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New owner with a misfire/stumble

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Old 07-23-2014, 07:49 PM   #1
smartin436
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Default New owner with a misfire/stumble

Hi all, I recently purchased my first corvette, a 95 base with automatic trans. It has what seems to be a stumble/misfire between 1500 and 2000 rpms. It seems to only be there when crushing, under acceleration I don't notice it. It also has a hesitation pulling off from a traffic light, not all the time, maybe once out of every 4 times.
I have no history on the car at all, bought it from a local dealer. It has 120k miles on it. It has a BBK throttle body, a set of Doug ceramic coated headers and Magnaflow mufflers under the back end, other than that, it appears to be all original.
I was wondering where I should start.......I checked codes and all I get is the c12.
Could this be symptoms of a optispark issue or does it sound like something else?

Thanx
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Old 07-24-2014, 12:39 PM   #2
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sorta does sound like carbon tracing setting in...

In general, what part of the country are you in? Pacific NW? NE? FL? Plains?

Weather matters... if you are in the SW - AZ or something, then the dry lets them live longer.

When was the last tune up done? plugs, wires, O2 sensors? I would replace unless otherwise noted... NGK plugs, Taylor wires, Delco, Delphi, Denso or NTK O2 sensors.
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Old 07-24-2014, 05:42 PM   #3
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I live in Mobile Alabama, very hot and humid here on the gulf coast. From what I can tell from the AR fax report, the car has been in the southeast all its life.
Not real sure on maintenance history of car.
I was thinking of doing just as you said...... plugs, wires, o2 sensors for sure...... not sure if I should replace the distributor or just the cap and rotor though.
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Old 07-24-2014, 09:49 PM   #4
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Quote:
Originally Posted by smartin436 View Post
I live in Mobile Alabama, very hot and humid here on the gulf coast. From what I can tell from the AR fax report, the car has been in the southeast all its life.
Not real sure on maintenance history of car.
I was thinking of doing just as you said...... plugs, wires, o2 sensors for sure...... not sure if I should replace the distributor or just the cap and rotor though.
If you have the extra coin, I would just replaIce the entire optispark. Youll be a few bolts away from getting out just to get to the cap n rotor anyway. Also, plan on doing the opti and water pump seals that reside in the timing cover. Lastly, get a new water pump too and do the complete job...dont forget coolant & distilled water.
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Old 07-24-2014, 10:17 PM   #5
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Will do on the seals...... I've read good and bad on cheap and expensive distributors. I want a good one, is Cardone good stuff? I lean toward the MSD but it ain't cheap.
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Old 07-25-2014, 04:57 PM   #6
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get the MSD... it will save you in labour every time you have to swap out the POS Cardone.
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Old 07-25-2014, 10:02 PM   #7
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Hello from a fellow 95 owner-Alabamian! I'm over in Auburn. I purchased my first corvette, my 1995 base coupe automatic a few months ago as well and had a misfire too. Test your injectors before doing the optispark. My injectors were bad. But then my water pump started leaking so I ended up doing the opti and water pump job. I only replaced my cap and rotor and that definitely improved the start up of my car. Good luck!
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Old 07-26-2014, 12:31 AM   #8
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Hey Rimo thanx for the advice, how many miles does your 95 have on it?
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Old 07-26-2014, 02:11 AM   #9
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The misfiring will come from a dirty ignition system,,like an old opti that the dealer got wet when he told the display crew to steam off that engine...kiss of death to an opti.....

once that's been done, call Jon @ FIC and speak to him about your injectors. The stock inj are of limited life expectancy with the alcvohol blended fuel. They also tend to gum up internally real bad from sitting. The coil will weaken just because its a cheap injector to begine with... Get some new Bosch-III Inj from Jon and nthe mis will be long gone !
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Old 08-01-2014, 06:13 AM   #10
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Thanks for advice everyone...

With 120k miles on the car, I decided to replace a few general maintenance things as well. Car is in the garage, parts are in. This is what I plan on doing over the next couple of days.

New opti
Plug wires
Plugs
Vac lines to opti
New water pump
New gaskets and seals
Belt
Idler pulley
O2 sensors
Fuel filter
Fuel pressure regulator
Injectors
Oil and filter change
Air filter
PVC valve

started tearing the car down yesterday, car has a set of Doug's ceramic coated headers on it, spark plugs were a serious pain to change. About 3 hours........
also previous owner had bundled the plug wires together with tie wraps, I'll go back with wire seperators.
I also removed the opti and when I pulled the coil wire off the cap, the cap broke and a white powder came out of the wire end and cap connection. Some kind of corrosion I'm assuming. This had to be affecting performance.
I also have a slight knock on right rear when I hit a bump in the road, hope to find the cause of that while I have it in the shop.
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Old 08-09-2014, 11:27 AM   #11
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All the work is done and stumble/misfire between 1500 and 2000 rpm is still there. Egr valve is clean and working properly, however I disconnected it today and engine seems to run a little smother.....
haven't checked fuel pressure yet, ill do that next I guess.

I run a megajolt on my v8 mgb and love it, if fuel pressure checks out I may put a megajolt on this car, I have all the parts I need laying around the shop...... very tempting....

Anyone got any other suggestions on things I should try?
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Old 08-11-2014, 04:17 PM   #12
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Default It's Fixed!!!!!

Yesterday I replaced the coolant temp sensor and the intake air temp sensor and my misfire/stumble is gone..........

I plugged the egr back in and a slight hesitation came back...... unplugged it and it went away again....

The car is running better than it ever has. Fuel mileage is hanging around 21 on the highway running 70/75. Wish that were better.
Someone suggested buying Tunercat software and the cable to connect to car. I'm told its wonderful for diagnosing issues and tuning as well.
For now, it sure is nice to drive a smooth running vette!
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