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Hi all,
for those that gave their valuable help and for anyone in the future who, like me, may need to search the archive for hints on fixing hesitations/misfires my problem is solved.
In short, the coil was going bad.
Some history:
Car: 1996 NG900S 2.0i (N/A) Auto.
I had a constant misfire at low RPMs once the engine was warm (fine when cold), a hesitation/8-stroking when flooring it from idle, and a misfire at 50mph with light throttle.
I also got a CEL come on , code 73 - short adaptation time, which the Tech2 said was P0171 system too lean.
It seems that although I thought I'd cured all my air leaks, there were still some getting through.
TIP: don't count on Blu-Tack to stop up the bore of a pipe. It gets sucked through!
I think the air leak was a secondary issue. I suspect that the code may have been due to the misfire dumping excess O2 in the exhaust. However, the mech said that he was getting the P0171 code almost instantly before he fixed the air leaks, and not at all afterwards, so maybe the Motronic is clever enough to tell the difference between misfire and lean condition O2 readings.
I observed that the misfire would happen even when the lambda sensor showed a rich mixture (it would obviously instantly show lean after the misfire). It seemed totally random, and pointed to either a very transient electronic problem governing the fuel, or much more likely an ignition problem.
As it had all the symptoms of a previous problem on another car which was caused by mat HT wires I tried a new set of plug leads, with no change. Spark plugs, dizzy cap and rotor were all new, fuel system cleaner had been tried. Again, no change.
I measured that the air mass meter seemed to work perfectly, but disconnecting it made the car run better. However, there appears to be nothing wrong with the AMM. I think that the limp-home mode makes for easier combustion for the dodgy spark.
So, although I measured the coil primary and secondary resistances with an analogue meter, and they seemed *roughly* in spec, when my mech measured it with a DVM, the secondary was 45ohms instead of 0.8 and the primary was also way out of spec. This fitted with the ignition problem theory, and a swap out to a new coil (£86 ouch!) has the car running better than I ever remember.
I guess it's no coincidence that the symptoms match the much-seen DI cassette failure on the turbo. Both cause poor sparks.
Hope this helps some other poor Saab owner in the future...
JonD
posted by 149.117.2...
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