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Coldstart vs warmstart

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Old 11-20-2018, 11:25 AM
  #16  
checkmate1996
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Old 11-20-2018, 04:19 PM
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GerritD
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Originally Posted by checkmate1996
Now this is a very useful thread : it exactly describes my problem : so I need to pinpoint the problem to either :
- Thermotime switch
- cold start valve
- aux air valve

easy to test.
Ofcourse when I found the culprit, I will need to recalibrate the CO mixture.
I'll keep you posted
Old 11-20-2018, 04:58 PM
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How do you plan on re-calibrating your CO? You need either the an exhaust analyzer, wideband C02 sensor or the original gas/test tube thingy to do correctly. Otherwise you are just flat out guessing and the CO mixture is SUPER SENSITIVE. A small turn either way could move you 1 point off your ideal stoichiometric 14.7...
Old 11-20-2018, 11:50 PM
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GerritD
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Originally Posted by checkmate1996
How do you plan on re-calibrating your CO? You need either the an exhaust analyzer, wideband C02 sensor or the original gas/test tube thingy to do correctly. Otherwise you are just flat out guessing and the CO mixture is SUPER SENSITIVE. A small turn either way could move you 1 point off your ideal stoichiometric 14.7...
I have a gas analyzer so I need to make sure that the CO value is around 1.5 till 2.5 to meet Porsches specifications
Old 11-21-2018, 09:56 AM
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ok good. I presume you have no cats on the car then??
Old 11-21-2018, 10:47 AM
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indeed no cats. I provide you feedback of my tests this weekend
Old 11-23-2018, 01:12 PM
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Question

Originally Posted by checkmate1996
ok good. I presume you have no cats on the car then??
Hi Brad, I was able to do some tests :
- I tried to start the car (temp outside is about 2 °C (35°F )) : car started for about 2 sec and died
- I tried to start the car with AAV bypassed, so I replaced it by a tube so that enough air could pass : car started for about 2 sec and died
- I then measured the voltage coming from Thermotime switch during start : about 9V, so Thermotime switch is giving signal/power to coldstart valve
- I then checked if coldstart valve/injector is spraying fuel during start : affirmative, so coldstart valve is working fine
- I checked the sparkplugs after start : they are not really wet, but they did smell like fuel

WHat now ???? Could it be the WUR ?? Or is there something else I can check ??
Old 11-23-2018, 06:16 PM
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Sounds like its only running on cold start injector. We need to see fuel pressure at WUR - system(65-75psi), and control(cold <20psi). Sounds like cold control is too high - blocked WUR? Have you tested delivery rate ~ 1350cc/30 secs? Do the injectors spray when air plated is deflected (or when cranking)? Try loading tank with oil (like berrymans, Marvel Mystery), bridge fuel pump relay and let fuel circulate for a few hours, this can clean out sludge sometimes.
jp 83 Euro S AT 57k
Old 11-23-2018, 06:44 PM
  #24  
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Originally Posted by jpitman2
Sounds like its only running on cold start injector. We need to see fuel pressure at WUR - system(65-75psi), and control(cold <20psi). Sounds like cold control is too high - blocked WUR? Have you tested delivery rate ~ 1350cc/30 secs? Do the injectors spray when air plated is deflected (or when cranking)? Try loading tank with oil (like berrymans, Marvel Mystery), bridge fuel pump relay and let fuel circulate for a few hours, this can clean out sludge sometimes.
jp 83 Euro S AT 57k
I suspect WUR again, since after overhauling my engine, the pressure of WUR cold was twice as high as it should be.
I knocked the pin (to which bimetallic plate is attached) deeper inside the WUR to lower the pressure.
This worked a while till I added a new fuel accumulator
Perhaps it influenced my control pressure again.
I will need to check again my pressures, I believe
Old 11-23-2018, 09:38 PM
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You need to thoroughly clean the insides of the WUR before playing with moving the pin IMHO. The brass screens can clog badly - best clean is to burn off the lint, the way Riyadh barbers burnt the fluff off my ear lobes. I got some pressure improvement by blowing carb or brake cleaner backwards through the WUR.
jp 83 Euro S AT 57k
Old 12-02-2018, 09:23 PM
  #26  
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Originally Posted by jpitman2
You need to thoroughly clean the insides of the WUR before playing with moving the pin IMHO. The brass screens can clog badly - best clean is to burn off the lint, the way Riyadh barbers burnt the fluff off my ear lobes. I got some pressure improvement by blowing carb or brake cleaner backwards through the WUR.
jp 83 Euro S AT 57k
Awaiting my pressure gauge installation (I have someone welding a pressure gauge in the WUR fuel line since I cannot find the correct fuel connectors)
i adjusted my mixture & idle by using the basic setup of a Kjet :
Turn the mixture screw closed (CCW) , then open it 9&1/2 turns.
BUT IN ORDER TO BE ABLE TO START MY CAR AND KEEP IT RUNNING, I HAD TO DO 14&3/4 TURNS!
THUS VERY RICH FUEL MIXTURE (measured CO was 10% instead of between 1,5 - 2,5 )

I tried to leaner the mixture but then my car does not keep running,
So does this mean my fuel pressure (control) is too low??
Old 12-02-2018, 11:07 PM
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You should be able to get a gauge and fittings kit from ROger - 928srus - and do it properly. You CANNOT properly tune a CIS car without knowing the pressures are in spec.
jp 83 Euro S AT 57k
Old 12-04-2018, 01:28 PM
  #28  
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Red face

Originally Posted by jpitman2
You should be able to get a gauge and fittings kit from ROger - 928srus - and do it properly. You CANNOT properly tune a CIS car without knowing the pressures are in spec.
jp 83 Euro S AT 57k
Here my first findings. I've added a pressure gauge in the WUR fuel line :
Pressure reading cold and engine not run (bypass fuel relay) : 3,6 bar (52psi)
This is way too high : should be between 0,9 and 1,6 bar (13 and 23 Psi)




Old 12-04-2018, 05:20 PM
  #29  
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In that state (3.6b), crack open the outlet of the WUR - (carefully, with extinguisher handy!) - if very little fuel comes out, and gauge barely drops, WUR is blocked. If gauge drops a lot, much fuel sprays out, blockage is further along the circuit. Note that 3.6 is higher than a good hot pressure should be - mine hot is 45psi(3.1b). If you have power on the wiring into the WUR it will heat the bimetallic and start lifting control pressure, so cold test is best done with connector removed.
Checked the return line at the tank for fuel flow ?
jp 83 Euro S AT 57k
Old 12-04-2018, 08:27 PM
  #30  
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Good thinking there to check where my system is blocked.
I will check and provide feedback.
Returnline is never checked. Perhaps I can also disconnect Returnline at the engine and put line into a large bottle.
If situation improves I know something is wrong with my return line
But I will first check my WUR
Btw European 928S has warm pressure (according to Porsche specs for M11/12 engines) at 3,6 +- 0,2


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