Hi

1994 convertible, LT1 , automatic

Sometimes she bogs at low rpms...have to feather the throttle a little

Misses and sputters at 4500 to 5000 rpms, unless I back off the throttle

Will rev to 5500 if I apply throttle smoothly...(most of the time without missing, if I remember correctly)

So, this weekend I'm going to put in new plugs and spark plug wires.

Also, going to do some other basic coolant, oil change, and 160 degree thermostat, little general services. Etc.


On another note,
I have already put in energy suspension bushings, Napa ball joints, and brakemotive brakes on the rear

I can post part numbers for other members to reference, or if anyone has any questions on the above fire them my way!


Now, any ideas on the engine not purring like a kitten? Oh, and I ran approx 3 tanks of gas thru, and put injector cleaner, seafoam, and additive to remove water from bad gas....basically all the liquids in the self help section at Auto zone! Haha

(I will find out more after I do plugs and other stuff listed above, this weekend)


Any engine ideas?

Thanks

Introducing the Sno Tiger! ❄️🐅. Rawwwwr!

 

Optispark (and you must use one with a mitsubishi optical sensor, not the chinese one)

also add a vent harness. Use RTV around the perimenter as a fail safe in case the seals crack.

good luck

 

mine just started doing the same thing. I've already changed the fuel pump and filter. now chevy is saying its probably the optispark distributor. the dealer wants 4.5 hrs to change it..

 

Hey fellas, thanks for the replies.

The two words I didn't want to hear..... Opti. And spark!


Well I'm going to start with plugs, wires, and also a fuel filter and hope for the best.


At least I know those parts will be out of the equation. Right?

Ok, so quick question...why does the engine rev smooth to 5000 rpms.....and it will hold that for 20 seconds or more and not miss?

(I posted above that the engine did miss, but on the drive home last night it didn't when I smoothly revved up to 4500- 5000 rpms)


Just asking..... Yes I have heard the optispark is a pita to change out....and u can get a bad one out of the box.

I will post back after this weekend with what happens.


In the mean time I am going to proceed with the following. summitt racing part numbers included!

Taylor spark plug wires.., blue in color, 6 ninety degree ones and two 180s (the pass side firewall back two wires)
TAY-74625

And ac DELCO plugs...copper 44s

ADO-R44LTSM6


And ac DELCO fuel filter. ADO-GF652

Engine is all stock, but might add the throttle body airfoil (got this one specially developed by NASA, and the US Air Force, along with Space Force engineers, in colaboration with Dick Vin MachSchnell.....a German/Holland dude. It's complicated, and I already to ya too much....)

And, after I sort out this issue, I want to do 1.6 roller rockers and muffler deletes. Anyone else do that stuff? I have 1.6 rockers on a 79 trans am.....so I know that is a good upgrade. What about the muffler deletes? Normal sound while cruising? Roaring and louder when punching it?


Thanks for the info...

Interior shot...door sill protectors and HP info plate installed

Any questions? I didn't think so! LOL



Big Al

 

Don't go to a 160* stat. there is absolutely no reason unless modifications are making it hard for the cooling system to keep the temperature down and you adjust the fan kick on temp with it. Your engine is designed to run with a certain amount of heat in it (Holding in a certain temp range). Heat is energy... don't just reject it out of the radiator without reason. Your car being close to stock and your upgrades you have planned don't warrant it.

No mufflers = Drone. The stock LT1 exhaust system is not a restriction at your power level or where you will be with the modifications you listed. It will all be about sound preference.

Yes, it is probably your opti. Changing plugs/wires/filters is never a bad thing. I am a big supporter of performing any PM that could relate to an issue. It needs done anyway. Slim chance that is what is causing your problem, but it's different than just throwing parts at it. These items need to be done at some point and if you don't know when the last time it was done, go for it. You might get lucky

Air foil... sure why not. It's not going to hurt anything and it may help

1.6RR are a good upgrade for an LT1 as well. Just about any SBC will benefit from them.

 

My optispark would stumble when the engine was hot and under load (up a hill) and high rpm.

some peoples would stumble at low rpm but again when hot and under load.


its not a question of getting a ‘bad one out of the box’. The original NOS part is not available anymore.

If you cant find an NOS one , there is a guy in ohio that puts a mitsubishi sensor into an MSD optispark (that usually doesnt have a mitsubishi sensor). This is your best bet.

the MSD optispark also has a vent harness (might want to check that vent is included for the 92-94 which doesnt hAve a vent but you will want to retrofit one).

if you were to go to the dealer and buy an optispark, they will give you a GM remanufactured opti spark. They send it to china And they do a great job replacing seals, bearings, but simply spray paint the optical sensor black (to look new)...

. It had some little paper in the box that said i can ‘rest-assured’, but rest-assured it didnt work. It would run for 3 minutes and stall once it got hot. Wouldnt restart for 4-6 hours until it cooled down.

 

Im running the 160’t stat and reprogrammed fans.

i used to see 220 f temps, but now only 174f temp even on hottest of days.

the upside to this is i believe it makes life easier on the optispark (and its seals).

the downside is emissions, i have a little bit of exhaust smell (but i have a cam and other mods).
So if you are worried about passing emissions, thatd be a reason to not go to lower temp tstat (and reprogrammed fAns)

 

Good morning and yes all good info....thanks!


Not that I wanna know about the opti, but if I have to do it...so be it.


Will report back with what I find after the maintenance items get done this weekend. And yes, I agree, these basic maint itmes have to be done anyway and it will baseline aka stage 0 the car.

Have a good day!


Big Al


Oh, and any stories of people who "got lucky" and it wasn't the opti giving runability problems?

What fixed it and smoothed out the engine? (Reaching for straws I know....)

 

Well, i once had engine run real rich, so rich it fouled out spark plugs (i had the platinum ones with little pucks and those little electrodes are easier to foul vs. std plugs).

ended up being o2 sensor

So i wont run platinum (or iridium/whatever) plugs anymore since they Are so sensitivd to fouling.


But yeah On this engine 92-94 yrs, its prob the opti

 

220*F is not a bad Temp on an LT1. Especially if it was holding steady on a hot day in traffic.

Just a note to OP, you have to either replace the switch to lie to the PCM or get the PCM flashed with the fan on temp changed to turn the fan on at a lower temp.

 

Ok, so if I do that, replace the switch or flash the PCM.....do I still need to change the thermostat right?

on hot days I see 235 degrees if I remember correctly...



Hmmmmm and yes the info on the iridium plugs, I bought stock copper plugs for that reason.

Thanks!

 

Good morning, going to get these items done today. Plugs , wires , fuel filter. Also, was reading up on optispark mods and putting in the mitsu sensor, and checking the Chinese sensor for loose wires and solder joints. But that's another topic.

And, thanks for the info on the exhaust, I will leave that alone.

Like the idea of 1.6 RR or 1.7 RR with new beehive springs....is there a huge difference between those two setups? I know the 1.6 is street able......would the 1.7 be ok? Would it give me a lopey idle, or is that a function of the camshaft grind?


And....ooops I lied! Haha. Maybe headers? Shorty or long tube.....but I will keep the mufflers and tails the same stock setuup it has now. Maybe delete the cats? (How many) I don't need emmsiions on the 94 in the state of VA.

Will report back later today! Enjoy ur Saturday everyone!

Big Al








Sept 14th , 2019 before plugs and wires and fuel filter.....that's on today's agenda!

 

On my 92 Vert, I had an idle miss and poor acceleration. I didn’t have any codes. I used a scanner and didn’t see anything wrong. I tried using Seafoam injector cleaner. Didn’t fix it. So I replaced the plugs and wires, fuel filter. Checked fuel pressure. Held at 42lbs. Changed O2 sensors. Changed water temperature sensor. Still missing. Changed Opti. I even adjusted the valves. Still had a miss. Then someone on this forum said to unplug each injector, one at a time, and see if it changed the engine idle speed. The idle speed increased when I disconnected the #8 injector.The #8. Injector turned out to be bad. Changed it and no more miss. Kevin

 

Be careful there surfbug,

This beautiful state of Virginia that we share is not that friendly with modified cars being driven on the public roads. I live in Fairfax and I see the exhaust scanners sitting on the sides of entrance ramps frequently. Here in Virginia they have un-manned exhaust stations they place in places where most people are accelerating like in a clover-leaf. IF your exhaust emissions are not right for a 1994 Corvette you will get a notice in the mail that gives you a specified time to get the repairs done. If they catch you driving the car regularly that will bite you if you have antique plates. I have regular plates on my 1968 C3 with its 427 and 4 speed and on my 1988 C4 coupe. One of my neighbors has a old Porch 944 and it has a cracked a-arm and it would not pass inspection. He waited until he could buy antique plates and started driving it all over the place with no inspections, some people scare the crap out of me.

You are not allowed to drive a car with antique plates for regular usage any more either. Better yet stop a State Trooper and ask one of them about removing mufflers and catalytic converters. To be a daily driver you need a standard license plate. With that you get the annual Safety Inspections and they will fail your car if they don't see the catalytic and or the muffler.

That is a beautiful Corvette you have there, I hope that you gets many years of smiles out of it.

Both of my Corvettes are running "Chambered Exhaust" and neither of them has any actual mufflers. This is legal as I do have full length exhaust systems but no mufflers. On my C4 I replaced the exhaust with a cat-back Chambered exhaust and installed a new aftermarket Hi-Flow catalytic converter and actually gained close to 14 hp for the effort. The exhaust systems I have were both purchased at Corvettes@Carlisle from Allen's Stainless Exhaust. They make a variety of systems out of alumanized steel or Stainless and are very affordable. The older system is on my C3 and has been since 1994 and the C4 got one a couple years later and they are both still functioning perfectly. You eliminate the catalytic and you will learn of the dreaded "Drone". Neither of my cars has any drone to speak of.

What part of VA do you hail from? We sure have a beautiful State to enjoy driving our Corvettes in!!

Best regards,
Chris

Buy a new Opti from a quality re-builder and then get a cookie jar and start throwing change in it everyday for the next Opti! That way you will be ready for the expense.

 

A lot of classic symptoms.

It's probably the opti. Symptoms are basically same as mine and same as many others.
Years ago I replaced the opti when they had good optical sensors. But today I would consider just doing the cap, I would not have considered years ago but today yes.

Inspect the opti, clean it up and try a cap. That’s what I am going to do next time around for myself. If there are no codes especially code 16 I think it's a reasonable bet.

To many replacement (new) opti's are failing in a short time losing the low resolution pulse and having codes.

 

Hey Kyle, have you seen THIS THREAD?

You're down on the 160 stat...but you're good w/the foil? Stats are about $5. How much is the foil? What does it do?

A stat and corresponding lower coolant temps will produce a bigger ET/Trap than a foil will.

 

you install the poly yourself? If so, any hints ? I have the complete set still sitting in the box like I bought them. I need to get moving on R and R the woreout bushings,

 

Beehive springs are the best thing since sliced bread. ,Using the bigger rockers may have valve cover interference. Ask around and folks will chime in.

 

Yes, you have to think of the cooling system as a complete unit. Just changing the thermostat will only delay the inevitable. It will open earlier and start rejecting heat in the radiator, but without the fans the heat transfer is lower due to a lower volume of air moving across the radiator. You are not changing your engine so it will still need to reject the same amount of energy. You will need the airflow to achieve this. Think of the thermostat as setting the base minimum operating temperature and the fans as what actually keeps the system where you want it. At highway speeds you generally don't need the fans because you are getting plenty of air flow. Depending on exterior temperature it could be enough air to keep you down on the thermostats set point.

there are probably a 100 ways to explain this, but I hope that gives you an idea.

That is actually not horrible if it is hot and you are setting in traffic. You should also make sure the radiator is free of debris and maybe give it an exterior wash down. When was the last time you had the coolant system flushed/cleaned/filled? In stock form these cars where tested in extreme heat and were able to maintain safe operation. Without stepping away from stock there is not much of a reason to have it operate cooler.

I could go deeper into it if you want, but heat is energy. Keeping a certain amount of it in the system helps. We all know engines need a certain amount of heat in them to run well and the Closed Loop tune is developed to operate in a expected heat range. Engine temp effects power, economy, and emissions. Then there are often trade offs. Jut ask some of the TPI guys how a bad Coolant temperature Sensor can cause some interesting issues.

 

Most of us do other things with our cars than just race. A dyno test at WOT over 3k RPMs doesn't tell you everything you need to know about a street engine.

Yes I am down with an air foil as much as I am with an AFPR... both can potentially show a benefit with out much risk of harm. Give you that SOTP placebo effect that you did something and may actually show up a few hp on the real dyno.

Changing engine operating temperature with no reason only stands to compromise the system. So, exactly as your thread stated... not much reason to do it unless you are doing other things (like adding in additional ignition timing) to take advantage of it. When it comes to cars you drive on the road, ET and Trap speed are not the only considerations.