Misfire - cold start

[carrera]

That makes much more sense to me now, I had never looked into this at all, thanks.

I know some people put vaseline on battery terminals...... I won't and remove any I see, horrible stuff for interfering with a good connection

[carrera]

I see you have already changed the CPS, and assume all the cabling / connections were fine.

Have you any basis for believing it is ignition rather than fuel ?

Can you identify that the misfire is on one particular cylinder, rather than being spread across them all.

Just a couple of ideas for you

[fka]

From the last techII session the count was higher on one cylinder by a factor of 10. Could be a dodgy injector, that's also on my list.. Fuel filter already replaced, pump a possibility too..

[sgould]

What you are doing with the grease on the rubber boot ends is correct. The last new Saab DI was pre-greased on the rubber only.

[carrera]

I doubt it is fuel pump related. The system runs at a pressure with injectors open for a certain duty cycle to provide fuel that the ECU calculates.

Let's say that the fuel pump switches off for a second, then restarts. The result for that second would be a drop in fuel pressure as residual pressure allows fuel to flow through the open injectors. With the drop in pressure there will be a corresponding reduction in the amount of fuel actually delivered, which would make the mixture a little lean across all cylinders, rather a single misfire on one cylinder.

Of course T7 being what it is, it will then try to adjust idle speed and increase fuelling based on the lambda readings.

Does that make sense ?

The fact that you have one cylinder where the problem is greater would have me looking at swapping plugs and injectors between cylinders, to see if the misfires follow either of those changes. Just an idea.

Injector issues can of course be as a result of problems with the wiring, so even a fuel misfire becomes electrical

[fka]

Thanks Will, I try to follow the WIS service guide and thought I was on the right track.. In fact I was worried I'd managed to somehow contaminate the terminals with silicon this time so took the DIC off and gave them another clean with IPA..

Makes perfect sense carrera the pump would of course affect all cylinders, I'd not actually thought along those lines to be honest.
The fact it's intermittent makes me thinks it's electrical, or dodgy fuel.
The manufacture date on my DIC is 09 so obviously new to the car, but that doesn't necessarily mean it was 'new' when put on the car.
Injectors is top of the list and I wish I'd known about switching to green giants when I went stage 3 as opposed to the 3.5bar fuel reg. Obviously if it is electrical new injectors wouldn't solve the problem.. I didn't replace the pollen filter today as I ran out of time but when i get the chance to do that I may see if I've got time to swap the injector round on the dodgy cylinder too.

[phoenix]

If you send the injectors off to get cleaned (normally about a tenner each) you will get a before/after flow test result, which could confirm or not a possible cause. Of course you need to label them individually when you send them...

[fka]

Think I'd sooner just replace the injectors if it came to that, being our only car I can't have it sitting immobile for any great length of time.
I've just got back from the Gower, so a few hundred miles, and I've not seen any more misfires on the motorway using cruise control or under load. Only a few misfires registered on overrun, which I believe I'm right in thinking is to be expected.. Really think I may be getting bad fuel from my local Shell garage. Might switch to Esso and see what happens..

[carrera]

V-Power or regular ?

[fka]

always V-Power

[carrera]

Well, there's that suggestion flying out of the window then 

Try some regular - good enough to eliminate the bad fuel, I would expect the injection system to be clean if you only use v-power