Two days in a row last week while driving home from work, my tach randomly dropped to 0 rpm and stayed there until i restarted the car, then it was ok. I tried hitting the dash, and pushin the cluster in as suggested by custom88 in a similar thread, but it didnt help. When it dies, i can actually feel the engine do something, it almost feels like a shift, but i cant narrow down exactly what it is

If this was caused by a intermittant cam/crank sensor, i should also get an SES light aswell.. correct? No lights come on at all

I dont think this a bad crankshaft sensor, mine was bad and i was running too rich, 13 mile/gallon and wasnt able to go WOT without loosing any power.

It happened to me last year, 2 time, the rpm was bouncing when i hit a hole on the road, but it never happened again.

I should think yes if crank/cam sensor malfunction a DTC would be set. Engine rpm is derived from the crank sensor via the PCM.

Ok, i have 2 related events since starting this thread.

1. Last week, i was stopped at a red light, turns green.. I hit the gas and it hesitated for a second, tach went to 0, then the car stalled (the tach died BEFORE the car did)

2. Today, on the highway, tried to accellerate, tach dies, then the car hesitates for about 5 seconds, then smoths out.. tach sits at 0rpm until next start cycle.

I think my first two events of this occurance the car didnt stakll because the TC was locked, forcing the engine to spin a bit through the fault, and the same with today because i was on the gas trying to accelerate.

NO SES LIGHT
Had the car scanned, and no codes are stored

I spoke to Toasty and mentioned he should test his coils and look over the ICM.

Mark..where does tach signal come from on 00+? I think it'* still derived from ICM???

I know the tach signal GOES to the ICM, but I'm not sure if it comes from there and goes to the Tach. It'* obviously not the cluster or gauge considering the other symptoms. What about the possibility of an electrical dropout? Gauge loses power? So does the ignition and fuel at the same time?

Do you have a scanner? code reader is not good enough.

The signal is from the pcm, scan while the car is idling, does the scanner read engine rpm? If it does then the issue is with the tach or the wiring.
If it does not display any engine speed with the scanner and there is no ses light the pcm is failing.
The pcm gets its speed signal from the ignition control module which in turn gets it from the crank posistion sensor.

First thing though is to scan it with the tach dead for a starting point.

thanks for the input guys

will: If i had an electrical drop out shouldnt things in theory return to normal when the power came back up... and nothing else is affected by this phenomenon, just the tach and the hessitation

pdad: a scanner isnt exactly readily available to me, and especially since i cant narrow down when its going to happen, so far there is no link between occurances that i can duplicate the event.



Maybe i should buy an aeroforce guage now to watch the RPMS when it dies
and if the PCM is on its way out, then intense could get another order

True. Low resolution engine speed (3X reference)-PCM Input-from the ICM The PCM uses this signal to calculate engine rpm and crankshaft position above 1200 rpm. Medium resolution engine speed signal (18X reference)-PCM input-The 18X reference signal is used to accurately control spark timing at low rpm and allow IC operation during cranking. Below 1200 rpm, the PCM is monitoring the 18X reference signal and using it as the reference for ignition timing advance. When engine speed exceeds 1200 rpm, the PCM begins using the 3X reference signal to control spark timing. Additionally, the IPC (Instrument Panel Cluster) uses the engine speed signal from the PCM to calculate engine speed. The tachometer defaults to 0 rpm if a malfunction in the engine speed signal ckt exists. Looking at a schematic, the PCM inputs the speed signal to the IPC. The crank sensor is where it all begins with the hall effect xdcers along with the 18X & 3X reference signals.

The gauge is a good idea and the pcm upgrade is fine too but theres nothing to say its your pcm at fault yet.

btw you dont need to mount the aerotech right away to start using it, just plug into your obd2 port and connect the posistive to cig lighter plug and your scanning.