924Board.org

[SecaBlue]

Update. WUR removed, ultrasonic bath clean for 30+ minutes, with other components carefully cleaned, re-install with new grease on pin etc. WUR resistance 17.9 ohms, and also tested over 12v and it heats up well. No better cold start issue. Does run marginally better warm, with less jerking on throttle application and release, and when warm runs very smooth at all rpm with even power delivery.

Here is video of first cold start this morning in 18degC ambient : https://youtu.be/1kUJRLVnZtA

Here is second cold start after running cold for approx 1min, then waiting 30+ seconds, and restarting: https://youtu.be/MkzAnxe2qb8

Here is cold start idle after running for a few mins but not yet warm: https://youtu.be/c4jGFwzr7j0

Now for the strange warm start and running issues:

When I drive it now, with the mixture tuned as best as I can without a C02 measure (judging by ear on smooth idle with 2.5 turns out on the idle screw), the car starts warm and idles at 800-850rpm. But after I rev the engine, it wants to sit at 1100rpm. Sometimes if I gently tap the throttle no higher than a few 100rpm, it will settle down again to 850. Also new warm start will sit again at 850.

The other warm issue is warm start: If I turn off the motor and re-start in a few seconds, no issues. If I turn off and re-start approx 30 seconds or more, it starts like it is running on 3cyl for a second or so before smoothing out to normal. I didn't have this symptom prior to cleaning AAV and WUR.

First video is warm running at normal idle and re-start: https://youtu.be/xuW_dkYdF6I

Second video is warm start after waiting 30 seconds: https://youtu.be/hVzOUtlMC9k

3rd video with high warm idle: https://youtu.be/0xumC7QGI84

4th video with warm start after a few minutes and normal idle to high idle: https://youtu.be/16k2gjVtNok

So please let me know what your thoughts are on all this after I am eliminating the variables. Just to reiterate, vacuum leaks have already been checked. I have also taken out the air filter and gently tested the movement of the fuel distributor arm and position. It seems to move up and down very smoothly, always resting back into the same position.

I am still trying to get a hold of a CIS test kit, but it is almost impossible down here in Sth Sweden

Thanks!
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[morghen]

I'll send you my k-jet tester kit as i dont need it anymore.
Send me an address on PM.

I think you're being a bit too pretentious in regards to idle stability.
I havent read all the stuff you did but have you tested the idle stabilisation valve? Have you tried another of those valves?
_________________
Supercharger and EFI kits
https://www.the924.com

[Raize]

Watched your videos.

1. Your 924 hates starting and idles like shit to begin with when cold. Mine used to as well, but two things have helped that:
- increasing cold control pressure at the WUR (my terrible cold idle was because the AFR was in the 9's when cold). You'll ideally need both a K-jet tester and an AFR gauge to get this perfect.
- putting the TIU on a dedicated relayed circuit (I only had 4 volts at the coil, now I have 9)
After that, my 924 starts perfectly on the first rotation of the engine.


2. I wouldn't worry about 850 vs 1100 rpm idles at all. As long as your 924 can re-start warm after 20 minutes, consider it a success.

[SecaBlue]

a bit of an update... Had the fuel filter replaced by Porsche, and then the engine CO2 re-tested. The old fuel filter was very dirty, and now since the new one is installed my engine no longer has the varying warm idle issue. Now idles spot on 800rpm all the time warm.

However, now it starts like crap warm if left for 5+ minutes. A warm start straight after stop is no worries, but I have to crank it a while to get a good start if left longer.

Cold start is still to be tested properly, as the days are too warm here for the AAV to open much at all. Maybe it is starting cold too rich or too lean... I just can't put my finger on it for the moment. All I know is it was actually slowly starting better and better cold before the new fuel filter. Before it would crank and instantly start with a strong rpm kick (from CSV), then stutter a little before quickly leveling out to around 750rpm. Now after the new filter so far one cold start it just cranked and cranked before stumbling into life and leveling out at 800rpm.

The other thing I noted is that the Porsche tech dialed the mixture lean to get the CO2 down. The engine still ran ok warm, but when I moved the mixture screw clockwise approx 1/8th, the engine immediately ran smoother with slightly higher rpm and no popping at exhaust on overrun.

Yes, yes, I know I need to get a CIS kit on it. Problem is My local Porsche centre doesn't have one and doesn't want to use equipment that is not theirs. No other mechanic within 70km can help. Doesn't sound like a lot of distance, but I am not wanting to sit on a motorway with my low-mile gem for risk of stone chips, damaged windscreen etc.

Hmmm.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[Cedric]

Maybe check with Fredrik Torkildsen "Gegge"? He has been in the 924 game for ages just like me , maybe he have one, my setup is a bit getto, not sure it would survive to be shipped, i can check. Doing any work on Kjet without knowing the pressures is very tough
_________________
1980 924 Turbo
www.instagram.com/garagecedric/

[SecaBlue]

I'm actually breathing a bit easier now after I have done some cold start testing.

It definitely starts better cold with a richer mixture - no brainer there. So now I have the CO values set at approx 3.5 when at normal operating temperature, which is within legal emission roadworthy testing (Besiktning) here in Sweden.

With that value, the cold start is instant - hardly even a crank! And then settles quickly to a nice idle at approx 800rpm. Warm starts are a little struggle if left more than a few mins - less time than that is starts perfectly. After that it just needs a slightly longer crank, splutters for a second of so, and then levels out to perfect idle. So looks like the new fuel filter did play a significant roll in the right fuel pressures.

I also looked back in the documentation, and see that a Porsche workshop did test all the fuel pressures in 2016 (approx 1000km ago), and values were fine.

While I am aware the "ideal" values for CO are around 2-2.5, I spoke to the Porsche mechanic here who knows K-Jetronic well, and he said there is no harm in running it slightly rich, even up to CO 4.5, as that is considered fine from an environmental impact too. With the slightly rich mixture, and new fuel filter, I also have dampened a lot of the jerky throttle response that was the start of this thread.

So I am going to just relax a bit now
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).

[Beartooth]

I can't think of anyone who's reported no issues with warm starts on a CIS car, so I wouldn't worry as long as it's not taking excessive time to start hot (like 15 seconds or more of cranking). Mine takes 10-15 minutes for it to set in, but I'd guess it takes around ten seconds of cranking every time after 30 minutes or so and up to 3 hours (if it's hot out; it usually gets better sooner when it's cool). What the Porsche tech said about CO makes sense to me: what I've always heard about idle mixtures suggests 12.5-13.5:1 for the smoothest operation. I'm not sure what that translates to in CO, but probably close. If you shoot for stoichiometric (14.7:1, give or take) or minimum CO, the idle will be rougher and more erratic.

Anyway, it sounds like the car is well-sorted now. CIS has some quirks even on the best days, but works pretty well in my experience. Time to enjoy a few nice drives while the weather supports it!
_________________
1980 931 diamond in the rough

[Cedric]

[SecaBlue]

I do have the 'traditional' vapour lock symptoms, and solve this with the 'foot to the floor' warm start, which then it kicks over immediately and immediately after lifting my foot settles to a nice 850rpm.

The cold start is still fickle. Yesterday it started perfectly cold at first crank, and this morning it took 5 seconds of cranking. No difference in temperatures etc.

I'll just put that down to personality
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold).