Hey guys i just bought a 95 z28 with the LT1. The mods it has are long tube headers, magnaflow catback, slp intake, wires plugs, electric water pump and new optispark. Now my father drove it hom efrom ohio got about 400 miles with it and it started giving him problems. First the car would sort of backfire and shudder a little bit, when slowing down for traffic, then at normal highway speeds it was fine. Next at about the 400 mile mark, he stopped for a coffee, and got back in went down the on ramp and the temp gauges climbed up to lik 230ish, and he shut it down. Now the cooling system is dirty looking and was a bit low, but why would it go that long with no problems then out of nowhere get hot quick. So we trailered the car to my house, filled it up with water (so we didnt watse coolant) and tonight started it up and took it for a drive, runs fine no smoke or anything. The only thing is the mysterious temp increase and now the car will not hold an idle it climbs to lik 1500 then dips down. It continued this in my driveway for lik 20 minutes then stalled out. Now it wont start and its sitting in my garage. Please help someone im disgusted!

Is the engine light on?

Unplug the battery for more than 30 seconds to clear any codes.

You said you had to add water to it? How much did you have to add? LT1's are reverse cooled, meaning they push the coolant through the heads first. This leads to all sorts of problems with tiny air pockets developing. That is why there are two small air bleeder screws in the front. One is on the water neck the other is on a small piece of metal tubing just above the water neck. I hope your dad didn't cook it. Aluminum heads don't like to overheat.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

There is no engine light on, it does illuminate upon turning on the ignition (so the bulb is present). I did try unhooking the battery for like 5 minutes i let it sit, we added maybe like 2 quarts of water, but it keeps eating it or maybe its those air pockets you were talking about. There are no codes on at all or on the scanner i put it on. My main question now is why it wont start. I have spark, no air restriction, and i have roughly 42psi of fuel pressure. Im running out of things to check. I did notice on the scan tool when surfing thorugh with keyonengineoff the idle was set to or read 3188? I found this weird. I have no idea whats wrong, it ran fine for 400 miles then pretty much just shit out. Im lost now???????

Well, the coolant is going SOMEWHERE, if you keep having to add it. It is either pissing out your overflow tank (very visible) going out your exhaust (visible) or filling your crankcase. Get a can of starting fluid and spray it into the intake tract (remove the air temp sensor to do so). If you have spark, it will fire. You say you have fuel pressure, that doesn't mean that the computer is telling the injectors to open though.

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1994 Z28 Black heads/cam th350 drag car
1995 Z28 Teal 'Vert bolt-ons 6-speed cruiser

yeah i know the coolant has to be going somewhere, im just not sure, i check the dipstick for like moisture or water and it looks fine. Also i was thinking that maybe the computer just shit out, and how would i check to see if the injectors are firing. Maybe disconnect and shoot them into a can or something?

you can have spark and fuel but could be at the wrong time what would ask could cause this cam sensor (controls when injectors to open and fire) carnk sensor (tells when to give spark) and are both cooling fans turning on if it obd1 96 and older put a paper clip connecting both pins together the only 2 pins that are right next to each other under the dash driver side right prom connection (aka diagnostic port)

or could be the map sensor or coolant temp sensor but need more descriptive prognosis does it only do it when its cold or running temp or all the time, or when cruising or idling or is there any symptoms like stumbling or to it just cut out all at once...

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94' Z28: #07-503-8 COMP CAMS CAMSHAFT. HOOKER HEADERS & CROSSFLOW NO CAT,11:1 COMPR MICKEY THOMSON E/T DRAGS, 370HP/410FTLBS

a way to test to see if the computer bit the dust is DISCONNECT the O2sensers and this will cause it to stay in open loop (rely on computers parameters) and if it is shot it should run horribly all the time cold or running temperture... the put it on a lift or ramps and RECONNECT the O2 sensors and drive it with them connected and at running temp if it runs better (no bucking/ stalling) with the o2 sensors connected (closed loop) commuter may still be screwed up and not making the correct or proper adjustments but the only way to find that out is to put a live data stream scanner like a snap-on and watch every sensors readings and see what the computer is doing as well just my $.02

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94' Z28: #07-503-8 COMP CAMS CAMSHAFT. HOOKER HEADERS & CROSSFLOW NO CAT,11:1 COMPR MICKEY THOMSON E/T DRAGS, 370HP/410FTLBS

Thanks camarobuff, however the car will not start at all, it turns over but it does not start. I was thinking it could be a sensor of some sort. It did run rough when you started slow down when it did run. And it would run perfect at about 60mph then all of a sudden it just shit in my driveway after idling for about 10 minutes.

optispark cap gone bad, coil, ignition module, cam sensor?!

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94' Z28: #07-503-8 COMP CAMS CAMSHAFT. HOOKER HEADERS & CROSSFLOW NO CAT,11:1 COMPR MICKEY THOMSON E/T DRAGS, 370HP/410FTLBS

I have power at the coil wire, and nothing at the plug wires, when cranking?