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Troubleshooting the Bosch CIS cold start system

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
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Reply to
Paul Halliday
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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.

Reply to
saabtech

My C900's have 8V NA engines, so I tinker a little with the CIS parts on my non-registered but running car (the fawn-coloured 1985 900i at "

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") to work out howit all interacts. 8-)

I think that's how it works. The cold-start injector is, I think, connected to the circuit with through the thermo-time switch and the warm-up regulator so as the thermo-time switch warms up, the warm-up regulator reduces the 'richness' of the fuel mix back to a certain level and the cold-start injector is disconnected from power after a pre-set time, or sooner if the engine is warm already.

That might be wrong, so anyone who knows better feel free to jump in here!

8-)

Did you measure this yourself? If you did, what sort of equipment did you use to work this out?

This area of the CIS system is the part I still don't fully understand.

Regards,

Craig.

Reply to
Craig's C900 Site

in article d0fe0c$sgi$ snipped-for-privacy@titan.btinternet.com, Tom@Saabtech at snipped-for-privacy@btconnect.com wrote on 06/03/2005 17:18:

Very comprehensive ... Thanks a bunch Tom.

That fills in a few gaps in my knowledge of the system. I'll do some testing as soon as I get my bonnet release issue sorted, but that's another story :)

Paul

Reply to
Paul Halliday

in article d0ftlc$j3a$ snipped-for-privacy@yoda.apana.org.au, Craig's C900 Site at snipped-for-privacy@lios.apana.org.au wrote on 06/03/2005 21:45:

I'll look into the WUR ... Tom has provided me with some troubleshooting ideas.

I did measure this myself. I have a Gunson gastester, which read 3.7% pre-MOT and the MOT station declared it 3.9%. I have re-checked since, but it was a little windy ... Hence my guess at between 3.5% and 4%.

Reply to
Paul Halliday

in article d0fe0c$sgi$ snipped-for-privacy@titan.btinternet.com, Tom@Saabtech at snipped-for-privacy@btconnect.com wrote on 06/03/2005 17:18:

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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Reply to
Paul Halliday

I have a 1985 900 with a cold start valve issue. During warmer weather the car tends to flood, unplugging the cold start injector lets the car start and operate normally. The question is which thermal switch does what? There is a 2 connectory thermal switch near the thermo housing and the one on the head... so what does what?

Reply to
mechtech

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