I have an 83 firebird that has a history of vapor locking. It has vapor locked with the original engine and stock fuel system. I made it work with an electric fuel pump near the tank and the mechanical one on the engine. It still did vapor locked just not anywhere near as often. I now have a 4.6l 47pol engine out of a crown Vic in it and it still vapor locks. I have a fuel cooler and return line to try to prevent this. One of the few things I haven't tried is the routing the fuel line away from the transmission and up and over the engine, but I'm afraid that this might not help because vapor lock is caused by cavitation of the fuel pump and not over pressureization of it. I can see it bubbling in the prefilter for my fuel pump.My other thought for why this might happen is that I don't have a heat shield between my muffler and fuel tank. Or it could be all external pumps suck.This car didn't used to vapor lock when I was going 80 on the highway in Utah. I did have a huge hole in my hood and didn't have the factory airdam, but the car stayed at about 180 and now it's staying at about 200 with an oversized airdam, hood vents and a hood scoop. Everything else has remained the same. Without the air dam the car will overheat here in eastern NM. At 60 degree temperatures. While when I was in Utah it was high 90s most of the time.

 

I'm going to say that air dam is not helping you at all. It sits way too close to ground level to work the way the air dams are designed to function. It is acting like more of a air wall pushing all air away from the front and out to sides. I would be willing to bet you have little to no airflow under the car. Which only contributes to hot fuel lines. There should be zero reasons a car setup as factory can't cool itself. It worked from the factory, it should work 40 years later with all parts up to snuff. If it doesn't, you have other problems.

 

Your thought is correct, since you say it vapor locked with the stock engine, you NEED to get the shield(s) off of a third gen junkyard (For example, Hawks) and see if that helps solve your problem. Without those, the muffler literally turns the fuel tank into an oven

I say "Shield(S)" because I seem to recall there being more than one piece to it. Also, dabomb6608 is correct in that the too close to the ground air dam ain't doing ya any favors either.

Lastly, are ya gonna show us pics of the Ford 4.6 you've installed in it? If it truly is a police car engine, could perhaps your radiator be too small? (I owned a 4.6 in an 03 towncar cartier and the Lincoln's radiator was HUGE compared to a stock thirdgen radiator)

 

It did have the heat shields on the tank until I had someone replace the tank and they didn't put them back on. They also didn't put the plastic cover for the fuel filler neck in the wheel well back on either.

 

I'm using the radiator and oil cooler out of the crown Vic. The reason for the air dam is because the radiator is sitting about 3 inches lower and is leaned back a lot. The air short circuits under the radiator between 35 and 75. I used a go pro and string to see this. This is the third iteration of the airdam progressively getting taller. This the only one that prevented short circuiting under the radiator at lower speeds. I could add something to funnel the air from the dam into the radiator and that may help with the cooling. Most of the air from the radiator goes under the car and a little bit goes through the hood vents. I do have my cats on this car and they sit right next to the torque converter and the fuel lines are in the factory routing.

 

The engine is put together with parts from a 2006 mgm and a 2006 crown Vic. The wiring harness, computer, air box is from the mgm and the engine and trans are from the crown Vic.

Because of the mgm computer the car does have a speed limiter normally it's 115 but because of the gearing and tire size difference it's 85mph. when I'm going 80mph I'm sitting at 2500 rpms and it doesn't even need to shift down for steep hills.


I have put about 6000 miles on it maybe more . Including 2, 1800 mile trips. The car only seems to develop issues when I'm in NM for some reason.

Please excuse the absolute trash wiring job. It went from temporary to semi permanent. Hopefully I can replace the computer with a haltech unit and manual swap it soon, but I need to figure out why it is having fuel issues and fix it first.

 

What fixed my issue was moving the fuel lines out of the trans tunnel and away from exhaust. I would vapor lock in heavy/slow traffic on hot sunny days, especially when sitting at a long traffic light.
I have them follow the "outside" of the trans tunnel frame and then they go up thru the fender, and then over my brake booster. Make sure you have the heat shields in place for the fuel tank.

 

I have some temps for when the vapor locking started to happen

Rear axle temp 140
Fuel tank temp 136
Fuel pump temp 116
Fuel filter temp 128
Muffler temp 156
Engine block temp 159
Fuel cooler temp 77
Trans cooler temp 80
Radiator temp 89

It is 80 degrees air temp right now it took me a couple of minutes to get the cooler temps so they may be a bit low

 

Your fuel tank and fuel filter are well into the boiling temp of gasoline. Fuel pump is on the edge of it.

You are lacking airflow traveling under the car and need factory heat shielding.

80* ambient temp is far from "hot" enough to be causing heat issues. Especially 80* dry heat with low humidity.

 

The air dam is 2 inches off the ground. It just looks like it's touching.


​​​​​​The fuel return line right before the tank is 87 degrees
Passenger cat is 498
Drivers cat is 438

I Took a couple of pieces of paper and taped one one the bottom of the axle tube and loosely set the other one between the axle tube and brake line. The top paper stayed and the bottom is gone. So there is airflow under the car might not be enough but there is airflow.

I am going to try to find a heat shield for the gas tank if I can't find one I'll make one. I am also going make a deflector to grab the air from under the car and push it up twords the fuel pump that's on the firewall infront of the gas tank.

I will update if this works or not and also the temps of everything as well. I did notice that when the fuel pump is hot that the engine temp creeps up to 200 and when it is cool it stays around 185.

 

I really think you are over complicating this issue.

From the factory these cars didn't require:

The air dam to be modified taller to keep these cars cool.
Didn't need air deflectors installed at the rear of the car pushing air up to the tank.
Didn't need electric fuel pumps to supply the mechanical fuel pump.
Didn't need fuel coolers.
Didn't need the fuel lines rerouted.
And it certainly didn't need the radiator core hacked to cram a bigger radiator in it.

You are putting band aid fixes on your problems. When troubleshooting problems you should always ask yourself "This might work but should I have to even do this in the first place to fix the problem".

Out of curiosity what radiator fan are you running?

 

internal fuel pump

otherwise get an external as close to the tank as possible.

 

I second the internal fuel pump.

When I was young and dumb(er) I didn't want to go through the fuss of dropping the fuel tank so I tried doing a external pump for a period of time. It worked but it didn't like 100* humid days, would eventually start boiling fuel and losing pressure. Installed an internal pump and never looked back. Lesson learned.

 

I was going to swap the sending unit out with a later model year one and a 58 psi pump, but seeing that the fuel tank is hotter than the fuel pump I don't think that would help.

 

This car is not stock. It has no stock drivetrain components. Even the rear differential has been changed at this point.

Stock crown Vic radiator assembly with the electric radiator fan.When it was stock the only things I did to it was put oil in it because of a leaking rear main seal. Change/ clean the spark plug on cylinder 1 every 1000 MI or so because of a leaking valve guide. Replaced the electronic quadrajet for a mechanical one because the secondarys wouldn't open. Had the gas tank replaced because my neighbor put a bunch of water in it and it started leaking soon after.(I already pulled the gas tank to drain it. I wasn't going to to do that again.) and put on the electronic fuel pump. The senior mechanic I was working with had that idea. He thought that the reason for it vapor locking was that the fuel lines ran over the trans and the transmission was going out creating more heat than usual. I did also do the normal teenager thing of cutting off the muffler and put on a down turn in front of the rear axle. The electronic fuel pump fixed it. Yes I know it was a band-aid but that was the point. I did not have the money to replace the transmission or time to reroute the fuel lines. I already knew at that point that the engine was beginning to go out. The original 305 died at 81200 miles because of a loss in compression on multiple cylinders and before it died it would diesel for minutes after I shut it off. And yes that is 81200 not 181200. The car sat for 7 years before I got it. Before that it was sitting in California. Also if anyone knows a guy named Bill Murphy that owned a 1983 s/e with charcoal and silver paint. His name is written in multiple places on the car

 

It might be the stock drivetrain but it was replaced with what appears to be a stock Crown Vic "police" motor. Which is nothing that would produce any more heat than a factory L98 (actually slightly less HP).

There are hundreds of people on this forum who run heavily modified motors with factory fuel line routing, internal fuel pumps, stock air dams, and no issues with heat. My Trans Am with a fully built 406ci SBC that are known for being demanding on cooling systems has zero issues with cooling system or fuel system heat problems. I run a brushless cooling fan from a C7 Corvette, factory air dam (not even running the outers), have a AC Condenser in place, 3 core radiator (honestly too big), and factory hard fuel lines to the rear. I am considering replacing the radiator with a 2 core replacement. I installed the cheap 3 core long ago and hate the fit. A 2 core should be more than enough when matched to my cooling fan. Since fan install I have yet to see coolant temps over 187* on my datalogs, which only occured after some spirited driving. Normally runs 180* to 185* with a 180* thermostat.

Another thing to keep in mind. You can have the best air dam setup conceivable, but that won't do much below 50mph. You gotta have equal or greater airflow at a stop as you do at 50+ mph. This is where a proper fan setup comes in play.

I'd put money that if you were to convert to a internal fuel pump you would fix not only the fuel boil issue but potentially the coolant temps rising as well because lean=extra heat. Fix the fuel issue and you fix the lean issue.

 

Yes the fuel pump getting hot and causing the engine to run lean is Creating more heat

The reason for the air dam isn't a band-aid to try to fix this. I already knew that before I put the airdam on. I put it on because the radiator fan isnt able to keep up even with everything not heat soaked. When I am towing my boat and motorcycle. Yes I tow with this car and I towed with the crown Vic I took this engine out of too.


The air dam has helped significantly to keep airflow from short circuiting the radiator to the point where if the car is stationary it will kick up dust from the fan. When there is no air dam It won't even do that. Also when there is no airdam it won't hold up a piece of paper against the radiator except at the very top of the radiator.

And yes I know the drivers side cylinder head says 46 and is not a 47pol head. The passenger side one still is I believe someone replaced a cylinder head on this engine.

 

I highly recommend doing a brushless fan conversion. Can be done rather cheaply and they move a crazy amount of air with significantly less amperage usage. And they can be setup as variable speed to even further reduce amp usage. I used a C7 Corvette fan assembly, but there are other options out there as well. Here is some reading for you to research.

DIY Brushless Radiator Fans
Variable Speed PWM Fan Control under $25 or less DIY - Page 2 - LS1TECH - Camaro and Firebird Forum Discussion
VARIABLE PWM FAN CONTROL works with ANY sensor, compare to Lingenfelter VSFM-002 | eBay
Radiator Fan C7
Brushless Fan Conversion


Keep in mind there isn't any actual difference in the longblock from a police interceptor 4.6 and a regular 4.6. They are the same motor internally and same heads. Regarding the motor they had external upgrades like an oil cooler, higher amp alternator, etc.

 

Responding to this after your edit.

I definitely don't recommend not running an air dam. A factory air dam is a must. I just don't think the extension is required when all of your other issues are resolved.

 

I'm using factory fan that does have a fan control module on it. I believe the air is short circuiting making that fan much less efficient. The other option was to make a shroud that went from the radiator to the k member to keep the fan from short circuiting under the radiator. I didn't go with this option because I didn't like the idea of the air dead heading in the engine bay. I have a Ford Maverick that did that.


When I was putting this together I wanted to lean the radiator forward because the corvettes did this and it worked very well, but I didn't want to remake the front crash structure and radiator support. I didn't want to stick with the firebird radiator because I wanted to have a/c and didn't want to deal with an electric radiator fan (I did this engine swap 4 years ago), or trying to adapt the different sized radiator hoses.

 

Corvettes leaned the radiator to allow room for the very low profile hoods. It wasn't done as a goal to improve airflow through them. Trophy trucks have rear mounted radiators with solely the fans doing the work and are creating vastly higher amounts of heat than a stock motor.

What exactly do you mean by air short circuiting? In factory form some of the late thirdgen cars, depending on ECM, shut down the fans above a set MPH because the air dams worked so well that they don't need the fans to maintain temp. Many modern fan assemblies have flappers to allow over pressure airflow to escape at highway speeds. This is why I mentioned I think you are overthinking things. You don't need to tape string or paper to the underbody to solve any of these issues. GM already solved all of them. Even if you have a different drivetrain, the basics are all the same regardless. If you follow the recipe the cookies come out the same every time...

You really only have two options for what is happening to the airflow at highway speeds. Either it is not flowing from the front of the car hard enough through the radiator to maintain temps . Or it is flowing hard enough and the shroud and fan are hindering the ability of it to travel through the radiator. In both situations having an inadequate fan setup becomes the problem. A fan that moves a bucket load of air will solve both situations and also solve low speed cooling issues.

 

I wish I could get a picture to show how that radiator is mounted but the pictures aren't uploading.


The radiator fan is a 22 or 24" fan with a full fan shroud connected directly to the radiator. The fan is taller than the radiator. The lowest part of that radiator assembly is the fan. The fan is blowing air twords the ground at about a 25 degree angle from vertical.


What is happening is that the fan will pull air under the radiator rather than through it. Creating a higher pressure zone behind the bottom of the radiator than in front of the bottom of the radiator. Once I get to a high enough speed the air will just push through that and force a higher pressure zone in front of the radiator.
​​​​​​
Since I do a lot of towing and low speed high load work with this car. I had to make sure it wouldn't short circuit below the radiator at low speeds. When I was testing this air dam I did it in a 1," 3",and 5" increments. The one inch one didn't affect anything because it didn't sit lower than the fan shroud. The 3 inch one worked well for speeds above 45 and is probably the one I will be running this winter. And the 5 inch one will keep the car cool without the radiator fan at 25.

I have been running the 5 inch one because I like to tow my boat to the lake and it does a really good job of keeping it cool on the winding roads. I never noticed the vapor locking since I put on the air dam because I haven't ran the car long enough to fully heat soak everything until 2 days ago. It takes about 2 hours of hard driving.

​​​yes I do have a truck, but why should I use it when I can get 25mpg towing with this. And besides it's funny watching people's faces when I back a boat into the water with a car. Another thing I should mention is that I did this engine swap for roughly $800. I bought both doner cars, misc fasteners, got the driveshaft made, and I had the fuel pump from another project. So nothing is how I want it to be.

 

You've compounded bandaids to fix other bandaids. The answers to your heat problems are in this thread. Can lead a horse to water but you can't make it drink.

 

internal fuel pump

fuel will only boil at a substantially higher temp in the lines when it's under pressure.

fuel will boil at a lower temperature in the lines when it's under suction

kinda a universal thing with phase change for liquids to gas