Thunor

Problem: stumbles and sputters out at ~1800-2000 RPMs and the engine won't rev any higher in gear.

I rebuilt the carter quadrajet 4mv that was on it initially about 3 times, same result. Adjusted its air valves, even endeavored with the APT feature to no avail.

Replaced the fuel pump, same result.

Bought a remanufactured rochester quadrajet from autoline recently, installed it. Same result.

Throughout all of this, I was under the presumption it was a timing/ignition issue as well. All new sparkplugs, firing order is correct, Checked all the wires, they work fine.

Tried various different combinations of initial timing/full centrifugal advance. Best running now at 16 initial 36 total, but the sputtering never seems to go away. Played around with the idle air mixture screws, same result.

Put all sorts of different combinations of distributor springs on, same result

Removed EGR valve and sealed the hole, same result.

I don't really know what I am doing here as this is my first muscle car, but I've been trying to get this motor to run good for almost two years, not even the mechanic could figure it out, he said I needed a new carb and fuel pump and obviously that's not the problem since I've just now replaced them.

The exhaust has no cats
I unhooked the EFE thing and made sure it was working.

I plugged up all the vacuum ports and changed out vacuum lines. Don't think I have a vacuum leak, but it sure seems like it? The only skeptical looking fittings are those choke heat tubes, but to my understanding those have nothing to do with engine vacuum?

I don't want to goof around with the secondary air valve spring since this carb should be set up properly, there's plenty of tension it's not sloppy.

Is it a metering problem? Should I play around with the idle air mixture screws some more? Should I look for another possible vacuum leak? Out of ideas

Long post!!!

Thanks!

Brian74n81

How does your fuel filter look? Also have you pulled the sending unit in fuel tank and checked the sock? Sounds like fuel delivery problem for sure.

drwet

Can you borrow a known good HEI distributor to swap in? Probably the fastest way to eliminate cap, rotor, and module. What about plug wires? I think you have pretty much eliminated carburetion as a possibility.

calwldlife

https://www.google.com/search?q=1979...hrome&ie=UTF-8

Thunor

Brian,

I have not, but I'm sure that component is probably ruined as the gas that I siphoned out of the car when I first got it was quite disgusting. The fuel gauge doesn't work. I blew compressed air through the fuel lines to make sure there wasn't a blockage and air flows freely. The fuel filter is near the carburetor, and I can see the fuel going to the carb.

Dropping the fuel tank might be in order soon though.

Thunor

No sadly, I don't have any car friends. I did check all the wires with a spark plug wire tester though.

Thunor

This might be it, but I don't know where this is located on the corvette? Is it near the distributor? I don't see anything like it.

Thanks for all the replies!!

vince vette 2

If you just want to get the sending unit out to check the sock you don't need to take the tank completely out. You do need to unbolt the support and at least loosen the strap nuts to the ends of the bolts (you may ultimately need to take them off too. But dropping it just a couple inches will allow you to get your hands on the lines to disconnect them and then remove the internals from the tank. I just pulled the tank out of my '80 this weekend. No real problem, I just saw the build sheet hanging out while I was working on pulling the suspension and diff and decided to get the sheet. It actually looked pretty good in there.

calwldlife

in dist mounted to the bottom/
black
2 connectors.
take to autozone for test
classic symptoms
stock is fine

blk79nj

It is the ignition module in side the distributor. When mine went in my 79, I was completely dead.

They are subject to deterioration from heat, and it might be your problem It's very easy to change as well.

vince vette 2

PS - I know you said the wires tested OK, but unless they are fairly new you might want to replace them in any case. In my 80 I ran the original wires about 10 years. At that point the thing would cough and sputter just as it was hitting the shift point under hard acceleration, usually in the high 4000's, then once it managed to shift it would be smooth again until getting into the higher RPM's. Just a thought.

Brian74n81

My fuel gage on 81 wasnt working either. Has the car sat for an extended time? My sending unit corroded and dropped down into the tank. Never could get it to run correctly before. Not sure if your year had plastic tank or not, but worth a look. Mine got to where i couldnt keep it running with fuel filter on. Take flashlight and have a look down in the tank after removing sending unit. At minimum replace the sock! I didnt habe to losen any straps on mine. Did it all from the top.

Brian74n81

What was left of sending unit



Sending unit cover bottom.



Rusted junk from sending unit and found the sock in the bottom

Thunor

Ok friends, I removed it and I'll replace it tomorrow.

Question, if I timed it with a bad ignition control module, will I have to time the engine again with a properly functioning ICM?

Thanks everyone!!

drwet

Unlikely. Just swap the modules. Make sure you apply plenty of silicone grease to the bottom of the module before you install it. It is there to facilitate heat transfer so the module doesn't overheat. That's what kills them.

slofut

Do as Brian says. Old cars, cruddy tanks. You have fuel at the carb, but not enough volume at speed. Better to pull the tank too. A simple rinse prob won't make a long term fix.

Big2Bird

Where are you located?

Brian74n81

Man i have chased those demons! Back and forth. Good idle, crappy wot...adjust, good wot, crappy idle. Never did get it to run right with poor fuel delivery.

vince vette 2

Boy that sender corrosion is incredible. I just pulled mine out of my 80 yesterday as I pulled the tank to get the build sheet while it still existed. I figured I would clean things up will it was out. The sending unit looked perfectly fine. and the actual plastic tank inside looked find. I know everything is original since I'm the original owner. And mine also sat for more than a decade before I started on it a couple years ago.

jim2527

Only car I had with similar symptoms had clogged catalytic convertor.