Help! 93 Badly misfiring when warm

[Ron93ruby]

Hi - I have a 93 ruby conv LT1 with 44,000 miles, garage kept that all of a sudden began misfiring badly when coolant reaches 180 degrees. It runs and idles smooth until it warms then it misfires so badly that it won't move. No check engine light and no hard codes set. It backfires a lot and won't idle, then dies. I have read alot of posts on opti spark problems but none that specifically addressed the problem of failure only when warm. Can the opti spark fail this way and is that the most likely failure?;help

 

[tcxd40]

Hi - I have a 93 ruby conv LT1 with 44,000 miles, garage kept that all of a sudden began misfiring badly when coolant reaches 180 degrees. It runs and idles smooth until it warms then it misfires so badly that it won't move. No check engine light and no hard codes set. It backfires a lot and won't idle, then dies. I have read alot of posts on opti spark problems but none that specifically addressed the problem of failure only when warm. Can the opti spark fail this way and is that the most likely failure?;help

.

Welcome the the fourm.

I just bought a '93 for my wife for Christmas it is doing the same thing. Factory manuals point to either the opti-spark or the TPS. See thread OPTI-SPARK OR WHAT. Lots of good info. in it.

tcxd40

 

[Ron93ruby]

Thanks, I reread that thread and it does address the temperature aspect of the Optispark failure so I guess my Optispark needs replacement.

 

[Paul Higg]

Not so fast with the Opti, you could have a bad O2 sensor, if that is the case it would never go out of open loop which can make a car run very rough.

Paul

 

[John Robinson]

Welcome

You might get some new insight into what to look at after you also read the following threads. What would cause a shake and

A few pictures are better than words .

I do not know how familiar you are with the Opti distributor on the 93 you bought. The big problem with the Opti in the earlier LT1 was it was not vented and therefore moisture would collect inside of it and and it would corrode the parts inside. In later years they put a vent on the opti and it allowed the moisture to escape to the outside and helped keep the insides of the opti dry. You apparently have found an exceptional 93 with only 44K on it and garage kept. The problems you may encounter with getting the car dependable are not the fault of the design of the opti and other items but rather the lack of use and the ravages of time and corrosion. The best thing you can do is get a Field Service Manual set and don't' be afraid to tackle the work yourself. Also before you start throwing money at parts get a full tank of premium and go for a drive until the tank needs refilled. Your car is in desperate need of being warmed all the way up and kept there for an extended period of time. After about a 100 miles you should notice a marked improvement in the way it runs.

I would bet on the EGR as a starter for the way you describe the way it runs. Check the threads here for information on how to remove and clean the EGR. A piece of carbon could be stuck in the EGR or it could simply be that there is a gummy build up on the pintle shaft that is causing it to hang open. I have found that Easy Off oven cleaner is a good solvent for carbon. If you have any additonal questions you can PM me.

 

[LT4man]

I agree with everything John has said in his post.

Closed loop with good fuel is always a good place to start. In all my years (almost 40) in the business, I wish I had a dime for every tank of bad fuel I ran into.

SAVE THE !

 

[formul8]

Is the check engine light on? Any codes?

If this happens when switching loops and fully warmed, then I would rule out the optispark,

 

[Ron93ruby]

Thanks to all who replied with info and suggestions. The problem turned out to be the oxygen sensors.

 

[LT4man]

Thanks to all who replied with info and suggestions. The problem turned out to be the oxygen sensors.

Thanks very much for the update. Do you have any idea how many folks never let the rest of us know what has fixed their problem?

Did the car throw any codes? Or did you just try doing that repair?

SAVE THE !

 

[John Robinson]

Follow Up

I also would like to say thank you for the information to close this problem.
With all I have done on my 93 to get it to run I have never thought of the o2 sensor so if my problems come back that will be the first place I look.:cool

 

[Ron93ruby]

No, it did not activate the check engine light or set any codes, at least any that can be retrieved by watching the check engine light flash.
I concluded it was the Optispark and knew i didn't want to tackle replacing it myself so I took it to a garage in Glen Burnie MD that works on vettes and classic cars and whose owner I met via the Free State Corvette Club. She diagnosed it as the oxgyen sensors and she also replaced the plugs as they were fouled from the misfiring, but that was ok with me as they had never been replaced and had 44,500 miles on them. I'm still a little concerned as I wouldn't think both sensors would fail at the same time but I haven't talked to the garage owner in detail yet. Maybe she replaced the second sensor as a precaution. I will ask her about it when I pick the car up later today.