Step by Step Manual for Diagnosing/correcting engine performance
Thread Starter
Advanced
Joined: Oct 2009
Posts: 64
Likes: 0
Step by Step Manual for Diagnosing/correcting engine performance
My '90 L98 is missing on one cylinder. I just bought it recently - I've replaced plugs/wires & redone the distributor, but it still misses. I'd like to learn how to diagnose & correct these problems - can anyone point me to the right tool & step-by-step manual to "get'er done?" Thanks....
Melting Slicks
Joined: Mar 2008
Posts: 2,300
Likes: 1
From: Quincy IL
I had that problem on my 85, long long long story short I had a bent valves in my heads. I confirmed by going to auto zone and renting a compression tester... they screw into where the spark plug goes... then I turned the engine over.... what I found was not compression.... that would be my first suggestion since plugs and wires did not work for you.
Team Owner
Joined: Jul 2003
Posts: 24,650
Likes: 8
a Bent valve typically results in a misfire into the intake or exhaust, same with a hung lifter.
Could be a wiped cam lobe.
Could be a dead injector. Easiest way to test this is to run the engine and use your finger to touch all 8 injectors, you can feel them "tap" or "click". The one that isnt doing that = dead.
Compression test will diagnose any catastrophic failures like a broken rod, broken valve, broken piston.
Leakdown test will let you diagnose less obvious problems like a burnt valve, wiped rings, etc.
Could be a wiped cam lobe.
Could be a dead injector. Easiest way to test this is to run the engine and use your finger to touch all 8 injectors, you can feel them "tap" or "click". The one that isnt doing that = dead.
Compression test will diagnose any catastrophic failures like a broken rod, broken valve, broken piston.
Leakdown test will let you diagnose less obvious problems like a burnt valve, wiped rings, etc.
Corvette Enthusiast
Joined: Oct 2007
Posts: 6,797
Likes: 2,721
From: So. Cal.
2025 C7 of the Year Finalist- Unmodified
2024 C7 of the Year Finalist - Unmodified
2023 C7 of the Year Finalist - Unmodified
My '90 L98 is missing on one cylinder. I just bought it recently - I've replaced plugs/wires & redone the distributor, but it still misses. I'd like to learn how to diagnose & correct these problems - can anyone point me to the right tool & step-by-step manual to "get'er done?" Thanks....
Team Owner
Joined: Jan 2003
Posts: 20,324
Likes: 250
From: Summerland B.C. Canada
Thread Starter
Advanced
Joined: Oct 2009
Posts: 64
Likes: 0
Yes, as far as I can tell, they are original (I'm the 4th owner.) I started the engine this morning and felt the pulsing in the injectors. There is one that is questionable and I'm going to give it a much closer look. I have the FSM manual, as well as Chilton's, and they've both been a big help. The car runs great, with this one exception.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Advanced
Joined: Oct 2009
Posts: 64
Likes: 0
Thanks. I already have the FSM. It's a big help, tho it's kinda hard to find exactly what you're looking for. I've spent most of the day researching this, checking ECM and CCM codes on the car. It's been a real learning experience. I really want to know what makes this baby tick!
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
The FSM can be intimidating, definitely not user friendly, but if you are persistent most of what you need is in there.
The book mentioned above is a great resource. Also check the fuel injector videos posted by FIC at the top of the Tech Forum, some great tips there for troubleshooting injectors which can be a problem on your year. You have a good outlook for learning, best of luck.
The book mentioned above is a great resource. Also check the fuel injector videos posted by FIC at the top of the Tech Forum, some great tips there for troubleshooting injectors which can be a problem on your year. You have a good outlook for learning, best of luck.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
You can use an (inductive) type timing light to troubleshoot the high tension side of your ignition system. i.e cap,rotor, wires, and plugs.
This test will tell you if there is a miss in the ignition system, by simply checking 1 cylinder at a time with a strobe light.
This test will tell you if there is a miss in the ignition system, by simply checking 1 cylinder at a time with a strobe light.