924Board.org

[noisybrother]

Hi all,

Since getting the 931 up and running and legal I've noticed a few thing which require attention:

1. The revs do not drop down as quickly as I'd expect which can cause overrevving when upshifting.

2. The idle was high at 1000rpm but can be adjusted down using the throttle screw on top of the TB. Shouldn't the DITC unit be regulating the idle speed or at least attempting to? I've tried the following instructions (http://www.924board.org/viewtopic.php?t=18355) and I get strange results, for example I don't see '0' or 'o' but a score across the flywheel with 'z1' but ONLY when I set an advance on the timing light of around 8 degrees. There is nothing with 0 advance.
_________________
2002 BMW 325ti Sport - Sapphire Black
------------------------------
Ex Porsches:
1982 931 S2 - Hellblau
1990 944 S2 - Zyclam 'Pearl Effect' Red
1989 944 S2 Cab - Tahoe Blue
1984 944 Lux - Guards Red

[Rich H]

My timing marks were obscured with filth and rust. I found another couple after slowly turning the engine over by hand.
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[noisybrother]

[Paul]

Yes you should see Z1, if not don't run the motor again until you do!
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Rich H]

I only had a vauge line at +10 (But it's an N/A) but investigation and a grubby finger revealed the other 2 lines.

Could your flywheel be on wrong? The N/A one can....
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

[Smoothie]

[noisybrother]

[noisybrother]

Had another crack at this today, I cannot seem to alter the timing at all following Smoothie's description in post http://www.924board.org/viewtopic.php?t=18355. I have had to set the idle using the TB screw. I've checked for vac leaks and replaced the decel valve with one I had lying around and get exactly the same results. When I increase the revs the timing gets more advanced so the DITC is making some desicions and it is fluctuating at idle ever so slightly though doesn't appear to be trying to keep the car at 800rpm.

If I richen the mixture by 1/8th of a turn then she starts to surge the revs up and down.
_________________
2002 BMW 325ti Sport - Sapphire Black
------------------------------
Ex Porsches:
1982 931 S2 - Hellblau
1990 944 S2 - Zyclam 'Pearl Effect' Red
1989 944 S2 Cab - Tahoe Blue
1984 944 Lux - Guards Red

[924RACR]

Usually you can set the idle mixture by turning first one way, then the other, till the engine starts to sputter; that usually gives a range of adjustment of about 180 deg, and then you set it to the middle of the two - gets you close, if not absolutely perfect. If you're only an 1/8th of a turn away from sputtering, I'm thinking your mixture may be a bit off, which could contribute to difficulty setting idle/timing.

Possible you still have vacuum leaks?
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[noisybrother]

Ok, cheers 924racr, I have managed to set the mix mid way between the 180 degrees splutter to splutter margin. Seems to be behaving but it may be fluke. I'll drive her tomorrow and see how she performs.
_________________
2002 BMW 325ti Sport - Sapphire Black
------------------------------
Ex Porsches:
1982 931 S2 - Hellblau
1990 944 S2 - Zyclam 'Pearl Effect' Red
1989 944 S2 Cab - Tahoe Blue
1984 944 Lux - Guards Red

[noisybrother]

I set the tuning today using a Gunson Colortune device. Very impressive, you can see the flame colour inside the cylinder with this. I first set the mix to the centre point (mid way between too rich and too lean) then removed plug number 1. It was showing signs of running rich as I had previously set it for safety. I inserted the glass sparkplug and fired her up. She was still running a bit rich as the burn was showing the occasional yellow flame rather than preferred 'bunsen' blue - at this point I'd like to say the engine was warmed up before I started this procedure - so I leaned her off a little to get a nice bright blue flame (too pale a blue is too lean) it only took the smallest of margins to get a decent result.

Interestingly I'd noted on another post last night whilst doing my research: when you rev the engine sharply the system enriches the mixture, this held true with my engine too - so when sharply revved it showed yellow flame and then when the revs were held high they turned blue again. Alternatively when you rev gently up to the same engine speed the flame stays blue all the way.

So the car was tuned to cylinder 1. I moved on to cylinder 2 (which you 931 afficianados out there will know is the most awkward one to get the spark plug out of!). Different story here, the cylinder showed a slightly richer mixture than number 1. So I either have a fuel delivery issue or an injector which is clogged on number 1.

I only had time to view the first two cylinders today and hope to look at the other 2 soon. However, I took her for a spin after putting her back together and she's definitely running better. The first positive thing I noticed was the engine seems to have lost a small vibration it had from 2500/3000 rpm upwards. And she certainly pulls very well, could be better though, I'm sure shes got more to give.

I'm booked in to a group dyno session at Silverstone racetrack with a bunch of 951s on 6th October so need to be tuned up before then, I can't let the side down, I'm the only 924 running that day!

Next job is to re-check and set the valve clearances as I've done about 350+ miles since the head rebuild and shes noisy on at least one tappet on startup so I'm sure I'll find some work to do in this area.

Meanwhile I'm going to run some more injector cleaner through, I've used some STP Injector Cleaner already and some Redex. Is it true that Redex the same as the USA's Techron?

Keep you posted...
_________________
2002 BMW 325ti Sport - Sapphire Black
------------------------------
Ex Porsches:
1982 931 S2 - Hellblau
1990 944 S2 - Zyclam 'Pearl Effect' Red
1989 944 S2 Cab - Tahoe Blue
1984 944 Lux - Guards Red

[Rasta Monsta]

[noisybrother]

http://www.gunson.co.uk/item.aspx?item=1822&cat=486

enjoy...!!
_________________
2002 BMW 325ti Sport - Sapphire Black
------------------------------
Ex Porsches:
1982 931 S2 - Hellblau
1990 944 S2 - Zyclam 'Pearl Effect' Red
1989 944 S2 Cab - Tahoe Blue
1984 944 Lux - Guards Red

[noisybrother]

Set the valve clearances today, the exhaust valves were bit tight so loosened them out to 0.40mm. The car runs a lot quieter now and the enigne starts and stops much more elegantly! The car seems to have lost some out and out power but runs more smoothly through the revs. The turbo seems to be coming on a bit earlier too.

One thing I instantly noticed was the revs drop down nice and quickly when she's cold but when warm she's still taking her time to return to idle. I forgot to mention that when I set the tuning (above) I did a check for vac leaks and couldn't find any pre or post throttle body.

Anyone got any clues as the cause of this annoying phenomenon?
_________________
2002 BMW 325ti Sport - Sapphire Black
------------------------------
Ex Porsches:
1982 931 S2 - Hellblau
1990 944 S2 - Zyclam 'Pearl Effect' Red
1989 944 S2 Cab - Tahoe Blue
1984 944 Lux - Guards Red

[seanski44]

Cool, I see you're fettling her for Saturday's tests!!

glass sparks indeed, sounds cool, can't wait to see 'em...

btw, do you need the beemer as backup vehicle or should I ride down with you?
_________________
1998 BMW Z3 2.8 arctic silver & red

1981 168HP 931 S2 blue/tan leather - SOLD
1985 121HP 924 2.0l na modded - SOLD!
1992 968 lux SOLD
1989 944 2.7 lux SOLD