Car would not start although engine cranked after using at night in stop and go traffic. Left alone for an hour or so and then started right up. Ran fine the next day, however, after parking at night wanted to move car to another spot and had same cranking problem. Next day ran just fine. I thought starting problem could be electrical because the nights were much colder than NJ. Drove from Boston to New Jersey, but during first hour of trip exprienced sudden engine surge and Tachometer went to 0. Engine kept running with no loss of power. Nest day when I took to dealer Tach was working normally. Left car for three days. They could not find any problems but thought it maybe the computer. Dealer suggested I hold up on computer replacement until symptom repeated. Today took a 30 mile trip without a problem. On returning home again experienced brief engine surge and Tach went to 0 but car still running OK. Got home, had lunch and started car. TACH WORKING!! Ran a short errand without a problem.

Does anyone know how the Tach senses the engine RPMs? Does it come from the computer? Any idea if the starting problem and the Tach problem are related?

Thanks for any help I cane get. The Customer service guy was not sure how Tach gets RPMs.

please put your year and hte trim level of your Bonne in your sig so we can help ya

Added Year and model to my signature, as suggested. Left car out overnight to see if cold temp had any effect. Used this morning with no problems. Tach working, however, I was driving locally could not drive faster than 45 mph and only used for less than one hour. Still hoping for some help as I we plan to go back to MA for Thanksgiving.

Well, I'm not too sure about that customer service guy. The PCM uses the 3X reference input from the crank sensor and in turn inputs this signal directly to the Instrument Panel Cluster (IPC). The signal comes out of the PCM on connector C2 pin#8. It comes into the IPC on connector A4 FW121.

My 89 Bonneville was having a similar problem 5 or 6 years ago. When the temperature dropped in the fall the car took longer to start. Before this it had always started with just a click of the key. Of course being the procrastinator that I am I didn't do anything about it until it got down to about 10 degrees & the car refused to start. I won't mention how much fun it is to work on a car when the chill factor is -10. To make a long story short it turned out the ignition coils were going. You can test yours by checking the resistance of the secondary windings. Just pull the plug wires off the coils (you might want to number them) & check the resistance of each coil. All three readings should be close.

My tachometer worked fine with the bad coils so you may have a different problem or two problems at once.
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Mark,

Thanks for the information. I was told that the computer indicated a crank sensor fault code but repair tech did not think it was bad. Problem with dealers is that we only get to speak to the guy who writes up the service problem order and not the mechanic doing the repair. When I had the problem a second time and called, the customer service rep did not say anything about the crank sensor probably because he does not know as much as you.

Could a problem with this sensor prevent car from starting?

Thanks again for your help. Now that I have this info, I may try a local repair shop.