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Howdy,
My wife's car ('92 245, M47, B230F, LH3.1, 230k miles) had been acting up for the last few weeks. The symptoms, as she described them to me, were: Occasional hard starts--maybe 7 or 8 seconds of cranking instead of 1 or 2, but only first thing in the morning, never after the car had been running. Occasional hesitation at low RPMs--like rolling through a stop sign very slowly in second gear. And finally stalling out (only did this once) when stepping on the clutch to coast to a stop.
Naturally, whenever I drove the car it was on its best behavior. Last Thursday, finally, it pulled a total no-start in the driveway. Could hear the fuel pump relay picking and the pumps running as normal. Pulled the coil wire and saw no spark. By the time I got out the Bentley and multimeter, spark had returned and the car started and ran as if nothing was wrong.
Checked codes, none stored. Disconnected battery and cleaned up fuse box, battery terminals, manifold grounds, and replaced plugs, cap, rotor and wires as preventative maintenance. None of these parts were that bad or that old or showed any signs of trouble. Just a good tune up I like to do before every winter, and it seemed a good thing to rule out the obvious stuff first in this situation.
After some more trouble shooting--plus reading through the archives, FAQ's, and Bentley--everything points to either a bad coil, bad ignition power stage (a.k.a. ignition amplifier/module), or both.
Swapped them both out with spares, and the car fires right up. Take it for a spin and it seems to be running much stronger than it has in a while. We've both driven the car a lot (and hard) in the few days since then and it seems to be totally cured of all ills.
Sorry to be long winded, but I guess the question is this: There's different values for testing the coil in the FAQ's and the Bentley. Between terminals 1 and 15, FAQ's call for .6-.9 ohms; Bentley (page 280-8) calls for 1.8-2.0 ohms. Between terminal 1 and the center tower, FAQ's call for 7,000-8,500 ohms; Bentley calls for 8,000-11,000 ohms.
The coil I pulled out of the car tested 1.0/11,500. The "known good" one I put in tested .9/8,000. I'm assuming Bentley is wrong here, but I'd kind of like some validation on that. A marginal coil will fry a marginal power stage and vise versa, and I'd like to not have to replace these parts again a few months down the road.
Any one have any input? Is there a list of Bentley mistakes somewhere? I know there's a few others that I've come across over the years.
Sorry for the long post--wanted to be as specific as possible in case someone else in the future is searching around trying to figure out an intermittent ignition problem with changeable symptoms. We all know how much fun those intermittent "honey the car did something funny today" problems can be....
Best,
Afton
'68 122, '87 '88 & 92 240's, all stick shift station wagons
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