Coldstart vs warmstart
11-18-2018, 12:41 PM
#1
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Thread Starter
Coldstart vs warmstart
Hi ,
I am struggling since quite some time with the cold start of my 928S euro of 1980.
1. before: unable to start car when cold
solution : measure control and system pressure with engine cold and not run
system pressure : 5,3 bar. within specs (5,2-5,8 bar)
control pressure: 3,1 bar => way too high : should be 1,2- 1,5 bar
so I overhauled the WUR : new membrane , seal and adjusted cold pressure by pushing pen deeper inside WUR
(on which inner spring and bimetallic plate is connected).
2. then : next day I tried to start car , it started but I needed to keep car running by pressing pedal down which causes some white/blue smoke
since I suspect too much fuel. but ran better after 1 min without pressing pedal.
3. Once car has run for 30min and thus good warm engine and components, no trouble and starts right away when warm
Even when starting car after few hours, I have no problem.
My question : is there still something wrong with my WUR or must I only adjust engine more lean
remarks : all components such as Auxiliary air valve, Thermotime switch are ok. I checked and measured them.
injectors and cold start injector are also ok : I checked them on leaks and fuel cloud spread is fine.
I am struggling since quite some time with the cold start of my 928S euro of 1980.
1. before: unable to start car when cold
solution : measure control and system pressure with engine cold and not run
system pressure : 5,3 bar. within specs (5,2-5,8 bar)
control pressure: 3,1 bar => way too high : should be 1,2- 1,5 bar
so I overhauled the WUR : new membrane , seal and adjusted cold pressure by pushing pen deeper inside WUR
(on which inner spring and bimetallic plate is connected).
2. then : next day I tried to start car , it started but I needed to keep car running by pressing pedal down which causes some white/blue smoke
since I suspect too much fuel. but ran better after 1 min without pressing pedal.
3. Once car has run for 30min and thus good warm engine and components, no trouble and starts right away when warm
Even when starting car after few hours, I have no problem.
My question : is there still something wrong with my WUR or must I only adjust engine more lean
remarks : all components such as Auxiliary air valve, Thermotime switch are ok. I checked and measured them.
injectors and cold start injector are also ok : I checked them on leaks and fuel cloud spread is fine.
11-18-2018, 02:53 PM
#3
Drifting
Do you have K-Jet F.I.?? If it ran with the control pressure at 3.1 bar and you now have 1.2>.1.5 bar, you need to adjust the A/F ratio screw ....Then the idle speed- air bleed screw,,,
11-18-2018, 03:34 PM
#5
Rennlist Member
Thread Starter
when I try to start without the cold start valve connected (disconnected the blue plug), I get the same result, it starts while sputtering at 400 rpm, and
after 30 secs I have 1000 rpm.
Normally when starting cold it should start and directly go to 1000 rpm, not ?
Gerrit
remark : when car has not run for a week, starting becomes more difficult. As if I have not enough pressure
to start.
11-18-2018, 06:24 PM
#6
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James,
when I try to start without the cold start valve connected (disconnected the blue plug), I get the same result, it starts while sputtering at 400 rpm, and
after 30 secs I have 1000 rpm.
Normally when starting cold it should start and directly go to 1000 rpm, not ?
Gerrit
remark : when car has not run for a week, starting becomes more difficult. As if I have not enough pressure
to start.
Cold start:
Like Jim Bailey says, the cold start valve, if working, will "light off" the engine when cold, regardless of the rest of the system. The engine should run for a second or two.
Cold running:
Once the initial "blast" from the cold start occurs, engine suction pulls the sensor plate down and the injectors start spraying. "Cold running" occurs as the WUR changes the pressure to the injectors.
From what you are ssying, neither system is working properly....
Last edited by GregBBRD; 11-18-2018 at 06:41 PM.
11-18-2018, 06:58 PM
#7
Rennlist Member
Thread Starter
You need to clarify the difference between cold start and cold running.
Cold start:
Like Jim Bailey says, the cold start valve, if working, will "light off" the engine when cold, regardless of the rest of the system. The engine should run for a second or two.
Cold running:
Once the initial "blast" from the cold start occurs, engine suction pulls the sensor plate is pulled down and "cold running" occurs as the WUR changes the pressure to the injectors.
From what you are ssying, neither system is working properly....
Cold start:
Like Jim Bailey says, the cold start valve, if working, will "light off" the engine when cold, regardless of the rest of the system. The engine should run for a second or two.
Cold running:
Once the initial "blast" from the cold start occurs, engine suction pulls the sensor plate is pulled down and "cold running" occurs as the WUR changes the pressure to the injectors.
From what you are ssying, neither system is working properly....
Well , I did a test by turning the CO mixture screw counter clockwise to make mixture so lean that no fuel is passing via my 8 injectors..
When trying to start the car it starts for 2secs and then dies. So I may suppose the cold start injector works since it sprays intermittent during start for
max 8 secs (open time by thermoswitch)
So when setting back the correct CO mixture, and after starting the cold,pressure is managed by the WUR....but since I tampered on my WUR to make cold pressure correct, could this influence my warm pressure.?
I overhauled my WUR myself by replacing the metal membrane and seal (Salvox kit) and pushed pin to which the bimetallic plate with
spring is connected further into my WUR..
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11-18-2018, 08:50 PM
#8
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Okay Greg, I now understand it better.
Well , I did a test by turning the CO mixture screw counter clockwise to make mixture so lean that no fuel is passing via my 8 injectors..
When trying to start the car it starts for 2secs and then dies. So I may suppose the cold start injector works since it sprays intermittent during start for
max 8 secs (open time by thermoswitch)
So when setting back the correct CO mixture, and after starting the cold,pressure is managed by the WUR....but since I tampered on my WUR to make cold pressure correct, could this influence my warm pressure.?
I overhauled my WUR myself by replacing the metal membrane and seal (Salvox kit) and pushed pin to which the bimetallic plate with
spring is connected further into my WUR..
nstall your pressure gauge. Disconnect vacuum to the WUR. Start the engine with the WUR disconnected electically. Verify the pressure is at the lower number you set it at, with the plunger. Connect the electrical connector and verify that the pressure rises to the 3.8 specification, in a couple of minutes. Hook up the vacuum hoses and set the mixture and idle.
This will give you a normal mixture when warm and an enrichened mixture, when cold.
11-19-2018, 02:34 AM
#9
Rennlist Member
Having leaned it right out so it only starts on cold start injector, richen (pump running but not cranking or running) with CO screw until you can hear injectors start to spray (usually audible), then LEAN back until injectors just stop. Should run at this setting enough for you to tune it properly. With Aux air valve, have you looked through it (with front and rear hoses removed) to verify its mostly open? My cold start idle went low, and Aux air valve was not open enough - opened it, adjusted spring, fixed - 1100rpm on cold start - readjust idle speed when fully hot. Once running check pressure at WUR - should increase control to ~45psi(3bar)when fully warmed through. BTDT.
jp 83 Euro S AT 57k
jp 83 Euro S AT 57k
11-20-2018, 02:02 AM
#10
Rennlist Member
Thread Starter
Having leaned it right out so it only starts on cold start injector, richen (pump running but not cranking or running) with CO screw until you can hear injectors start to spray (usually audible), then LEAN back until injectors just stop. Should run at this setting enough for you to tune it properly. With Aux air valve, have you looked through it (with front and rear hoses removed) to verify its mostly open? My cold start idle went low, and Aux air valve was not open enough - opened it, adjusted spring, fixed - 1100rpm on cold start - readjust idle speed when fully hot. Once running check pressure at WUR - should increase control to ~45psi(3bar)when fully warmed through. BTDT.
jp 83 Euro S AT 57k
jp 83 Euro S AT 57k
As for the aux air valve , could it be that mine is not enough opened when cold (below 20degree) :
How do you change the opening permanently? you said that you adjusted the spring, can this be done easily without damaging the aux air valve?
11-20-2018, 02:07 AM
#11
Rennlist Member
Try cleaning the AAV first. Looks like a lot of grease in there. Could be blocked. You can hook 12v directly to the AAV to see if the strip heats up and moves. Also, with CIS, the Temp Sensor is notorious for going out of range and causing cold start issues. See threads by me on this topic.
11-20-2018, 03:19 AM
#12
Rennlist Member
Thread Starter
Try cleaning the AAV first. Looks like a lot of grease in there. Could be blocked. You can hook 12v directly to the AAV to see if the strip heats up and moves. Also, with CIS, the Temp Sensor is notorious for going out of range and causing cold start issues. See threads by me on this topic.
many thanks for your input. When I connect 12V to the AAV, it will normally close, correct? But should it in cold status not be more open than
just the square opening of the disc?
As for the Temp sensor : I measured the resistance at cold (below 20degree Celsius) between pins and body and they seem all within specs.
Is this sufficient to decide that temp sensor is fine ?
Is there something else I can check? Perhaps the voltage output to cold start valve during start ?
kr
Gerrit
11-20-2018, 03:21 AM
#13
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Try cleaning the AAV first. Looks like a lot of grease in there. Could be blocked. You can hook 12v directly to the AAV to see if the strip heats up and moves. Also, with CIS, the Temp Sensor is notorious for going out of range and causing cold start issues. See threads by me on this topic.
Temp sender? As in thermotime switch for the cold start? Porsche made a change to the thermotime switch....but I can't remember what year this occurred. Are you aware of when?
Anyone?
11-20-2018, 03:34 AM
#14
Rennlist Member
Thread Starter
Yes, good detail! Frequently the AAV is burned up and stays open or closed. If it stays open, the idle screw will be screwed down tighter than normal. Either way, there is no additional air, making the cold start function too rich.
Temp sender? As in thermotime switch for the cold start? Porsche made a change to the thermotime switch....but I can't remember what year this occurred. Are you aware of when?
Anyone?
Temp sender? As in thermotime switch for the cold start? Porsche made a change to the thermotime switch....but I can't remember what year this occurred. Are you aware of when?
Anyone?
11-20-2018, 11:22 AM
#15
Rennlist Member
I know you said it was in spec but it looks corroded. And yes, what Greg said -- thermotine switch...temp sensor is for later cars...