1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle - ZR-1 Net Registry Forums

J & J Speed Shop · 07-23-2013

Looking for some help or something that I missed. I am working on a 1990 Corvette ZR-1. The vehicle originally came in and the dual mass flywheel was banging like crazy at idle. I ordered the brand new injectors from FIC and replaced both the primaries and secondaries. The idle misfire was greatly improved and 4-5 injectors were bad 3-4 ohms and about 3-4 were questionable under 10 ohms. The vehicle has new spark plugs, coil and oxygen sensors. There is still a slight miss at idle BLMs rich at 115 and INT around 89-94. If I drive the car down the street it is fine at part throttle, but once you try to go WOT in normal power mode the car falls on its face misfires like crazy and will not clean up. Turn the switch to full power mode and it will stumble for a split second and then accelerate normally. I have already checked fuel pressure, and I have spark with a tester on all cylinders including 2 & 7. Did a compression 215 psi and leakdown and everything checks out. If I pull the plugs they all look normal except 2 & 7. Both of these plugs have a good amount of carbon buildup. I also saved the old plugs I removed before I started this job and noticed 1 plug from each bank was more carbon'd then the rest of the plugs. I don't know weather it was 2 & 7 but I assume it was. At first I was thinking maybe I received 2 bad primary injectors but the plugs before the injectors kind of ruled that out in my mind.

I was thinking maybe a bad ECM ?? Suggestions please help

Schrade · 07-23-2013

Welcome onto the boards there...

J & J Speed Shop · 07-23-2013

Quote:

Originally Posted by Schrade

Welcome onto the boards there...

Thank you. If this car wasn't driving me crazy I would be doing a lot better

FU · 07-23-2013

2 & 7 share the same coil.
Wire's on right ?
Bad wire's on 2 & or 7
Coil bad

J & J Speed Shop · 07-23-2013

Quote:

Originally Posted by FU

2 & 7 share the same coil.
Wire's on right ?
Bad wire's on 2 & or 7
Coil bad

2 & 7 do not share the same coil. Coils are 8/5 1/6 4/7 3/2

Yes I have the wires firmly on the coils as well as the spark plug end. The coils are all brand new and I checked the one wires and had approx 17,000 ohms of resistance on the number 2 which is a long wire

FU · 07-23-2013

Oops 4 & 7 - 3 & 2

Check 4 pin connector at the coil pack maybe not connected right.
Arching wire.
Mile's on car ?

J & J Speed Shop · 07-23-2013

Quote:

Originally Posted by FU

Oops 4 & 7 - 3 & 2

Check 4 pin connector at the coil pack maybe not connected right.
Arching wire.
Mile's on car ?

Checked all the coil pack connectors and the car has approx 20,000 miles

WARP TEN · 07-24-2013

Did you eventually figure out what the problem was? It sounded from your initial post that you were quite thorough in your work, but there are a few idiosyncrosies to these engines. If not, and if you have not done so already, you might contact Marc Haibeck (website www.zr1specialist.com). He should be able to shed some light on it. Good Luck--Bob

jimmy b. · 07-24-2013

Double check all the vacuum lines especially the map sensor , this could cause some of the symptoms you described. Hope this helps..jimmy

FU · 07-25-2013

curious to know what the problem was-is.

07-23-2013	#1
J & J Speed Shop Join Date: Jul 2013 Location: Western New York Posts: 4	1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle Looking for some help or something that I missed. I am working on a 1990 Corvette ZR-1. The vehicle originally came in and the dual mass flywheel was banging like crazy at idle. I ordered the brand new injectors from FIC and replaced both the primaries and secondaries. The idle misfire was greatly improved and 4-5 injectors were bad 3-4 ohms and about 3-4 were questionable under 10 ohms. The vehicle has new spark plugs, coil and oxygen sensors. There is still a slight miss at idle BLMs rich at 115 and INT around 89-94. If I drive the car down the street it is fine at part throttle, but once you try to go WOT in normal power mode the car falls on its face misfires like crazy and will not clean up. Turn the switch to full power mode and it will stumble for a split second and then accelerate normally. I have already checked fuel pressure, and I have spark with a tester on all cylinders including 2 & 7. Did a compression 215 psi and leakdown and everything checks out. If I pull the plugs they all look normal except 2 & 7. Both of these plugs have a good amount of carbon buildup. I also saved the old plugs I removed before I started this job and noticed 1 plug from each bank was more carbon'd then the rest of the plugs. I don't know weather it was 2 & 7 but I assume it was. At first I was thinking maybe I received 2 bad primary injectors but the plugs before the injectors kind of ruled that out in my mind. I was thinking maybe a bad ECM ?? Suggestions please help Last edited by J & J Speed Shop; 07-23-2013 at 02:26 PM.

07-23-2013	#2
Schrade Join Date: Dec 2012 Location: NC Posts: 1,783	Re: 1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle Welcome onto the boards there...

07-23-2013	#4
FU Join Date: Mar 2004 Location: Found Member Posts: 4,327	Re: 1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle 2 & 7 share the same coil. Wire's on right ? Bad wire's on 2 & or 7 Coil bad

07-23-2013	#6
FU Join Date: Mar 2004 Location: Found Member Posts: 4,327	Re: 1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle Oops 4 & 7 - 3 & 2 Check 4 pin connector at the coil pack maybe not connected right. Arching wire. Mile's on car ?

07-24-2013	#8
WARP TEN Join Date: Apr 2007 Location: Lake Bluff, IL Posts: 2,147	Re: 1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle Did you eventually figure out what the problem was? It sounded from your initial post that you were quite thorough in your work, but there are a few idiosyncrosies to these engines. If not, and if you have not done so already, you might contact Marc Haibeck (website www.zr1specialist.com). He should be able to shed some light on it. Good Luck--Bob __________________ 2016 Long Beach Red Z06 #10281 "POPS Z" 1995 Polo Green #409 "WARP TEN"--Haibeck 350/510 package, 4.10s, Hurst, Stock Exhaust with QTP Cutouts --Sold but still running strong 1993 Quasar Blue #161 "HIL KING" --Sold but still running strong, now with more than 120,000 miles 1967 Marlboro Maroon/Saddle Corvette Coupe 300 hp/4-spd --Sold a long time ago ZR-1 Net Registry Founding Member #95 NCM Lifetime Member Favorite Quote--Attributed to Mickey Thompson: "Too Much Horsepower is Almost Enough"

07-24-2013	#9
jimmy b. Join Date: Jan 2012 Location: New Jersey Posts: 308	Re: 1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle Double check all the vacuum lines especially the map sensor , this could cause some of the symptoms you described. Hope this helps..jimmy

07-25-2013	#10
FU Join Date: Mar 2004 Location: Found Member Posts: 4,327	Re: 1990 ZR-1 Misfire Carbon'd up 2 & 7, BLM 115 at idle curious to know what the problem was-is.