New owner. Engine noise
Thread Starter
Intermediate
Joined: Jan 2026
Posts: 29
Likes: 3
New owner. Engine noise
Hello,
I have recently become the proud owner of 1990 ZR-1. Love the car so far, however when the engine is up to temperature it makes a heck of a rattle:
https://photos.app.goo.gl/eBWV9tiD2499TbHw8
The noise is present when the engine is cold but very quiet. As you can see from the video it is very loud once up to temperature.
The car had been sat for many years before I got it but I have put in fresh oil / plugs.
Initially thought it could be a stuck lifter but not familiar enough to know if they are loud at all temperatures or just when warm (logically they should be loud all the time I would think)
Any ideas welcome, ideally ones that don't involve too much time out in the garage, it is freezing here!
Thanks
Ben
I have recently become the proud owner of 1990 ZR-1. Love the car so far, however when the engine is up to temperature it makes a heck of a rattle:
https://photos.app.goo.gl/eBWV9tiD2499TbHw8
The noise is present when the engine is cold but very quiet. As you can see from the video it is very loud once up to temperature.
The car had been sat for many years before I got it but I have put in fresh oil / plugs.
Initially thought it could be a stuck lifter but not familiar enough to know if they are loud at all temperatures or just when warm (logically they should be loud all the time I would think)
Any ideas welcome, ideally ones that don't involve too much time out in the garage, it is freezing here!
Thanks
Ben
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From: Compound in the Grove, Ga.
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St. Jude Donor '16
Just a guess could be the flywheel as it sounds like a rotating sound.
Race Director
Joined: Feb 2002
Posts: 11,593
Likes: 1,053
From: Compound in the Grove, Ga.
2026 Corvette of the Year Finalist - Unmodified
2025 C4 of the Year Winner - Unmodified
2024 C4 of the Year Finalist - Unmodified
2020 C3 of the Year Finalist - Unmodified
2019 C4 of Year Finalist (performance mods)
2018 C4 of Year Finalist
2015 C4 of the Year Finalist
St. Jude Donor '16
Race Director
Joined: Feb 2002
Posts: 11,593
Likes: 1,053
From: Compound in the Grove, Ga.
2026 Corvette of the Year Finalist - Unmodified
2025 C4 of the Year Winner - Unmodified
2024 C4 of the Year Finalist - Unmodified
2020 C3 of the Year Finalist - Unmodified
2019 C4 of Year Finalist (performance mods)
2018 C4 of Year Finalist
2015 C4 of the Year Finalist
St. Jude Donor '16
I'm sure others will chime in with help I'm out . But Yes they do go bad.
Thread Starter
Intermediate
Joined: Jan 2026
Posts: 29
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Racer
Joined: Nov 2008
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Hello,
Very basic question on this, have the injectors been replaced? with quality injectors? there are many threads and resources on this topic. the 90 - 92 years are prone for injector failure due to the ethanol in newer gases. It eats the windings the the injectors and the problem gets worse as the engine gets warmer/hot. there are detailed electrical tests that can be done on the individual injector harness when the engine is cold verse hot. the primary symptom is when hot the flywheel sounds is unbalanced/broken. This might be you...
Low mileage cars tend to run ok and when they go bad is a crap shoot, they will go bad. How many miles does it have?
John
Very basic question on this, have the injectors been replaced? with quality injectors? there are many threads and resources on this topic. the 90 - 92 years are prone for injector failure due to the ethanol in newer gases. It eats the windings the the injectors and the problem gets worse as the engine gets warmer/hot. there are detailed electrical tests that can be done on the individual injector harness when the engine is cold verse hot. the primary symptom is when hot the flywheel sounds is unbalanced/broken. This might be you...
Low mileage cars tend to run ok and when they go bad is a crap shoot, they will go bad. How many miles does it have?
John
Drifting
Joined: Apr 2007
Posts: 1,290
Likes: 33
From: Chicago IL
I would check and test your fuel injectors. If they are original they are probably bad.
Pro
Joined: Mar 2008
Posts: 698
Likes: 12
From: Pendleton, IN
Thread Starter
Intermediate
Joined: Jan 2026
Posts: 29
Likes: 3
I have been reading various threads and one theory is that bad injectors (it is a 1990 and they are original) cause bad idle which the DMF compensates for which makes a noise. This would tie in with the noise being much worse when the engine is warm as bad injectors tend to show up with temperature.
My next task is to measure the resistance of the injectors which I am putting off doing because it is absolutely freezing here today and my cart lodge is open fronted! If I need injectors I will then wait a few weeks for a friend coming from the US to bring them, I know I can get them shipped directly but am reluctant to pay US postage rates ($50 to ship a $30 gasket for instance).....
Thread Starter
Intermediate
Joined: Jan 2026
Posts: 29
Likes: 3
Thread Starter
Intermediate
Joined: Jan 2026
Posts: 29
Likes: 3
Was a bit warmer today at merely 5 degrees above freezing so I got outside to measure the resistance of the injectors.
In summary one primary and one secondary were below 3 Ohms (cold) and the rest were in a 10 - 12 Ohm range. This means that probably none of them are in great shape. My shopping list is now:
- Plenum gaskets
- Injectors x 16
- Coil packs as a while I am in there job
Anything else I might need / should do when the plenum is removed?
Ben
In summary one primary and one secondary were below 3 Ohms (cold) and the rest were in a 10 - 12 Ohm range. This means that probably none of them are in great shape. My shopping list is now:
- Plenum gaskets
- Injectors x 16
- Coil packs as a while I am in there job
Anything else I might need / should do when the plenum is removed?
Ben
Drifting
Joined: Jul 2002
Posts: 1,932
Likes: 116
From: LPE Aerobody 416 ci, Oklahoma
Was a bit warmer today at merely 5 degrees above freezing so I got outside to measure the resistance of the injectors.
In summary one primary and one secondary were below 3 Ohms (cold) and the rest were in a 10 - 12 Ohm range. This means that probably none of them are in great shape. My shopping list is now:
- Plenum gaskets
- Injectors x 16
- Coil packs as a while I am in there job
Anything else I might need / should do when the plenum is removed?
Ben
In summary one primary and one secondary were below 3 Ohms (cold) and the rest were in a 10 - 12 Ohm range. This means that probably none of them are in great shape. My shopping list is now:
- Plenum gaskets
- Injectors x 16
- Coil packs as a while I am in there job
Anything else I might need / should do when the plenum is removed?
Ben
Primary Injector Lwr Seal Set: Seal Set, Fuel Injector, Lower Primary VITON 90~92 [7.5D8] - Jerrys Gaskets
Fuel Feed & Return Block Seal Set: Seal Set (2), Fuel Feed & Return Block (VITON) 90~95 [7.5D8] - Jerrys Gaskets
- Injectors x 16: Fuel Injector Set (16), 90~95 [13B2] - Jerrys Gaskets
- Coil packs as a while I am in there job: Coil Set of 4, Ignition, NEW, 90~95 [6B3] - Jerrys Gaskets
Anything else I might need / should do when the plenum is removed?
If valley is oily dirty, suggest you remove everything down to & including starter
1.Consider replacing Injector Housing Gaskets
2. Replacing Fuel Rail-Regulator Seals
3. Remove all 13 M6 bolts to Crankcase Ventilation Cover
4. All bolts & threaded holes: clean threads with spray brake cleaner to remove oil residue, blow dry with air, install with med strength thread locker (Loctite 242 or 243...other brands), tighten to specified torque
Pro
Joined: Jul 2002
Posts: 506
Likes: 26
From: Wichita Falls TX
Did you try a stethoscope to try to narrow down the source? I know rod bearing noise can sometimes lighten up with rpms (on regular v8 anyway) There is a ZR-1 for sale on the board that shows to have had rod bearing replacement.