Problem P0654

[littless]

ok i have asked before but now it is an issue. i have put a LQ4 into a 1987 R-10 and thus far have had no issues. truck runs great. i wanted to install an aftermarket tach as the truck does not have one. i read al the threads about the tachs and installed the 680 ohm resister and everything but the tach still does not work. i then looked further into it and forgot that i had a P0654 code a while back and i deleted the code. it sets the SES light so i just deleted it. well after looking further into i desided i wanted the tach to work now.
the code is for ENGINE OUT PUT SIGNAL MALFUNCTION or something close to that. i followed the flow chart for diagnostics and it states to check pin 10 green connector for at least 9.5 volts. well i don't even have 1/2 a volt. it then states to repair the ground. well here is the problem WHAT GROUND!?!?!?! i got the schemetic for the engine speed sensor but there is no ground listed to it, oh by the way the ground repair also says repair ground in vehicle speed circut. what the hell does the RPM have to do with vehicle speed sensor. my other tech buddies think it is just a typo.
has nayone ever seen this or had problems with it. i do not have the 4l80 in the truck yet as i figured i would just wait till i blow up the turbo 350 but does that make a difference.

PLEASE HELP!!!!!!!!!!!!!!

[r6z4o6]

Does the "vehicle speed circuit" list a ground? Sounds like you would have to fabricate a ground that wasn't originally there on your '87.

[ff_jeff]

+1

[NITROUS]

P0654 is the "Engine RPM Output Circuit" or P0654 is the "Engine Speed Output Circuit" so it could be either. I'd look at what the tach output signal is connected to "pin 10 - white wire - engine speed tach output signal unless you already have. What tach are you using?

[littless]

^^^^^^^^^^^^^^

i am using the sport comp 5" tach with shift light. i read the thread on how to hook the 12v with a 680 ohm resistor on it.
the voltage at pin 10 the white wire should read 9.5 volts but it doesen't i would also think that if i had a 12 volt wire jumpered into it like the schematic said on ls1tech i should at least seee the 12 volts correct? i am stumped i am thinking about pulling it all out and starting over again as explained in another thread and hooking just the red to 12 volt hot ign. black to ground white to lamps and green to pin 10 i do however have only the brn and blue wire on the back of the tach. but i also have hptuners and guess i would need to switch back the res to 6 instead of three and then clip the tach wires correct?

[NITROUS]

The tach should be hooked up like this:

Black wire to a good ground.
Red to 12 volt ignition.
White to a 12 volt dash lighting.
Green to Pin 10 white wire on the C2 connector.
Set wire on back of tach as a 4 cylinder - Clip the brown and orange wire and then insulate both ends.

I'm still concerned about the tach output but put the resolution back to 6 and try it.

[littless]

thanks nitrous
i will give this a try ommorrow when i get to work. i have to install the posi as well.
this is th tach i have
http://www.autometer.com/download_instruction/1076A.pdf
it states to clip just the blue wire so again i am not sure becuase the tach i have goes by pulses hmmmmmm not sure on this one maybe i just need a new tach lol

[littless]

ok so i have done everything i can to make this damn thing work and still nothing. i have read all the boards and done all the suggested fixes and still nothing. so i finally call autometer and guess what they say that if you modify the computer in any way it will cause pin 10 to stop working :bsflag: they have talked to engineers and nobody can explain why this happens again :bsflag: so now i have to buy the damn module for 70 dollars and hope this works. i can not believe they say that pin 10 stops working once you modify the computer jeesh!!!!

[RedHeartbeat]

Maybe your wire has a short in it or the PCM just has a bad lead. Have you tried a different PCM?

[littless]

i have tried two pcm's and nothing. i have access to dealerworld (gm's website for techs) and have follwed the flow chart and i can not get any of the results per the flow chart. which it states to replace pcm but i have done that as well.