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Date: Tue, 14 Dec 2004 20:05:06 GMT
From: Dexter J <>
Subject: Re: irreproducible bucking

Salutations: On Tue, 14 Dec 2004 12:24:41 -0500, ajs <> wrote: > My 9000 had the exact same symptoms, car and dealer, when the Direct > Ignition Cassette went bad. I found a new mechanic who sourced me a new > cassette and the bucking has been gone ever since. > > "Tom Reingold" <> wrote in message > >> My mechanics must think I'm nuts, because over the years, I have >> described tons of problems that they have been unable to reproduce. >> Well, I guess it's all in a day's work. >> >> THE CAR: >> >> 1995 Saab 9000CS with 167,000 miles (269,000 km; I'm in the US) >> turbo replaced recently because the waste gate got stuck open >> >> THE PROBLEM: >> >> Upon acceleration, especially at low speeds and low RPM (under 3,000 or >> 4,000), the car bucks rather hard. It feels as if I am jabbing the brake >> twice a second. I can get it to go away (or at least lessen) by backing >> off the accelerator. >> >> Any advice? >> >> Thanks. >> >> Tom Reingold >> Noo Joizy >> I am up against a 'hesitation' problem on my '93 Aero. I'm having the alternator refreshed and probably adding a modern dry cell battery as it's showing 50amps at the battery while running with 4 volt swings at the dash meter occasionally. I think it should be up around 80-90amps and steady at the dash voltmeter if I understand what the model draws cold once running without any extra devices or audio systems on (although no one seems to actually know exactly). I had a severe bucking issue on a non-DI '89 CD Turbo and it turned out that is was a fascinating oil triggered ground at the rotor that was tripping the engine management system to cut off fuel in cycles based on an interpreted engine knock. In effect, the engine management computer read the 1 or 2 cycle misfire in the range you describe and would cut the fuel on and off in very rapid succession causing a *very* severe buck at the wheels. My take is that the knock trigger in the management computer is the culprit in both instances. In the first, the effected plug only showed clear cylinder ignition variation after they had been in for a full service term. In the second, I have a slight pressure variation at #3 which I'm willing to bet is misfire fuel lightly thinning the oil on the rings. If the system does rely on feedback directly from the plugs (and I think we all agree this is actually the case and not some marketing blipvert for NGK in the owners manual) - the knock algorithms in the chipset must be impacted in some way by operational plug feedback. Therefore - anything that impacts or makes the engine miss might come to be read as a knock and cut back the fuel supply momentarily based on the software trigger. When the system is hesitating or bucking (rather than shutting down to limp mode and holding) - I think it is running a reset check and, finding that the misfire has passed, releasing fuel again. I have been trying to find some reliable measures to check over the DI on the '93 to see if #3 coil is exactly within specification because I'll wager a nominal coil would be greatly exacerbated by a low amperage situation. I wonder if a swinging voltage situation could cause a coil to heat a little higher over time? I gather there is a very deep diagnostic factory service manual regarding known voltages and amperages throughout the system. Must keep an eye out for one. Best wishes for the seasons brother and sister SAAB flagellants. Uncharacteristically clement for December on the story North Atlantic, will no doubt therefore have very severe weather through February for Dunlop DSP2 reports! -- Radio Free Dexterdyne Top Tune o'be-do-da-day Xmas - Charles Brown - Bringing in a Brand New Year all tunes - no cookies no subscription no weather no ads no news no phone in - RealAudio 8+ Required - all the Time

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