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Discussion Starter #1
Anyone have an answer I am all ears. I was driving this weekend in my roadster (92 vert) on a very twisty road with a lot of hills, average speed on this road is 25-40 mph on the curves, open and hill sections 55 mph. Here's the problems I had, we had a cruse going with a line of vette's of many years and we were having a little fun going through the curves faster than a standard auto. While entering into a curve (hard 90 deg left hander down hill) grade was a little steep, I hit the brakes hard to make the turn and while getting back on the throttle the car hesitated for about 1 second before allowing the fuel to kick back on. What could have caused this hesitation? It was like there was nothing when I hit the throttle......... any ideas? Fuel injectors? I have never had a problem with this engine, although I was running it a little hard for about 30 minutes prior I don't think this should have happened. Any help would be appreciated.

Thanks

G-Man
 

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Discussion Starter #2
Anyone have an idea ?
 

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DC Crew
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First I was thinking the fuel filter may need to be replaced but I would think you'd notice more hesitation issues at idle and low speed if that were the case.

Then did a search on the forums for optispark issues and came across something that sounded very familiar:

Optispark. With the car running and out of gear, floor the gas pedal quickly and hold it down for a second, you'll most likely get a flat spot/bog and then it will stumble back to life, you'll really notice it when the A/C is on too. Have you changed out the thermostat lately or hosed down the motor? Sometimes you'll get some antifreeze/water running down the front of the engine and guess where it goes? :drink:
ref: http://www.digitalcorvettes.com/forums/showthread.php?t=56597&highlight=hesitation

Worth a shot to use the search engine for more advice, until someone can chime in after dinner time. Always good to check your DTC's if you have a chance.

:thumbsup:
 

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Discussion Starter #5
My tank was almost full
 

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DC Crew
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Drive way test for Optispark:

1. start car, leave running w/AC on high and in NEUTRAL
2. floor the gas quickly and hold it down for a second, watch tach
3. major bog= failing Optispark
4. No bog= possible fuel delivery issue

This is just a quick test at home without scanning for codes, but you will know at that moment if your Optispark is bad. I have nailed that problem for alot of C4 owners without ever spending a dime on a diagnostic machine. :thumbsup:
 

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Discussion Starter #9
I did this test (Drive way Test) after my cruse Saturday evening and here is what happened, with the AC on full and car idling punched the gas and it responded rather quickly, although there was a slight pause. That’s why I thought it was more of a "bad fuel" thing or a fuel filter and not the opti. Yesterday afternoon I took the car out and filled the car with non-oxygenated fuel. (Fuel with no ethanol) I always buy premium unlead 92 oct or higher. The car seems to respond better and better mileage with the non-ox fuel. The slight hesitation seems to have disappeared. I retested it the same way and I don't have that slight hesitation. I am wondering if it has anything to do with crappy fuel (fuel with ethanol).........???
 

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Discussion Starter #10
I noticed after doing a wash down in the engine compartment yesterday for a show this weekend, that I have a real low end hesitation issue. It ran fine after washing it down but this morning I started it up and it really ran rough idling and felt like it wanted to back fire almost. I ran to the store in it and it ran poor but got better after warming it up and running it hard for a mile down the road and then stopped and did a u-turn. Back and forth about 6 times. It got better but I still notice a low end hesitation. (opti-Spark)? This is my first C4 and never have dealt with a opti-spark. I did the full on AC and hit the gas hard and it wants to bog down for about 1/2 second and then catches up. Does anyone have experience with this type of problem. The car runs fine other than taking off from a dead start. Anyone have ideas?
:WTF

G-Man
 

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i have a similar problem with my 87.... which does not have an optispark. ive been told it may be a fuel pump problem and as soon as i get some time (and extra cash) im going to chack it and (maybe) replace it.
 

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DC Crew
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I noticed after doing a wash down in the engine compartment yesterday for a show this weekend, that I have a real low end hesitation issue. It ran fine after washing it down but this morning I started it up and it really ran rough idling and felt like it wanted to back fire almost. I ran to the store in it and it ran poor but got better after warming it up and running it hard for a mile down the road and then stopped and did a u-turn. Back and forth about 6 times. It got better but I still notice a low end hesitation. (opti-Spark)? This is my first C4 and never have dealt with a opti-spark. I did the full on AC and hit the gas hard and it wants to bog down for about 1/2 second and then catches up. Does anyone have experience with this type of problem. The car runs fine other than taking off from a dead start. Anyone have ideas?
:WTF

G-Man
The 1992 Optispark did not have a vent system, so basically if you get any water or antifreeze down in there, it will be a problem. If you did my driveway test and you get that bog, and it will do it without the A/C on as well, then the Optispark is going bad. It is a good rule of thumb to change the water pump out when you do the Optispark replacement, not cheap but certainly good insurance. I've seen cases where owners just did the Optispark and a few months later the old water pump shits the bed and takes out the new Opti. which sits right under it, common problem with this set up.
 

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Discussion Starter #13
What did it cost for a new optispark?
 

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DC Crew
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What did it cost for a new optispark?

Well it was several years ago, but the Optispark plus GM labor was around $700, w/water pump changeout included it's around $1K.
 

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Discussion Starter #15
well that gives me incentive to do it myself.............
 

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DC Crew
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i have a similar problem with my 87.... which does not have an optispark. ive been told it may be a fuel pump problem and as soon as i get some time (and extra cash) im going to chack it and (maybe) replace it.
hi ozvette i have a 88 c4 with same problem,i have changed my fuelpump-fuelfilter-fuelregulator,and i still have the problem.my next move will be a scantool to see if something shows up.Jesper Dahl.Dk
 
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