sothpaw2

Hey All,

I have a new (1 month, 1500 mile) 1996 optispark and new water pump in my car right now. This weekend, in heavy traffic in the rain and oppressive humidity, the engine began to run rough under load and at idle.

It would continue the rough running until dead. I pulled to the side and after waiting, I restarted it and it would run fine for a while, then the problem would happen again. It seemed like, the longer I waited, the longer it would stay running. On start up , the engine seemed normal.

There were no codes in the CCM or ECM other than H74 for CCM, which I am sure is unrelated as I have seen it before and looked it up.

Could this be the new opti?
Could it be my new Ed wright chip?
Could it have to do with the fact the car was recently jump started?

Thanks!

Strick

I'm hoping you only got a bad tank of gas. When was the fuel filter changed last?

ittlfly

With 1500 miles on a new opti, more possibly a fuel problem. Have you checked your fuel pressure when it's running badly? It may be a fuel pump going south.

sothpaw2

Fuel filter was changed 1 year ago, less than 7000 mi.

I need a tool to check the pressure, right? I was on the road and had
no tools, and I don't think I have that one anyway.

Why would letting it sit for 10 min or so help with a bad fuel pump?
I think you might be right, it's got to be fuel or spark or clogged cats.

STL94LT1

It does sound like a failing opti, maybe it just got wet and will dry out.

ittlfly

Absoluty YES as a symptom of a bad pump with the 10 minute intervals. I have had this exact same problem on my Explorer. Now it may be the opti but with it being so new, I'd give it the benifit of the doubt. You need to get a fuel pressure guage (about $40.) so you can diagnoise the fuel system. It's a good investment and better than just giving the $ over to a high priced mechanic. :D ..at least you have gained a tool and become more familiar with your car.

sothpaw2

If the fuel pressure fluctuates wildly when this is happening, does that eliminate the opti or clogged cats/exhaust as possibilities?

Strick

I think there should be required reading before entering this forum. The first thing a true Vette owner should have is the Helm's Service Manual. It answers most of the questions asked on the forum. It gives you the procedures to check your fuel system. I'm surprised that as a mechanical engineer, you don't already have one.

I agree, it sounds like an opti problem, but it is so new. When it was installed did you put a small bead of RTV around the seal between the cap and the base? Is it vented? :grouphug:

sothpaw2

It's vented, yes. Had a good mechanic install it.

I do have a Haynes manual and a partial GM shop manual, but since I work and this happened last night I haven't had much time to read these. I know there's a fuel press. guage you can buy. Also, the car is not even at my house to inspect, I had to ditch it sooner at my parent's house.

Strick

The Haynes books are good for general reading, but you should get the set of service manuals for your specific year Vette. Even if you don't do the work yourself, you'll at least know what the mechanic is telling you. The more you know, the less the mechanic can :bs you. Hey, bring it back to him and ask what's wrong.

aggie88

This is a timely thread. I have a 95 LT1 and I too have been experiencing the rough idle and hesitation/stumbling problem under load. Its a 6 speed car so I first thought it was clutch slippage. With 45k miles on the clock, it is worn. I run 50 psi fuel pressure with a 52 mm TB (orginal fuel filter) and the car has always run strong and passes the sniffer tests here in Houston. I dumped in some 104 boost and the car ran better. A mechanic drove my car and suspected either bad fuel or the Optispark on its way out. When I filled the tank this morning (different gas station) without the 104 boost, the stumbling came back. So I went from Clutch to Fuel to Optispark and now back to Fuel as the culprit. HELP!!!!! :confused:

sothpaw2

Mine runs fine until it hits 190 deg on the oil temp. Then it starts running rough, at idle and especially under load, and it gets progressively worse until the engine stalls within a few minutes.

I am guessing clogged cat?

aggie88

Yikes - dont want to touch that with a 10 foot pole. I dont get the stall problems. You may want to check the plugs/wires and the O2 sensor(s) before going after the Cats.

SPD DMN

Check for codes. Sounds like either the opti or possibly the ignition module. Could also be the wires if they are not properly seperated.

STL94LT1

If you are running a stock LT1 50 psi is too high. Try setting your fuel pressure at 39/41 psi and your symptoms should disappear.

Black85L98

FP guage is <$40 auto zone and you should get on. Test the FP and go from there.

When you pick it up and it has had time to dry out it may run fine.

Good luck. Fuel pump is an easy replacement job from the top.

sothpaw2

No codes are present with this, in the CCM or ECM.

What is temperature dependent? What would choke off air or spark or fuel at as the engine is just warmed up?

LT4Sam

When my opti went I had no warning and no codes either. The only thing that gave it away was the random misfire I'd see when monitoring the engine. It idled fine but would crap out under load, and did die on me once. I changed out the gas, checked the fuel system, verified the wires were okay, then finally got it on someones scanner where we saw the complete random misfires under light and above loads. New opti and it runs like a top again.

Sam