1997 Buick LeSabre surging and tach problem

[mickietx1]

I have a 1997 buick LeSabre V-6 problem. When driving a constant speed of 40-50 mph the car starts to surge and the tach fluctuate erratically and then sometimes drops to zero. I've tried several things from pushing the pedal slightly to flooring it to pumping it and it makes the car sluggish. If I LET UP on the gas pedal and then press down again it sometimes corrects the problem after several attempts. Last week this surging and tach flucts happened again after driving the car for about 45 minutes doing a range of speeds. I floored it then let up and the surging stopped but I could not get the tach to register. I turned it off then restarted it after several hours and the tach showed up again. This problem is not associated with how long I drive or whether its hot or cold out side. It has never stalled or even acted like it was going to stall. It starts right up and idels just fine. This confuses me to no end.
History on the car......... opcorn: I was given this car about 4 months ago from my aging mother who drove it very little however my dad was a houston cop for years (retired back in the 1980's) so you can just imagine the toll this car took while he was driving it. My dad did however take very good care of this car. Made sure that the oil was changed regularly and that hoses and plugs and wires were changed and maintained regularly as well. It has 80K miles on it. When my parents gave me this car they mentioned that the tach was wacked and that it sometimes hesitates but that no mechanic could figure out what was wrong. So here I sit working on another car. I had a 1990 Honda that I worked on till I sold it so I'm sorta up with the mechanics of cars. Mind you I am a women though and so we think differently when it comes to the understandins of car problems.

Other than this surging and tach issue the car is in great shape. The engine is clean so clean that it looks brand new. I love this car and want to stay loving this car but if I cant fix it my love will surely turn ugly
Any suggestions here would be helpful.

[BNaylor]

Welcome to AF.

Based on your symptoms your problem is consistent with a flaky crank position sensor (CKPS). Tach dropping off to zero rpms or no tach even though the engine runs is classic. Either bad 18X or 3X signal pulses from the crank position sensor since it is actually two sensors in one. The CKPS sensor provides the ignition timing for the engine and fuel injection system via the ignition control module (ICM) all controlled by the PowerTrain Control Module (PCM).

Also, it may not set a DTC so there may be no SES/CEL light (service engine soon or check engine light).

[HotZ28]

I concur with BNaylor (Bob) concerning a flaky CKPS and I will include some pics to help you identify where it is located and what it looks like. The harmonic will need to be removed in order to replace it.

Before replacing the CKPS, you may want to eliminate all other possibilities that could cause random problems like this. First, you should check the battery terminals for corrosion and clean if necessary. Next, check the ignition control module (ICM) and associated wiring. The tach signal originates at the CKPS, then goes through the ICM and out of the ICM (white wire) to the tach. The ICM is located under the coils and has a 14-wire connector plugged into the end with a small bolt to keep it secure. Remove the bolt and connector and check for loose connections or corrosion and reinstall with dielectric grease. In addition, you can have the ICM tested @ AutoZone free. If all this checks out good, it's time for the CKPS!

[BNaylor]

.........

Just a comment but from my experiences the Autozone ICM bench test most likely won't detect this particular problem and it will probably pass. BTDT.

Just to give her an idea since she appears to be DIY capable here is the process to replace the crank position sensor otherwise it might be a good idea to take it back to one of those mechanics but tell him you suspect the crank position sensor and/or associated circuits-components. Link below is for a Pontiac Grand Prix but the same procedure and process for the LeSabre or any GM car with the Series II 3800 engine. Take note of the special bolts needed for the puller and removing the harmonic balancer.

Click here

[mickietx1]

I talked to a shade tree machanic, not really I guess cuz he does work at a local shop. But anyway, I told him about the idea of it being the CRANK SENSOR and he kept throwing me to "you mean the camshaft sensor" I'm like "no I said CRANK not CAM" he just laughed at me. But so far the Crank sensor Idea works better than the cam shaft sensor so I'll play with my car this weekend and see what happens. thanks for your quick response to my post.