'93 9000 Aero misfire...

in article snipped-for-privacy@bt.com, Hywel at snipped-for-privacy@btopenworld.com wrote on 12/10/2006 22:54:

Does your '93 have a distributor with a vacuum advance? It sounds like the timing is getting messed up at the point it needs to be advancing. Just guessing ...

Paul

Vart tog vägen vägen? SAAB : Nothing on earth comes close

Check your vacuum hoses -

- from the fuel pressure regulator (little can about size of stack of quarters sitting on the passenger side end of the fuel rail feeding the injectors) vacuum line runs about 6" to the intake manifold.

- from the charge air bypass control valve on the drivers side wheel well by the battery - 3 hoses run down behind the relay box by the battery and then - 1 branches off to the nipple on the 'hooter' and the other two run alongside the bottom of the batter - 1 to a 'wye' connector with a line feeding into the aquarium (and then into the dash for the boost gauge, I think) and one up to the underside of the throttle body (at least this is the setup on the electric throttle body for a '95 w/ TCS system)

- from the boost pressure controller at the upper drivers side of the radiator, 3 lines - 1 to the turbo waste gate, 1 to the intake manifold and

1 to the turbo

look at quasimotors site for photos that show the connections of the hoses to the BPC

it could be other things, but the vacuum lines tend to rot in the engine compartment heat and are the easiest culprits to check and replace

if they are all good - when was the last time the plugs were changed or re-gapped, was dielectric grease used to keep the spark from arcing down the plug insulators and and how's the direct ignition cassette doing?

What about the DI cassette?

Maybe the ECU is cutting off the fuel in response to dangerously high boost pressure?

John

When this happens it is like someone dropped an anchor out the back! It throws you forward into the seat belts, not what I would describe as a misfire.

The only way to see if it might be the cassette is to substitute another. One should always carry a spare in any case so it would not be a waste of money to buy an extra.

93 9000's do not have a distributor. They have a DI cassette. No spark plug wires either.

Charles

Paul Halliday wrote:

Could this be a turbo overpressurization with dumping thru the waste gate??

Sounds like a problem I had with my '93 Aero ...

The 'Check Engine' light came on. So I checked it by turning the key in the ignition to the 'on' position (without starting the car). Sure enough, the light flashed three times indicating a faulty air temperature sensor, but then it flashed five times indicating a faulty throttle position sensor.

So I left it for a while - and continued on my way down the parkway - when suddenly there was a 'jolt' or 'shudder' - quite violent. Almost as if the turbo was 'on' and 'off'. After that though, there was no turbo boost at all. In fact it behaved just like a normally aspirated car ...

I replaced the APC solenoid (top of radiator - three hoses going into it) - as I was told it was this that was causing the 'misfire'. But, this didn't solve it.

I checked the turbo wastegate actuator - but that looked fine.

I checked the vacuum lines - but they looked fine also.

So in desperation I took it to my local Saab garage where I was told that the diagnostic equipment couldn't communicate with the ECU and that I'd need a new one! (sod that I thought and left).

So I limped back home and decided to check the spark plugs and DI cassette - and lo and behold there was a crack in the DI cassette.

Now I don't know if this is what is causing the misfire - but I've ordered a new one - and will probably fit it this weekend along with new sparkplugs.

I'll let you know if this cures my not-very-fast-anymore Aero ...

(if it doesn't - I'll start looking for a second-hand ECU I suppose...)

Steve E. wrote:

Or is it the usual DI? Last about 60k miles, but is sensitive to overheating. If it's the DI going, the symptoms will worsen over a couple of weeks.

it sounds to me like the engine is boost cutting, this happens when the boost pressure is to high the ecu closes the throttle for a split second causing a violent jult. I would try a new boost pressure control valve and check the air lines connected to it for leaks or splits. Good luck let me know how you get on. MTech

I did once have this problem on my 2.0 lpt, but not since i used higher octane fuel, e.g. Shell Optimax or V-Power as it's now called. I don't know what the V stands for, perhaps Vertical take-off?