Possible vapor lock or ??? 454 / 496 GM motor

[jeff york]

I had an odd incident last night. I pulled my 1977 Airstream Argosy 454 / 496 GM powered coach out of storage. I ran it about 10 minutes before leaving and then drove about 25 miles and stopped for gas. I pumped about 22 gallons of regular gas into it. It sat maybe 20 more minutes running while I pumped the gas. Then, right after I pulled out, the motor shut down. I got it to restart and then as soon as I got through the intersection it shut down again. I could hit the key and it would sputter and fire up and quickly shut down. I had to pump the heck out of it to try and keep it running. But, it would quit. I took some starting fluid and got it to start again and it quickly shut down. On the second try with starting fluid it started and I drove it about a block to a Walmart parking lot. I shut it off I think. After a few minutes, I started it back up and decided to try and get it home about 4 miles away. It ran just fine the whole way. So, now I am wondering what happened. 

Back ground. I recently replaced my mechanical fuel pump with an electric fuel pump. I test drove it quite a bit before taking it out on the road so I thought everything was ok. I think after it shut off last night I checked the fuel pressure control valve and it may have been set as low as 2-2.5 PSI. It was dark so I am not sure. I pushed it up to 4 PSI and thats when I started it and it ran the rest of the way home. However, it ran fine for the first 20 plus miles and probably an hour. Its a Rochester Quadrajet carb. The fuel lines at the motor I changed to flexible neoprine ( I think) and on the mechanical pump it was a hard line from the mechanical to the carb. AS per electric fuel pump installation, I placed a pre filter in front of the pump to filter large particles and a new filter to filter small particles at the carb. 

There is no return line on the electric pump. 

So, did I get vapor lock ? Odd this happened right after re-fueling. Was my fuel pressure set to low ? Do I need to add something to insulate the gas lines from heat to prevent vapor lock ? Do I need to add stand offs on the fuel line to get them farther from the engine to stop heat soak ? The fuel line sits pretty close to the intake manifold and the valve cover. Sorry for the lenght. Just trying to throw out all the details.  

[Jim Stoltz]

The back butterflies are always closed unless the secondaries are open. The front one is the choke. I think you ran out of gas. Question is why.

[Lakota Wolf]

Another possability could be a *failing fuel pump. I mentioned this because when I hooked up my Aux. 3 rd fuel tank, I installed an electric fuel pump to pump the fuel from 3rd tank to number 1 tank... I switched on the aux. fuel pump and it hummed for a bit pumping fuel, then a loud hum, realizing the pump was failing.(It was brand new BTW.) I double checked the fuel pump by using a 5 gallon fuel can and pumped it into another 5 gallon can... It started off real good then started pushing air bubbles with the fuel, till no fuel. (I didnt want to drop the tank thinking it was a calapsed fuel screen or hose).Local parts house replaced it for me being it had a lifetime warrantee.

[jeff york]

Kevin Wright. I think yo ucould be true on the bad gas but, to take a fuel sample, it must be taken from the bottom of the tank. Its a wast of time to sample gas unless you have a way to get the bottom gas. 

John T Nordoff. could point on where the electric fuel pump is located. It is located as close to the bottom of the tank as I could get it and its at the tank as it should be. I took Jim Stoltz supplied article to determine where to mount it before I installed it. 

You all made me think of that night when it shut down and I was in a bit of a controlled panic to get it out of a very busy intersection. I do recall the back butterfly being closed but the front butterflies where open. SO, was the chock not working correctly. It would start but I had to pump the heck out of it. That seemed at the time to be a too rich situation as if the choke was stuck closed on a warm engine. But, I eventually sprayed starting fluid in it and got it to start. But, that was several minutes later so if it had been flooded and then enough time took place befoer I put starting fluid in it, the flood may have evaporated. But, then in theory, I should not have needed starting fluid, that would indicate an no fuel, but, after using starting fluid it ran continuously for at least 20 minutes. filling the tank after sitting in a damp storage unit could have easily stirred up water in the tank and that hitting the hot lines at the engine and the heat rising from the engine idling for 20 minutes while I filled it up and no air passing over and through the engine compartment could have caused a vapor lock from heated water in the fuel line. ???? 

[Jim Stoltz]

Good point on the safety switch, John. They typically use an oil pressure cut out switch that you tee in by the stock oil pressure switch. My friend with the '87 Allegro was going nuts because his "mechanic" wired it up incorrectly when he replaced the fuel pump. Long story short, the pump would only run while cranking. Once oil pressure built it would shut off. But that's not the problem here. I guess my point is that if Jeff didn't work in a safety switch with his install, he probably should.

Without going back to read Jeff's original post, I do believe that the pump is mounted by his saddle-type tank in the rear. This is where GM recommended putting them after their vapor lock study in 1983. It's still possible that the electric pump could be sucking a rubber line shut between the tank and pump but I doubt it (it would be more likely to happen at speed, not idle). The choke theory is good, but it would have flooded making it impossible to start. Based on his description it sounds like it was out of fuel for some reason.

[John "T" Nordhoff]

  Sorry if I missed it, BUT WHERE IS YOUR ELEC FUEL PUMP LOCATED back at the tank (where it should be in my opinion) or up front near the engine???????

 Its easier to push fuel then suck/pump it so if the pump is back near the tank I don't see vapor lock as the problem. If its up front and there's air bubbles or vapor in the suction line THAT CAN BE A PROBLEM.

 The later elec fuel pumps have the circulation and return line so they had far less problems, but I still had single line (no return) elec fuel pumps back at the tank work fine.

 Ive heard of soft rubber fuel lines (on suction side) sucking down closed by an elec pump!! Another reason to have pump at the tank.

 SAFETY many RV's have a safety tumbler shock switch in the fuel pump elec circuit so a shock or accident cuts off fuel pump power.

 So long as the fuel pumps pressure doesnt override the carbs needle valve and seat Id run it near the high end 

 John T

[Jim Stoltz]

Despite 2 rebuilds, I can't get the choke on my QuadraJet working properly. I have it adjusted so its wide open all the time. I'd do the same if I were you to eliminate that possibility.

It does sound like you ran out of gas for some reason. Even pressure as low as 2 PSI would at least allow it to idle.

I'm pretty sure it didn't vapor lock. The electric fuel pump is supposed to eliminate vapor lock. I still have the mechanical pump and have gotten the 454 REALLY hot and it's never vapor locked.

[Kevin wright]

As a long shot, could be shitty gas. Take a sample in a clear jar, put in fridge overnight, look for water or sediment or cloudy.

[jeff york]

Lakota, Russell, I think you are on to something. The bolt that holds the heat tube to engine block, the tube that hot air comes up from the exhaust manifold is sheared off. I just went out and checked and the tube is gone. I either didnt put it back on or I lost it on the way to the gas station. I guess I thought even with out it, the open hole in the air cleaner tube would allow enough heat to come up into the air cleaner to allow it to effect the chock as needed. Maybe not. I did put a couple of bottles of HEAT dry gas in the tank last night to to eliminate any possible water that may have been stirred up in the tank due to filling up the tank. All your comments have given me a great list of things to check and take care of. Note, after you all mentioning the choke I now remember very specifically that when the engine quit running I took the top off the air cleaner and the rear butterfly choke was completely closed for sure. I am positive of that. It didnt hit me conscientiously at the time yet I remember flipping it with my fingers. I was sort of panic to get the vehicle moved as it was in a very high traffic  intersection and I feared backing up traffic and getting a big ticket from police. I have a few more details to clean up and this choke is I think a very important detail. thanks you guys so much 

[Lakota Wolf]

Sounds like what Russell mentioned,, the choke,,, They have a tendency to flutter back to CLOSE position,,, Its like the heat spring cools down and it goes into close/choke mode.

Most Quads run at about 4 p.s.i. off the pump.

[Rich Thomas]

I was thinking maybe dirt in the fuel lines, possibly air? I have the old q jet as well but I've not had this problem. mine has a tendency to fall off and die just at start off and I have to feather the throttle a bit but I always starts back up. once its warmed up it dose ok though. hope you find the fault Jeff. Wish I was of some help.