Troubleshooting the Bosch CIS cold start system
Paul Halliday
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
http://saab.go.dyndns.org/
Tom@Saabtech
"Paul Halliday" <pj...@blueyonder.co.uk> wrote in message
news:BE4FB345.13743%pj...@blueyonder.co.uk...
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.
Craig's C900 Site
>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!
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
"http://www.saab900classic.net/gallery/craig.dewick.yellow") to work out how
it all interacts. 8-)
>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?
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-)
>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.
Did you measure this yourself? If you did, what sort of equipment did you
use to work this out?
>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 :)
This area of the CIS system is the part I still don't fully understand.
Regards,
Craig.
--
Craig's Saab C900 Page --> http://lios.apana.org.au/~c900 Sydney, NSW Australia
Craig's Saab C900 Workshop -- For all Saab C900 Enthusiasts world-wide!
http://www.saab900classic.net http://www.saab900.org c9...@lios.apana.org.au
Come and explore our site, and check out our web-forums, mailing list, etc.
Paul Halliday
> It sounds like you may have a problem with the warm up regulator, [fixed to
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
Paul Halliday
c9...@lios.apana.org.au wrote on 06/03/2005 21:45:
>> 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?
>
> 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.
I'll look into the WUR ... Tom has provided me with some troubleshooting
ideas.
>> My air/fuel ratio is set to between 3.5% and 4% carbon at warm idle.
>
> Did you measure this yourself? If you did, what sort of equipment did you
> use to work this out?
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%.
Paul Halliday
saab...@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,
Craig's C900 Site
>> 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.
>I'll look into the WUR ... Tom has provided me with some troubleshooting
>ideas.
I read Tom's comments too since the CIS injection system in my C900's (1983
900S and 1985 900i - both NA) is still a bit of 'black art' to me. 8-)
I've been told to try changing the warm-up regulator to see if that fixes
the cold-idle problem with my 900i (the car that I fixed the brake master
cylinder on yesterday), and i do have a brand-new one here but it's a
different part number (doesn't end in 136) so I'm not sure if it has the
same pressure settings. Apparently there are many variations of the warm-up
regulators that are set up with different pressure settings to suit the
engine they're intended to be used with.
The warm-up regulator still fitted to the dead engine in my 1983 900 gli is
a different part number again. So I have two I can try. doesn't look hard to
change - just relieve the fuel pressure, disconnect the two fuel lines, the
electrical harness, and unbolt the old one. Reverse that to install the new
one. Anything else that needs to be checked to change a warm-up regulator?
Perhaps Tom might comment about this?
I don't have anything in the tech library section on my C900 Workshop site
at "http://www.saab900classic.net/library.html" about warm-up regulators but
there are some good references in other sites (might have one of those
already linked).
>>> My air/fuel ratio is set to between 3.5% and 4% carbon at warm idle.
>>
>> Did you measure this yourself? If you did, what sort of equipment did you
>> use to work this out?
>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%.
Ah ok I actually used one of Gunson's Eezibleed kits to bleed the brakes on
the 900i yesterday. The old brake fluid which the new fluid pushed out was
horrid! Almost black like old engine oil in the line to the right-rear
caliper.
Oh one other thing - anyone who does buy an Eezibleed kit to do
brake-bleeding themselves should use the thin 44 mm washer in the plastic
cap supplied with the kit that fits on the brake fluid reservoir mounted
over the master cylinder. I used the thick washer but it didn't make a 100
percent seal so when I had the air supply hooekd up to the 'Gunson chamber'
(the chamber holding the brake fluid supply that's pushed by air pressure
through a tube into the fluid reservoir on the master cylinder as the lines
are bled out), brake fluid was very slowly leaking out the top of the cap
screwed onto the master cylinder reservoir so I was flushing it away with
clean water out of the plastic watering can every 5 minutes or so. 8-)
Paul Halliday
saab...@btconnect.com wrote on 06/03/2005 17:18:
> 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.
Hi Tom ... Just to recap on this one. When the engine warms, how does the
system lower fuel pressure? Does the bi-metallic strip open or close current
to the fuel distributor?
Craig's C900 Site
AFAIK, the warm-up regulator is the primary device that controls master
pressure in the fuel distributor. The other devices used during the
cold-start and warm-up phase (thermo-time switch, cold-start injector,
auxilliary air valve) do their job and are no longer taking part in the fuel
pressure regulation after the engine has come up to normal temperatue. The
airflow sensor plate linked to the bottom of the fuel distributor controls
how much of the master pressure fed to the fuel distributor is delivered to
the fuel injectors.
That's probably a very simplistic overview. Cars with turbo's have
additional features which interact with the devices in the fuel system, but
my C900's are all non-turbo cars so I'm not able to relate anything about
cars with turbo's from a technical point of view.
mechtech
--
For full context, visit https://www.motorsforum.com/saab/troubleshooting-the-bosch-cis-cold-start-system-32350-.htm