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/dd353/scottcollier/91%20Knock/?action=view&current=KnockFromEngineBay.mp4
Video from Under Motor:http://s531.photobucket.com/albums/dd353/scottcollier/91%20Knock/?action=view&current=KnockUnderEngine.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]

:o 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.:cry:

Good luck with the new toy Scott!

:cheers:
Tom

[ScottZ95ZR1]

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.

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!

:o 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.:cry:

Good luck with the new toy Scott!

:cheers:
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! :icon_scra



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

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!:thumbsup:

[GOLDCYLON]

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! :icon_scra



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

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!:thumbsup:


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]

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

[ScottZ95ZR1]

Thanks George - I know, I will always miss our car! :cheers:

[Demps]

Thanks George - I know, I will always miss our car! :cheers:

It's been in my garage. I was following it yesterday and thought I should have bought it instead of talking Steve into it. Beautiful car!

Ted

[ScottZ95ZR1]

It's been in my garage. I was following it yesterday and thought I should have bought it instead of talking Steve into it. Beautiful car!

Ted

I told you it was worth making room for one more. And your wife might even have gotten over it by now and let you move back home!

[Z51JEFF]

I didnt even check out the video and I can tell you a dead injector will cause the flywheel to knock.Cant help but think the cam chains might be jumping around as well.I put a new set of OEM coils in my car and one died at 8000 miles.MSDs in there now.

[ScottZ95ZR1]

I didnt even check out the video and I can tell you a dead injector will cause the flywheel to knock.Cant help but think the cam chains might be jumping around as well.I put a new set of OEM coils in my car and one died at 8000 miles.MSDs in there now.

Thanks Jeff. I wouldn't know the difference between the flywheel knocking and the cam chains jumping around.
I've never had a car make this noise before and that's why I posted the video.
I believe it's the flywheel now as nobody has listened to it and suggested it was something else.

Regarding the coils, I've searched out and read every post I could find related to pulling the plenum and several guys recommended against using aftermarket coils,
which is why I chose to stay OEM. Thanks for sharing a different perspective. I guess there's always an off-the-wall chance that one out of four new coils can go south
fresh out of the box, regardless of manufacturer.

[tomtom72]

:onot to be a wise guy Scott.......but remember that most of us are just a phone call away if you have any Q's that need answers quickly!:handshak:

:cheers:
Tom

[ScottZ95ZR1]

:onot to be a wise guy Scott.......but remember that most of us are just a phone call away if you have any Q's that need answers quickly!:handshak:

:cheers:
Tom

Thanks Tom. I know and really appreciate that! :handshak:

[tomtom72]

You are welcome Scott!


:o I figured that you knew that, but sometimes it's better if some one just mentions it just so a Brother knows it's still out there. No ZR-1, and no Brother of the Beast left behind!:thumbsup:
:cheers:

[GOLDCYLON]

Thanks Jeff. I wouldn't know the difference between the flywheel knocking and the cam chains jumping around.
I've never had a car make this noise before and that's why I posted the video.
I believe it's the flywheel now as nobody has listened to it and suggested it was something else.

Regarding the coils, I've searched out and read every post I could find related to pulling the plenum and several guys recommended against using aftermarket coils,
which is why I chose to stay OEM. Thanks for sharing a different perspective. I guess there's always an off-the-wall chance that one out of four new coils can go south
fresh out of the box, regardless of manufacturer.

Hell I've seen a lot of car parts bad right out of the box. If I remember Dom had an initial nightmare with his aftermarket coils years ago. I stuck with Delco because after 17 years of heat under the plenum they worked still like a champ. I just replaced them because I was there type of thing. Time, Mileage and heat all play a factor.
As to the always buy OEM crowd well I dont subscribe to that either. Do I dare mention OEM fuel inectors? I went to RCs because they were stainless steel sleeved and could hold up to the changes in the fuel that the OEM ones could not. A lot of folks have bought Accels injectors about 4 and 5 years ago so maybe that crowd can start chiming in on if they are still running strong. FICs now for two years as well. Dont get me started on OEM weatherstripping.


One of the reason why I like this forum is there is always a member who had been there already and done that. Most of us are becoming competent in our cars because we are the ones who can fix problems. When was the last time someone from GM did a plenum pull?

[DaveK]

When was the last time someone from GM did a plenum pull?

1993? :dontknow:

[ScottZ95ZR1]

Hell I've seen a lot of car parts bad right out of the box. Dont get me started on OEM weatherstripping.

Thanks Darryl and I understand. Part are parts and can be bad even when new, OEM or aftermarket.

One of the reason why I like this forum is there is always a member who had been there already and done that. Most of us are becoming competent in our cars because we are the ones who can fix problems. When was the last time someone from GM did a plenum pull?

I agree and that's why I had no problem proclaiming my ignorance in this thread and asking for guidance here. You guys are great!

I'm sure I'd have been fun to watch measuring the primary injectors resistance for the first time. As easy as it was I did it twice to make sure I got it right - but I never contemplated taking it to the dealer!

When my car is right mechanically, I'm going to be back asking for your thoughts on weatherstrippingl :mrgreen:

Thanks again!

[tccrab]

I put Accels in my Z....hmmmm.... must have been 4 or 5 years ago, still working fine.

One thing I'll pass along, be very careful how you test the injectors especially if you probe the ECM plug with your DVM.
The probes on most DVMs are much bigger than the inside diameter of the female pins on the ECM plug.
Shoving the probes in the holes causes them to stretch and then they don't make good contact when plugged into the ECM.
It could take you YEARS to figure it out....ask me how I know this.....
http://www.zr1.net/forum/showthread.php?t=10828


TomC
'Crabs

[ScottZ95ZR1]

I put Accels in my Z....hmmmm.... must have been 4 or 5 years ago, still working fine.

One thing I'll pass along, be very careful how you test the injectors especially if you probe the ECM plug with your DVM.
The probes on most DVMs are much bigger than the inside diameter of the female pins on the ECM plug.
Shoving the probes in the holes causes them to stretch and then they don't make good contact when plugged into the ECM.
It could take you YEARS to figure it out....ask me how I know this.....
http://www.zr1.net/forum/showthread.php?t=10828


TomC
'Crabs

Thanks Tom - Luckily yours was one of the threads I found and studied before I got up the nerve to pull the ECM A connector.
I did not use the meter leads and was most gentle after reading of your unfortunate experience. :cheers:

[Z51JEFF]

One other thing to think about is getting Marc Haibecks DVD on the plenum pull.The one section most helpful is for system checks.Its possible to checkout the secondary vacuum operation with the plenum off plus pressurize the fuel system to check for leaks before the plenum goes back on.

[ScottZ95ZR1]

Thanks Jeff. I do have it and agree it's very informative and helpful. :cheers: