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Topic: Just bought 1986 Base C4 with 3700 miles starts runs then.....

in Forum: C4 Engines


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Just bought 1986 Base C4 with 3700 miles starts runs then..... (1/20)
 12/28/23 8:06pm
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

Hello Everyone

We just bought a gorgeous 86 which had been in a climate controlled environment since new. Driven VERY little with only 3700 miles.  Battery fine. Driving it back home it started to run rough after it had warmed up, but then would idle roughly and stall out completely. Fortunately, I could slip into neutral and it would start immediately back up and run.  The service engine light would flash. I bought the little GM tool to plug into the OB1 port (vs using a paperclip)  It reveals a code "51" stating that the computer ECU module / Prom is the cause.  Ive started it up several times in my garage, fires right up. However after idling up until around 130 - 150 degrees that's when the motor starts running very rough - the service engine light flashes and then stalls. Always starts right back up.  It DID have a replacement ECU installed and a new mass airflow piece replaced earlier this year. Any insights much appreciated!

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Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (2/20)
 12/28/23 8:28pm
manchester
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Equinunk, PA - USA

Vette(s):
1993 LT1 convertible triple black 4L60 2003 Zo6 Electron/Black 6 sp


Joined: 11/12/2017
Posts: 61

Just a guess, maybe mixture or delivery of fuel. 

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (3/20)
 1/10/24 2:49pm
GUYSC4
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OSWEGO, IL - USA

Vette(s):
1994 TORCH RED GARAGE QUEEN. THREE TIME TROPHY WINNER. ONCE BEST OF SHOW AND TWICE BEST IN CLASS


Joined: 4/14/2020
Posts: 2

CONGRATULATIONS ON YOUR  CORVETTE PURCHASE. 

SINCE YOU ALREADY REPLACED THE ECU I WOULD CHECK THE FUEL SYSTEM. IF THE CAR SAT FOR A LONG TIME THERES A GOOD CHANCE THE SYTEM CAN BE VARNISHED UP. TRY REPLACING THE FUEL FILTER AND PUT A CAN OF SEA FOAM FUEL TREATMENT IN. IF THAT WORKS I WOULD PUT A CAN OF SEA FOAM IN EVERY TIME YOU FILL UP FOR THE NEXT 3 OR 4 TANKFULLS. 

GOOD LUCK. I KNOW YOU WILL ENJOY OWNING YOUR CORVETTE. I HAVE OWNED MY 94 FOR 20 YEARS AND I STILL GET EXCITED EVERY TIME I SIT IN THE DRIVERS SEAT.

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (4/20)
 1/10/24 6:30pm
neonedge
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Joined: 1/10/2024
Posts: 2

Is this an aluminum or CI head version?

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (5/20)
 1/11/24 11:12am
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

Thanks so much for your suggestions!

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (6/20)
 1/11/24 11:13am
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

I honestly don’t know…how would I verify?  

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (7/20)
 1/11/24 11:26am
manchester
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Equinunk, PA - USA

Vette(s):
1993 LT1 convertible triple black 4L60 2003 Zo6 Electron/Black 6 sp


Joined: 11/12/2017
Posts: 61

An aluminum head is lighter and stays relatively shiny when cleaned up with solvent. A Cast Iron head will be dull when cleaned up, and heavier. Aluminum is softer and will scratch or dent easier. Cast Iron is harder, and will not deform as easy. 

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (8/20)
 1/11/24 12:02pm
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

Thanks for suggestion

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (9/20)
 1/11/24 12:03pm
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

Thanks!  Learned something new from you.  Will check next time under the hood!

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (10/20)
 1/15/24 10:52am
Bob DeCardenas
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Cocoa, FL - USA

Vette(s):
1990 C4 convertible Polo green/tan interior&top 1991 C4 ZR-1 red/tan 2020 C8 coupe Rapid blue/silver stripe/red interior


Joined: 8/21/2022
Posts: 15

Check your fuel pressure, the fuel pump has a tendency to fail. Also with that low mileage the tank has a tendency to collect moisture. You can YouTube either of those jobs, the fuel pressure kit is available at a reasonable price on Amazon. BTW you will enjoy your new addition. I started with a 1990 convertible with 145,000 miles then added a 1991 ZR-1. I never get tired at looking at how beautiful they are.

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (11/20)
 1/15/24 10:56am
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

Hey! - THanks for your suggestions!  It's so frustrating as it happens EVERYTIME it hits about 178-180 degrees. Shut off - let it sit - fires right back up.  Will look into the fuel pump suggestions!  Enjoy your Vette!

 

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (12/20)
 1/30/24 5:17am
Dennis L Brooks
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Williamsburg, OH - USA

Vette(s):
1985 light blue metallic bone stock 4+3 coup


Joined: 11/11/2019
Posts: 13

 

 



|UPDATED|1/30/2024 2:17:50 AM (AZT)|/UPDATED|
Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (13/20)
 2/7/24 1:43pm
lotus
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Caldwell, ID - USA

Vette(s):
Black 1987 Corvette Engine-383, 450 HP. Transmission- 700R4 with shift kit and 2300-2500 monster torque converter Wheels- 9 1/2 front, 11" rear.


Joined: 11/26/2017
Posts: 4

Just use a magnet, won't stick to aluminum.

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (14/20)
 2/21/24 5:26pm
Geno56
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Battle Creek, MI - USA

Vette(s):
1993 40th Anniversary Corvette, 6 Speed, Ruby Red


Joined: 2/10/2024
Posts: 1

That sounds like the problem I had with my ‘93 but it is li  oh ely something else. The 93 cars have bad distributors which often need to be replaced. Just in case, has someone checked your distributor?

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (15/20)
 3/6/24 12:30pm
TLAVAC
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beaufort, SC - USA

Vette(s):
1990 Turquoise Corvette (his) & 1990 Turquoise Corvette (hers)indy festiville car for sale


Joined: 9/1/2009
Posts: 39

Check the idle control valve and clean the throttle body

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (16/20)
 3/6/24 2:14pm
LilRicky53
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Sun City Center, FL - USA

Vette(s):
1986 Corvette white convertible


Joined: 12/22/2023
Posts: 7

Hello and thanks for your suggestion - turns out - the company I ordered a refurbished ECM did NOT program it correctly  - have been able to get it to run just fine and now doesnt stall out - however, it is still not programmed correctly!  The Service Engine Light stays on all the time!   So - time to remove the entire ECM AGAIN - hopefully this time the unit WILL be propertly reprogrammed.. soon!

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (17/20)
 5/4/24 10:24pm
snapper 23
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Vette(s):
1991 corvette convertible, yellow in color, black interior with a 6 speed tranny..


Joined: 7/3/2011
Posts: 13

Good Day,

Congratulations on your new ride.  Buying a classic car that has sat for some time do need some TLC to get it up to peak performance.  All the other members have made some very good advice.   I have taken care of a private car collection for some time and I would recommend changing all the motor fluids and the drivetrain oils.   The Anti freeze is often forgotten but it is important due to the rust inhibitors that break down over time and no longer provide protection and that starts to deteriorate the seals and gaskets.  The C4 Corvette is real easy to change the in tank fuel pump and completely remove all the old gas.  There are lots of you tube videos that can guide you.  The fuel injectors in the L98 motors are very sensitive to harsh fuel cleaners so be careful how much you mix in the fuel.  The injectors have coated wires inside and the fuel washes over these wires and disks and if too harsh a chemical will deteriorate the wire coating and the fuel injector will fail.  I learned this the hard way on my personal car.  Changing the injectors on a tuned port injected car is quite involved and will be a 2 day project.  

Once you get all the maintenance done these cars are very reliable and a blast to drive.   Save the wave and enjoy!!  

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (18/20)
 5/4/24 10:24pm
snapper 23
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Vette(s):
1991 corvette convertible, yellow in color, black interior with a 6 speed tranny..


Joined: 7/3/2011
Posts: 13

Good Day,

Congratulations on your new ride.  Buying a classic car that has sat for some time do need some TLC to get it up to peak performance.  All the other members have made some very good advice.   I have taken care of a private car collection for some time and I would recommend changing all the motor fluids and the drivetrain oils.   The Anti freeze is often forgotten but it is important due to the rust inhibitors that break down over time and no longer provide protection and that starts to deteriorate the seals and gaskets.  The C4 Corvette is real easy to change the in tank fuel pump and completely remove all the old gas.  There are lots of you tube videos that can guide you.  The fuel injectors in the L98 motors are very sensitive to harsh fuel cleaners so be careful how much you mix in the fuel.  The injectors have coated wires inside and the fuel washes over these wires and disks and if too harsh a chemical will deteriorate the wire coating and the fuel injector will fail.  I learned this the hard way on my personal car.  Changing the injectors on a tuned port injected car is quite involved and will be a 2 day project.  

Once you get all the maintenance done these cars are very reliable and a blast to drive.   Save the wave and enjoy!!  

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (19/20)
 5/24/24 11:16am
LuckyLowMiles
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Vette(s):
1994 Vette


Joined: 4/11/2024
Posts: 1

I had a slightly similar problem with my 94; the previous owner only drove the car about 500 miles a year.  My car was hard to start especially when the engine was near operating temp, but it seemed to run great otherwise.  I replaced several sensors to no avail.  I took it to a REAL mechanic, and he solved my issue in no time flat.  The problem was the fuel pump.  In retrospect, I think the pump may have been compromised due to the prevalence of the corn oil or whatever they toss in gasoline now-a days.  I am not saying that the fuel pump is the issue; it might be the carb.  

 

Bob

Re: Just bought 1986 Base C4 with 3700 miles starts runs then..... (20/20)
 5/29/24 4:38pm
TLAVAC
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beaufort, SC - USA

Vette(s):
1990 Turquoise Corvette (his) & 1990 Turquoise Corvette (hers)indy festiville car for sale


Joined: 9/1/2009
Posts: 39

Try the idle control valve 

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