My 94 vette has veen having a really nasty habit of deciding to bog and hesitate as if its got a bad miss. only problem is that this problem aint consistant. sometimes it happens, sometimes not. when it does happen its most noticeble between about 15 to 80% throttle input and is accompanied by lots of pinging in the engine almost like im running bad fuel. if i floor it, it will still go, but with a nasty miss. i have been told an exhaust leak can cause this but im pretty sure its not that. i have also noticed recently that on the highway my temps are up in the 215 to 223 area, which has never happened before, its normaly 200. i have always had problems with heat in traffic, usuall seeing 225 and 230 on occasion on the 90 degree days. i havent done any real investigation into this because i drive my vette everywhere and if it has downtime i go nowhere. an help would be greatly appreciated

 

Doesn't sound like an opti to me it would backfire at low RPM's, too.

I'd tape a fuel pressure gauge on your windshield and see what the fuel pressure does at those rpms. Could be faulty injectors.

Also, what shape are your plug and coil wires in? If you have more than 60,000 miles on your O.E.M. wires, it's time to swap them out. Change the plugs, too, while you're in there.

 

Ohm check the injectors w/VOM...check when cold and again when hot should be around 16 ohms. On the overheating (since you only mentioned highway speeds)...check for debri between radiator and condenser externally OR radiator may be partially blocked internally. External blockage should show up at all speeds...internal partial blockage can sometimes show up more at highway speeds. Also check the thermostat and be sure it's open all the way. A very lean condition can cause overheating--ie bad injectors or low fuel pressure---the above idea of taping a fuel pressure gauge to the windshield and check if the pressure drops when it is acting up...is a good idea. The temps you mentioned are not out of the ordinary for the LT1...but the temp shouldn't rise from "normal" only on the highway since you should have more air flow across the radiator.

 

Just another suggestion from my recent episode last weekend. I ran a stretch of road for about 5 miles at 55mph and when I came to a light noticed the car was running rough. Looked at the temp and it was 235. Like OP my first thought was it should be a lot cooler than that. Long story short, it looks like I have a blown head gasket.

 

How many miles on the car?

Also, how many miles/years on the anti-freeze and thermostat?

Presume your quoted temperatures are based on the digitial dash temps.

I agree with checking for debris (bags/rags/leaves/etc) in front of the AC condensor (visible when laying on your back just under the front bumper) and no leaves/etc in between the AC condensor and the radiator (visible from the passenger side where the AC lines pass through the radiator cover).

If you do not find any or just very little debris, then it might instead be the thermostat or old anti-freeze.

If the anti-freeze is old, it will not prevent spot-boiling, which due to the reverse coolant flow, can cause hot spots in the heads, and contribute to pre-ignition (pinging).

Also, if the thermostat is not openning enough or has slightly seperated and is closing off the internal passageways more than it should (the LT1 thermostat has an extra plate on the bottom which is mounted to the main plunger and can become seperated -- happened to me).

If the anti-freeze or theromstat is older than 4 yrs -- consider replacing both.

It's easy and can be done at home -- buy 12 gallons distilled water and 3 gallons of old style anti-freeze (Texaco brand or Zylex do not use dex-cool or dex-cool compatible), good technique is: with car cool -- remove radiator cap, drain via radiator pet-****, close, slowly add 2 gallons of distilled water, run till up to temp, start draining via petcock, then open radiator cap (reduces chance of spilling coolant all over), then use a shop vac on 'blow mode' to push out the rest via the radiator cap hole, close petcock, slowly add 2 gallons of distilled water, .... repeat ---- once the drained out coolant is clear, then remove/repace the thermostat (reason to wait is now it is only water to spill on the OPTI). Also drain/clean the overflow bottle (by bumper) wet shop-vac to suck it out works good), then slowly add 1/2 system capacity of pure anti-freeze, top off with distilled water, run for no more than 1-2 minutes while topping off, cap, then cycle rpm's from idle to 3k in 30 second intervals, watching the temps. if all seems ok, take the car for a drive to see how everything seems.be careful, DO NOT drive the car hard until at least 3 complete warm-up/cool off periods to give a chance for the anti-freeze and water to competely mix.

 

Any codes set?

 

Check your injectors (OHM). Check your fuel pump and fuel filter. Check your wires (plug) and coil and module.

Look at your dip/stick....oil for brown bubbles and look at your water for a residue not there before.

 

Update time

the car has over 115000 miles on it i never touched the coolant but i put a new thermostat in it 8 months ago, its a 160 degree one so its fully open earlier

I drove from North carolina to virginia yesterday and again the tmps started to rise. they were in the 220s so i decided to pull off and try to put some water in it since the coolant was low. bad decision, temps rose even higher 236. i stopped in va and temp finaly peaked at 242. i opened the surge tank and a geyser of water shot out, i ten opened the radiator cap and it released pressure but no fluid. i added coolant this time(the old not the new) and i noticed temps in the low 220s. i belive the reson to be a combinaton of bad coolant and a messed up radiator cap (the lower seal on the cap is dammaged). there were no bubbles or water in the oil or exsessive bubbling in the coolant that would indicate a blown head gasket. no white smoke from the exhaust either. when i checked my tranny fluid for ****s n gigles i noiced it was burnt and had a good deal of bubbling on the dipstick

as to the igntiton issue, i changed the spark plugs and wires last year

 

A bad lower gasket will prevent the cap from retaining any pressure in the system -- NOT GOOD -- it risks overheating and warpage of the heads -- Replace the radiator cap ASAP with an ACDelco RC27 (be careful, there is confusing info out there on which cap to use on our 94).

when you say "i opened the surge tank and a geyser of water shot out", did you mean the black tank near the windshield or the semi-clear plastic tank near the bumper? Presume you meant the semi-clear tank near the bumper -- which is the 'overflow' tank -- thereby the 'geyser' makes perfect sense and is due to the caps lower gasket allowing water/pressure out of the system.

If my presumption is correct above, then this also explains why when you removed the radiator cap from the black tank near the windshield (aka pressure or surge tank), that it only had "pressure", it's because most of the fluid had already been allowed to escape to the 'overflow' tank, and what was left was vaporized.

Unfortunately, the thermostat has also likely been damaged (they don't like being steamed without fluid around them and use a quality brand e.g. ACDelco 131-100) --- and I agree with you -- the antifreeeze is shot -- suggest following my previous post on doing a flush and replace it ASAP.

Remember anti-freeze is also 'anti-boil', but when it gets old, it looses its ability to prevent spot-boiling -- and it also looses its ability to prevent corrosion (aka galvanic corrosion). Therfore, a few hours of maintenance now can save a blown-head gasket (or worse) later.

 

well, i thought i had fixed the problem with a simple coolant flush but its back. while driving back to nc. the temps hovered in the 225 range on 95, not as bad as before but still undesireable. the cuttin out problem was gone too. however today while driving home from work (10 miles took over an hour) temps were in the 228 to 232 range. sure enough that stupid pinging noise came back and once when i had some open road i really lay into it but i was met with severe bucking and missing, like i was getting no fuel. it ran like crap the rest of the way home