Cold Start Warm up Problem

[kasi]

Hallo guy's ! I bought a few month's ago the car of (David H,member)and now the car is almost perfect ! it's a 78 3.0 sc,bored to 3.2 with 964 cams , if i'm not mistaken ! I have had warm up problems since i got the car , so now i have replaced the warm up regulator, it's a lot better no but when i start the car in the morning it start's without problems and it idle's constant on 1000 rpm!!! But when i want to push the throttle the first 30 sec the engine backfires but only 1 or 2 times !!! After 1 minute the car runs great on idle but when i start driving and i have to stop the rpm drop's till 600 rpm and the engine dies !! After 3miles also this problem is gone and the car runs perfect even with airco !!!! If i put the idle higher ,i don't have this problem anymore but when the engine is warm it runs on 1600 rpm and i guess that's not the way it has to be! Thanks a lot and greeting's from Aruba !!

[vizail]

It sound's like adjustment. Then again check the Ignition dist vacum advance mechanism. with a proper vacum pump for proper operation. By elimination you'll get to it.
Hope I can help

Vic

[kasi]

Thank's a lot for your fast answer vic !!! i adjust the timming already (without timming light ) if i put the distributer more in advance i get knocking and if i turn it the other side the engine does not idle steady and i get less performence !!! But on how much degree btdc should i put it with this cams ??

[vizail]

I suspect the cams are giving you a faster Idle . Do you have a centrifugal dist. or you still use the vacumm advance? The distribuitor Vacum advance in my 82 SC is defective and I get detonations and back fires when I conect the advance vacum line. I have been using my 911 in centrifugal advance mode. I disconected the vacumm lines and plug them. Is working Ok.

Vic

[acapella8]

Would his 3.0 it not follow 5 Degrees before TDC?

Or would it be different due to his cams?

[Gunter]

Setting timing without a light? How do you verify correct setting? Use a stroboscope (Meaning timing light) and start with 5 deg BTDC.
With your set-up, JW recommends a total advance of 33-35 deg BTDC.
The timing is very important because of possible detonation issues.
Do it right. If need be, let a shop do it.
It sounds to me that you need a correct mix adjust along with timing.

[jwmarc]

Does your car have the aux air valve?.. this works inconjunction with the warm up valve supplying additional needed air during warmup.. approprite air volume feedback may not be happening by simply ajusting the idle....Since during warm-up critical pressure adjustment is necessary on the fuel distributor any out of sync component will affect operation.

[kasi]

Hi guy's !! Thanks for your answers !!! Yes i still do have vacum advance ,and to me it's working fine !! i always thought i only need it on higher rpm , or am i wrong ?
Gunter , is it possible that you speak German ? I know also a lot about Lochkunde !!! Very nice !!! Actually i have all the stuff ( timming light,special tool's for bosch K-Jetronic ) i got primery pressure 72 psi,with cold engine (95 degree here on aruba) i got 30psi control pressure ! And yes i have the aux air valve, i was also thinking about this but since i know that this thing is going to cost me 800$ i want to try all other options !!! now i go ,get my tool's ,messure and adjust again and let you know later !! Thank's a lot and greeting's from Aruba!!

[kasi]

Hi guy's !! Thanks for your answers !!! Yes i still do have vacum advance ,and to me it's working fine !! i always thought i only need it on higher rpm , or am i wrong ?
Gunter , is it possible that you speak German ? I know also a lot about Lochkunde !!! Very nice !!! Actually i have all the stuff ( timming light,special tool's for bosch K-Jetronic ) i got primery pressure 72 psi,with cold engine (95 degree here on aruba) i got 30psi control pressure ! And yes i have the aux air valve, i was also thinking about this but since i know that this thing is going to cost me 800$ i want to try all other options !!! now i go ,get my tool's ,messure and adjust again and let you know later !! Thank's a lot and greeting's from Aruba!!

[kasi]

Ok,guy's i messured again ! Engine cold (24h standing) primery pressure 72 psi,control pressure 27 psi ! timming was on 4 deg btdc now on 5 !! Is it possible that the primery pressure is to less ? I have read a few times that you need 75-80 psi !! Thank's in Advance !

[Gunter]

$800.-???An Auxillary Air Valve (AAV) is not that expensive. Have you checked the Auxillary Air Regulator (AAR)??? That's the one with the electric connector. It's simple: When cold, disconnect the vacuum hose, use a little mirror and look inside. You should see a halfmoon-shaped opening meaning: air gets through. Re-connect the hose. When hot, after warm-up, the opening should be closed.
As for pressure: According to the Bentley SC manual 240-12 to 240-15, the System pressure is given as 65-75 PSI.
Control Pressure for SC '78 shows a graph for: Cold and running, and different settings with/without vacuum line attached/removed when Hot and running.
Do you have the Bentley?

[kasi]

Hi Gunter ! No i don't have the Bentley ! But i got a lot of original Porsche books ,Bosch and Haynes ! But i will check this also ! this morning i start the car and the engine idles fine on 800rpm!! I went for a quick test drive and after 3 miles the problem is gone ,with the engine far under operating temp !!! But i check it out !
Man lernt nie aus !!!

[Mysterytrain]

If the control pressures are correct and the timing correct and the mixture correct and the idle speed correct (when warm)..then I would be looking at the AAR. This little bugger is nothing more then an electro-mechanical hand throttle. When the engine is cold the AAR provides some bypass air allowing the engine to idle fast..1.2k or so. As the car heats up there is voltage being applied to the AAR heating element. As the element gets hot it begins to close off the bypass air and lowers the rpm's in the process. Once closed it should be out of the picture, unless its leaking. The AAR should be fully closed in 6 mins or so. I would ck to see if there is 12 volts at the connector when the car is running. You should also ck to see what the resistance of the AAR heating element is, they vary from 17 ohms to about 33 ohms. I believe the higher value is better because it allows the engine more time to warm up at high idle. If there is no resistance then the element is defective. You can buy a new AAR or rewire what you have. I posted something awhile back on rewiring an AAR.
AAR Revisited

[kasi]

Ok,Mysterytrain i guess you solved my problem ! Because my primery pressure is 72 psi the control pressure was 27 psi ,the t
timming is on 5 deg btdc and the car drives on Lambda 1 (14.7:1)
I know this because i have also a small computer ,i use it to adjust my carbs on the mustang or alfa ! works perfect ! i was driving the car for maybe 3 min ,then it was closed already ! so tomorow i am going to check this out ! Thanks so much you just saved me 800$!!

[ruf-porsche]

Originally posted by Gunter
Setting timing without a light? How do you verify correct setting?

Probably the same way some mechanic can set valve clearance without a feeler gauge. We call it a "WAG" in our industry
Wild Ass Guess.

[Gunter]

The AAR either works, or it doesn't; it cannot be adjusted. The heater element may work but the valve itself can be sticky.
The AAR will warm up (close) faster in Miami than in Alaska.
Control Pessure of 27 PSI sounds low to me; the WUR is still suspect here.
What is this $800.- you keep referring to?

[Hladun]

Kasi,

Excellent post. Your first post exactly describes how a CIS system doesn't work when the AAR malfunctions. Initial cold idle should be around 1500 to 2000 rpm. If you don't have an AAR (or a hand throttle) learn to live with the car stalling.

[kasi]

Ok, unfortunately i,m located on a beautyfull island called Aruba !!! By the time i have it here (shipping,import duty ) it will cost me ca.800$ , Like the warm up Regulator ,730$ and it takes min 1 Week !! i checked the AAR ,and if a space of 3 mm is enough then it's working,and i start the car without the AAR , no difference !! what now ???

[Gunter]

Before you dish out $800.- for a new WUR, make sure it's the culprit.
If you have a '78 CIS, you'll need the correct WUR Bosch 0 438 140 045.
Check the numbers.
Get a used one from this board for spare. I believe in spares like CDI, pump, WUR because they are so damn expensive.

A 3mm opening on the AAR might be alright because you are in a warm climate.

[vizail]

You can Always re-built the AAR. Make a search in this forum for this particular issue

Vic