possible vapor lock
Thread Starter
Teching In
Joined: Feb 2010
Posts: 21
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From: Lynwood, Ca
possible vapor lock Had something weird happen to me that has never happened. I was at the hammers over the weekend, while on the trail the rig begin acting like it was running out of gas. Now I know I was not out of gas because we topped of the tank before we headed to the hammers and I do not have a gas leak. I asked a few friends of mine if they had ever experienced this on their rigs and a few said yes or said no. Those that said yes told me that its possible that I experience vapor lock. Is it possible to experience vapor lock on a TPI engine (LT1 camaro engine)? When I check the fuel pressure gauge it was at ZERO. Trying to turn the rig back on was difficult, almost like it was flooded. Fuel pump was functioning. What do you guys think?
Now. If in fact it was vapor lock. How do I either limit it or completely get rid of it?
Temperature was about 75-85 degrees.
Now. If in fact it was vapor lock. How do I either limit it or completely get rid of it?
Temperature was about 75-85 degrees.
Back up...you don't provide any info on what you're driving (rig?) or what mods you have. Remember this is mostly an f-body site, so not everyone knows exactly what you're talking about.
TECH Enthusiast
Joined: Dec 2009
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personally, i have never seen anyone experience vapor lock, i actually think its a big myth.. usually its a weak fuel pump, even in carbed applications..
gasoline can boil at 400degrees farenheit, thats what would cause vapor lock..
gasoline can boil at 400degrees farenheit, thats what would cause vapor lock..
Last edited by brucer; Jul 27, 2010 at 04:55 PM.
Portions of gasoline actually start to vaporize as low as 130deg.
The fuel pressure associated with EFI raises the boiling point to above a range that will likely never let the fuel vaporize in the pressure side of the system.
What the problem is, fuel being returned to the tank is hot due to the heat of the fuel pump & the heat removed from the rails in a return style system.
You likely have fuel returning to the tank over 100deg. This continues to get hotter as it is constantly recycled. At some point the fuel will vaporize when the pump attempts to suck it out of the tank. Then the pump gets airlocked & you lose fuel presure. This is vaporlock, but not at the engine.
This is much worse with an external pump as it has to work harder to pull fuel from the tank.
A way to minimize this is to keep the line to the pump as large as possible & not run a restrictive filter between the tank & pump. Also be sure the tank is vented so it does not get under a vacuum as fuel is used, otherwise the pump has to draw harder to get fuel out of the tank.
As a ballpark number, the boiling point is raised or lowered about 3 deg (from memory) by every pound of pressure/vacuum exerted on it. So you see why it will not likely boil with 45psi pressure in the system.
... but get the fuel in the tank about 130deg with a vacuum on it & you can easily see how it can boil in the line to the pump.
The fuel pressure associated with EFI raises the boiling point to above a range that will likely never let the fuel vaporize in the pressure side of the system.
What the problem is, fuel being returned to the tank is hot due to the heat of the fuel pump & the heat removed from the rails in a return style system.
You likely have fuel returning to the tank over 100deg. This continues to get hotter as it is constantly recycled. At some point the fuel will vaporize when the pump attempts to suck it out of the tank. Then the pump gets airlocked & you lose fuel presure. This is vaporlock, but not at the engine.
This is much worse with an external pump as it has to work harder to pull fuel from the tank.
A way to minimize this is to keep the line to the pump as large as possible & not run a restrictive filter between the tank & pump. Also be sure the tank is vented so it does not get under a vacuum as fuel is used, otherwise the pump has to draw harder to get fuel out of the tank.
As a ballpark number, the boiling point is raised or lowered about 3 deg (from memory) by every pound of pressure/vacuum exerted on it. So you see why it will not likely boil with 45psi pressure in the system.
... but get the fuel in the tank about 130deg with a vacuum on it & you can easily see how it can boil in the line to the pump.
Thread Starter
Teching In
Joined: Feb 2010
Posts: 21
Likes: 0
From: Lynwood, Ca
Vapor Lock Ram Air,
The engine is a transplant from an F-body Camaro (1995). Has no mods, but I did remove the EVAP, A/C and the cats. Running a fuel cell with an external pull pump. My fuel line might be routed too close the exhaust, Ill check that out.
Lonnies,
Great information.
My fuel line size from the fuel cell to the fuel filter>fuel pump is inch. I believe the fuel cap has a vent on it.
The engine is a transplant from an F-body Camaro (1995). Has no mods, but I did remove the EVAP, A/C and the cats. Running a fuel cell with an external pull pump. My fuel line might be routed too close the exhaust, Ill check that out.
Lonnies,
Great information.
My fuel line size from the fuel cell to the fuel filter>fuel pump is inch. I believe the fuel cap has a vent on it.
Registered User
Joined: Aug 2010
Posts: 1
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I have the same problem, running a TPI from an 85 camaro. On the trail during steep inclines, if the engine temps climb above 230 and bam, no power, will not start.
I have to disconnect the fuel line at the filter and all the vapor escapes. I am fine for another 30-40 mins of hard wheeling and then it does it again. It sucks because it gives no warning, so you are always looking for a place to bail on the trail.
Anyway, I have done some research. The F-body's radiator is angled down, for maximum air flow over the core but also the fans dump all the heat out of the bottom of the vehicle. The inlet/return of the fuel rail is on the front of the engine just below the throttle body, but just above the water pump. My rad points right at the water pump, sooo....
All the heat from the throttle body, water pump and rad dump on the inlet/return of the fuel rail. I have thought of 2 solutions:
1) Divert the fan air down away from the front of the engine and add a heat shield between the throttle body/water pump and the fuel rail fittings.
2) Take off the fuel rail and take it down to a speed shop to be retrofit the inlet and return to the back of the engine.
I think the 2nd will be more expensive than the first, but ultimately have a better chance at success. More to come...
Thanks,
kirk
I have to disconnect the fuel line at the filter and all the vapor escapes. I am fine for another 30-40 mins of hard wheeling and then it does it again. It sucks because it gives no warning, so you are always looking for a place to bail on the trail.
Anyway, I have done some research. The F-body's radiator is angled down, for maximum air flow over the core but also the fans dump all the heat out of the bottom of the vehicle. The inlet/return of the fuel rail is on the front of the engine just below the throttle body, but just above the water pump. My rad points right at the water pump, sooo....
All the heat from the throttle body, water pump and rad dump on the inlet/return of the fuel rail. I have thought of 2 solutions:
1) Divert the fan air down away from the front of the engine and add a heat shield between the throttle body/water pump and the fuel rail fittings.
2) Take off the fuel rail and take it down to a speed shop to be retrofit the inlet and return to the back of the engine.
I think the 2nd will be more expensive than the first, but ultimately have a better chance at success. More to come...
Thanks,
kirk
Thread Starter
Teching In
Joined: Feb 2010
Posts: 21
Likes: 0
From: Lynwood, Ca
Happen again Changed the fuel pump for whatever reason (Airtex ES200). I thought it went bad but it was the relay that took a dump... no biggie got a replacement for free (warranty).
So i took the rig out this past weekend to Truckhaven (local offroad park). Weather was in the low to mid 80's. Cranked the rig early in the morning before it was warm. Allowed it to warm up and took it for a short spin before we went out on our run. When i shifted in 2nd gear I punch it to get the engine going and got nothing from the engine, it just stumbled and popped. The more i keeped on the throttle the less it moved. Fuel pressure was around 60 psi, thought it was a little high so I turned it down to 43-45 psi. Took it for another quick spin and had the same results. I don't understand why this is happening.
Like a previously mentioned. The only thing I can imagine that is causing and issue is the fact that the fuel lines are running about 6" from the xover pipe and the muffler. Other than that, I can't come up with anything. Fuel cell is ventilated properly. Fuel pump is new (Although is was making a LOUD grunting noise) when the rig was on, when it primed it made the "normal" priming noise.
What else can I check? Mine next move is to move the fuel line to the opposite side of the exhaust or wrap the xover pipe and muffler.
This is really giving me a headache. I've got to fix this issue.
ANY HELP or suggestions would be greatly appreciated.
So i took the rig out this past weekend to Truckhaven (local offroad park). Weather was in the low to mid 80's. Cranked the rig early in the morning before it was warm. Allowed it to warm up and took it for a short spin before we went out on our run. When i shifted in 2nd gear I punch it to get the engine going and got nothing from the engine, it just stumbled and popped. The more i keeped on the throttle the less it moved. Fuel pressure was around 60 psi, thought it was a little high so I turned it down to 43-45 psi. Took it for another quick spin and had the same results. I don't understand why this is happening.
Like a previously mentioned. The only thing I can imagine that is causing and issue is the fact that the fuel lines are running about 6" from the xover pipe and the muffler. Other than that, I can't come up with anything. Fuel cell is ventilated properly. Fuel pump is new (Although is was making a LOUD grunting noise) when the rig was on, when it primed it made the "normal" priming noise.
What else can I check? Mine next move is to move the fuel line to the opposite side of the exhaust or wrap the xover pipe and muffler.
This is really giving me a headache. I've got to fix this issue.
ANY HELP or suggestions would be greatly appreciated.
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