Date: Sun, 6 Mar 2005 17:18:05 +0000 (UTC)
From: "Tomnospamtech" <>
Subject: Re: Troubleshooting the Bosch CIS cold start system

"Paul Halliday" <> wrote in message > Hi everyone ... My car is a 1989 900 T8 Special. I have the Bosch CIS fuel > injection system and the cold start/warm idle is really bugging me! > > If I setup the cold start right, it's great ... Then when it's warm, it's > too warm. If I set the idle right when warm, I have to hold my foot on the > accelerator a little more than I want while the car warms up. > > Okay, I understand that until the car warms up, the auxiliary air valve will > be open and the cold start injector will be pulsing fuel into the intake > manifold. My auxiliary air valve has no current when cold and about +12V > when warm ... That's good. What is supposed to happen to the cold start > injector? Should it have current when cold and none when warm? > > Also, I have setup the throttle stop screw to "just touch" the throttle > plate and then a further one third of a turn. This is perfect for cold > starting. When the car warms up, the vac is sometimes right and sometimes a > little too much at idle. The car runs a little warm too. I'm thinking it > could be a vac leak but can't trace it by clamping hoses when warm. > > My air/fuel ratio is set to between 3.5% and 4% carbon at warm idle. > > Any ideas? My mixture metering plate seems to be able to be pulled up a > little too easily ... Could this be an issue? I read in the Bosch CIS manual > that there should be even pressure when lifting the plate up ... Whatever > than means :) > > Your thoughts, as usual, will be very much appreciated. TIA, > > Paul > > 1989 900 Turbo S > It sounds like you may have a problem with the warm up regulator, [fixed to the side of the cylinder head by the thermostat housing], it should have a 12 volt supply all the time the engine is running. The 12 volt supply and heat transfer from the the cylinder head works on a bi-mettalic strip which controls the fuel pressure to the fuel disributor and thus the injectors, when the engine is cold the pressure is higher and as the engine warms the pressure lowers [control pressure], If said device is fault then it makes it immpossible to correctly set idle speed for both cold and warm. You really need a fuel pressure gauge to diagnose properly, but a good indication is if you have access to a co meter, disconnect the vacuum/pressure hose that is fitted to the regulator, plug the manifold and apply about 10 psi to the regulator and this should increase the co to about 7%. If no difference or a small increase is noted then the diagphram inside the regulator is knackered. The cold start spray valve should only have a 12 volt supply when the engine is cranking and cold. the purpose of the valve is to aid initial start up only and is controlled by the thermo time switch [fitted between number 2 and 3 inlet manifold tract or under the thermostat housing on later cars. In normal UK temperatures ie above about -2 c the car should start ok with the spray valve disconnected. I would also say that the correct co at idle with a hot engine is 1.5 - 2% co. One of the modifications we used to do was to fit an auxillary air valve from an automatic 900, It has a larger opening when cold and therefore increases the idle speed by about another 150 - 200 rpm and the period of faster idle lasts a bit longer HTH, Regards, Tom, Saabtech.

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