i own a1991 saab 9000 2.3i ,which has recently developed an annoying misfire at low revs .if you accelerate hard there is no noticeable misfire but drive normally and try to pull from low speed there is amisfire around 1500 to 2000 rpm.i have checked plugs and the throttle postion sensor and found nothing.
can anybody point me to the source and how to check.
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Mark
I do not profess to be a mechanic like others on this site that may well advise you....... but having had similar misfires found the fault in the high tension leads.
At 10 year old they may need replacing.
Stand by for real advice from others......
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Mark,
Quite difficult without properly testing the car, but .............
I would think it more likely to be a fueling problem than ignition. I am assuming yours is a 16valve with Bosch LH2.0 management and Cat.
First priority is to establish there are no inlet air leaks, or exhaust leaks close to the Lambda (Oxygen) Sensor. The Lambda Sensor outout needs to be checked on a slow-screen oscilloscope, and it should switch between 0 volts and 1.0 volts approx 12 to 15 times in 20secs at idle, quicker as revs rise.
Next stop would be the Mass Airflow Sensor - output can be checked by voltmeter, but a 'scope will be better for identifying glitches in the output.
If all of this checks out I would try a good injector cleaner (I use Forte, but the Texaco or VAG products are good).
After that it gets complex........!!
Regards, Adam
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Isn't this the model with Direct Coil Ignition? One coil pack per cylinder, like we find on today's vehicles?
I think there have ben problems with these coils - misfires are the giveaway.
Dead catalysts are the result.
Any SAAB experts out there?
David
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David,
If it is coil per cylinder I agree absolutely that that is the first port of call, but according to my data they only happened in '93. Data is always fallible, of course, so we need to know which system the car has.
Mark,
Does the engine have a distributor cap and visible HT leads. If NOT it is coil per cylinder.
Regards, Adam
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I inadvertently found how easy it was to detect leaky HT leads. Just touching them instantly pointed out the faulty lead. Ouch!
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Mark - Two replacement direct ignition units in 30000 miles on a 93 9000 cse certainly points to this as the first port of call in my experience - if a 91 car does in fact have a di unit. My first one gave rise to misfire and the second died completely in the outside lane.....Can you borrow one to try it? My first cost £300+ but now they can be had for about £120. Good Luck!
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Had a v. similar problem with my 9000. The very nice man from the AA said that he'd dealt with, and heard of, numerous problem with the coil pack.
A replacement pack sorted the problem.
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see townsendimports.com or saabnet.com for stuff on meding saabs
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