Topic: Engine runs fine then stalls after driving 20 - 30 miles

[AliceKelly]

I've replaced the carb with a real deal $500 quadrajet. Replaced all the fuel filters. Replaced any rubber lines. Replaced two mechanical fuel pumps and one edelbrock electric pump.

When I drive it about 20-30 miles it stalls like it's fuel starved.

I tried putting an electric pump near tank hoping that it would push fuel to the front but alas it started doing it again.  So I moved the electric pump to the front and bypassed the mechanical pump.  It ran wonderfully for two whole weeks and ate the electric pump like a fat kid eating chocolate.

So I put the hoses back on the mechanical pump and limped home.

I'm almost positive it's a heat issue as it only happens after driving a while. There's a spot near the passenger side door where the exhaust manifold starter brake lines and fuel lines sort of jumble together.

My only thought is to cut my fuel line and re rout it over the top of the fender we'll in hopes that it cools the fuel before entering the pump..  I've spent close to a year trying to figure this problem out and like $4000


Any help is appreciated
ps there's nothing in the filters so it not the tank

[LJ-TJ]

Sounds like you may be on to something with the heat and the fuel line.

[Rickf1985]

Are you absolutely sure this is a fuel issue? Have you checked fuel flow and or pressure when it happens? An electric pump is not designed to pull fuel so it has to be mounted back near the tank. They are designed to push fuel only with very little vacuum on the inlet. Chevrolet has always had heat issues around that starter but it is usually the starter that is the problem. I am asking about the fuel issues because a failing ignition module will give the same symptoms.

[AliceKelly]

Ya I changed the. Module as part of the tune up I did when I first got it. The other part is I've changed two starters with same results.  I'm thinking to run that fuel through a rubber fueline for a couple feet on the other side of the Fram.  Right now it's on the side facing the starter. Perhaps the other side of the fra. E. Would help?

[Oz]

Vapor lock due to exhaust heat is actually a fairly common problem. 
It certainly wouldn't hurt to route the fuel and brake lines farther from it.  And any wiring as well.  Cutting a piece of tin and installing as a heat shield anywhere they're close is a good idea also.
This may even cure your problem.   

[yellowrecve]

Does your year / model use a vented or non vented fuel tank cap?

[AliceKelly]

Vented

[Elandan2]

I reread this thread and the other one you posted about this problem and noticed you didn't mention changing the ignition coil. Maybe another place to look?

[AliceKelly]

Whenever I do a tune up I do the coil, module, plugs, wires, cap and rotor and the condenser if I can find one. Coil and module are so cheap I replace them at least once a year

[AliceKelly]

What do you think about the possibility of a cracked hose leading into the pump?  Would it suck air as the hole widened and die!?

[Oz]

I think it would, but I also think it would happen long before driving 20 - 30 miles.

[tmsnyder]

When it happens, take off the fuel line and see what kind of volume you get while cranking.   Should be a lot. 

Prep it in advance for an easy check.

[mytoolman]

To further Rick's post and suggestions.  Before I would re engineer a fuel system that professional engineers have designed, I would make sure all the basic tests were done to find more usual failures that just are not that obvious. What is the fuel pressure that your needle and seat inside your carburetor operate with? An electric pump can put out too much pressure so a regulator may be needed to reduce the pressure going to your quadrajet and its needle and seat. I know you have spent a bunch of  money already but a regulator and a fuel pressure gauge are important and very INEXPENSIVE components for YOUR system and to find out what is actually happening. Take care of one system at a time. Eliminate EVERY item/component in that system before moving on to another. You have changed so many parts already you dont know if one of the replacement parts you think is golden because it is new isnt the culprit or contributing. Lots of us have replaced parts thinking them good because they were new and instead of success we ended up chasing our own tail.  Start with a good mechanical fuel pump. Check its pressure to verify it is good. Run a separate line from it to a REMOTE five gallon gas tank to make sure your rig will run THAT WAY.  If it will run that way then you can start looking at putting one piece of the fuel system back in play at a time to see what isnt functioning. If it does not run with your minimalized for testing fuel delivery separate tank and new verified lines to it, then find out what electronic or other issue is causing the failure.. dont go put the fuel system back together until you get the rig to run well.  The goal is to isolate each system to make sure they each are functioning correctly. Sorry you are where you are in all of this but you can get to the bottom of this if you still have the will to AND will systematically work through each system.

[Eyez Open]

I too agree with not tinkering with the fuel line engineering, there would be a few feet of rubber hose back in the gas tank area that may well need replacing..

This $500 quad is it a new one or a rebuild? New carbs in a box are out there, but those to need a rebuild after being in that box for over 25 yrs....

[Indian72]

Some of the replies are a little lengthy and I apologize for not reading through them all. If it wasn't mentioned,  An important test also would be to see if the engine will fire up again and run after sitting for just a few minutes. If it does then there is a possibility of substantial debris and/or rust in the fuel tank that is sucking up onto and completely blocking the pickup screen in the tank. When you shut the engine off, the suction stops and the debris falls off the screen allowing gas to flow again. This was happening with my generator pickup until we figured out the cause. I hope this information is helpful to you. I will add that one of the most helpful gauges I added to my dash was an electric fuel pressure gauge. The setup I purchased was a simple T fitting, an electrical sensor, and a gauge. It works like a charm and allows me to monitor the fuel pressure at all times, especially when climbing some of the serious grades out west. When climbing steeply out there I have seen fuel pull away from the pick up tube with as much as 1/2 a tank. It has been super helpful.

[udidwht]

One thing about new carbs. They are never buy then install. They must be torn down and cleaned then verified as far as float/s, their height adjustment etc...

[Winningbago]

Can you elaborate on what you mean by "real deal Quadrajet"? If you paid $500 for it I take it that it was professionally rebuilt correct?

Do you have the LARGE spacer gasket that goes between the intake manifold and the quadrajet? It should be about 1/4" thick. If you do NOT have it, or it's thinner than 1/4", then it sounds like vapor lock or fuel boiling in the carb.

Taking a look at your mechanical fuel pump, it should have 3 fittings. Does yours?