comes to CIS systems.

 

Rob,
Cold pressure range for the 930/68 at 32C is 2.2-2.6bar so yes you are lean.
You can tap in the top plug to adjust. Shoot me an email if interested in having it rebuilt.

 

Mark,

Thanks for the reply! The first part made me laugh! My car is a 1987

I rechecked my cold control pressure and at 33c it's 3.3 bar. My warm pressure is 3.8 bar. How do check the thermo switch on the left side of the chain cover? I believe my CSV is working because the engine tries to start when cold but chugs and dies

Thanks!
Rob

 

Well now crap, Brian, I'm batting zero today! My manual, section 25 in the Fuel Section, for my 930/68 engine past 1986, I swear the graph shows the cold pressure zone between "charge pressure and no charge pressure" @ 30C to be anywhere between about 2.5 ro 3.0 bar....the 3.0 being the "no charge" pressure limit. Per the graph, it should be 2.0 at 15C, but Rob's readings were at 32C. Even my Brian Leask WUR is set at 2.0 @ 15C.
One, two, or all three of us are confused. Probably me, old and tired tonight. Where are you finding your info?

 

Brian/Mark

Thanks for the replies!

Page 25-16c in my Porsche book reads; for cold control pressure should be equal to outside temperture. That being said, should the cold pressure rise with the temp?

Thanks again!

Rob

 

Yes, that's the whole idea of the WUR changing control pressure in reaction to temperature. Cold, you need a lower pressure to make a richer mixture. As the engine warms, the pressure slowly inches up to lean things out for warm running. Look at the chart I referred to, assuming we have the same manual. Unless I'm interpretting it wrong (wouldn't be the first time, I assure you). My 2.0 @ 15C would follow the graph slope and end up being 3.0 @ 30C, with my final fully-warm control pressure settling in at 3.75.

 

I'm sure we have the same book and graph tells the story.

I'm getting harassed at work with ice jokes, all in fun. I really need to get my problem solved, I already built plenty of character on this one.

How do you check the thermo switch on the keft chain cover?

Thanks!

 

Mark,

Update, I tried your first idea and pushed down on the metering rod for 2 seconds and the engine fired right up.

Bad CSV or thermo-swiitch? How do I check them, Ohm meter?

Thanks!

Rob

 

Didn't mean to barge into the conversation, you never know when the thread will go dead and questions left unanswered.
The graph that I used is out of my 1978 shop manual with adendums for later years. What I have seen is that as the CIS system ages you need to be more in the middle of spec for things to work right.
The CSI has very little function in warm climates such as Florida. I have blocked mine off (I live in AL) so it does not function at all. If you must get fuel to the engine in order to have a quick fire then a more rich mixture when cold is needed. Yes I would also verify that your CSV and TTS are working properly before adjusting the WUR. Once that is done you will know if a WUR adjustment is needed for things to work optimally.

 

You didn't bud in, you were adding info to the thread and that's how problems get solved. I appreciated your info and Please keep chiming into threads.

Tomorrow I will look at the CSV and TTS and hope to end my cold starting issue. I will update the thread when my problem is solved.

Does anyone know the ohm values or how to check the CSV and the TTS?

Rob

 

Here's some info from some unknown person, posted to a question on K-Jetronic diagnostics. I just Googled it.
May or may not be accurate, but it's a starting point at least.

resistance at the cold start injector should be (ignition off, injector disconnected) 2-4 ohms across the terminals,


thermo time switch, across the terminals, 20-40 ohms when cold, 50-90 ohms above 40 degrees C,

looking at the terminal on the switch, pins horizontal, plug locator lug facing upwards, left terminal and earth resistance readings should be as above,

right terminal, zero ohms when cold, 100-200 ohms above 40 degrees,



Read more: http://www.justanswer.com/questions/...#ixzz0q6AQh1Fe

 

Mark,

Thanks for the info!!!!

Looking at the schematic's I realized the Rt/SW wire from the thermo-switch is the wire providing the ground to the CSV to fire during cranking. I didn't have continuity at Rt/Sw terminal and ground. I disconnected the RT/SW wire from the thermo-switch and grounded it and the engine fired right up.

What I did is exactly with the above website from Mark with having zero ohms at the Rt/Sw terminal below 40 degrees.

I will order a new thermo-switch.

Thanks!

Rob