Moparts
Vapor Lock/Fuel Boil
Posted By: 53fopar
Vapor Lock/Fuel Boil - 08/31/13 11:57 PM
I've got a vapor lock issue that I can't seem to fix.
The engine is a 1977 360, stock heads, Summit intake, Edelbrock 1405, and Headman headers. Running Vintage Air. Three core AL radiator with full shroud and electric fan and 160* thermostat. Engine runs cool, normal 170. Gets to 180-185 if sitting in traffic with AC on. It does get very hot under the hood with the puller electric fan. This all in a 1953 Ford F100 panel truck
For the past few weeks when it's hot (90-95*) the engine will vapor lock if I drive it for an extended period. When engine is cool it starts and runs fine. Even hot re-starts are no problem. However, if I run it for a long run with the AC and the engine temp gets up to 180* it will die. When I look under the hood the small in-line Mr. Gasket fuel filter up by the carb is empty. No amount of cranking will re-start. Tried to vent the gas cap and removing fuel line, no help. The only way to get the engine to re-start is to allow it to cool some and then dump some gas in the carb to prime it. If I just let it sit for 2 to 3 hours the fuel filter refills and the engine will start with one or two pumps. I can repeat the problem by letting it idle with the AC running for about an hour and then it will die and fuel filter will be empty.
I have tried the following: new electric fuel pump (Holley 12-125) mounted next to fuel tank. One inch plastic spacer under the carb. Re-ran all the fuel line away from headers. Came along the floor and up the fire wall with all new 3/8 fuel line. Tried to keep fuel line out of engine bay as much as possible. Line comes from behind distributer to back of carb. The only original fuel line is about 18" coming out of the tank.
So, where do I go from here? The only things I can think of don't seem likely to help. Rebuild carb? Insulate the fuel line? Is there a way to ventilate the engine bay?
Posted By: bobby66
Re: Vapor Lock/Fuel Boil - 09/01/13 12:12 AM
Do you have any kind of vapor return in the fuel system?
Posted By: ahy
Re: Vapor Lock/Fuel Boil - 09/01/13 12:16 AM
Boy... it sounds like you have done everything. Fuel lines, carb spacer, electric pump. If the electric pump won't push fuel up there I don't know what will.
A couple of suggestions. Have you bypassed the OE fuel pump completely? Also how about the tank and pickup? If there is debris in the tank that is clogging the pickup screen that could shut her down when things get hot. Also, most important with an electric pump is low restriction on the suction side. Clean tank, clean screen, preferably 3/8"+ suction line and fuel pump as low as possible help.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 01:11 AM
No return line. I thought about that but I think I'd have to drop the tank to get a fitting for the return. Could I drill in the side of the tank near the top to install a fitting? Is there any type "self tapping" fitting you can install?
Posted By: topside
Re: Vapor Lock/Fuel Boil - 09/01/13 01:18 AM
You might have a different problem, that's throwing off your analysis.
I'd be inclined to look inside the tank, make sure there's nothing in there that can block the pickup, and make sure the lines are clear & the sock isn't collapsing. Then I'd look at the carb float levels. Your rig doesn't seem to get hot enough for heat soak.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 01:22 AM
The OE pump is gone and hole blocked. There is some small trash in the filter before the fuel pump. I never had the tank out. It runs fine if it's not hot so I am thinking it's not a trash issue. Is there some way the heat would increase the trash problem?
There's about 18" of steel 1/4" fuel line coming from the tank pickup then changes over to 3/8" hose. When it vapor locks the fuel filter between the tank and the electric pump stays full so I don't think it's a suction issue. Really seems like vapor lock or fuel boil since it's directly related to hot operation.
Posted By: Challenger 1
Re: Vapor Lock/Fuel Boil - 09/01/13 03:36 AM
Quote:
The OE pump is gone and hole blocked. There is some small trash in the filter before the fuel pump. I never had the tank out. It runs fine if it's not hot so I am thinking it's not a trash issue. Is there some way the heat would increase the trash problem?
There's about 18" of steel 1/4" fuel line coming from the tank pickup then changes over to 3/8" hose. When it vapor locks the fuel filter between the tank and the electric pump stays full so I don't think it's a suction issue. Really seems like vapor lock or fuel boil since it's directly related to hot operation.
First I would suggest to get a better fan that moves more air.
Second you can't have 1/4"ID on the suction side and expect the pump not to struggle when it get's hot. Also I suspect the filter you have in front of the pump is a 10 micron filter which is too fine for hot weather/hi volume use.
I suggest to only use a new strainer before the fuel pump, not a filter.
Gas is really hard to suck, especially during hot weather. You can restrict the flow with too small of line size and filters before the pump.
Normally you would return the fuel through the sending unit, maybe you should put one back in your tank?
Good luck.
And this should be in the general section since it's not a Mopar.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 04:43 PM
Thanks everyone for the ideas.
The fan is a 3500 cfm as I recall. I'll check to see if I can go stronger.
I'll have to drop the tank to change out the 1/4" line from the fuel pickup. Guess that would be the time to add in a return line and give the tank a good cleaning and seal. That may have to wait till I have some time.
The in-line fuel filter is a Mr Gasket 9748. They don't show a pore size for it. The filter before the fuel pump is a NAPA Gold 3003.
I also have a fuel pressure gauge up next to the carb but I don't think that should cause any issues. Fuel pressure runs 6 psi till the vapor lock happens. Then it jumps all over the place till it drops to 0. I don't have a pressure regulator in the system. I have a regulator somewhere around the garage, but I don't think I'll add it now since that's not the issue. I'll have to add the regulator if I end up doing the return line.
I am going to try the following one things at a time to see what I get:
1. Remove in line filter at the carb.
2. Insulate fuel line under the hood
3. Rebuild the carb.
4. Drop tank and replace 1/4" pickup and add return line
Maybe I need to go old school and cut some louvers in the hood?
Anyone have any other ideas to add to the list?
Posted By: Challenger 1
Re: Vapor Lock/Fuel Boil - 09/01/13 04:49 PM
Don't remove the filter after the pump, it needs to be there and is not the cause of your problem.
The filter before your pump part of the problem, I can promise you that much.
I don't feel that under hood temps is causing your problem, it's fuel supply issues, I'm sure.
Can you remove your hood for a day and go drive the truck and see if I'm right?
A good strong pump is because it has a large unrestricted supply of gas to it. That's why pumps work good.
A good working pump will easily push fuel into a hot engine compartment.
The hotter it get's the harder it is to suck gas, it vaporizes real easy under vacuum conditions and no fuel pumps can suck or pump vapor. It might work alright during cool days but when it get's hot out, it the gas turns to vapor real easy on the suction side of your pump.
If that's the case then the fuel pump will have a shorter life too.
Posted By: TJP
Re: Vapor Lock/Fuel Boil - 09/01/13 06:52 PM
if you are running ethanol based fuel it will definitely cause your symptoms due to the fact it has a lower boiling point. Even the electric pump will not cure the problem. It does not affect newer vehicles as their systems are constantly recirculating. I have read that if you are stuck with the ethanol fuel due to your location the only known fix is to run a return line with a restricted orifice (.060 or so). This allows the pressure to stay at 6 PSI but keeps the fuel recirculating thereby preventing it from boiling while sitting in the line.
On one particular car that was a bit stubborn(48 Ford with a 360 and A/c) I fabbed a .125 aluminum spacer plate that stuck out in front, back, and over the heat crossover passage on the right side. It was installed between the manifold, Phenolic spacer plate and the carb The idea is to block the radiant heat rising up from the intake. The aluminum dissipates heat well,it's been fine for 4 years now
Gm used a similar thing on some of their perf. apps back in the day.
only other thing I can add is to make sure the line under the vehicle has adequate clearance from the exhaust etc.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 07:13 PM
No, not ethanol problem. I run ethanol free marine fuel.
I went out and removed the Mr Gasket in-line filter next to the carb and put plastic wire loom over the fuel line in the engine bay. No other changes. Ran the truck with cardboard in front of radiator to get engine temp up to 195-200. Then went for a ride. No vapor lock. As I drove the temp came back down to 180. Repeated with the cardboard and still no issues. Did several hot re-starts without problem.
I am going to drive the truck some more this afternoon and see what happens.
Could the glass/metal in-line filter be acting like a heat sink and suck up the heat from the engine bay?
Posted By: Mr.Yuck
Re: Vapor Lock/Fuel Boil - 09/01/13 08:08 PM
1/4 inch line???? should be 5/16th I'd think.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 08:19 PM
Yeah, it might be 5/16". The only section of it is on top of the tank coming from the pick-up. It's up tight to the floor board and I can barely see it, let alone remove it.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 08:26 PM
Well, back to the drawing board. Took it out this afternoon and drove it hard. After about an hour and half it died. Fuel pressure gauge reads 0 with the pump running. No fuel in the carb. Fuel filter between tank and fuel pump is full. Temp when it died 185*.
Posted By: Challenger 1
Re: Vapor Lock/Fuel Boil - 09/01/13 08:35 PM
Quote:
Well, back to the drawing board. Took it out this afternoon and drove it hard. After about an hour and half it died. Fuel pressure gauge reads 0 with the pump running. No fuel in the carb. Fuel filter between tank and fuel pump is full. Temp when it died 185*.
Don't be confused, by the time you look at the filter that shouldn't be there is has turned back to liquid and you can't see vapor lock at the inlet of the pump. That's where it occurs, not up by the engine with a electric pump.
Just trying to help you, been there and have done it more than once.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 09:07 PM
OK Challenger 1, I am off to the parts store.
Can't find any pore size info on the NAPA or Mr Gasket filters I was running.
The instructions with the Holley pump say 100 micron filter between tank and pump and 40 micron filter after pump before carb. Sound right to you?
Posted By: Challenger 1
Re: Vapor Lock/Fuel Boil - 09/01/13 09:11 PM
Yes
Posted By: moparcanuk
Re: Vapor Lock/Fuel Boil - 09/01/13 10:13 PM
You need a fuel vapor separator. Standard equipment on 69 1/2 A12 Road Runners.
Posted By: Supercuda
Re: Vapor Lock/Fuel Boil - 09/01/13 10:32 PM
It may be possible your fuel line before the pump is leaking air into the fuel. As it warms up, the crack opens up, heck it could very well be your pump overheating and flaking out.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/01/13 10:51 PM
None of the local stores stock the Holley fuel filters and the numbers don't cross to any other brand. The Holley's are billet cases with replaceable elements, about $70 each. Ouch.
None of the other filter makers publish the pore size, so it's hard to cross to another brand.
Guess I'll order the Holley's from Summit unless someone has some part numbers for a 100 micron and 40 micron filter.
I don't think there is any air leak in the supply line to the pump. It's double clamped at the tank and tight at the filter. All new line.
The pump does get hot. I am not sure how much is too hot. I can touch it when it vapor locks for what that's worth. And I can hear it's still running when it vapor locks, just not pushing fuel down the line.
Posted By: ahy
Re: Vapor Lock/Fuel Boil - 09/02/13 04:44 AM
If you have a clean sound "sock" on the fuel pickup that should protect the pump. It serves the same purpose as the 100 micron filter before the pump. Personally I'd pull the pickup next and have a look see. If the sock is intact and is clean or can be cleaned, simply remove the filter before the pump for a test.
Summit does have the 100 micron filters if you really want or need one. A local speed shop, if there is one near you, should have them also.
Posted By: Challenger 1
Re: Vapor Lock/Fuel Boil - 09/02/13 05:48 AM
Quote:
If you have a clean sound "sock" on the fuel pickup that should protect the pump. It serves the same purpose as the 100 micron filter before the pump. Personally I'd pull the pickup next and have a look see. If the sock is intact and is clean or can be cleaned, simply remove the filter before the pump for a test.
Summit does have the 100 micron filters if you really want or need one. A local speed shop, if there is one near you, should have them also.
Exactly...
But this is a ford panel truck... I bet your sock/strainer in the tank is old/dirty and could be causing the restriction.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/02/13 04:06 PM
I am going to try the 100 micron filter before the pump to see if it was a flow restriction there.
The only way to check the sock/pickup is to drop the tank. But, I still don't understand how that could be the problem. The engine runs fine in cool weather (anything under about 80*). This ONLY happens when it's hot outside. I still think it's a vapor lock/fuel boil issue.
Posted By: ahy
Re: Vapor Lock/Fuel Boil - 09/02/13 07:00 PM
Any restriction on the suction side of the pump can encourage vapor lock. Higher temps worsen the problem. The fuel in the tank is getting warm also as you run - if there is any restriction on the suction side it can start vapor locking.
If that rear mounted pump was putting out 5-7 PSI like it should it would push fuel up and overcome vapor in the engine compartment. If you still aren't positive, suggest you rig your fuel pressure gauge right after the pump. I bet it does the same thing you see at the carb.
For reference, I run a '47 Power Wagon. The original design fuel system has a long steel line in the engine compartment on the same side as the exhaust manifolds. Mine would vapor lock running down the road in hot weather and really lock up after a hot soak with engine shut off for 10-20 min. After shutdown, the only way to get her going was to hose down the long fuel line and fuel pump in the engine compartment. I installed an electric booster pump on the frame rail with check valve so the engine could run on its mechanical pump also. As a test, I ran it in hot weather with electric pump off. After 40 min or so it started cutting out. Flip the toggle to turn on the electric pump and it smoothed right out and stayed that way. As a second test, I let it hot soak for a while and tried to re-start without the booster pump. No go. Hit the booster pump and she started right up. I could smell the fuel vapor being pushed out of the lines but it started and ran fine. That's why I'm pretty sure a correctly functioning electric pump shouldn't be affected by engine compartment heat within reason.
The pump may be shot by now also as they don't like to suck vapor.
Also check/replace any rubber fuel lines on the suction side at least. With time and alcohol they can soft and get sucked shut by the pump. I had that problem on a brand F PU and it created the same symptoms you are having.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/04/13 03:41 AM
Rain today, wasn't able to do much. Used the cardboard over the radiator to force a shut down sitting in the garage. A buddy loaded me his infrared thermometer and I shot temps on the carb base and intake while running and after shut down (think I need to buy on of those things). Base of carb stayed at about 130* while running and at shut down. Warmed to about 135* after shut down. Fuel pressure came back after 20 minutes with carb temp at 128 and engine restarted. So, I guess that indicates that fuel boil is not the issue. That leaves me with flow restriction from the tank as most of you said.
Before I go through dropping the tank, I think I'll try a test. I am going to pull the fuel line off the tank and put it in a gas can. I'll also remove the filter ahead of the pump. If it still shuts down running from a gas can, I'll have to re-think. If it runs, I'll drop the tank, clean, seal and new sock. Sound like a reasonable plan?
Posted By: ahy
Re: Vapor Lock/Fuel Boil - 09/04/13 03:57 AM
Posted By: JohnRR
Re: Vapor Lock/Fuel Boil - 09/04/13 02:31 PM
Quote:
Before I go through dropping the tank, I think I'll try a test. I am going to pull the fuel line off the tank and put it in a gas can. I'll also remove the filter ahead of the pump. If it still shuts down running from a gas can, I'll have to re-think. If it runs, I'll drop the tank, clean, seal and new sock. Sound like a reasonable plan?
This is a good test , use a boat fuel tank for max safety and lose the pre pump filter.
One thing you did that made zero sense was removing the filter AFTER the pump , you should have removed the filter before the pump it's too fine for the pump to suck thru.
Posted By: TJP
Re: Vapor Lock/Fuel Boil - 09/04/13 06:15 PM
I wouldn't seal the tank. I have seen all too many sealed tanks fail and create a mess. If your tank is contaminated just put a new one in they are relatively inexpensive
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/05/13 02:12 AM
Quote:
This is a good test , use a boat fuel tank for max safety and lose the pre pump filter.
One thing you did that made zero sense was removing the filter AFTER the pump , you should have removed the filter before the pump it's too fine for the pump to suck thru.
I was thinking the in-line Mr Gasket was drawing heat since it was up front by the alt. I've ordered the Holley 100 micron pre pump and 40 micron post pump filters and will mount them by the pump.
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/05/13 02:16 AM
Quote:
I wouldn't seal the tank. I have seen all too many sealed tanks fail and create a mess. If your tank is contaminated just put a new one in they are relatively inexpensive
New tank for this truck is $500 plus oversized shipping. I am going to try the KBS clean/seal system. I seen several good reviews. Anyone here used it?
Posted By: Challenger 1
Re: Vapor Lock/Fuel Boil - 09/05/13 02:19 AM
Are you going to take the tank out?
Posted By: 53fopar
Re: Vapor Lock/Fuel Boil - 09/05/13 02:28 AM
Posted By: ahy
Re: Vapor Lock/Fuel Boil - 09/05/13 03:55 AM
Great! For reference I have used the Eastwood 3 step tank cleaning kit on rare/expensive tanks. It uses strong detergent, Acetone and Muriatic acid to clean and a durable sealer. Worked well.
Posted By: 340SHORTY
Re: Vapor Lock/Fuel Boil - 09/05/13 04:14 AM
Fuel Cell
