Electrical vs Mechanical

[FJLC74]

I have seen several posts regarding Electrical vs Mechanical fuel pumps but to be honest, they are about 10 + years old. Any new suggestions going from M to E fuel pump? Pro vs Cons. This would be for my 74 FJ 40. I tend to have problems on hot days and altitude. Last time I let the engine cool down and added fuel down the carb... perhaps not very smart but it worked after awhile.

Thanks.

 

[cbmontgo]

I can say that I’ve seen a lot more electric fuel pumps fail than mechanical. Vapor lock is definitely the downside.

 

[Rzeppa]

X2 stick with stock.

 

[FJLC74]

Much appreciated!

 

[FJLC74]

I can say that I’ve seen a lot more electric fuel pumps fail than mechanical. Vapor lock is definitely the downside.

So are you saying that with an electrical pump, I should not have VL issues?

 

[cbmontgo]

So are you saying that with an electrical pump, I should not have VL issues?

An electric pump near the fuel tank pressurizes the fuel towards the engine, which raises its boiling point. The mechanical one near the engine pulls a vacuum, which makes the fuel boil faster. So yes, an electric fuel pump will seriously reduce vapor lock.

But I still prefer mechanical.

 

[Runnin on E]

As an average, gasoline will boil at around 85-100 f. This is at atmospheric pressure. At best a carbureted engine mechanical fuel pump will output at about 2-5 psi. Even an electric fuel pump still has to deliver the fuel pressure to the carb at around that same pressure. If it delivers at a higher pressure it will over come the float/needle valve pressure ( flooding the carb). So either way the operating pressure for the fuel into the carb is the same for those pumps. A fuel injection system operating pressure is somewhere around 45psi ( or higher depending on mfg) The boiling point of gasoline at 45 psi is around 180-200f. It is difficult to get any really accurate numbers because of the different blends involved in gasoline and not just summer or winter blend. But on an average the boiling point will be as pretty close to that. At altitude the boiling point at atmospheric pressure is even lower and add to that under hood temps of 150-200f it is easy to see when vapor lock will happen. If you have an infrared thermometer check the temp of your carb fuel bowl immediately after a hard run and then do the same after about 15 minutes. It will most likely be higher due to radiation. Insulate the carb and fuel line from this radiation. Fiberglass sheathing works really well on fuel lines. A phenolic carb spacer or metal heat shield can reduce vapor lock. I had an old Chevy that would vapor lock in the summer (3600 ft altutude). I put a fiberglass cover over the fuel line going to the carb and it never happened again. (well..I built a fuel injection system for it too.....)

 

[Rzeppa]

That's why newer carburetor Land Cruisers have a fan that points at the carb and runs until it gets below a certain temperature. I don't know when that started, but my '76 FJ40 had one and my '71 didn't. My 60 had one pointed straight at the carb, the 40 is more toward the left front corner and is ducted.

My understanding (without looking it up) is that throttle body injection uses a lower pressure than direct injection.

But yeah, wheeling up in our high country definitely can lead to more vapor lock than sea level. @MountainGoat and I were wheeling Radical hill several years ago, he was in his 3rd gen 4runner and I was in my 60. He got to the top and waited for me. I stalled about halfway up. I got out and popped my hood. It took around 15 minutes to cool down enough to start back up and get up the hill. When I got to the top I remember him telling me that as he was watching me he said to himself "I hope I don't see that hood open"

 

[Runnin on E]

That's why newer carburetor Land Cruisers have a fan that points at the carb and runs until it gets below a certain temperature. I don't know when that started, but my '76 FJ40 had one and my '71 didn't. My 60 had one pointed straight at the carb, the 40 is more toward the left front corner and is ducted.

My understanding (without looking it up) is that throttle body injection uses a lower pressure than direct injection.

But yeah, wheeling up in our high country definitely can lead to more vapor lock than sea level. @MountainGoat and I were wheeling Radical hill several years ago, he was in his 3rd gen 4runner and I was in my 60. He got to the top and waited for me. I stalled about halfway up. I got out and popped my hood. It took around 15 minutes to cool down enough to start back up and get up the hill. When I got to the top I remember him telling me that as he was watching me he said to himself "I hope I don't see that hood open"

Wow dynamic high pressure ducted temperature mitigation!
Fuel injection is cool! Direct injection is a different animal than EFI. DFI is much higher pressures that EFI , more along the lines of deisel injection. Throttle bodies are still in the neighborhood of 45psi. They have fewer injectors than port injection and they inject more fuel per pulse. Throttle bodies are an easy FI conversion because they are usually based on carb flange bolt patterns.