After replacing my alternator when my other one bit the dust my 87 Z28 (305 TPI) has been acting strange. Fi9rst off when i start it it lopes between 500 and 700 no mater how long I leave it running. However i knew when i put the PROM chip in it would idle differently but it wasn't doing this before the alternator swap. Also even using 93 octane it still hesitates. Finally when i shut the car off all the gauge needles shoot up to the top of the gauge. I took the chip out and it still doing these things. Anyone had these issues before?

 

double check all the wiring, make sure nothing is grounded that shouldnt be. Do you still have the old alternator?

 

check all your engine to body or frame grounds.....usually behind the drivers side cylinder head there is a strap to the firewall. make sure the connections are clean. I personally run 2 engine grounds, 1 to the body, and another one to the frame. as well as the ground from the battery to the engine.

 

I wish i did have the old alternator but it went in on the core charge. I will take a look at the grounds and let you know what i find. Thanks for replying.

 

Test the alternator output voltage directly at its output stud. If the DC voltage is correct, check the AC voltage. If there is more than 0.2 VAC, the AC contingent of the power supply to the ECM could be causing all sorts of erratic phenomena.

Unacceptably high AC voltage can result if there is a poor positive connection between the battery and alternator, if the alternator or battery grounds are not intact, or if a rectifier in the alternator is failing.

 

OK..found a bad ground and fixed it. So thanks everyone for your help. However now i am spitting raw gas out the tailpipes I can't tell if it is the pump or the regulator because i have no pressure gauge to see if it is in the 38-43 psi range. It keeps flooding itself and now it fouling plugs. Any ideas?