Date: Tue, 08 Mar 2005 19:10:42 GMT
From: Paul Halliday <>
Subject: Re: Troubleshooting the Bosch CIS cold start system

in article d0fe0c$sgi$, Tomnospamtech at wrote on 06/03/2005 17:18: > > "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 Given that I couldn't get into my engine bay until today (my car went to the mechanics for a new bonnet release cable), I asked them to look over the mixture and possible links to the warm running and odd vac reading. They said that the mixture was 3.5% CO at idle which is pretty much what I got out of my little Gunson machine. When the throttle is blipped, fuel enrichment occurs and when the RPM is increased slowly, it leans. Looking good then. I did some more diagnostics in the engine bay and it all checks out as described by you Tom. Thanks a million for your reply. What I did find was my RPM decreased and the vac reading settled to about 21 InHG at idle when a certain pipe was squeezed. I have replaced that vac pipe and it's much better on the idle and the idle vac readings. I'll drop the mixture down to about 2% CO at the weekend, since my garage said that they usually set mixture to about 2% CO. I had been given some duff information on a forum board about 3.5% :) Anyway, the engine temperature is still a little too high. My oil was changed just the other week, so I can discount that. I'll do the usual diagnostics on the radiator and thermostat too when I have a few clear hours at the weekend. Thanks again, Paul 1989 900 Turbo S

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