I recently just bought a 1979 Chevy Corvette with 81k original miles and I am the 3rd owner. I am no expert mechanic but I know my way around if need be. I love the car to death but I am now clueless on what to do. Here is the problem.

Car ran great a-b no problem untill the car started to stumble on accel. As I was driving 45 mph with the pedal half way down to keep at 45, the vehicle suddenly started decelerating. As i pumped the pedal to accelerate, the car quickly decelerated faster until the engine actually died. So I pulled over in a neiborhood and tried cranking her, and nothing. gave her 5 min and she came to life like nothing happened. She kept doing this during the next week, dying 2-3 times a day! So I asked a couple of friends what the trouble could be since they are chevy-holics and gave me some pointers. 1)Replace the carb 2)vaccumm lines gotta go 3) EGR has gotta go

So I did, letting them do it since they have done this first hand to their nova's and charger's. I now have a Edelbrock 600 on. Edelbrock intake. Vaccumm lines astray. And a custom plate to cover the EGR.

Drove the car some more that following day and she seemed to be more attentive. But died even more! So I asked a technician and he gave some following pointers. 1)Fuel filter 2)Fuel lines leaking 3) Fuel Pump.

I changed fuel filters (Good thing, they were black). I checked all fuel lines and replaced all (Good thing, one was leakin). and replaced the fuel pump from Advance Auto (Factory Replacement).

Drove the car for a full two days without a Acceleration Stumble/Die problem. Then what do you know? It happens again, but this time its less abundant. But this time, any time I put the car under full load/acceleration, it dies. I can drive the car city wise, but on highway, it doesn't even perform.

So I asked the mechanic again what could be happeneing, and he said most of the time when fuel delivery (dunno even if its fuel delivery problems yet) that there is a 'sock' in the gas tank and could be getting clogged. And i need to hook up a compressor to the fuel line going to the tank bipassing the fuel pump and blow it out.

So I did that too.

The damn car still stumbles and dies just the same. I have now been told to switch out fuel tanks because mine could be dirty but I DO NOT want to put the labor in it when I dont know if that could be the definite problem! That's dropping the rear-end!

So do you guys have any ideas? Have you had this happen to you? What was your rememdy? Also, i have been thinking that it might be the modual in the distributor? I have no idea. Could be missing vaccumm lines too. Im counting on expierence now. Thank You in advance for trying to help.

 

First of all...Never throw parts at a car on a hunch, That can get very expensive very fast.
Now ...You need to isolate the problem.
The next time it dies, remove the air cleaner, and look down the carb as you throttle it once or twice. If you see gas, then I think you may have an ignition problem.
Let us know.
Remember what Lars always says..."90% of carb problems are actually ignition problems"
Good Luck!

 

Did you check the new fuel filter since you have installed it?

If the tank is that dirty the filter should be dirty again.

Also a bit confused as to whether the Edelbrock carb was brand new when you installed it or if you got it used.

 

You could have dirt in tank or a clogged "sock" in the tank. Both happened to me with different cars and with your symptoms.

 

You've focused on fuel delivery issues, and not at all on ignition/spark. Make sure you're barking up the right tree.

 

Agreed. As I said on your thread in the General section...Check the coil / wires and distributor.

 

well i had a suggestion on taking off the Vacuum advance line and run the vehicle. To see if it will die on me. Well I drove the car for 3-4 straight hours with no problem, even on highway! then at about 1am it died. On the highway... I stumbled it back. What that tells me is that the distributer/plugs/wires/and vacuum advance needs replaced right? thats my next step...

what brand is optimum for my 350? should i just go to the parts store for factory replacements? or should i go msd? I just hope to god, that ignition/timing is my issue...

What do you guys think?

 

Which port was the vacuum advance hooked up to and did you plug the hose after you removed it??
Theres ported vacuum (supply's vacuum when under acceleration) and manifold vacuum which loses vacuum when under acceleration.

You can test this with a vacuum gauge or even by holding your finger or a small piece of paper over the port on the carb and giving it some throttle.

I would certainly check all ignition components before I did anything else.

 

When your car dies and won't start, check for spark and fuel and you'll eliminate one. I'm still betting it's fuel and a good chance its the sending unit sock in the tank. The continual sucking by the fuel pump for years of driving will tend to weaken this part allowing it to bend and shut fuel delivery off under load. After the car sits awhile, the sock will open back up and all is well, for a while. I went through this with a '69 Pontiac GP and it drove me crazy until someone said to check it.

 

Fuel- Check for kinked supply hose to fuel pump.

Ignition
Check the pickup coil for continuity. That system is considered to be very reliable. Many say the pickup coils do not fail. The movement of the vac. advance can cause the leads to break internally- may not be noticeable looking at them. Move the vac. advance while checking.
Typical HEI pickup coil ohms about 800.
It's possible to disassemble the pickup coil & repair the leads.

Ignition Module - if 10+ years old, would be best to replace even if good. AutoZone has Wells (OEM supplier).

 

well tomorrow is the big day. Installation baby!

I just got the Distributor Ignition Shaft with the Vacuum Advance supplied, Cap, Rotor, Autolite Spark Plugs, 8mm wires And cap cover.

Am i missing anything?

Well, Im going to try this first, since it seems to be the least of labor intensive jobs. Praying that this will solve my problem. I dont have a volt meter to test the leads ether. Which i should have checked first. But hey, i just got payed and the origianl has never been tuned up. So i gotta do it sometime...lol

So i will keep you up to date and see if this fixes the problem or if it might be the 'sock' problem. So if i was playing the devil's advacate and the 'sock' was bad, would it be wise to just get a new fuel tank or clean the old one and get a new fuel sending unit? Plus taking down the rear-end is NOT gonna be fun since i dont have a lift.

Again you guys rock for helping me through this. Just in case and if you live in Kansas city, and maybe wanna call and give a walk through IF the 'sock' is bad, that would be awesome. Maybe some beer might be rewarded...lol

 

What about the ignition module in the distributor. It's a plug-in gizmo that sits about where points did on earlier models. Sounds to me like you have a module going bad when it gets hot...kind of a common problem, as I remember. They aren't expensive. That's my guess! Good luck.
P.S. It appears you did some good things during this investigation, even though it didn't solve the immediate problem. You probably "staved-off" some future problems.

 

You said you changed your fuel filters and that they were black? How many filters do you have and where are they located?

Sounds like you may have more filters than stock. If that is the case then maybe the previous owner had a similar problem?

If I remove a fuel filter and find it to be black, I would continue to evaluate the condition of the fuel system. No fuel filter should ever be black, regardless of how old it is.

Following your fuel filters being changed you drove the car for two days with no stumbling or problems. I would go back and recheck condition of new filters and I can almost bet that you will find they are black once again. My money says you have a problem in your fuel system (sock, bladder failure or contamination in your fuel tank).

 

Try this simple clean out it may work out temporarily but did the trick on mine permanently (50,000 miles since) and it will take no more than 20 minutes.

Disconnect the return and fuel supply lines from the pump.
Blow a gentle amount of compressed air through both, you'll hear it bubbling in the tank make sure to remove the gas cap. Use a scavenger or some form of suction and empty that tank. I used my boat bailer and try to keep it directed to the bottom were all the gunk is.

My symptoms were identical to yours and my filter clogged daily since the car had sat for 10 years. It could very well be ignition but this will cost you nothing and if it wasn't the problem at least you'll have a slightly cleaner tank and sock.

 

Well tonight is the night! I replaced all the equipment listed in my last post. Well I have found that my Ignition coil on the top of the distributer was cracked in half?!?! Holy Cow!

Bad news, since i took out the timing rod, i have lost the time for the motor. And on the bottom of the timing rod shaft there are only two ways to install it. Well, first when i put it on the car would crank over but no start and smoke would pour out of the carb....NO GOOD, so reinstalled it 180 degrees. The only other way the shaft would install. Well i cranked it over again...no smoke, no start still; but more of a putt putt out the exhaust. Better, but still no good.

So now im really in a quirral with the car. I gotta find someone who knows how to time a 350 and a timing light. Sometimes i feel like a bone head.

Again your replys are helping a hella lot. I hope that coil was my problem, but if not, hey, at least i know everything that is done on the car and im corning the problem. So knock on wood that it isn't that %^$ing 'sock'! lol

My days with the vette arnt going as well as planned, and i missed the car show today too.

 

OK. Take a deep breath. It's not as bad as it seems. First of all, the oil pump drive shaft is not "timed" with anything...it just gets driven by the bottom of the distributor shaft. You can take a long shank flat-blade screwdriver and turn the oil pump shaft to any position you want. The important thing is to get the distributor gear in the correct position with the cam drive gear.
Remove your #1 sparkplug. Find the TDC (top dead center) timing mark on your harmonic balancer and use a marker to fill in the groove so you can clearly see it. Pull the coil wire out of your coil so that you get no spark. Have wife or friend "tweak" the ignition on the car while you place your thumb close to the #1 plug hole {keep hands and clothing clear of any rotating belts, etc.} and keep an eye on the TDC mark on the balancer. As the TDC mark comes around to the timing scale, the air from the plug hole will either be a strong puff or a weak one. The strong puff cycle is when the cylinder is under compression and that is when the #1 plug will fire when the TDC line is on the timing scale. Keep tweaking the engine over until you just feel the "strong puff". If the TDC mark is near the timing scale, stop there. if it is short of the scale, just bump the ignition until it is near or on the scale. The engine is now close to top-dead-center position.
Now take the dist. [with cap off], and rotate the rotor so that the contact is a bit CCW of the #1 firing position (check motor manual/book for that position). [Note: It needs to be a bit CCW of that #1 position because the helical gear engagement will cause the rotor to turn CW as it is fully installed.] Put a strip of duct tape across the rotor to the dist. body so that the rotor won't move much as you install it.
Now get a light and look down into the dist. hole in the intake and see where the slot is in the oil pump drive. Check where the mating drive tang is at the bottom of the dist. shaft. Use that long screwdriver to turn the oil pump shaft so that it will line up with the dist. drive tang when you install the dist. Drop it in and see if you hit the drive slot (if so, the dist. will go full down; if not, it won't). "Have fun" until you get it engaged. Then verify that the rotor is still pointed to the #1 position. THE WORST IS OVER.
Get out the timing light, snug down the dist. clamp so that you can just make the dist. turn with some effort, reinstall the coil wire and try to fire it up. KEEP FACE AWAY FROM THE CARB IN CASE IT BACKFIRES and keep one hand on the dist. so that you can quickly turn each way to make the car run better when it starts. Once you have it running OK, remove and plug the advance can vacuum line and do the timing "thing". {Using Lars Grimsrud's timing method is best for your engine, but setting it to the emissions tag settings is OK, as well. Once dwell is set and timing is set, reconnect the vacuum line and tighten down the dist. clamp.
Finally, wash hands, sit down, then drink beer! I hope all goes well.

 

Very good instructions!!!
Way to go 7T1vette

 

I just followed your advice and my car is running full throttle! Omg The timing is just a little too advanced but me and my buddies are going to time it tomorrow! The car is running so well. No more stumble on acceleration!

Repeat! No stumble on acceleration! Wow guys. Kick butt and take names. Major props to all!

Again, this just shows how good these forums actually work here on the corvette site.

ThaNk You , Derek

I again love my 79 corvette!

 

Congrats in getting it running.
Kudos to 7T1vette

Post a pic of that coil if you would. I would like to see one cracked like that.

 

I bet Bubba installed it!

You're welcome for the advice; I'm glad it helped.

7T1vette