Okay, finally got my SDPC 402ci LS2 in today, fired her up and everything ran awesome ... I am really happy.

The only problem is, that the RPM gauge doesn't move. It seems the computer know's what's going on as it finds a perfect idle, even after I turn on the A/C.... just that the gauge panel isn't reading it.

Could it be the cam sensor wires that were extended aren't connected properly, or is it something else? Basically just looking for something common to use as somewhere to start, as it could be so many things.

Thanks.

 

I just went to talk to our service mgr about this problem, and from everything we looked at chances are it is in the cam sensor harness. What you realy need to do is take any scan tool, tech 2, Snap-on, or any other that will read rpm and see if you get a reading. If you do, it's possable that you have a cluster problem (I doubt you do). Another thing to check is make sure you have 12 volts at the green wire that goes to the crnk sensor and 12 vlts on the red wire to the cam sensor. I realy think when you run the scan tool there will not be a reading, and when you check the cam sensor harness you will find a loose connection, a bent pin, or something to that effect.

 

That is exactly what I was thinking last night. I am going to attempt to check that out today.

Thanks Kris.

 

No problem!! If there is anything else I can do, just let me know. If you think about it pm me with what you find just so I will know....thanks.

 

I have been doing research...I am converting a C5 corvette to a "Big Stuff" ECM.

I was told by a very reputable sorce that the stock PCM get the tach signal from the crank sensor only. The cam sensor is used in conjunction with the Crank sensor to detect misfires.

Please let me know if I am right/wrong and please give me some detailed info. .....it would help me tremendously.

I even have the GM manuals (3) and they dont make it very clear where the tack gets the signal from....

Thanks Tom Ulrich

 

From the research I did yesterday you are correct. The Crank sensor does send the signal for the tach, and the cam sensor is used basicly to keep everything in time. I could be wrong but I understood that the pcm needed a reading from the cam sensor for the tach to work. This might not be true, I will research this more latter today and see what I can find out.

 

Let me know what you find out....I appreciate the help.

I quess one way to find out is to unplug the Cam sensor completely and see if the tach stops working.

I dont have a spare car around to do this....wish I did..

Let me know what you come up with ..

Tom Ulrich

 

My cam position sensor recently threw a high input error code, and my tach stopped working. Tach is cam position sensor driven. Autotap or HPTuners will still be able to read the RPM. I guess EFI gets its rpm from the crank position sensor, but the stock tach is definately cam.

 

2 wires are crossed at the Cam sensor.The car will actually run better when you switch them back.

 

Okay this is the update.

I checked the cam sensor wire extensions that were created, and all looks good. I also checked the crank sensor connections, and they look good as well. We scanned it and apparently the computer can see the RPM with no problem, but it is not getting to my gauge or my shift light (which is connected to the RPM output wire). This was working fine before the engine was installed, is there possibly a way he could have grounded or disconnected this wire somewhere?

I will keep the updates coming if I find out anything else.

 

well, are you actually throwing any codes?

 

Okay, I finally had it scanned today.

It throws these codes.

P0121 - TP Sensor Error.
P0342 - CMP Sensor Circuit Signal Low.

This help anyone?

 

If its a cam position sensor [b]low[b/] signal error, that means either the sensor is faulty, or the wires are cut, plug not making a good connection, etc. Autotap, HPTuners and other PCM scanners read the RPM viat the crank position sensor. The stock tach is driven by the cam position sensor. Reading the RPMs via a scanner does not mean thet the cam position sensor is actually working. I would check the plug and the wires once more.

 

.
I'll check it over again and see what I can do. I'm thinking it may be a bad sensor. We'll see. Thanks again.

 

I am not so sure the Cam sensor has anything to do with RPM signal. There is a thread somewhere on this forum....if I find it I will post it.

This guy did a conversion....using Big Stuff 3 .....he essentially removed all stock engine sensor connections. Wired the Big Stuff to the sensors on the engine. At this point he had no RPM/tach signal.......until he jumped the Crank sensor....wires to the stock PCM.

The stock PCM is only hooked to his crank sensor.....and his tach works fine now!!!

This shows you the tach is run of off the crank signal ONLY!

Tom Ulrich,.....

 

Research some more. The PCM does get its RPM signal from the crank sensor, however the tach in the stock gauge cluster is driven off the cam sensor. When my cam walked and I got a cam sensor high input error, my tach stopped working, however, using a scan tool (HP Tuners) the PCM was still displaying the RPMs. If you have an aftermarket tach, it may be fed off the PCM by way of the crank sensor, but in a stock gauge application, the tach most certainly is cam sensor driven.



https://ls1tech.com/forums/showthrea...ach+cam+sensor
https://ls1tech.com/forums/showthrea...ach+cam+sensor
https://ls1tech.com/forums/showthrea...ach+cam+sensor

 

Humm, that is weird .... but I think it is incorrect.

I have the service manual, and it states the stock tach is driven off of the Cam sensor.

It also states that the PCM uses both the crank sensor, and the cam sensor to determine engine position. The crank sensor is used just to tell when a piston is at TDC, while the cam sensor tells the PCM whether it is the intake or exhaust stroke. The computer can be without either of these signals, but will have problems with it. For instance, sometimes when I start my car, the PCM doesn't know which stroke the piston is on, since there is no Cam sensor, so it just picks on ... if it picks wrong, the car will just crank for 5-10 seconds until it switches to the other stroke .... then it will start right up.
.

 

I disagree........TOTALLY. I have the serice manual for my 98 vette.....I know exactly what you are reading. It does not say....the Tach is run off of the cam sensor......it is actually somewhat unclear....in the discription as to where the PCM get sthe tach signal.

As a test......tonight went to my neighbors house...he has a 2001 vette.....we managed to disconnect the cam sensor.......we got a service engine light........BUT Tach worked completely fine....

This is a real world test that tells (at least on a 2001 vette) that the cam has NOTHING to do with tach signal......

 

Think maybe it has something to do with 98 LS1's being a different animal than 99+ LS1's? If i recall (atleast in f-bodys) 98 was the last year for the working tach and temp gauges, after that the tachs always lagged.

 

As a test, when my cam bolts loosened and my cam moved out of alignment, my tach stopped working. This is a real world test that tells (atleast on a 2002 z28) that the cam sensor has EVERYTHING to do with the tach signal.

In the end, since we're talking about a WS6, I think the f-body results are more important in this particular case.