My 1986 Grand National (re) Build Thread

[TexasT]

I saw where the pwr lgr had two inputs you can configure. I wondered if the one transducer was feeding data to both the gauge and the pwrlgr. Good stuff with motorhead zeroing out the transducer to correct an erroneous reading with residual pressure.

[Steve Wood]

Tap the signal wire to the gauge and run the tap to positions 4 or 5 on the analog block...

[GavinHunyady]

Thats sort of what I figured, and I get 43psi at 43psi on the gauge... I'll check for the offset that Mike mentioned, but it would be super weird if those lines crossed right at 43psi. All good tests though.
 


I drove the car all the way to Warren for the employee car show today. Everything seems to have survived... need A/C in a bad bad way though.

[daveismissing]

Anyone find a statement of accuracy on the autometer sender?

[GavinHunyady]

like what is the tolerance band on the reported output? I've not seen one.


I've also not seen a better method to log fuel pressure. I am open to suggestions though! 

[Steve Wood]

If I read you correctly, the autometer gauge appears correct but the PL output is lower?

Have you verified the gauge against a mechanical gauge?

Disconnect the feed from the autometer gauge and feed only PL with the signal from the transducer for the moment.  Still read low?  What battery voltage is PL reporting under boost?


Also look at the voltage being reported by PL and calculate the pressure yourself to see if you get what PL calculates

[GavinHunyady]

Correct, BUT... I'm not 100% that the gauge is correct. It moves too fast for me to see it with absolute certainty, while driving.


I like the idea of checking the sender voltage and checking, I'll also go back and check battery voltage in the log.


I checked the gauges at idle with the vac hose off... so that would be a mechanical gauge at 43psi, power logger at 43psi, and the gauge at 43psi at the same time. I can only assume that isnt chance.


I'll shotgun it with a new fuel filter just out of principal.

[motorhead]

Do they all bleed down to 0, and at the same rate?

[daveismissing]

You could plumb sender and mech gauge to compressed air and adjust the reg to confirm correlation. 

[motorhead]

Unless the transducer has two outputs it may be corrupting the signal by having the PL listen to it; unless the gauge has its own I/O feeds.

[daveismissing]

Interesting hypothesis. One would hope the sender and gauge designers did impedances correctly.  A digital voltmeter across the sender should be able to verify if the PL loads the sender when attached.