1994 corvette LT1

[mky1969]

Originally Posted by thcardoc

Give Jim a call. He can direct you to someone in your area with experience on these.

Thank you!

[thcardoc]

You can use the iATN member directory to find top shops.

http://autorepair.iatn.net/#http%3A/...41437707997809

[carsandcycles]

A crank position sensor also comes to mind. Heat soaking of the electronics is a hard problem to chase. If you can get a scanner and scan (just after it happens before shutting the engine down) you may be able to 'trap' a pending code. Some codes, will not set, unless the condition is repeated (a certain number of times).

[thcardoc]

Originally Posted by carsandcycles

A crank position sensor also comes to mind. Heat soaking of the electronics is a hard problem to chase.

The "distributoir reference" signals come from inside the opti-spark distributor. This engine doesn't have or need a crank sensor in the same concept that many of today's engines use.

If you can get a scanner and scan (just after it happens before shutting the engine down) you may be able to 'trap' a pending code. Some codes, will not set, unless the condition is repeated (a certain number of times).

The problem with a possible pending code setting is that pending codes only relate to OBDII non continuous monitors. (Remember this Corvette is not a full OBDII) Non-Continuous monitors are things like the catalyst, evaporative emissions, O2 sensor performance etc. Primary sensor inputs fall under the comprehensive monitor and simply set during a single event provided the code set criteria are met. An example might be a P0335 (crank sensor signal) where the PCM can see the cam sensor signal, indicating that the engine is turning but the crank sensor signal is missing. Keep in mind that it has to occur for a long enough period of time which can on occasion mean a fault can be occurring but be too short of a duration for the computer to respond with a trouble code.

[thcardoc]

I thought about this for a minute and I'll throw out a common silver bullet with this engine. A thermostat gasket leaking (or uipper hose at the thermostat) can and quite often, and actually does cause this reported symptom.

Anyone want to try and say why?

[mky1969]

Originally Posted by thcardoc

I thought about this for a minute and I'll throw out a common silver bullet with this engine. A thermostat gasket leaking (or uipper hose at the thermostat) can and quite often, and actually does cause this reported symptom.

Anyone want to try and say why?

Id like to know why and would this leak be noticable or would it evaporate or dry and you not notice any drips?
unless the answer would be that the coolant runs down the block to the distributor. The mechanics that have looked at my car havent noticed any visible leaks.

[thcardoc]

First it often will evaporate dry so your only evidence is actually seeing the leak, and of course some chalky traces left behind from the leak.

The coolant travels right down to the opti-spark distributor and gets inside of it. That's one of the reasons that replacing the cap and rotor (and plugs and wires) quite often takes the car from a condition of a hard failure where the spark has a steady path to ground inside the distributor to a condition where it works most of the time, similar to what you have described. Replacing the cap and rotor temporarily eliminates an easy path for the spark and gets the plugs firing again. (Remember the first response about checking for spark with the ST-125)

The second problem with coolant getting into the distributor is it gets onto the window vane for the optical sensor, or onto the sensor itself. This causes some of the sensor profile to be obscured and that results in timing errors, and quite often no-spark for certain cylinders. The result is identical in feel and testing to the sensor inside the distributor failing. BTW, the repair is the same, fix the coolant leak, AND replace the distributor.

Lastly I will stress again, this has to be confirmed to a failure event. You can prove a coolant leak, (don't forget the intake manifold gaskets as possible sources for coolant seepage) and still have something else lurking and actually being "THE PROBLEM"

[mky1969]

OK, I'm having the car towed over to a mechanic's garage. He's a GM technician thats been in the business for over 20 years and has experience with the LT1 motor. Wish me luck and I'll post back with the findings. To many times on forums people post the problems they're having and don't post the fix. So what ever we find, I hope it helps anyone having a similiar issue. I appreciate all the help and advice. After recieving the "silver bullet" I looked real close around the water pump and intake. After taking it around the block, which it barely made it back, I could smell coolant. I finally saw what looked to me, coolant seeping through the front of the intake and while looking down the front of the engine by the coil I could see what looked to be a dirty oily spot on the top of the optispark (the entire front of the engine block looked pretty greasy). So far with the wiggling the ecm and getting the engine to skip and bog down (only for it to act up doing this a couple times), and changing the fuel pressure regulator, the filter and pump after there was no change when I unplugged the vacuum and there is still no change even with the new regulator (ac delco this time- and I dont have a fuel guage by the way) and now it actually runs much worse I feel like I'm finding some problems that definately needed addressed so hopefully this guy can track them all down and find the main culprit. I'll keep you posted, this has been going on over a year.

[mky1969]

Ok. I finally got my car to the mechanic. I heard back from him Wednesday and he said the fuel gauge I had was reading correct and it was only at 20lbs. Went up to 22lbs when started. He's replacing the new delphi pump with an ac delco pump and then go from there. He also smelled the anti freeze leak but hasn't located it as of yet. He is going to pressure test it. I have heard of the pulsater on the sending unit above the leaking and losing pressure but not sure what this part looks like or what it does. I'll post back as I hear what he's found.

[mky1969]

I got the car back from the mechanic and he replaced the delphi fuel pump with an ac delco pump and the fuel pressure shot up to where it was suppose to be, I believe he said it was 49lbs with just the ignition on. He seems to think the fuel pump (the origianls was going out because it was showing 20lbs when it acted up and the replacement delphi pump was bad) was the problem the whole time. He pressured the coolant system and it held 132lbs for an hour so he does't think the intake was leaking, he couldn't or didn't see it leaking also. He did however smell the coolant under the hood but couldnt locate it. So far Ive put almost 200 miles on it and it hasn't acted up. Still keeping my fingers crossed

[olddog]

Thanks for reporting back. We appreciate that very much.

I think you missed a decimal point. I think that was 13.2 psi. I don't a future reader to destroy a radiator putting too much pressure in it.

[mky1969]

Thank you for correcting that. Theres nothing worse then wrong information to make a problem worse.