Engine Appears sluggish
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Engine Appears sluggish
Car was running fine the last time I dove it. It has been about 6 weeks since then. I usually disconnect the battery as well. When I went to start it the battery was about dead, not enough juice to turn it over. I hooked up my remote charger and she fire right up with the usual guide chain rattle for a few seconds but this time she barked out a bit of smoke momentarily but that cleared up. When I drove it, it seemed to lack power, it idles fine but when I give it some gas, it is unresponsive. It feels like i am driving on 4 cylinders. The idle is smooth, there has always been a slight vacuum leak, the pump runs once every 2.5 seconds with engine off and when running maintains a steady 17" of vacuum. There is spark on all 8 cylinders. The car is drivable with no engine codes. The only thing left I can think of is bad or fowled fuel injector....or the fact I have been driving my 700 HP 434 cuin C3 around all week....
Any thoughts?
Any thoughts?
Last edited by KJL; Jul 4, 2016 at 06:39 PM.
Racer
Joined: Apr 2012
Posts: 461
Likes: 20
Car was running fine the last time I dove it. It has been about 6 weeks since then. I usually disconnect the battery as well. When I went to start it the battery was about dead, not enough juice to turn it over. I hooked up my remote charger and she fire right up with the usually guide chain rattle for a few seconds but this time she barked out a bit or smoke momentarily but that cleared up. When I drove it, it seemed to lack power, it idles fine but when I give it some gas, it is unresponsive. It feels like i am driving on 4 cylinders. The idle is smooth, there has always been a slight vacuum leak, the pump runs once every 2.5 seconds with engine off and when running maintains a steady 17" of vacuum. There is spark on all 8 cylinders. The car is drivable with no engine codes. The only thing left I can think of is bad or fowled fuel injector....or the fact I have been driving my 700 HP 434 cuin C3 around all week....
Any thoughts?
Any thoughts?
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Great question, perhaps that is the key to all of this. I wish I paid closer attention to that. The storage unit is quite dark as well and is was hard to tell the smoke color. I will check the PCV valves and keep a close eye on the coolant level. Also will check voltage while running to make sure alternator is functioning properly.
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Back from trip, registration is due so it will be interesting to see if I can pass the emissions test in current state. Bringing car tomorrow. This is the last year! WhooHoooo!
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
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
Pro
Joined: Sep 2012
Posts: 613
Likes: 10
From: Magnolia Texas
Car was running fine the last time I dove it. It has been about 6 weeks since then. I usually disconnect the battery as well. When I went to start it the battery was about dead, not enough juice to turn it over. I hooked up my remote charger and she fire right up with the usual guide chain rattle for a few seconds but this time she barked out a bit of smoke momentarily but that cleared up. When I drove it, it seemed to lack power, it idles fine but when I give it some gas, it is unresponsive. It feels like i am driving on 4 cylinders. The idle is smooth, there has always been a slight vacuum leak, the pump runs once every 2.5 seconds with engine off and when running maintains a steady 17" of vacuum. There is spark on all 8 cylinders. The car is drivable with no engine codes. The only thing left I can think of is bad or fowled fuel injector....or the fact I have been driving my 700 HP 434 cuin C3 around all week....
Any thoughts?
Any thoughts?
Like you, my '91 exhibited the same symptoms, vacuum pump cycling about every 3 seconds and sluggish performance on dyno and driving. Only put down 241 rwhp after full headers, 3" exhaust and tune. Secondaries appeared to work fine when tested in the shop with the engine running. Turned out to be a faulty check valve in the secondary vacuum line coming from the vacuum pump. This check valve is a cheap part, but its under the plenum in the engine valley. Impossible to reach without pulling the plenum. I replaced it and moved it to the side of the plenum for easy access. Problem solved. Engine runs perfectly and secondaries open solid upon acceleration. You can read through my thread above and see if this offers any solution for you. Good luck!
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
I am starting to lean in that direction. Problem appears intermittent. Runs fine for awhile then will hesitate and stumble upon acceleration only sometimes. It just passed emissions test and was running great when on my way home I lightly accelerated up a hill and the engine sounded like it pinged for a second enough for the service engine light to come on. 5 minutes later the light turned off. Intermittent issues are a PITA to track down. Some issues only happen when the engine is hot.
Another thing I hear but I think it has always done this is kinda whistle when the throttle is applied. As far as I can tell it is air passing through the small throttle opening when blades first start to open. Again, only lasts a couple of seconds as the main blades start to open.
Another thing I hear but I think it has always done this is kinda whistle when the throttle is applied. As far as I can tell it is air passing through the small throttle opening when blades first start to open. Again, only lasts a couple of seconds as the main blades start to open.
Pro
Joined: Sep 2012
Posts: 613
Likes: 10
From: Magnolia Texas
If you're getting check engine light and hearing knock, it sounds more like fuel or timing. Can you recover the code? That may shed some light. If the secondary vacuum pump cycles, you should still chase that down and repair unless you want to eliminate this system and keep secondaries open all the time. Agree that intermittent problems are a pain. Stay at it. We all learn from each other's headaches!
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
If you're getting check engine light and hearing knock, it sounds more like fuel or timing. Can you recover the code? That may shed some light. If the secondary vacuum pump cycles, you should still chase that down and repair unless you want to eliminate this system and keep secondaries open all the time. Agree that intermittent problems are a pain. Stay at it. We all learn from each other's headaches!
Cyl 3 Primary Injector: 6.1 ohms
Cyl 5 Primary Injector: 9.9 ohms
Cyl 8 Secondary Injector: 9.9 ohms
All others 12.2 to 12.6 ohms
Coil Packs Secondary with Plenum installed cold:
1/6: 20.5 ohms
2/3: 20.8
4/7: 18.2
5/8: 20.6
FP-1: 40 psig
FP-2: 40 psig
AND, what ever GM engineer thought it was a good idea to put fuse blocks up under the passenger side dash with no access doors need to be fired. If he has already retired, they need to re-hire him so they can fire him. WTF???
Team Owner
Joined: Mar 2001
Posts: 66,921
Likes: 86
From: Santa Cruz CA
St. Jude Donor '15
I just finished checking some things and found the following:
Cyl 3 Primary Injector: 6.1 ohms
Cyl 5 Primary Injector: 9.9 ohms
Cyl 8 Secondary Injector: 9.9 ohms
All others 12.2 to 12.6 ohms
Coil Packs Secondary with Plenum installed cold:
1/6: 20.5 ohms
2/3: 20.8
4/7: 18.2
5/8: 20.6
FP-1: 40 psig
FP-2: 40 psig
AND, what ever GM engineer thought it was a good idea to put fuse blocks up under the passenger side dash with no access doors need to be fired. If he has already retired, they need to re-hire him so they can fire him. WTF???
Cyl 3 Primary Injector: 6.1 ohms
Cyl 5 Primary Injector: 9.9 ohms
Cyl 8 Secondary Injector: 9.9 ohms
All others 12.2 to 12.6 ohms
Coil Packs Secondary with Plenum installed cold:
1/6: 20.5 ohms
2/3: 20.8
4/7: 18.2
5/8: 20.6
FP-1: 40 psig
FP-2: 40 psig
AND, what ever GM engineer thought it was a good idea to put fuse blocks up under the passenger side dash with no access doors need to be fired. If he has already retired, they need to re-hire him so they can fire him. WTF???
Thread Starter
Melting Slicks
Joined: Nov 2000
Posts: 2,738
Likes: 53
From: Bogart GA
Currently looking for someone to do the port work or do it myself. There are some folks that do it but the very expensive.
Last edited by KJL; Aug 11, 2016 at 08:40 AM.