Sometimes, it is really unpredictable, the car will turn over and miss really bad. You have to keep half trottle to keep it running, but runs very very rough. When it does this and finally dies, the tach will pulse in a bout 100-200 rpm increments. You can let the car sit a while and then it will be fine. You know the car will start when the tach stops bouncing. This really has me boggled. I have replaced the opti and the ignition module.

thanks in advance,
Dan

 

Have you checked the starting system wires? To me it sounds like you have a poor connection of either the positive cables or ground. Either at the battery or at the cluster(s) on the fender. It would also be advisable to check the ground strap from the engine to the frame as well. While you're there, check the ground at ICM, above the starter and front core support near the radiator.

Start at the battery and don't just wiggle them to see if they are tight, pull them off, brush them and put them back. Be sure the mounting point is clean and shiney as well.

 

So a bad ground or bad starter could cause the Tach to pulse with the key on. After it dies the car will usually turn over and start again, but runs really rough about 500 rpms missing with half throttle. There is also a slow battery drain somewhere. If I leave the car sit for a couple of days w/o starting it will need charged again.

 

Had the same thing happen to me when I lost my opti. I know you said you just replaced it but I wouldn't rule it out. I completely lost my tach signal though when it went out and it kept setting a cam sensor high resolution signal code. Have you tried pulling codes on it to see if it comes up with anything??

I would also get your battery issue figured out first. I've seen many VERY strange problems with low battery voltage situations.

 

Haven't drove the car in a couple weeks so I charged it up over night. With a full charge the car did the pulsing tach problem right off the bat. Usually I can let it sit for a little while and it will clear itself and start right up. Now the car never clears up and the tach constantly pulsed about 100 rpms whenever the key is on. I am clueless.

thanks in advance

 

Mine was doing that stuff and it was a broken wire in the plug going into the map sensor.

 

I'll definitely check the map sensor tomorrow. I would also like to add some more information. I can tell if the car is going to start or not before I ever crank the starter. When I get in the car and turn the key to on, the tach will pulse. I leave the key on and go out under the hood, i can hear the coil firing. I unplugged the module and it stops. This used to be an intermittent problem but now I can't even get the car to start at all. If it tries to start it seems like it is firing on the wrong cylinders and pops out exhaust and requires me to keep the throttle half way, then will just eventually die. I'm really confused by this. I had this problem very rarely before I replaced the opti (for a different issue), but it has continued to get worse. Thanks again everyone for your help.

 

Tach signal should be coming from the ICM. Check it out, sounds like its been getting heatsoaked dying and then you let it cool off and it starts working again. Tach signal also comes from the opti so that is a possibility... the only other place the tach signal should be coming from is the pcm.

 

do you have a laptop with datamaster or something? if you do, you could see what/if the pcm is seeing the rpm signal. strange stuff for sure. for some reason the icm is firing the coil.

shoebox page with info on the icm troubleshooting

 

Look familiar? If so check coil wiring and then change the opti again.

http://s35.photobucket.com/albums/d1...t=100_0159.flv

http://s35.photobucket.com/albums/d1...=Crazyness.flv

http://s35.photobucket.com/albums/d1...100_0158-1.flv

 

The first video looks the most familiar, only when the key is on the tach will pulse a lot faster. When you say check the coil wiring what exactly are you talking about and what would cause this problem in the first place.

thanks again