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Vapor Lock?

MGD7038

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Sorry for the long post, I was hoping someone out there can point me in the right direction. I have poked around on the forum in search of answers and I’m coming up a bit short. The wife and I took my 74 Challenger for a drive two weeks ago before it gets too hot here in AZ.

We drove for 80+ miles without any problems until we exited the freeway to head into Sedona. As soon as I approached the stop sign the car died. The engine would crank and I had spark, it just wouldn’t fire. It has an Edelbrock multi-port EFI and I checked the gauge under the hood and showed 60 pounds of pressure. There was no overheating issues, temp gauge was perfect and there was no boiling or steam in the radiator. We let the car sit for 30 minutes and it fires right up and we decided to head back to Phoenix.

I drove about 15 miles to a gas station to get gas and it died again as soon was we came to a stop at the station. I let it sit for 30 minutes and it fired up. I drove it to some nearby by shade with the hood up and let it cool for an hour. After that I drove it home without incident. In hindsight I noticed there was some slight throttle response delay when I eased off the accelerator and then got back on it. That was after we had been climbing hills and been out for an hour. Everything seemed ok.

Since then we have been able to drive it around town without issue. I decided to check my lines and see what happened. My best guess is the lines got hot enough to cause air gaps or bubbles in the lines. That caused the hesitation when driving but since the engine was rotating and I was back on the accelerator it pushed the air through the EFI but when stopped the amount to fuel being pushed through the lines was less and the rpm’s dropped allowing the car to die.

The fuels lines have the metal dressed sleeves on them and are a few inches from the exhaust and the engine. The electronic fuel pump is under the passenger door and is a good 8-10 inches from the exhaust. The fuel filter in is line right after the pump.

I’ve heard the new gas, at higher octane has a lower boiling point. I’m going to try a lower octane rating gas to start. I know vapor lock is more common in carbs so I’m a bit at a loss other that fuel line placement that seems to be ok.

Any advice is much appreciated.
 

Steve340

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Vapour lock would cause your gauge to read 0 or close to it. The pump is designed to pump fluid not gas/vapour which equals no pressure.
Location of the gauge could be a factor hard to say. Is the gauge faulty? Reading 60 no matter what?
However the metal shields and fuel pump location are not ideal. The fuel pump should be as close to the tank as possible. Preferably in it.
Anything that traps heat in the fuel lines is not good.
I had a similar problem with a motorcycle it would intermittently cut out.
The problem was the electronic ignition.
If the just die and will not go thats one thing, but the intermittent fault can be a pain.
You have a tricky one good luck.
 

MGD7038

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Steve340 thanks for the response. I’ll definitely look into putting a heat barrier over my lines, pump and filter. I know DEI and Heatshield have products for this. I’ll move the pump and filter further back as well and see what happens. The gauge seems to be working it does fluctuate with the pump (doesn’t mean it’s accurate). I would like to put the pump in the tank as well but it’s pricey for now.
 

Steve340

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If your problem is vapour lock any restrictions before the pump will increase the tendency to vapour lock. Even a kink in the fuel line can make things worse. Your stock fuel tank filter/sock can be removed and replaced with a strainer/course filter prior to the pump. The actual filter should be after the pump in the high pressure part of the lines.
With the pump at the back of the car with air flow around it should not need shielding. They build up heat during operation you do not want to "trap" it in.
 

Drivun

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Steve340's thinking is on the mark. An MSD advisor told me that if pushing the accelerator solves the problem, its fuel. If it doesn't its spark. I am surprised you get vapor lock on the highway as both fuel flow and air flow should be best then.

I'd check fuel sock/filter/lines first. My 66 vette had a chronic problem on Power Tours that turned out to be a cup of sugar in the tank(!!). I thought it was ignition so I got good at replacing the MSD/coil on the roadside. By the time I replaced them the sugar must have settled back down in the vertically oriented fuel filter, so the car ran for most of the day until it got really plugged up again.

With the Vette's cramped engine compartment, sidepipes, and the hi ethanol content in mid-America's fuel, I did get into vapor lock in the last 2 years when the air temps were 95-115 and the lines were really slow/long. Did a lot of research to learn that electric pumps are pushers - not pullers- so the pump must be as close to the tank as possible with a 100 micron filter before the pump and a 10 micron at the engine.

My vette is carbed with a good mechanical pump so I added the filters, improved the supply line routing, and ran a return line. No issues now at 115 ambient in 2 hour lines.
 

quapman

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Do you have a single feed line system or a return line? If it's a return line system, there shouldn't be vapor lock issues. I know pump location relative to the tank is important, too, but I don't recall if it's above or below, so someone with more knowledge on that should chime in. I believe Spectra makes an EFI ready tank now.

eCatalog - Product
 

MGD7038

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I do have a return line. I’m going to crawl under and see if I can find a better mounting location.
 

rogue

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i know this isn't heat related but if you don't have a baffled tank and the car gets lot on fuel, slosh can cause problems with the pump picking up fuel. When i put EFI on my car i spend the extra bucks for a baffled tank and in-tank pump and have never had fuel delivery problems (we get upper 90s to over 100 degrees in the summer)
 

AUSTA

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Do you have a return line filter they can block & still give you 60 psi at the EFI also is the tank venting my vent line was blocked with factory undercoat caused the tank to swell after 10 minutes took of the cap & it landed about 10 feet away due to the pressure .
 

MGD7038

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Augusta, I do have a filter on the return line as well. I seem to have a bit of a venting problem in the tank as well. The four tubes for the emission were disconnected and soldered closed. I drilled two small holes in my Stant fuel cap to help with pressure. If I don’t watch it I will get a fuel leak where the filler neck enters the tank, it seems to suck the rubber grommet in allowing gas to leak. The drilled holes have helped but I’m in search of a gas cap that vents. It’s hard to find one that will fit under the chrome gas cap cover that is on the car. Whether that is related to my other problem I don’t know.
 

quapman

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The return line filter may be hindering the flow of the whole system.
 

Steve340

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I would say you may be able to remove that return line filter. You filtered the fuel as it left the tank. Does not seem as though it needs more filtering before you put it back in the tank.
Why give the pump a heart attack.
The fuel return should be in a tube that goes under the fluid level so it does not aerate the fuel as it returns to the tank.
That fuel tank vent needs sorting out properly, it is critical to the performance of the system.
If it is sucking in the filler tube rubber gasket that tells me your venting is non existent.
As in quapman post earlier I believe you would be wise to invest in a new fuel tank complete with pump and correct venting.
 

MGD7038

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I agree. At this point I think I should just eliminate all the things I know are wrong in one shot. I’m going to plan on replacing the tank with a baffled one and install a submersible pump. That way the venting is fixed and the pump is put in the right place.
I’m going to remove the return line fuel filter as well to free things up for now. I’ll keep everyone posted with the results.

Thank you
 

Steve340

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I think you are definitely on the right track - eliminate the things you know are wrong.
Smart move.
It may pay you to do a little research on the venting as it has a big impact on things like unwanted fuel odours, filling and of course the main one keeping the tank at atmospheric pressure when the pump is operating.
You may want to reinstate the standard venting system I have found on my car it works really well. In short the venting system allows the tank to breath and the filler cap allows pressure out or air in. It deals with fuel expansion in hot weather and is also connected to the PCV system so I get zero fuel smells.
I have a completely stock fuel supply system, stock fuel pump feeding a 680 Quickfuel carb and no problems at all whether the fuel tank is low or full. Dodge designed it and it works good.
The number of people I come across who know more than the factory about how to build a car is amazing. I still take their money though.
My mantra is if the factory did it they did it for a reason so copy it and you cannot go wrong.
It is OK but change things but it pays to understand how they work before you throw it away.
The tank in rogue's post looks nice however it appears to be made to work with stock vent system.
 

rogue

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The Tanks Inc fuel injection tank does not work with the stock vent system... there is a provision for a vent line on the in-tank pump... that works well for me and i have no problems with it
 

Steve340

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Cool good to know the system works very well and you have no problems.
It must be a good product.
 

MGD7038

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Rogue, that is great info thank you. I was looking at the Aeromotive but I think you changed my mind. My big issue is the previous owner took all the original equipment out. So I would literally be starting from scratch. One question, how did you run your vent line?
 

rogue

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so actually both the tank itself and the fuel pump have vent fittings... so i ran a line from each over to the original vent tubes... then ran the other end of what they connect to a remote mount vent valve that i think came with the pump
Remote Mount Rollover Vent Valve
 
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