Hello!

I am new to the forum and would appreciate any help with my Buick Century.

I have a 1987 Century with a LG3 3.8L V6 that is registering now signal from crank sensor. I have been searching the forums and have completed the following tests from this post:

https://www.gmforum.com/trouble-shoo...m-test-299761/

and I have zero volts on the last 2 tests.

I have new ignition coil pack and new crank position sensor. before I replaced those items I had driven the car about 120 miles with some stopping and restarting. I went to my last errand of the day and when I came out of the store car would not start. I was stuck in a parking lot with no tools other than a folding plier multitool. found I was not getting spark on cylinders 3 and 6.
I replaced the ignition coil thinking it failed as 3&6 coil was too hot to touch. after replacement I had the same result, crank but no start. went and got a fuel pressure gauge and it was reading roughly 50 psi.
I had the car towed home and started internet searches to see if I could find anything and I replaced the crank position sensor based on some quick reads. after getting sensor in place the car started and ran really rough. ran diag using snap-on mt2500 and it said ECM in limp home.
I did the basic pull plug wires while running and found when 3 or 6 was pulled engine performance never changed. I followed the instructions found on this site and that is when I found no voltage change on last 2 tests.
I verified that I have power to the green/ white stripe lead to the crank position sensor plug and the black/yellow stripe and black/green stripe wires showed 0.9 ohms across both.
I also visually verified wire condition from crank sensor to ICM.
this is a LG3 3,8L with the solid lifters, not sure that makes a difference.

any help would be much appreciated!!! the ICM test was a huge help!!!

Is the 3/6 coil still getting hot and no spark? If so, The driver for that coil may be bad. That would be the ECM.

it did, but not since I got it home and installed the new crank sensor. not sure if that is due to it running or because I won't run it very long. I was going to reinstall the crank sensor again, maybe I let it slip and the clearance increased.

I will update after I reinstall. I was leaning to ECM, but was hoping I was wrong.

thanks for the reply!

tried reinstall of crank sensor to measurement of 0.022 and now no start. I attempted the last 2 ICM tests again and still no voltage. I guess at this point the only suspect left is the ECM.

Update:

Replaced ICM, crankshaft position sensor, ECM, coil pack, plugs and wires. Still same result. Crankshaft position sensor not talking to or being seen by ECM.
New ECM goes into limp home mode with same message, no distributor.

At a loss at this point.

I will update if I actually figure this out.

you said replaced pcm but you make no mention of transferring your PROM chip. Does a lg3 not use prom snd the computer is engine, year specific? I don’t think that makes sense to me, so put your prom chip from old ecm In your new computer

also, you literally have narrowed it very obviously with your wording, you replaced every component except the assoiated wires... check the wires for continuity from the ecm connector and probe also the connector ends. Use an actual probe, or use a pin throug the wire and use liquid tape when done. If your wire doesn’t make it all the way it’* not gonna work

I also seem to remember reading an lg3 was often doomed by a plastic cam gear that v6 harshness kills over time and miles? That would only kill your valves if it hit and your cam sensor signal, not a crank signal. But you mentioned distributor somewhere. Does an lg3 drive ignition off camshaft much like a small block Buick I think did ? I forget the diffferences so pardon if I misremember

No distributor in the LG3, all electronic ignition. No distributor is the error I get on the MT25 scanner tool along with no crank signal. The MT25 scanner also tells me the ECM is in limp home. Either ECM I plug in gets the same reading.
I've checked the crank sensor wires from crank sensor plug to ICM and get continuity. I also get 6.5v at crank sensor with key on engine off and zero volts when key off.
the plastic gear is the crank timing gear, it used nylon teeth. I don't think I've jumped time as the car cranks without unusual noises.

again, you completely glossed over prom I mentioned. You can swap ecm all day but if it doesn’t have any calibrations it won’t do much.

also, your ICM then was it converted to the 88 style or was it the early type. Early type is notorious for problems you could have sheared teeth.

your ecm needs to see it’* 3x and 18x signals and without both it won’t work, limp home can be caused by numerous issues. Does your engine have the right interuptor teeth as in balancer. Also is your 12 volt from the ecm present at your ICM

That vintage car had a tsb for connectors on he ecm, the test requires pulling all the pins and doing a tension test. That’* annoying, so easier to verify continuity on both sides of connector on related wires.
your ecm is looking for a 600rpm or so tachometer reading from your ICM to enable injectors. I’m pretty sure that would tell the car limo home