Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 20 of 30 Posts

·
Registered
Joined
·
393 Posts
Discussion Starter · #1 ·
Morning all,

I trust you all had a nice Easter break? I went to Edinburgh for a few days and in the 1000miles of driving I did the car behaved impeccably, and did so for the next few days after returning home.

But, yesterday morning it started misfiring (I think), running very roughly. This is present at all revs, from idle up to running speeds, and there is a consequent loss of power. The exhaust smells very strongly of petrol, although it is not smoky. I took off the DI unit and pulled all the plugs which were all uniformly black, so it doesn't appear to be a particular cylinder that is affected. The idle speed is normal and stable (at about 900-950rpm).

The check engine light doesn't come on or flash so the management system doesn't seem to think there is a problem. So, has anyone got any ideas? Is it most likely to be the DI cartridge? (which is 9 years and 136k miles old).

For what it's worth, over the past year the car has very occasionally stuttered slightly, always occuring while motorway cruising (or at least this is when I've only ever noticed it). It only lasts a second or two and then disappears. Could this have been an indication that the DI was on its way out?

Everything under the bonnet looks fine. As well as plugs/ignition the Haynes manual suggests other things such as the fuel pump, the fuel injection system in general, blocked crankcase breather pipes, and probably some other things I've forgotten.

Any help would be much appreciated!

cheers,

Ben.

p.s. does anyone on this list own a 9000 CS with the registration number M900OCS? Nice. I saw it in Edinburgh last week.
 

·
Registered
Joined
·
11,343 Posts
Hi Ben

I am no expert (as most know
) but the surefire way to diagnose the DI is to replace it with a known good one.

MarkE was having problems with his 9000 2.3CSE a few weeks ago, so we stuck my DI on his Saab and it ran just fine.

So, yes, it may be the DI ...but someone more expert will be along in a moment to give you the correct answer.
 

·
Registered
Joined
·
58 Posts
Hi Ben,
Not had quite the problem you have listed.

However I have had misfire problems before.

Causes I have found are usually

1/. Dead Plugs cheap ones last 6k on a Turbo before going off and by 12K seriousely bad.
2/. Leads, and distributor cap if you have one.
3/. Ignition coil dieing
4/. Blocked injectors

I also have found that cleaning all the "in line" Air sensors and bits between the Air filter and the injectors helps economy no end.

I took them off and sprayed with break cleaner until they looked clean and stopped running black.

Do not recomend this unless spares are avalable for more expensive Air Mass sensor.

Thinking about it very very badly blocked injectors might cause some of the problems you are having?

I think the Di module though might be worth checking if the problem was "sudden" as opposed to gradual with all the problems I have listed above.

Sorry not near enough to Woking to help.

Regards

Bill A.
 

·
Registered
Joined
·
393 Posts
Discussion Starter · #5 ·
Thanks Bill. The plugs were changed 1k miles ago and looked fine (apart from perhaps being too black - fuel/air mixture too rich?). My suspicion is the DI unit, which I've heard is prone to failing with age. Mine's 9 years old and has 136k miles worth of firing under its belt.
 

·
Registered
Joined
·
1,245 Posts
Ben,

I can only think of two causes for your symptoms. Either, the ignition is failing to ignite the sparks, in which case it's the DI, or the mixture is excessively rich for some reason.
On an LH system with an Air Mass Meter, if a leak develops on the pressure side of the inlet between the AMM and the manifold then a rich mixture situation will occur. This is because the AMM adjusts the mixture for the amount of air going through it but all of that air isn't going into the engine hence the incorrect fuel/air ratio with misfiring and poor performance. If there was a faulty sensor the "check engine" light would show.
The only time I experienced this was when the bottom intercooler hose was leaking at the clamp but I could hear this from inside the car.

I suspect that a Trionic system would show the "check engine" light with such an air leak, but I might be wrong and even if it didn't I think you would get different symptoms with a MAP instead of an AMM.
Either way it is worth checking for air/vacuum leaks before changing the DI
 

·
Registered
Joined
·
393 Posts
Discussion Starter · #7 ·
Hi all, since I got home from work I've tried a few things, so time for an update.

First off I've checked for obvious leaks and can't find any.

But, I have been fiddling...

With the engine running I disconnected power to each fuel injector in turn. 3 times out of 4 (cylinders 1, 3 and 4) this made the car almost stall, but one time (cylinder 2) it made no difference to the rough running. So, I checked the spark plugs, and the one from that cylinder was much blacker than the others. Maybe a duff plug? If so it should behave the same way in a different cylinder. So, I swapped it with the plug in cyl 1 and did the same injector-disconnecting. When I disconnected the injector from cylinder 1 with the suspect plug the engine almost stalled, whereas when I disconnected the injector from cylinder 2 which originally made no difference, there was... no difference.

I hope this makes sense!

So, does this tell me anything useful? Does it rule out the DI unit? Probably not - I assume it can fail such that one of the coils dies before the others.

Could it be an injector problem?

Any more ideas out there?

cheers.
 

·
Registered
Joined
·
696 Posts
If you say disconnecting injector 2 doesn't make a difference then. You could try using a Injection cleaner. Just poor it in the tank when it's half full. And do some heavy duty drivng till the tank is almost empty. Then try if it makes a difference.
Or indeed change the DI.
 

·
Registered
Joined
·
8,216 Posts
To confirm it is an injector problem, you could swap No.1 and No. 2 injectors and repeat the test. If the problem moves, then it is an injector problem. However, since the exhaust smells of fuel, it sounds more likely that the fuel is being squirted, but not being lit. This would suggest an ignition problem (or a mechanical problem leading to little or no compression, but let's not go there for the moment
).
 

·
Registered
Joined
·
970 Posts
Have you tried swapping the ignition leads about so that the one for cyl 2 is moved elsewhere. The when you remove the 'new' one on cyl 2, are the results the smae?

Hope I'm not talking ar5e. I am not yet familiar with DI but that is what I would do on normal ignition stuff.
 

·
Registered
Joined
·
8,216 Posts
Originally posted by bambo:
[qb]Hope I'm not talking ar5e.[/qb][/b]
Perfectly sensible suggestion, but this wouldn't work with DI as there are no plug leads. DI is the system where each plug has its own ignition coil sitting on top.
 

·
Registered
Joined
·
393 Posts
Discussion Starter · #13 ·
Morning guys,

apologies for not telling you what the car is, which might make a diagnosis easier!
It's a 1994 Aero 2290cc turbo.

The way the car is running at the moment, and with almost a full tank of petrol I don't think I can go down the injector cleaning route just yet. But, I had already decided that it would be a good idea to swap the injector from cyl 2 to somewhere else and see if the problem followed it. Something for the weekend I think.

However, I'm still supicious of the DI because of the petrol smell in the exhaust and the blacker plug in that cylinder.

Anyway, thanks for your continued help!
 

·
Registered
Joined
·
1,261 Posts
Not withstanding the excellent advise given above, a misfire and 9 year old DI cassette on 136k miles would lead me to believe that if it's not the DI at fault, it will be before long as most seem to pack up at the 100k-140k mark.
 

·
Registered
Joined
·
14,305 Posts
My money's on DI-

Ben, your car will be Trionic, which is actually relatively insenstive to air leaks on the intake as it has a MAP sensor rather than AMM.(I know, I forogot to tighten up the rubber elbow to the inlet manifold and then had it blow off during max boost whilst overtaking
but the engine carried on happily, just (a lot) less
).

The petrol smell indicates unburnt fuel. If it were a lambda problem, you would probably get a check engine light due to rich running on all cylinders. The single black plug and injector disconnection test certainly focuses down on no 2 cylinder, and a lack of combustion.

The next step is certainly to get a replacement DI to try. The motorway cruising symptoms you speak of are typical of a DI on it's way out.
 

·
Registered
Joined
·
393 Posts
Discussion Starter · #17 ·
Thanks Guys. The simplest thing would certainly be the DI, so all I need is a fully functioning DI-equipped Saab to pay me a visit so I can try it out because the car really isn't driveable as it is, but, if push comes to shove I may have to go somewhere to try one.

cheers,
Ben.
 

·
Registered
Joined
·
393 Posts
Discussion Starter · #20 ·
Thanks for the offer Mark. I don't really think I'd want to drive the car to Marlow, although from Winnersh it can't be much more than about 10-12 miles. However, what I could do is bring my suspect DI unit and see if it performs the same way on your car.

I still think it's worth my while checking the injectors. My dad seems to think that if the injector was stuck open or delivering too much petrol it might give similar problems to the cylinder not sparking and combusting. Unless of course people out there know otherwise!
 
1 - 20 of 30 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top