OK so I don't know what the deal is but for some reason my car keeps missing and cutting out and when it does it my tach needle is erratic and goes back and forth. Just watch the video below and see what I mean. Also if you listen close you can hear the car cutting in and out.

CLICK HERE FOR VIDEO

Anyone have any ideas on what it could be? It's gotta be some kinda electrical problem but I just can't narrow it down to what.

Thanks in advance!

 

The very first thing you should do is scan it. If you have a DTC16, the problem is the low res feedback signal from the distributor. This 5 volt square wave is fedback to the PCM and as well as controlling (if you will) the ignition, the PCM uses this signal to determine the speed of the engine and sends a tach signal out to the instrument cluster.

A DTC16 will shut down the engine but will NOT set a SES.

If it were just the tach signal from the PCM to the instrument cluster dropping out, the engine will still run fine so that's why I think the root signal is dropping out and causing both the tach and the engine to die. Since you need a place to start, this seems to make the most sense.

At this point you need to eliminate as many causes as possible. First check the wiring from the opti to the PCM. Check all 3 connectors for bent pins or corrosion which is common as well as ohm the wiring from end to end. If all that looks ok you could be sure the PCM grounds are in good shape. Last, you could actually view the feedback signals to see if they show any signs of a problem.

Last, put all pertinent information in either your bi-line or your signature. It would be nice to know if you have OBDI or II among other things. Since I like OBDI I assumed you have the same.

 

Yea sorry guess I should have clairfied what were workin on here. It's 96 Z28 OBD-II obviously. There are no DTC codes present right now.

So your saying that a DTC 16 won't pop up as an SES light but it will only show up if I use something like Datamaster to scan the car? That won't be a problem I can always just throw in one of my OBD-I ECM's in the car and then scan it with that.

Also you mentioned the PCM grounds. Which ones are you talking about? The only one I can think of is the one that goes down on the passenger side of the block. Where are the other ones located at?

 

Also I forgot to mention that after driving around for a min the tach will just sit on ZERO RPMS all together and won't move at all... I checked the car with the scanner and it's showing that the ECM is reading the RPM's correctly even when the TACH in the dash is being erratic.

 

OK now the tach will not even move at all... Well it does if I rev it up sometimes but now most of the time it just hangs out at ZERO..

 

Edit button is your best friend...

With the tach it can be a bunch of things, if the car is running and your tach sits at zero then theres something wrong with the tach. When I has my suburban my tach would jump around if there was low voltage.

 

A loose connection does that at least my sister's jeep cherokee did that because of such. Try tapping on the cluster to see if maybe its a loose connection.

 

I also have a 96 Z/28, my tach did this, car cut off and sometimes it would start back up and drive fine...first i would check my wire harness from my opti, they're known to give problems. Mine did not throw a light or any codes either when it happened, so i ended up replacing my opti and ICM (just to be safe) and i never had the problem again. Like i said, it seemed like it would drive normal and it did all the way to where i was parking it, and just before i reached my parking spot, it cut off and i rolled to where i would fix it. So i would check my harness, then i hate to say it, but i would turn to my opti. good luck, hope it all works out.