KJL

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?

Z51JEFF

I'd drive it abit and see if it clears up.

jay1055

Hose popped off back of plenum?

KJL

Everything appears to be in place. That was the first place I checked. I was also thinking maybe a fouled plug but it doesn't seem like it is missing. Probably should check them regardless.

RICHARD TILL

What color was the smoke that you saw?

KJL

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.

Paul Workman

FWIW, a stock 90 ZR will finish the 1/4 mile at approx 112 mph in 13.1 sec. (500 feet AMSL). You can use that as your benchmark for comparison.

KJL

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!

jss06c6

https://www.corvetteforum.com/forums...t-working.html

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!

KJL

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.

jss06c6

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!

KJL

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???

ZR-71

jss06c6

Are you still running the original injectors on this engine? You might be experiencing ethanol issues with them if not changed yet. Just a thought based upon some of your symptoms.

KJL

Yes, I believe they are original. The car only has 21000 miles on it and most of the stuff is original including the tires.

illenema

Passing the emissions is good. Id put in a fresh set of injectors, no question here. Give it another run after that

KJL

Yup, that is the plan this fall. Planning a top end refresh including port work, new orings on fuel lines, General under-plenum clean up and vacuum leakage checks, Haibeck chip etc.

Currently looking for someone to do the port work or do it myself. There are some folks that do it but the very expensive.