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Misfire! Saab 9000CS LPT Auto 1993

Saab 9000CS LPT Auto 1993

I'm posting on behalf of my brother who's Saab is having major spluttering / misfire problems. Misfire seems to only happen when the engine is at normal temp and not when cold. It's like the engine is not running on all 4 cylinders but sometimes it will be running ok without misfire and then all of a sudden without warning the engine dies and will not restart. Leaving it a few minutes it then starts again. It's had new plugs & air filter and even tried another Di cartridge but with the same results. Grateful for any tips as to where to look first. A bit puzzled as it only seems to happen when the engine's warmed up!

Reply to
Mark
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Have the HT leads been changed?

Reply to
Jeremy

Doesn't have leads, it got the Direct Ignition fitted. I've read that these buggers always go but it was swapped with one from another Saab but it hasn't made any difference.

Reply to
Mark

No HT leads, uses a DI unit.

This would be my first suspicion - the DI unit. Get it checked out, or swap it for a known working one.

Next thing would be the injectors. Check that non of them is sticking.

Reply to
Grunff

Ah, you've already swapped it.

Check the injectors. When it stops working, remove the whole rail, point into a container, and turn it over. Do they all spray.

Reply to
Grunff

musty read properly next time

Reply to
Jeremy

Will a compression test be ok to determine if it's head gasket?

Reply to
Mark

If it was an 1989 - I would say it sounds almost like the engine management system is cutting off the fuel upon interpreting a knock.. Which isn't to say there is a knock - but - it may be reading one on a short or some other engine variance (timing - water in the fuel)..

Is the management system less sensitive or more comprehensive on the

1993?..
Reply to
Dexter J

Sounds like primary ignition breaking down when hot- does the rev counter begin acting up when the engine does? Have a good poke around at the CAS and wiring plug. Get some freeze spray (computer or plumbers shop) and and spray it onto the CAS next time it plays up when hot. I think you will find you are loosing spark which is the root of your problems.

Tim..

Reply to
Tim..

The DI unit was my first suspect, but the OP says he's swapped out the DI for a known good one.

Reply to
Grunff

But I didnt mentiont he DI unit- we know he's already swapped it. I was talking about the primary trigger- the CAS.

Tim..

Reply to
Tim..

Sorry, my mistake - I didn't recognise CAS - do you mean the crank sensor?

Reply to
Grunff

Today I had a look at the car for myself and to make absolutely sure it wasn't the Di unit our local saab dealer kindly sold us a brand new unit (200ukp) with the option to return it for a full refund if that wasn't the fault. Also put in a new set of NGK sparkplugs and set the gap to

1mm. Well the misfire was still there but at least we now know for certain it's not the Di. The misfiring appears to come when the engine is under slight pressure like driving up an incline but not if you drive the car very hard using full throttle. That's as far as we've got so far but will keep trying.
Reply to
Mark

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