Place your bets...Cam sensor or crank sensor?

[qiksho]

Well on my way to class just now tach died on me. Car still ran fine. Restarted car and the tach worked...did it a few times...tach seemed to be fine. No CEL.

So what do ya think...I will pull codes after I get off work tonight, but I am shure hoping its not the crank sensor. I know the waterpump and crank sensor are about 35-45k old. No idea on cam sensor. There is no oil leaking on the cam sensor either. Resealed the top end about 6k ago.

So what do you think cam or crank??

 

[Rob94]

Cam has no function on the tachometer. I say crank, or perhaps a lose connection to the DIS.

 

[ckinart]

Cam has no function on the tachometer.

I could be wrong here, but I believe the signal supplied to the tach is a combination of inputs from both the crank and cam sensors.

 

[SHO#7]

Cam has no function on the tachometer. I say crank, or perhaps a lose connection to the DIS.

I left my cam sensor unplugged once and there was no tach. She did not run well either though...

Good Luck in either case.

 

[AutoSHO]

If the car stalled, chances are it lost the PIP signal, which means the Crank Sensor is to blame.

Could also be a fuel pump, or something like that.

 

[qiksho]

If the car stalled, chances are it lost the PIP signal, which means the Crank Sensor is to blame.

Could also be a fuel pump, or something like that.

Ran fine for probly 10 minutes with no tach, and it never stalled.

 

[Rockledge]

Cam has no function on the tachometer. I say crank, or perhaps a lose connection to the DIS.

I agree, that's how I understand it. Which is why I can't figure how a disconnected cam sensor would cause a "no tach" situation.

 

[Rob94]

I agree, that's how I understand it. Which is why I can't figure how a disconnected cam sensor would cause a "no tach" situation.

A disconnected cam sensor wouldn't send it's signal to the DIS control module. Perhaps the module needs a signal from both sensors to display a tach reading?

 

[sdpatt]

If the crankshaft position sensor fails, the engine dies. Period. The tach signal is a combination of the CPS and CID signals. Since the engine was still running, I will ask if you had any problems trying to start the engine after that.

 

[Rockledge]

If the tach signal is a combination of the CPS and CID signals, then it involves something more than measuring RPM and how fast the crank is turning. I didn't realize that the tach signal also accounts for the postion of the #1 cylinder.

 

[projectSHO89]

The signal used to drive the tach is properly referred to as IDM - Ignition Diagnostic Monitor. In addition to the driving the tach on the instrument panel, it is also fed to the PCM so that ignition system performance may be monitored.

On the DIS module, connect your AC (not DC) voltmeter between pin 12 (top pin of front connector) and a good electrical ground. Run engine. Meter should read between 4.0 and 5.0 VAC. If it does, then either your tachometer has died or there is an open circuit between the DIS module and the tach input.

Rockledge: It doesn't account for the position. However, it requires the presence of the CMP/CID signal in order to pass the composite signal back to the PCM. Think of a Boolean logical AND function. Someone recently posted a copy of the timing waveforms for the PIP, CMP, SPOUT, IDM, and COIL signals but I can't locate it at the moment. If someone finds it, post a link.

Steve

 

[qiksho]

Just ran the codes

KOEO
111 - System checks OK

Stored

542 - Fuel pump open bad ground or always on

KOER
116 - ECT sensor out of range...well I guess it was in the 50 degrees F range outside and I didn't warm it up first.

411 - Idle speed system not controlling idle properly (generally idle too high)

Car has been taking longer to start last few weeks. I was thinking I would replace the fuel filter as it very well could be original with 142k on it. Since the one time tach not working incident the tach has been working fine.


Steve thanks for the info, if I can find someone here at school with a meter I will check that also today.

 

[projectSHO89]

116 - Operating temp first, please.

411 - Usually the IAC.

Steve