Knocking sound and disconnected hose, Help!

[MLC ZR1]

90Z with 62k miles

Need expert help and insight after a plenum pull for a manifold vacuum line repair and fuel injector inspection. Once I got the car back it immediately developed a loud knock at idle (will attach audio) along with a bunch of other symptoms I'll list below. While inspecting the engine I noticed the Fuel regulator hose was disconnected from the regulator. Luckily, I took a video of the knock immediately after I got the car back and in the clip you can see its disconnected. I have images of it connected days before drop off. I just didn't catch it until now. Can this be the cause of all the issues im having with the car, I feel like the regulator has now gone bad as a result.

VIDEO - https://youtu.be/IFdDZnwwwf8

Since getting the car back while hose was disconnected:
-Strong fuel smell out exhaust after cold and hot starts
-Long start times, most of starts I have to hold for 5+ seconds before it starts, struggles to hold but doesn't die just sputters till RPMs rise enough, spits out large puffs of white smoke that smells like fuel from exhaust. RPMs shoot up to 2500-3000 then levels at 8-900 after about 10 sec.
- Knocking sound heard at idle, Knock subsides when giving it gas, but has died on me when doing this while the car is parked. The whole car shakes when the knock is present.
-Drives very sluggish and feels lean at times and rich at others (coming out exhaust)
-multiple backfires
-Poor fuel economy


Recent Work
All fluids and plugs changed to Marc's recs.
Original Injectors but all checked out ok and flow and ohm tested good.
Plenum pull with manifold vacuum line repaired and some gaskets changed.
Fuel pressure was normal during inspection at rail and held.
Fuel Pump and filter replaced in 2021 at 60k.
Battery replaced.
Transmission and clutch replaced 2021 at 60K, not sure if flywheel was done.

[Marc Haibeck]

From your overall detailed description of the running condition I wonder if a fuel injector wire is pinched under the plenum. The front primary fuel injectors on both banks are the most susceptible to this. You might be able to see the pinched wire without removing the plenum. Look at the black wire on the left side. Look at the black/light green wire on the right side.

The banging noise is from a misfire. Maybe because a short circuited fuel injector is not contributing torque.

White smoke at idle can be caused by a fuel injector that is spraying full time due to a shorted drive circuit. A connection to ground turns the fuel injector on.

The 850 rpm idle may be due to a vacuum leak.

The disconnected fuel regulator vacuum hose has nothing to do with your problem. On a healthy engine the control system tunes around the disconnected hose and the car drives normally.

Marc

[MLC ZR1]

Originally Posted by Marc Haibeck

From your overall detailed description of the running condition I wonder if a fuel injector wire is pinched under the plenum. The front primary fuel injectors on both banks are the most susceptible to this. You might be able to see the pinched wire without removing the plenum. Look at the black wire on the left side. Look at the black/light green wire on the right side.

The banging noise is from a misfire. Maybe because a short circuited fuel injector is not contributing torque.

White smoke at idle can be caused by a fuel injector that is spraying full time due to a shorted drive circuit. A connection to ground turns the fuel injector on.

The 850 rpm idle may be due to a vacuum leak.

The disconnected fuel regulator vacuum hose has nothing to do with your problem. On a healthy engine the control system tunes around the disconnected hose and the car drives normally.

Marc

Marc,
Thank you for the feedback. It appears on inspection the drivers side black wire was very kinked at one point closest to the connector and it was also slightly wedged between the rail and connector. I freed it up and rounded out the wire, so far this morning its still having hard starts, misfiring "knocking", and heavy fuel smell on just starting it. I will check it again and drive it around later today. Otherwise no codes and fuses look good.

If it continues, I'll will to take it back to mechanic and have him check what you mentioned as there's got to be a short, ground issue, or low resistance, something should come back abnormal this time. It's very strange to me this all started when I immediately got the car back. Either way, perhaps it's time to switch to some FICs if I gotta pull the plenum again.

[Marc Haibeck]

You can use an ohm meter to test for a short circuit on a wire that is hidden. With the battery disconnected, each of the fuel injector drive circuits should measure 18 to 22 ohms to ground. A shorted wire will measure from four to one ohm.

The pinout for the ECM A connector is shown here:
http://www.zr1specialist.com/HAT%20W...Resistance.htm
The A connector is the one nearest to the outside of the car. The pin numbers are marked on the connector.

[Z51JEFF]

Got the car back meaning someone worked on it? The normal response to that is take it back and have them fix it but that could only make things worse,if the plenum has to come back off and you can't do the job yourself you might need to really look to find a competent mechanic to look at the car. Any good competent mechanic can easily work on these and why the misfire causes a knock is a combination of the flywheel and the cam chains. Can you work on the car at all?

[MLC ZR1]

Originally Posted by Z51JEFF

Got the car back meaning someone worked on it? The normal response to that is take it back and have them fix it but that could only make things worse,if the plenum has to come back off and you can't do the job yourself you might need to really look to find a competent mechanic to look at the car. Any good competent mechanic can easily work on these and why the misfire causes a knock is a combination of the flywheel and the cam chains. Can you work on the car at all?

The plan was to go back to the shop that last worked on it for proper diagnosis, it's actually a recommend shop on the list posted in this forum so competency shouldn't have been an issue. I will give them the opportunity to take a further look as this was their work. I initially took it to them for long starts, sluggish, fuel smells. I did confirm the regulator is in fact bad and has been spitting fuel, sometimes you have to sit there and wait longer and you'll see it come out the port, just takes time. Didn't help they left the vacuum hose disconnected exposing fuel over the engine compartment. I can work on the car for basic mechanical and maintenance but I know when to stop and consult on something like this. A number of things would be going on. My differential is down to Fuel regulator, and/or injectors and maybe the coils/plugs are fouled. The "knock" isn't the flywheel, the sound is 100% coming from a misfire. I could just do the regulator myself and see if that fixes things one thing at a time. I'll post an update as this is an interesting case.

[Young1]

I can fix it for you. I have a fuel regulator in my stock. I live in Ocala, FL. PM me if interested. I have had plenty of experience in pulling plenums and everything under them.

[dredgeguy]

You will be in good hands with Steve!