Daniel6718

before i start throwwing new parts at it...got a 95 z28 took motor out replaced oil pan intake rear main timing cover gaskets, now got the motor back in the car and have no fire...

got on all data and checked i have igniton at the icm amd ground but i dont have the 1-4 volt signal, it had .1-.3 volts

tried new icm it was easy, checked and ohm the opti harness from side of intake to opti...all is good icm didnt fix it

no spark going into the opti either

so my opti went bad and isnt sending the rpm signal to pcm? or wiring between the pcm and opti?

alldata says check wire from B5(black connector) to the coil terrminal b...those are open in my volt meter but at the pcm its a white wire and at the coil its black and white? is that correct?

i threw a code 41 for icm circuit open? i tried juming wire B5 to coil prong b...no luck

Guest47904

Seems as though you were on the right track. It also appears that someone has added an end(black w/white) to the white IC wire at the ICM(not the coil). And no that is not correct. the wire should be white from end to end. So the question is when you say you jumped that wire, did you add a second wire all the way from B5 of the PCM to the ICM or did you do some other kind of jumper?

You probed the ICM for the presence of 1-4 volts at the ICM like you should but were you on the AC scale of the meter? When you did not see the correct voltage at the ICM did you then measure it at the B5 terminal of the PCM?

If it's not there you have to go back and look at the distributor signals.

Injuneer

If the optical cam position module in the Opti was not sending the cam position signal to the PCM, you would have DTC 16 and/or DTC 36.

Daniel6718

ok code 41 was wrong i had a wire in the short opti harness pushed out...thats fixed code gone and code hasnt come back...

the wire at the pcm is white...and at the icm is white i just double checked..the wire is so dirty even after i cleaned it looks yellow...at the icm white with black stripe was pin d...sorry for confusion

seems as if everything is in order...if im not gettin 1-4 volts my opti bad?
its simply hard to believe that i puled it apart and put it right back together and something went bad...


the meter was on the ac scale...

Daniel6718

neither

Guest47904

Check the white wire again for 1-4 volts. If you don't get it, unplug it and check at the PCM while someone cranks the engine. Be sure your opti is plugged in and you don't have any codes when you try. If you don't see it after cranking, check for codes again.

Remember that for some codes to appear, there must be enough rotations. So if nothing appears right away, you may need to check a couple of times.

Injuneer

Then, since you didn't actually have DTC 41, but "had a wire in the short opti harness pushed out", what code did you have?

Daniel6718

ive got between .25 and .40 volts ac when cranking...11.8 in the battery

opti harness is good...pcm to icm is good...so what possibilities do i have...sounds like opti...

also my scanner says 50rpm all the time...cranking or not

this will be my first opti failure in 6 years ive seen
95 car if i didnt mention before

Guest47904

You haven't proved anything. Did you crank it and check the white wire for signal while it was disconnected from the ICM?

If you suspect the opti, did you check any of the feedback signals? The only signal that should matter from the opti is the low res signal and if it was gone, you would have a code 16.

Daniel6718

yes the white wire at the icm has between .2 and .40 volts AC when cranking...my scanner says 50rpm all the time cranking or not...and no i havent checked the low res signal im not sure how to...and i have no codes

Injuneer

Its normal for the PCM to show 50rpm, even when the engine is not running.

If you have a wire out of the short Opti harness, you should have had one of the codes I mentioned.

Daniel6718

im not sure..no codes...no cranking rpm...no wires damaged

Guest47904

I ask again. When ever you have 2 items connected together. One with an output and the other with an input and the signal is not there. You don't know if it's not coming out of the output or if is but the device at the input is sinking it down to near nothing. So when ever there is no output, you disconnect it and check it again. It could be the ICM is sinking the signal down to near 0. The only way to know is disconnect it and check.

As far as the opti is concerned, there are 2 outputs that make essentially a 5 volt square wave. If you look at the signal with a DVM and rotate the engine slowly over by hand, you could see the drop to 0 and back up to 5 volts.

Daniel6718

yes while the white wire on the icm was disconnected i had virtually no signal..less then .4 volts ac

Diplomat

Did you at any point remove the Opti Spark unit. They are really fragile and they are even know to arrive at their destination from a factory damaged by shipping. I had this problem too and it looks like your Opti unit is defected.

Here is a site that I found helpful to figure out that my unit was damaged.

http://www.gmhightechperformance.com...ing/index.html

Its like reading Chinese at first but it will help dude!