Motor Knocking and Failing Injectors - A Few Questions

[ScottZ95ZR1]

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.

[Kb7tif]

At full operating temp is were the injectors have the best chance of failing.
I listened to your clips. I think 1 injector is not firing a cylinder and your dual mass flywheel is knocking. This is no big deal at all-change the injectors and all should be well. FIC has matched sets for 380 or so and there are other excellent injectors also at higher cost. Good luck.

[Paul Workman]

I didn't think my idle was "rough" before changing to the new injectors (last Saturday), but the instant I fired her up with the new injectors, the difference was obvious - smooth as silk and low speed drivability was noticeably improved as well!

The Corvette dealer had the injectors changed (at a GM dealership) before I bought the car 3 years ago. But, apparently "Mr. Goodwrench" replaced the original injectors with more of the same! My point is that even if a GM dealership replaces your injectors, you want to be involved to be sure the injectors installed are for a 93 MY or newer...You don't want them to do as they apparently did in my case - put the same crap back in that was initially installed in the first place!

Change your injectors and go from there. Not only can a bad injector rob power and create rough idle, but it can lead to melting valves too...ask me how I know!

Good luck. let us know how the new injectors work out for ya.

P.

[tomtom72]

another vote to toss the OEM injectors.....quickly!

On the wires,I'm using Magnecore 10mm wires along with my GM coils ( new ofcourse ) and have no issues save that they don't fit easily in the OEM looms at the backs of the cam covers.

Good luck with the new toy Scott!


Tom

[ScottZ95ZR1]

Originally Posted by Kb7tif

At full operating temp is were the injectors have the best chance of failing.
I listened to your clips. I think 1 injector is not firing a cylinder and your dual mass flywheel is knocking. This is no big deal at all-change the injectors and all should be well. FIC has matched sets for 380 or so and there are other excellent injectors also at higher cost. Good luck.

Thanks. It's good to hear someone with more experience than myself (zero) believes the knocking sound to be from the flywheel.

I already have the injectors from FIC and those guys are great to deal with.

Originally Posted by Paul Workman

Change your injectors and go from there. Not only can a bad injector rob power and create rough idle, but it can lead to melting valves too...ask me how I know!

Good luck. let us know how the new injectors work out for ya.

P.

Thanks Paul.

I just read a post in which you shared that the method of pulling a plug wire with the motor running might be harmful to the ECM. A perfect example of why my lack of knowledge scares me!

Originally Posted by tomtom72

another vote to toss the OEM injectors.....quickly!

On the wires,I'm using Magnecore 10mm wires along with my GM coils ( new ofcourse ) and have no issues save that they don't fit easily in the OEM looms at the backs of the cam covers.

Good luck with the new toy Scott!


Tom

Thanks Tom. I love this new car and know this is just part of the experience. But when I get half a mind to work on it myself the other half reminds me that Marc's shop is just a 3 hour trailer ride!

Thanks very much guys - I certainly appreciate everyone's advice and support!

[Kevin]

my injectors went pear shaped a few years ago and it was like trying to drive a washing machine. If you've got a 90-92 ZR-1, ditch the GM injectors and go aftermarket

[tomtom72]

Scott, the thing about the pulling of the wires one at a time while running is a recent nugget supplied by Tyler. I would guess that since ours is a waste spark system you cause a big upset in the resistance when you pull a wire....maybe it causes an electrical shock wave to the main board in the DIS? I wish I understood this kind of stuff better! Figure one cylinder on compression, gas & air squashed almost to a solid must equal a lot of resistance? The other cylinder on the same coil is on an exhaust stroke so I guess the less dense gas yields less resistance? If we pull the wire off of the cylinder that is on a compression stroke that resistance must go to zero??? Where is the electrical energy going to go? Like I said I wish I understood this stuff!



I was in the camp of "what's wrong with doing it that way?" until I saw what Tyler posted!

Just change the injectors and give a good eye to all the stuff under the plenum, you know clean up any loose ends. You know the drill!

[GOLDCYLON]

Originally Posted by tomtom72

Scott, the thing about the pulling of the wires one at a time while running is a recent nugget supplied by Tyler. I would guess that since ours is a waste spark system you cause a big upset in the resistance when you pull a wire....maybe it causes an electrical shock wave to the main board in the DIS? I wish I understood this kind of stuff better! Figure one cylinder on compression, gas & air squashed almost to a solid must equal a lot of resistance? The other cylinder on the same coil is on an exhaust stroke so I guess the less dense gas yields less resistance? If we pull the wire off of the cylinder that is on a compression stroke that resistance must go to zero??? Where is the electrical energy going to go? Like I said I wish I understood this stuff!



I was in the camp of "what's wrong with doing it that way?" until I saw what Tyler posted!

Just change the injectors and give a good eye to all the stuff under the plenum, you know clean up any loose ends. You know the drill!

Yeah we ALL know the drill take your time while under there. Might want a few zipties for the hoses and such. Glad to hear you going to the OEM coils. Good time to uprade the baffle hoses to those silcone ones as well. D

[ScottZ95ZR1]

Originally Posted by GOLDCYLON

Good time to uprade the baffle hoses to those silcone ones as well. D

Thanks Darryl, you're right - I definitely want to change those too.

[BlackWidow#2]

Hi Scott,
You should not have sold the 95!!!
I have MSD wires and they work fine with stock coils.
George