Cam Signals

[silvergs]

I have a Buick 455 with a 4L80E running on a LS 411 ecm. I am using a Grand National distributor that I have cut half the "hat" so it gives a signal of 180 on and 180 off. It runs good but will set the cam signal high error after it runs for a while. Any idea's why? I have looked high and low and can't find the information on the signal output on the GN sensor.

Mike

[tayto]

with the '411 why not just run CnP and be done with it?

[ScottP]

Great to see someone else running a 411 PCM on an old school motor. I've got a 411 running a '70 Pontiac 455 backed with a 4L80E as
well. I took a slightly different approach, and retrofit the L31 cam position sensor into an old Pontiac HEI distributor. I don't know what
your Buick GN sensor is going to produce, but what the 411 PCM cam sensor input is looking for is a 0V signal when low and 12V when
high. I'd start with a DVM and measure the cam position signal you're providing to the 411 when the signal is blocked and not blocked
to see if you're close to these levels. Or, better yet, if you have access to an oscilloscope, plot the signal and confirm that it really is
producing a 50% duty cycle output (180 degrees on and 180 degrees off).

Also, are you running in 24x CNP mode, or 4x mode with a conventional single ignition coil?

-Scott

[silvergs]

Scott,

The VOM meter shows 12V high and 0V low but still sets the code. Wish I had access to an o-scope.

For the crank sensor I just took a stock ls 24 wheel and mounted it on my bottom belt pulley. Made a bracket off the fuel pump mounting holes and after finally figuring out where the sensor to wheel needed to be at #1 TDC all was good.

I mounted all the coils on my valve covers like the ls to keep my wires short.
14870
Open plane manifold drilled for injectors with a Holley elbow and ebay 102mm throttle plate.

So far seems to run good with the stock motor so when my new "slightly" bigger and hotter motor is here I can move everything over and start really tuning it.

[ScottP]

Not to get too far off topic, but USB based scopes are crazy inexpensive now. You might want to
consider buying one, as it'll pay off huge when troubleshooting a project like this. Here's one for
$58.

https://www.amazon.com/Hantek-HT6022BE20Mhz-Digital-Oscilloscope-Bandwidth/dp/B009H4AYII

The Pico 2000 series are also very affordable:

https://www.picotech.com/oscilloscope/2000/picoscope-2000-overview

The Analog Devices Discovery 2 is also very much worth considering, and is what I use
most often when a conventional scope isn't handy.

https://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/

Here's a shot of what mine looks like. I'm bouncing back and forth between 4x and 24x mode as I get the crank
position sensor setup sorted.

14871

Here's a 24x wheel mounted to my PowerBond Pontiac damper:

14872


What's the exact DTC being set?

-Scott

[silvergs]

P0343

[ScottP]

So, that code in the 411 means that the PCM has detected the signal is in the high state for more than
1.5 seconds (which I'm guessing you already knew). I'll throw a couple of guesses out there:

1 - The GN cam sensor is beginning to behave intermittently with heat soak

2 - Something mechanically in the modified distributor is expanding/moving with
temperature and is behaving intermittently

Got a spare cam sensor to try?

[silvergs]

Unfortunately I don't have another sensor to try. This is a new sensor but that doesn't mean anything. I am leaning towards something about the signal going into the ecm not having enough "load" to make the sensor turn off. Might try a resistor to test this theory.

Mike