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Truck dies when hot out

brnc72

New Member
Joined
Jul 27, 2016
Messages
5
Hello, I am new to the forum, but I am running out of options.

I have a 72 Bronco with a 99 Mustang 302 fuel injected motor. When the temperature is more than about 85 degrees out, the truck will sputter and die when accelerating after about 30 minutes of driving and will not start again for another 30 minutes. I have had it in the shop about 4 times. It has 2 fuel filters, for some reason, 1 was cut out. I have had the tank dropped because one thought was that the fuel line would get hot and pinch. I have had all kinds of diagnostics on it. It runs fine in the winter, but that is short here in Texas.

There is an electronic fuel pump mounted right under the drivers seat.

I have had numerous debates with mechanics about the possibility that the fuel could be vaporizing in the fuel lines. Most don't agree that is the issue. Any thoughts or experiences? Can you wrap the lines, or do you need to reroute them?

Or do a need to put a fuel pump in the actual fuel tank?

Or some other thoughts?

Thanks for the feedback.
 

Killer Frogs

Full Member
Joined
Nov 5, 2007
Messages
317
Loc.
Amarillo, TX
Welcome to the addiction! I had a '67 with the same problem living in El Paso at the time. I sold it before figuring things out, it was before this site was as helpful.

What type of fuel return do you have? My guess is you might not have a return line from the fuel rail. If you don't you might have to get a new fuel rail. Then you can go with an accumulator to return the fuel to. BC Broncos has a nice setup that uses two pumps, high and low, outside the tank. That is what I am running. http://www.bcbroncos.com/acctank.pdf

Good luck.
 

Quick & Dirty

Sr. Member
Joined
Feb 15, 2004
Messages
842
Does it have TFI ignition? (Are you sure it's a '99? Last year for 5.0 in Mustang was '95. '89? Explorer?)

The early ones with the TFI mounted to the distributor had issues overheating and shutting down. Later ones were remote mounted to a heat sink on the core support where it got a good flow of cool air.

If you have TFI, make sure the module is kept cool.

.
 
Last edited:

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,344
What kind of fuel pump is it? High pressure pumps work well but only when they have a good supply of fuel to them. They don't pull fuel well. It would be better to have the HP pump mounted as close to the bottom of the tank as you can. That usually means on the bottom of the crossmember just in front of the tank.

Think about it. Fuel boils when it gets hot enough. If it's under pressure (between pump and engine) it won't boil until it gets much hotter. Fuel between tank and pump is actually under partial vacuum (negative pressure) when the pump is running and will boil at a much lower temp than fuel that isn't pressurized at all.
 
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brnc72

brnc72

New Member
Joined
Jul 27, 2016
Messages
5
Thanks all

Quick and Dirty, I guess you are right, it must be a 95 or that timeframe. I thought one of the mechanics said 99, but I have no documentation on the exact year. I looked up TFI and I did find one mounted to the distributor. How do you keep it cool? Or do I need to replace the TFI. Just watched a video on YouTube on replacing, but still looking for the easiest way to keep it cool. Thanks again.

Does it have TFI ignition? (Are you sure it's a '99? Last year for 5.0 in Mustang was '95. '89? Explorer?)

The early ones with the TFI mounted to the distributor had issues overheating and shutting down. Later ones were remote mounted to a heat sink on the core support where it got a good flow of cool air.

If you have TFI, make sure the module is kept cool.

.
 
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OP
brnc72

brnc72

New Member
Joined
Jul 27, 2016
Messages
5
Sorry, I am working on it now and just realized that the brake light is tied to the computer and it's on. So I used a jumper and counted the blinks. It looks like it is throwing codes 81, 82, 85, and 84 in that order. Is that related?

Thanks all

Quick and Dirty, I guess you are right, it must be a 95 or that timeframe. I thought one of the mechanics said 99, but I have no documentation on the exact year. I looked up TFI and I did find one mounted to the distributor. How do you keep it cool? Or do I need to replace the TFI. Just watched a video on YouTube on replacing, but still looking for the easiest way to keep it cool. Thanks again.
 

Viperwolf1

Contributor
electron whisperer
Joined
Aug 23, 2007
Messages
24,344
Sorry, I am working on it now and just realized that the brake light is tied to the computer and it's on. So I used a jumper and counted the blinks. It looks like it is throwing codes 81, 82, 85, and 84 in that order. Is that related?

Those are codes referring to EGR and air injection which probably aren't installed on your conversion. They do not inhibit anything.
 

B RON CO

Contributor
Bronco Guru
Joined
Jun 29, 2016
Messages
2,439
Loc.
Statesville, NC
Hi, you don't say if you are stalling because of spark or fuel. Put a spark tester on it when it is not running. No spark was common on engines with TFI modules. They would fail when they got hot, and come back when they cooled down. We always had a spare, and the grease, and the special little ratchet tool. Good luck
 

Past_Miner

Contributor
Bronco Guru
Joined
Oct 22, 2003
Messages
1,021
There is an electronic fuel pump mounted right under the drivers seat.

I have had numerous debates with mechanics about the possibility that the fuel could be vaporizing in the fuel lines. Most don't agree that is the issue. Any thoughts or experiences? Can you wrap the lines, or do you need to reroute them?

I have two broncos with external fuel pumps and EFI and both of them suffer from this exact same issue in hot weather. I can get my fuel so hot on the trails that you can hear it boiling in the tank. At that point, the fuel vaporizes in the line on the suction side of the pump and the pump will vapor lock, just as Viperwolf describes. I'm dead until the whole system cools off enough to get liquid back to the pump. Sometimes it is a long wait.

On my trail rig I wrapped the fuel lines and have had better luck but after about 95 degrees I only get an hour or so of run time and it continues to happen. In my opinion, the best solution is an in-tank pump and fuel lines routed on the outside of the frame rail, away from the exhaust. A pump that is actually submerged can't have fuel vaporize before it enters the pump. Once it's at higher pressure, it will stay liquid until it gets on the low pressure side of the fuel rail. At that point you don't really care if it vaporizes in the line. Running the lines on the outside of the frame just keeps them from adding extra heat into the system from the exhaust. My son's bronco is built this way and he can run all day long in 100 degree weather without problems.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
35,392
Sounds like a spark issue to me. TFIs do fail, they usually do so suddenly. Coils are well known for failing when hot, but working again when they cool off again only to fail again when they get hot again. To me the failing coil better matches your failure mode.

Quick TFI check. When the engine is running right, shut it off, hold the throttle to the floor (clear flood mode) and crank the engine. It should NOT start. But while cranking watch the tach. Depending on how it is wired it may or may not work while cranking. If it does, good. When it dies again, watch the tach while cranking the engine. If it moves, the TFI is feeding pulses to the coil. TFI is good. If it doesn't, the TFI could be bad or the coil is bad clamping off the pulses from the TFI.

Another oddity (and this is rather odd and not very likely) is the tach may be warming up and shorting the tach signal to ground. This is one of those heard of it but never seen it happen things.
 

surfer-b

Contributor
Bronco Guru
Joined
Sep 7, 2006
Messages
2,974
Mine did something similar but it would just not start back until it cooled down a few mins, no sputtering, turned out to be the coolant temp sensor for the PCM. Yours doesn't really sound like that's what is happing but it may be something to keep in mind if everything else checks out. Yours does sound more like a fuel issue.
 
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brnc72

brnc72

New Member
Joined
Jul 27, 2016
Messages
5
Thanks! I am going to try wrapping the fuel lines to start. I was originally thinking from the pump to the motor, but based on what I am hearing it should be from the pump back to the tank. The problem is the fuel getting too hot before it gets to the pump and pressurized. If that doesn't work I think the submerged pump is the next guess. Thanks again for all the great advice.



I have two broncos with external fuel pumps and EFI and both of them suffer from this exact same issue in hot weather. I can get my fuel so hot on the trails that you can hear it boiling in the tank. At that point, the fuel vaporizes in the line on the suction side of the pump and the pump will vapor lock, just as Viperwolf describes. I'm dead until the whole system cools off enough to get liquid back to the pump. Sometimes it is a long wait.

On my trail rig I wrapped the fuel lines and have had better luck but after about 95 degrees I only get an hour or so of run time and it continues to happen. In my opinion, the best solution is an in-tank pump and fuel lines routed on the outside of the frame rail, away from the exhaust. A pump that is actually submerged can't have fuel vaporize before it enters the pump. Once it's at higher pressure, it will stay liquid until it gets on the low pressure side of the fuel rail. At that point you don't really care if it vaporizes in the line. Running the lines on the outside of the frame just keeps them from adding extra heat into the system from the exhaust. My son's bronco is built this way and he can run all day long in 100 degree weather without problems.
 

PaveBronco

Sr. Member
Joined
Oct 30, 2012
Messages
912
Just like Viper said high pressure pumps don't pull fuel well and under your seat (assuming you only have a high pressure) is way too far from the tank to pull fuel. there are several threads on EFI fuel pump setups so do a search. The in tank pump is the best but at least for me I can afford that, so I did the dual high/low pumps.
 

DirtDonk

Contributor
Bronco Guru
Joined
Nov 3, 2003
Messages
48,743
As someone already asked though, do you see a return line system in your Bronco? That would be two separate lines up at the engine's fuel rail, then tubing running back at least to behind the pump somewhere. Usually the tank, but can be anywhere the builder put it.
Without a functioning return system, all potential fuel heat issues are magnified.

If you're not sure about the fuel rail, the different years had the fittings (usually) at either the driver's side rear of the engine/intake manifold, or the passenger side front. We like the rear ones because it's cleaner on an EB, but many have used the front ones too. Functionally they're the same.

An easy check too, is fuel pressure at the rail. There is a schrader valve (tire inner tube looking thingy) on the rail near the regulator. Easy enough to put a fuel pressure gauge on it to check when it is and is not running.
If you see 40-45 psi when it's running, that's good. If you see any less when it's not running, then you know you have a fuel issue.

The regulator should have a vacuum tube from the manifold on it by the way.

Some pics of the layout under the engine compartment would be helpful if you get the chance too.

Paul
 
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