CIS Hard cold start -headscratcher

[Vereeken]

I have become full circle with this one (twice).

EURO SC 1982 - 089 WUR as with all EURO deliveries after 81. No ECU no frequency valve no lambda. Dizzy with only vac advance.

WUR cold control following porsche specs with vac applied. I put all at the low end of the curve. Basically I have 1.6 bar at 18°C vac applied. Ohm at 32 so spot on.

Ignition timing set to 25 BTDC at 4000 RPM as per workshop manual vac disconnected.

AAR works as indicated, takes 4-ish minutes to close.

On a warm engine no issue. But leave the car standing for +7 hours and starting takes a tremendous amount of cranking (let us say 10 seconds). it fires up and slowely builds RPM to about 1200.

Coil changed for a known good one, CDi box changed for a known good one, CSV tested a zillion times.....

No way I can get this car started after a long sleep in a normal manner; which is 1 flick of the key and varooom....

All suggestions taken....

I am left with the fuel distributor and the 2 chambers in the distributor that might be clogged....

Michel

[wolds]

Have you confirmed that the cold start valve and thermo time switch is functioning?

[Vereeken]

Twice. Once with light and once to check the spray pattern with CSV out of its hole. No issues.

[SkiVT]

Long shot but

CIS Hard Cold Start - If You've Ever Had This Problem PLEASE READ THIS

[SkiVT]

I had a similar issue so have a small long of things to check. Have you tested the AAV?

The auxillary air valve (AAV) is a saucer shaped diaphragm device that is piped in parallel with the auxillary valve regulator (AAR). The diaphragm in the AAV is held open with a spring, when the engine is started and intake vacuum is established it will suck in the diaphragm and close off the air path. My understanding of AAV is that allows more air in initially to start the engine, after the engine is running it doesn't do anything.

[Reiver]

I have the exact same issue in my '83 930-10.
Overnight hard start only..… cranks on first touch after that.
I start it by depressing the accelerator in the morning and it fires right up that way . I suspect (as I've everything newish in the fuel line except the fuel pump) that the pump is allowing some leak back over long periods so I need to change out the check valve but have not gotten around to it.
OTOH....with the slight delay and open throttle one does not have to worry about a lean start either...
The other probability is a slight air leak in the fuel system like the injectors....when running the injectors are actually sucked inward by vacuum...overnight...no. Just a thought.

[Vereeken]

I checked the AAV and it holds vac and pulls in as it should.

I also replaced it with a known good one.

I will follow the Long Shot advice. I can see how this could be the culprit.

Thx for the suggestion.

[T77911S]

when cold, turn the key on and lift the sensor plate then start it.

pull the FP rly. check for pwr at pin 87 while cranking

[coomo]

Fuel accumulator is failing.Potential air leak.Possible clogged WUR.

[Vereeken]

When I do that it shoots fuel into the intake runners.

I will let it sit overnight and measure power at 87, need to get a second pair of hands ;o)

[JK McDonald]

Hey Vereeken - If the cold start valve is working properly - often when a CIS injected engine is hard to get started after they've been parked a while it's because your residual fuel pressure has bled off. Perhaps one of your injectors or the fuel pump check valve is leaking down.

I have added an under dash spring loaded toggle switch to ground in parallel with the fuel pump "Safety Ground Contact" monitoring the position of the Air Inlet Throttle Plate. The toggle switch allows me to pre-run my fuel pump to charge up the injectors prior to trying to start all my CIS cars.

Since the toggle switch is spring loaded to the open or "OFF" position, it does not eliminate the "Fuel Pump Shut Down" function when the engine is not running and the throttle plate is at rest.

Of course chasing down the reason for the loss of your residual fuel pressure is the recommended and best fix...

Good Luck - Michael

[pmax]

Bypass the FPR. Get the fuel pump running for a few seconds, then try cold starting and see if it makes a difference.

[boyt911sc]

Originally Posted by JK McDonald

Hey Vereeken - If the cold start valve is working properly - often when a CIS injected engine is hard to get started after they've been parked a while it's because your residual fuel pressure has bled off. Perhaps one of your injectors or the fuel pump check valve is leaking down.

I have added an under dash spring loaded toggle switch to ground in parallel with the fuel pump "Safety Ground Contact" monitoring the position of the Air Inlet Throttle Plate. The toggle switch allows me to pre-run my fuel pump to charge up the injectors prior to trying to start all my CIS cars.

Since the toggle switch is spring loaded to the open or "OFF" position, it does not eliminate the "Fuel Pump Shut Down" function when the engine is not running and the throttle plate is at rest.

Of course chasing down the reason for the loss of your residual fuel pressure is the recommended and best fix...

Good Luck - Michael

Michael,

Sorry to disagree with your post above. Running the FP prior to START will not primed the fuel injectors nor the fuel lines to the injectors. As a matter of fact, you could disconnect all the fuel lines to the six (6) injectors and no fuel should be delivered unless your fuel distributor is defective.

Please explain how you could prime the fuel injectors using your method. I could learn something new today. Thanks.

Tony

[bluelectron]

Originally Posted by boyt911sc

Michael,

Sorry to disagree with your post above. Running the FP prior to START will not primed the fuel injectors nor the fuel lines to the injectors. As a matter of fact, you could disconnect all the fuel lines to the six (6) injectors and no fuel should be delivered unless your fuel distributor is defective.

Please explain how you could prime the fuel injectors using your method. I could learn something new today. Thanks.

Tony

I tried this past weekend and 100% agree with Tony.

I was having hard cold starts too. Adjusting my mixture with an Air Fuel Ratio gauge fixed it. I had to adjust my cold control pressure too.

[Vereeken]

I have to agree with Michael on this one partially.

I will give some extra info, which to me is meaningless because I do not understand what is going on, but maybe one of you might make something of it.

Priming the fuel pump in the morning for a brief moment helps the start; it does not make it perfect but it starts right up. Agreed the injectors do not inject fuel; for that the Air Plate needs to rise first.

It gets even weirder. When I put my CIS pressure gauge between FD and WUR its starts even after 7 hours. Take the gauge away and after 7 hours hard cold start.

I did another test yesterday. I start the car after 12 hours. Laboured cold start.
let it run for a minute.
Next I bled all the pressure from the system. Started again, and no laboured start.

I bled the pressure again and let it sit for 2 hours. Laboured start again.


Something in the system happens after the pressure bleeds away....

I stress again that I am CCP wise, CO wise in the graph that Porsche intended for my euro SC. Zero air leaks.
When I put my co on 1% (middle range for the 089) it remains rock solid on the diagnose system.

[T77911S]

did you do a residual pressure check

pull injectors and do a flow test. with and without injectors.


you can leave the connector off on the top rear of the AFM, that will run the pump when the key is on. (as a test for now).
I would also try lifting the sensor plate for a few seconds then start it.

[Vereeken]

Residual pressure perfect. Pressure stays at 1.2 even after 2 hours.

[Dave Kost]

I would go back to basics and start by setting the mixture. After setting the mixture set the CO as specified in the manual.

This is from CIS Flowtech (Larry Fletcher) Web site on set the mixture.Bosch K-Jet Mixture Setting

posted on August 31, 2009 by Larry Fletcher | Comments Off on Bosch K-Jet Mixture Setting
After assembly of the fuel system, run the fuel pump and depress the air flow sensor plate for a couple of seconds to bleed air out of the fuel distributor. Remove one injector line from the top of the fuel distributor, and while looking into the injector port in the top of the fuel distributor turn the mixture adjustment screw clockwise until the port just starts to fill with fuel then turn the mixture screw 1/2 turn counter clockwise. Reinstall the injector line, start the engine and adjust mixture when it reaches operating temperature. This is the Bosch recommended procedure for initial mixture setting and adjustment.


Bosch K-Jet Leak Down Test - CIS Flowtech

[JK McDonald]

Hey Tony - You are right, I should have explained myself better when suggesting my (Parking Lot Emergency Get-Me-Home) fix for a loss of residual fuel pressure.

When the fuel pump is being run in the pre-start mode using the added toggle switch, the cold start injector and the control plunger in the distributor is being pressurized. Of course, as soon as the throttle plate is lifted during a start, the already running fuel pump and available pressure is headed to the partially filled injectors sooner than just grinding on the starter.

I was only suggesting (?) that a loss of residual pressure after a car has been parked for a while, could be one of the reasons for it being difficult to start. For me, using this toggle switch method if needed to pre-charge the fuel system takes much less time for everything to settle down into a nice idle....

Good Luck - Michael

[pmax]

Originally Posted by Vereeken

Priming the fuel pump in the morning for a brief moment helps the start; it does not make it perfect but it starts right up.

A fuel pump on its way out will draw more current. I would check that. Need enough juice to power all those on start.