tach drops to Zero/ bucking

[mickaz]

Hi

I need some help from you fellow 60*ers.

I have a little problem with my car. When I drive it as I accelerate the Tach drops to zero and goes back to pick up its rpm. I happens at accel,decel and cruise. at accel there is sometime "holes" where the RPM don't climb up for a second, and then keep climbing up as if nothing happened. on decel the gauge goes to zero then pick back up ( very random no pattern .) While crusing the engine sometime buck when it goes to zero. sometime at idle I feel as if the engine wants to stall then picks back up and goes.

the car idle really well and when I rev it in park it seems to have no more rev limiter? ill test it out again tomorrow.

If you have any idea I'm open to them...Ive changed my Crank position sensor and my ICM and my CPS. oh and its on the Beretta 3500 OBD2 and It has no check engine.

[pocket-rocket]

With the items you've replaced already, I would probably look at your CPS wire first.

[mickaz]

With the items you've replaced already, I would probably look at your CPS wire first.

well I replaced the parts with part I had from my others engines that were known to work LOL. I will look into what you say, but pocket do you have ,by any luck, a wiring diagram from a ignition module? that would help me out. thanks for the help.

[pocket-rocket]

This is a DOHC, but should be the same (not sure how I get them scanned in sideways when they look straight on the platen...). Hope this helps

[95SleeperAcheiva]

He may have a gauge problem. I remember years back I was able to send out my gauges to have them repaired and recalibrated. I don't remeber who or where anymore. Last time I did that was literally 20 years ago. i f anyone knows who still does gauge cluster repair I'd be interested. My stock tach is jumpy and I have a Catera with an oil pressure gauge thats faulty too.

[mickaz]

He may have a gauge problem. I remember years back I was able to send out my gauges to have them repaired and recalibrated. I don't remeber who or where anymore. Last time I did that was literally 20 years ago. i f anyone knows who still does gauge cluster repair I'd be interested. My stock tach is jumpy and I have a Catera with an oil pressure gauge thats faulty too.

]

yeah i tought so but the engine will also misfire or buck when I mash on the accelerator.

[Schmieder]

I may be way off but I'de always check the battery connection integrity. To me, my first thought was your voltages are jumping around causing chaos w/ tach signals and injector fire rate.

I do know a weak battery can cause the tach and speedometer to jump wildly while attempting to crank it over. And sometimes the entire system would shut down for a few minutes then return.

Maybe you have a short circuit that isn't permanent but on/off like a wire only making contact during stress.

I once had a host of very strange and intermittent issues. I was warping my brain trying to find the cause.

Ends up it was a bad connection in the negative battery cable to ground. My Batt is a trunk mount so the ground cable was the only route to the frame grounding (it wasn't shared). It was failing like a bad 1/4" audio cable would. When I ran the car with the neg. jumper, ALL symptoms disappeared just like that.

I ran a jumper line from the (-) battery terminal to the frame as a test. It can't hurt to check.

[robertisaar]

He may have a gauge problem. I remember years back I was able to send out my gauges to have them repaired and recalibrated. I don't remeber who or where anymore. Last time I did that was literally 20 years ago. i f anyone knows who still does gauge cluster repair I'd be interested. My stock tach is jumpy and I have a Catera with an oil pressure gauge thats faulty too.

i've recalibrated the speedo and tach in the wife's GP before(cost a whole ~$2 to do it as well), but W-body GP UB3 clusters are known for being crap.

[mickaz]

I think I found out the problem!

I was waiting for the engine to heat up and I herd a something rubbing the fan. well what do you know, a wire was stuck in the fan and cut a three place and shorting! no test drive yet , but I am pretty sure that I nailed it because it's the wire to the sensor behind the crank pulley.