ZR-1 Net Registry Forums - View Single Post - Motor Knocking and Failing Injectors

ScottZ95ZR1 · 10-17-2010

My '91 runs fine at start up but after driving to full operating temp it develops a miss and an alarmingly loud knocking sound that I believe is the flywheel.
I've attached a couple of video links hoping the noise is clear and might be familiar to some of you.

Video from Engine Bay: http://s531.photobucket.com/albums/d...mEngineBay.mp4
Video from Under Motor:http://s531.photobucket.com/albums/d...nderEngine.mp4

I pulled one plug wire at a time and only the wire to the #3 cylinder made a noticeable difference. Removed that plug and it was black compared to the rest.
Installed a new set of plugs but knew it wasn?t supposed to be that easy. No luck there.

Believing the injectors to be original, I measured the primarys resistance with a hot engine and the #3 injector read only 1.7.
All others measured normal between 13.4 and 13.6, except for the #2 injector at 10.5.

So, I know it's time for new injectors - at least. The car has just shy of 18K miles on it and I'll replace the coil packs and wires while the plenum is off.
I have a NOS set of BOSCH II injectors from FIC and a set of MSD 8.5 wires, just need the coil packs and I'll probably stick with the AC Delco from posts I've read here .

A few questions come to mind:

Can anyone confirm just by hearing the video that my knock is the DM flywheel?

I have one primary injector gone and a second going. Is it quite possible that is my only problem? Can just one dead injector cause such an alarming knock?

Is there any reason I should NOT use the MSD wires with AC Delco coil packs? I guess I'm just looking for confirmation they aren't too much wire for the stock coils.

I greatly appreciate any feedback and advice.

10-17-2010	#1
ScottZ95ZR1 Join Date: Mar 2008 Location: Pendleton, IN Posts: 674	Motor Knocking and Failing Injectors - A Few Questions My '91 runs fine at start up but after driving to full operating temp it develops a miss and an alarmingly loud knocking sound that I believe is the flywheel. I've attached a couple of video links hoping the noise is clear and might be familiar to some of you. Video from Engine Bay: http://s531.photobucket.com/albums/d...mEngineBay.mp4 Video from Under Motor:http://s531.photobucket.com/albums/d...nderEngine.mp4 I pulled one plug wire at a time and only the wire to the #3 cylinder made a noticeable difference. Removed that plug and it was black compared to the rest. Installed a new set of plugs but knew it wasn?t supposed to be that easy. No luck there. Believing the injectors to be original, I measured the primarys resistance with a hot engine and the #3 injector read only 1.7. All others measured normal between 13.4 and 13.6, except for the #2 injector at 10.5. So, I know it's time for new injectors - at least. The car has just shy of 18K miles on it and I'll replace the coil packs and wires while the plenum is off. I have a NOS set of BOSCH II injectors from FIC and a set of MSD 8.5 wires, just need the coil packs and I'll probably stick with the AC Delco from posts I've read here . A few questions come to mind: Can anyone confirm just by hearing the video that my knock is the DM flywheel? I have one primary injector gone and a second going. Is it quite possible that is my only problem? Can just one dead injector cause such an alarming knock? Is there any reason I should NOT use the MSD wires with AC Delco coil packs? I guess I'm just looking for confirmation they aren't too much wire for the stock coils. I greatly appreciate any feedback and advice.